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TYPE Review
PUBLISHED 10 November 2023
DOI 10.3389/fspas.2023.1243615
OPEN ACCESS
EDITED BY
Yi Xu,
Horia Hulubei National Institute for
Research and Development in Physics
and Nuclear Engineering (IFIN-HH),
Romania
REVIEWED BY
Zilong Chang,
Indiana University, United States
Antonio Caciolli,
University of Padua, Italy
*CORRESPONDENCE
Michael S. Smith,
RECEIVED 21 June 2023
ACCEPTED 17 July 2023
PUBLISHED 10 November 2023
CITATION
Smith MS (2023), Nuclear data resources
and initiatives for nuclear astrophysics.
Front. Astron. Space Sci. 10:1243615.
doi: 10.3389/fspas.2023.1243615
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Nuclear data resources and
initiatives for nuclear
astrophysics
Michael S. Smith*
Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN, United States
Research into the cosmic synthesis of the elements, the evolution and explosion
of stars, the nature of the early Universe, and other important topics in nuclear
astrophysics are at the forefront of nuclear science. These studies are motivating
laboratory measurements and theoretical calculations that, after signicant
investments, are pushing the boundaries of what is possible. The latest nuclear
results, however, must be specially prepared before they can be used to advance
our knowledge of the cosmos. This processing requires a set of resources
unique to nuclear astrophysics, and an impressive collection of nuclear reaction
and nuclear structure datasets, processing codes, thermonuclear reaction rate
libraries, and simulation codes and services have been developed for the eld.
There are, however, some serious challenges to these eorts that will only
worsen in the future, making it important to develop strategies and act now to
ensure a sustainable future for this work. After detailing the specic data types
needed for nuclear astrophysics and the available data resources, the major
challenges in this work and their implications are discussed. A set of initiatives
are proposed to meet those challenges along with suggested implementations
and possible ways that they may advance our understanding of the Universe and
strengthen the eld of nuclear astrophysics.
KEYWORDS
nuclear astrophysics, nuclear data, nuclear reactions, nuclear structure, evaluations,
cross section, software, simulations
1 Introduction
1.1 Importance of nuclear astrophysics
Nuclear astrophysics addresses many fascinating unsolved puzzles in the cosmos.
Some of these are broad questions, such as the origin of the elements heavier than Fe
(NationalResearchCouncil, 2003). Others are more specic, such as: the cosmic origins
of the rare 180Ta (deLaeter and Bukilic, 2005), 92−94Mo and 96−98Ru (Blissetal., 2018); the
origins of the very abundant (and fragile) 19F (Sieverdingetal., 2018); and the formation
of 7Li 3minaer the Big Bang (Cyburtetal., 2008). Some mysteries are tied to specic
astrophysical environments, such as: the heaviest elements created in nova explosions (Bode
and Evans, 2012;Liangetal., 2020); the nucleosynthesis in neutron star mergers as driven
by neutron captures on n-rich unstable nuclei (Wanajoetal., 2021); the formation of heavy
elements in core-collapse supernovae (Yamazakietal., 2022); and the possible ejection of
p-nuclides from X-ray bursts (Petrovicietal., 2019). Some puzzles impact the Universe as
a whole, such as a constraint on the total amount of baryonic matter via the formation of
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Smith 10.3389/fspas.2023.1243615
light elements in the early Universe (Walkeretal., 1991;Smithetal.,
1993). Others focus on the dynamics of particular events,
such as the mechanism of thermonuclear supernova explosions
(Poludnenkoetal., 2019), or broader questions such as the overall
impact of the 12C(α,γ)16O reaction rate on stellar evolution
(Pepperetal., 2022). e popularity of the eld of nuclear
astrophysics is growing due to new astrophysical observations [e.g.,
neutron star mergers (Wanajoetal., 2021)], new observatories
[e.g., the James Webb Telescope (Natarajanetal., 2017)], and
new accelerator facilities [e.g., FRIB (Weietal., 2019), RIBF
(Motobayashi and Sakurai, 2012), FAIR (Scheidenberge, 2017),
RAON (Hong, 2023)]. For these (and many other) reasons, nuclear
astrophysics has become rmly established as a major component of
low-energy nuclear physics research, as reected in long range plans
for nuclear science in the US (NuclearScienceAdvisoryCommittee,
2015) and Europe (NUPECC, 2017).
1.2 Importance of nuclear data for nuclear
astrophysics
Nuclear data is essential to study the mysteries mentioned above.
One reason: nuclear interactions drive the evolution of stars and
their synthesis of elements, so data on these provide an empirical
foundation for nuclear astrophysics studies. Another reason is that
nuclear data is needed to plan new laboratory measurements of cross
sections and level properties that are critical for nuclear astrophysics.
Furthermore, nuclear data provides valuable benchmarks for
reaction models that provide thousands of cross sections that
are inaccessible to measurement. Finally, processed nuclear data
in the form of thermonuclear reaction rates (discussed below)
are critical input for the astrophysical simulations that advance
our eld. Some specic examples are simulations that determine
the sensitivity of billion-dollar satellites to detect exploding stars,
identify high priority measurements at radioactive beam facilities,
determine the astrophysical impact of recent measurements, and
assess the uncertainties of astrophysical model predictions to enable
quantitative comparisons with observations.
e experimental and theoretical eorts in nuclear physics
needed for astrophysics studies are well documented in numerous
review articles [e.g.,Smith and Rehm (2001);Adelbergeretal.
(2011);Käppeleretal. (2011)], community white papers (e.g.,
Schatzetal., 2022), and nuclear science long range plans (e.g.,
NuclearScienceAdvisoryCommittee, 2015;NUPECC, 2017).
However, the eorts to compile, evaluate, process, and disseminate
this information for use by the nuclear astrophysics research
community—essential steps to ensure the best nuclear data is used
to advance the eld—are generally not included in such review and
planning documents. ese steps form the “nuclear data pipeline”
(Schnabeletal., 2021), and they ensure that the most up-to-date,
precise, and accurate results from measurements and theoretical
calculations are utilized in astrophysics simulations to advance the
eld.
is document addresses these essential nuclear data steps
and their associated resources. First, the data types specically
needed for nuclear astrophysics research are briey described in
Section1.3. In Section2, details are given for the available resources
in nuclear reaction data, nuclear structure data, thermonuclear
reaction rates, simulation codes, processing codes, soware services,
and more. e goal of Section2 is to inspire researchers to
fully utilize this impressive breadth of resources to facilitate their
work. Unfortunately, some of these datasets are missing the latest
experimental and theoretical results, some of the services are based
on decades-old technology or outdated data, and most of the
resources lack a path forward for updates and upgrades. ese
and related problems will be discussed in Section3, followed by
a prioritization of the most critical data needs going forward in
Section 4—along with possible solutions in the form of initiatives.
Finally, the challenges of implementing these initiatives is discussed
in Section5.
1.3 Specialized nuclear data needs
e overall nuclear data needs for nuclear astrophysics studies
are quite specialized [see, e.g.,Smith (2003);Smithetal. (2008);
SmithMS. (2011)], spanning nuclear reaction data, nuclear
structure data, and processed data (i.e., thermonuclear reaction
rates); these data types are described briey below. Because of
the specic nature of these reaction and structure data needs
(e.g., which isotopes, which reactions, which properties, which
energies), specialized eorts are required to obtain the data through
measurements and theory. However, specialized eorts are also
required to subsequently compile, evaluate, process, and disseminate
these important data so that they can be used in astrophysical
studies.
1.3.1 Nuclear reaction data
Reaction data is essential in nuclear astrophysics to track
the changes in composition and the generation of energy inside
stellar systems. Reactions are divided into two classes, strong
(e.g., captures) and weak (e.g., decays). For strong reactions,
interaction probabilities are characterized by cross sections. Nuclear
astrophysics studies do not, however, require cross sections of all
reaction types at all energies; Figure1 shows the set of reaction
types most predominantly utilized in this eld. Noted exceptions
to this are the important 12C + 12C, 12C + 16 O, 16O + 16O, and
similar reactions occurring in carbon and oxygen burning stages
of massive stars where the low abundance of light nuclei causes
heavy ion reactions to dominate (Nagorckaetal., 1971;Rolfs and
Rodney, 1988). Furthermore, cross sections for dierent reaction
types are needed for nuclei in dierent locations of the nuclear chart
(Figure1). For example, neutron captures are important for stable
nuclei and those that have a neutron excess, while proton and alpha
captures are needed for stable nuclei and those with a protonexcess.
Similarly, beta decays are critical for nuclei with excess neutrons,
while positron decays are needed for nuclides on the p-rich side of
stability. Finally, cross sections are needed at the low relative energies
(typically ≤1MeV/u) characteristic of the interactions of nuclides
inside stars. Such low interaction energies are both a help—by
placing only modest requirements on accelerators and detection
systems—and a hindrance—by causing much lower yields due
to the Coulomb barrier—to direct measurements of astrophysical
reactions.
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Smith 10.3389/fspas.2023.1243615
FIGURE 1
Reactions of importance for nuclear astrophysics shown on the N-Zplane for stable nuclei (center), and as lists for proton-rich nuclei (right), and
neutron-rich nuclei (left).
1.3.2 Nuclear structure data
Extensive data on the structure of nuclei are also needed
for astrophysical studies. e properties of single-particle levels
that are within ∼1MeV of a particle threshold are of particular
importance: these levels have the correct energy and conguration
to be readily populated by particle capture and other reactions
that drive astrophysical processes. In contrast, such reactions do
not favor populating levels at higher excitation energy or with
collective congurations (e.g., rotational or vibrational excitations).
By measuring single-particle level properties—or calculating
them with theoretical models—the resonant cross sections (and
thermonuclear reaction rates, discussed below) can be determined
(Rolfs and Rodney, 1988). is “indirect” approach at estimating
thermonuclear rates is especially valuable for nuclei far from
stability (Smith and Rehm, 2001) where capture reactions cannot be
measured directly, forcing a reliance on other reaction measurement
approaches (e.g., transfer reactions, surrogate reactions, decay
studies) or on theoretical models. Because resonant contributions
to reaction rates depend exponentially on resonance energies,
precision energy values are needed. Other important level properties
include the partial and total widths, spectroscopic factors, spin-
parities, and separation energies (e.g., reaction Q-values or nuclear
masses).
Signicant experimental and theoretical eorts have been
directed at nuclear mass determinations, leading to high precision
measurements [e.g., with particle traps (Kankainenetal., 2020)]
and sophisticated global models with RMS dierences from
measurements as low as 600keV (Goriely, 2023a). Machine
learning has been utilized in numerous recent studies of
nuclear masses—as well as in other areas of nuclear physics
(Boehnleinetal., 2022)—with some studies achieving ∼200keV
RMS deviation from evaluated masses (Shelley and Pastore, 2021).
Because there is so much activity in nuclear mass research, a
comprehensive review of progress would greatly benet the eld;
many advances have been made in the 20years since the last review
(Lunneyetal., 2003).
For stable nuclei, many of the relevant properties have been
measured, with the exception of a fair number of partial widths and
spectroscopic factors for near-threshold single-particle levels. For
studies of individual nuclei, shell model codes [e.g.,Brown (2004)]
and ab initio approaches [e.g.,Hergert (2020)] are commonly used.
Calculations over the entire nuclear chart are absolutely essential to
provide all the necessary data for certain astrophysical simulations.
Such “global” calculations are, for example, critical for the neutron-
rich, far-from-stability nuclei that are the epicenter of the rapid
neutron capture process (r-process) (Cowanetal., 2021), because
few of the relevant level properties have been measured and most
are experimentally inaccessible. A recent review article (Goriely,
2023a) provides an in-depth discussion of theoretical approaches
to model structure information, including level densities, optical
model potentials, gamma-ray strength functions, ssion product
distributions, beta decays, and nuclear masses.
ere are other structure data needs in addition to those
mentioned above. For example, the properties of bound levels are
necessary to calculate the direct reaction cross section component
(Brune and Davids, 2015). Also, spontaneous and neutron-induced
ssion yield distributions are important to treat the synthesis of the
heaviest elements in the r-process (Côtéetal., 2018); details of this
are discussed in Section2.7. Finally, for weak reactions, beta- and
positron-decay lifetimes are needed, as well as delayed single- and
multiple-particle emission probabilities aer decay; weak reactions
are described in more detail in Section2.3.
1.3.3 Thermonuclear reaction rates
Cross sections can be converted to thermonuclear reaction rates
through a convolution with the Maxwell-Boltzmann temperature-
dependent energy distribution of interacting particles in a star (Rolfs
and Rodney, 1988). is holds for cross sections obtained from
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FIGURE 2
Thermonuclear rate for the 17F(p,γ)18Ne reaction.
laboratory measurements, as well as for those calculated from a
reaction model or from the properties of relevant levels. e rates
of charged particle reactions depend exponentially on temperature,
with some rates varying by 30 orders of magnitude or more
over the 107K–1010K temperature range relevant for astrophysical
environments. Figure2 shows a typical example, the rate for the
17F(p,γ)18Ne reaction that plays a critical role in the synthesis of 17O
in nova explosions (Bardayanetal., 1999). Collections of hundreds
to thousands of individual reaction rates—rate “libraries”—are
the core nuclear physics input for simulations of astrophysical
environments.
2 Available resources
2.1 Nuclear reaction data and codes
2.1.1 The evaluated nuclear data le (ENDF)
e Evaluated Nuclear Data File ENDF (Brownetal., 2018;
NationalNuclearDataCenter, 2023a) is a reaction cross section
database that is managed and hosted at the National Nuclear
Data Center (NNDC) (Brookhaven National Laboratory, 2023b)
in the US. ENDF has an overwhelming focus on neutron-induced
reactions because of their importance in nuclear energy and nuclear
science applications. ENDF only has entries for reactions that
have been measured in laboratories—that is, it contains no cross
sections calculated entirely from theoretical models. ENDF entries
are evaluated, meaning that nuclear reaction models (discussed
below) are used by experts to combine multiple measurements
to quantitatively determine the “best” value, to extrapolate to
higher (∼20MeV/u) or lower energies, to calculate all reaction
channels at all angles, and to determine robust uncertainty
information in the form of covariances (SmithDL., 2011;NNDC,
2023a).
Data from individual experiments are not stored in ENDF;
these are stored in the EXFOR database (Zerkin and Pritychenko,
2018;IAEANuclearDataServices, 2023a). Members of the nuclear
data community work with researchers to compile and import
experimental results into EXFOR for subsequent dissemination
to the community. ENDF evaluations, which are coordinated by
the Cross Section Evaluation Working Group (CSEWG) (NNDC,
2023b), are signicantly expedited by importing data into the
standardized EXFOR format.
ENDF is not the only evaluated library of its kind: other
similar libraries include the Joint European Fusion File (JEFF)
(NuclearEnergyAgency, 2023), the Japanese Evaluated Nuclear
Data Library (JENDL) (JapanAtomicEnergyAgency, 2023), the
Russian Nuclear Data Library (ROSFOND) (InstPhysPowerEngr,
2023), and the Chinese Evaluated Nuclear Data Library (CENDL)
(ChineseInstituteofAtomicEnergy, 2023). e ENDF database
format, unchanged since the 1960s, will soon be replaced by the
Generalised Nuclear Data Structure (GNDS) format (NEAOECD,
2023). is follows more than a decade of work by international
data experts to bring this critical database into the modern
era.
2.1.2 ENDF and nuclear astrophysics
Because ENDF contains neutron capture reaction cross sections
on stable isotopes, it can be used in simulations of the slow neutron
capture process (s-process) (Käppeleretal., 2011) in AGB stars
(Bussoetal., 1999). In Section2.3 below, the generation of reaction
rates from ENDF cross sections will be discussed. It should be noted
that, for s-process studies, there is a need to supplement ENDF
cross sections with cross sections of neutron captures on long-lived
radioactive “branch-point” isotopes (Bisterzoetal., 2015) that are a
few mass units from stability.
During the evaluation process, the cross sections in ENDF
are adjusted to agree with benchmarks from nuclear criticality
safety and nuclear reactors. While this is ideal for nuclear science
applications, it does mean that the cross sections are optimized at
energies above those typically found in astrophysical environments.
Additionally, since the ENDF evaluation methodology (Brownetal.,
2018;NationalNuclearDataCenter, 2023a) includes all reaction
channels and angles over a broad energy range, it is rarely followed
by researchers in nuclear astrophysics. Rather, more streamlined
reaction evaluations focused on the total cross section (and
uncertainty) at astrophysical (i.e., lower) energies are oen favored
in the nuclear astrophysics community. Such reaction “assessments”
(using this term to distinguish from full ENDF evaluations) that
are streamlined and optimized for nuclear astrophysics can, in
some cases, generate signicantly dierent cross sections than those
in ENDF—and which can subsequently produce dierent element
synthesis and energy generation in astrophysical simulations [e.g.,
Zhangetal. (2022)].
Because ENDF does not contain cross sections for the thousands
of neutron capture reactions on short-lived, neutron-rich unstable
nuclei that are critical for the rapid neutron capture process (r-
process) in neutron star mergers (Wanajoetal., 2021) and core
collapse supernovae (Yamazakietal., 2022), this database is not
suitable for r-process studies.
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2.1.3 Nuclear reaction codes
Nuclear reaction codes play an invaluable role in data analysis
and in data evaluations. Examples widely used for charged-
particle induced reactions include FRESCO (ompson and Nunes,
2009) for analyzing angular distributions using coupled channels,
DWUCK (Kunz, 1996) and TWOFNR (Igarashi, 1977) which use
a Distorted Wave Born Approximation (DWBA) approach, and
AZURE (Azumaetal., 2010) for multi-level R-matrix ts. For
neutron-induced reactions, the SAMMY (Larson, 2008) code is
widely used for multilevel R-matrix ts to neutron data with a
Bayesian approach. SAMMY has long been an integral part of the
ENDF evaluation methodology.
Nuclear reaction codes are also critical for estimating cross
sections that have not yet been (or cannot practically be) measured.
For capture reactions in astrophysical environments, the total cross
section is the sum of three dierent components: direct capture
into bound states (Brune and Davids, 2015), resonant capture into
low-lying (non-overlapping) single-particle levels, and capture into
overlapping levels. Given the bound level properties, the direct
capture component can be treated with a code like RADCAP
(Bertulani, 2003); given properties of the individual resonances, a
standard Breit-Wigner formulation can be used for the resonant
capture component. ese level properties are usually obtained from
experimental results (e.g., ENSDF or XUNDL) or from theoretical
models as discussed in Section2.2. e third component, capture
into overlapping levels, oen dominates the direct and resonant
capture contributions to cross sections. e third component is
usually treated with a statistical (or Hauser-Feshbach) reaction
mechanism model (Hauser and Feshbach, 1952).
2.1.4 Statistical model reaction codes
Statistical model codes, in fact, provide the overwhelming
majority of reaction cross sections that (aer being processed
into reaction rates) are used in astrophysical simulations. Popular
modern statistical model codes from the nuclear data community
include CoH (Kawanoetal., 2010;Kawanoetal., 2016), EMPIRE
(Hermanetal., 2007), and TALYS (Gorielyetal., 2008;Koning,
2023a); older codes include GNASH (Youngetal., 1992) and ALICE
(Dityuketal., 1998). Of these, TALYS has obtained wide acceptance
for many studies in basic and applied nuclear science—including
nuclear astrophysics. is code performs advanced global nuclear
reaction modeling with robust uncertainties, and contains multiple
reaction components including pre-equilibrium reaction eects,
multi-particle emissions, width uctuations, coupled channels,
nuclear deformation, ssion products, and many choices for nuclear
level densities.
TALYS is used to generate TENDL, the TALYS Evaluated
Nuclear Data Library (Koningetal., 2019;Koning, 2023b), which
combines reaction evaluations with TALYS calculations to obtain
reaction cross sections with nearly complete coverage of the nuclide
chart for certain reaction types. is coverage makes TENDL very
useful for certain astrophysics studies—specically, of s-process and
r-process nucleosynthesis driven by neutron-induced reactions. It
should be noted that TENDL cross sections areoptimized at energies
above those needed for astrophysics and are provided, for many
reactions, on a ∼1MeV energy grid—which does not have sucient
delity for the low energies needed for studies of most astrophysical
systems.
e nuclear astrophysics community has also developed their
own statistical model codes. Early eorts, such as those by
Woosleyetal. (1978), set the approach followed by later eorts:
calculate all binary reactions where an intermediate-mass nucleus
(in that case, oxygen to krypton) reacts with a proton, neutron,
alpha particle, or gamma ray over a broad energy (temperature)
range characteristic of astrophysical environments. e codes also
generally use theoretical expressions for nuclear partition functions
and the nuclear level density, unless experimentally determined
excited states are available. F. ielemann developed the SMOKER
code (ielemannetal., 1987) that was later advanced by T.
Rauscher into NON-SMOKER (Rauscher and ielemann, 2000;
Rauscher, 2023a). is Hauser-Feshbach reaction model code is
ne-tuned for astrophysical applications and has been used to
calculate rates for (n, γ), (n, p), (n, α), (p, γ), (p, α), (α,γ),
and their inverse reactions on nuclides from Ne to Bi and for
isotopes ranging from the neutron to proton driplines. Reaction
rates generated from NON-SMOKER are the foundationof the JINA
REACLIB (JointInstituteforNuclearAstrophysics, 2023a) reaction
rate database described below. Nucleosynthesis simulations were
used to benchmark NON-SMOKER rates (Homanetal., 1999) and
demonstrate their advantages over some earlier statistical model rate
collections [including Woosleyetal. (1978)].
2.2 Nuclear structure data and codes
2.2.1 The evaluated nuclear structure data le
(ENSDF)
e Evaluated Nuclear Structure Data File (ENSDF)
(NationalNuclearDataCenter, 2023b) hosted at the NNDC
(BrookhavenNationalLaboratory, 2023b) is the international
standard database for evaluated structure properties of nuclei. Some
of the information contained in ENSDF includes level energies, spin-
parities, total and partial widths, spectroscopic factors, reaction Q
values, 1- and 2-particle separation energies, BE (2) values, beta
decay lifetimes, binding energies, pairing gaps, decay schemes
and branching ratios, bibliographic tags for measurements of
these properties (that link to Nuclear Science References (NSR)
(Pritychenkoetal., 2011)), and much more. ENSDF contains
evaluated data on many low-lying, single-particle resonances that
are critical for thermonuclear reactions, as well as on bound levels
needed for direct capture cross section calculations.
Evaluators from around the world (International Atomic Energy
Agency, 2023) contribute to ENSDF evaluations. A companion
database, the eXperimental Unevaluated Nuclear Data Library
(XUNDL) (Brookhaven National Laboratory, 2023a), holds data
from individual experiments that are used by evaluators for their
ENSDF evaluations. e formats for ENSDF and XUNDL are being
modernized along with the database structure, and the visualization
by NuDat (NationalNuclearDataCenter, 2023c) is being upgraded
with new capabilities.
2.2.2 Other evaluated nuclear structure data
ere are other sources of level information on nuclei. One
is NUBASE2020 (Kondevetal., 2021), which is a companion to
the 2020 Atomic Mass Evaluation (AME) (Huangetal., 2021;
Wangetal., 2021) (discussed below). NUBASE contains properties
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of the ground state, and any metastable states, in over 3,100 nuclides;
in contrast, ENSDF contains the properties of all levels in over
3,400 nuclides. e NUBASE evaluations are consistent with the
masses in the AME, but are evaluated independently from ENSDF.
NUBASE is online at the Atomic Mass Data Center (AMDC)
(AtomicMassDataCenter, 2023), hosted at the IAEA Nuclear Data
Service (InternationalAtomicEnergyAgency, 2023a).
For neutron resonances, the Atlas of Neutron Resonances
(Mughabghab, 2023) is a valuable source of experimental
information. is work contains an extensive list of the individual
resonance parameters for each nucleus as determined from
analyzing available captures, ssions, and total neutron cross
sections. ermal cross sections are also contained in this work,
along with average resonance parameters. For charged particle
reactions, there are numerous targeted studies in the nuclear
astrophysics community that contain resonance properties to
calculate capture reactions. Some of these just contain information
on one or a few nuclei [see, e.g.,Smithetal. (1993);Bardayan and
Smith (1997);Nesarajaetal. (2007)] while others aremore expansive
in scope [e.g.,Iliadisetal. (2001)].
2.2.3 Structure information from theoretical
models
ere are numerous resources for theoretical structure
information. Predominant among these is the Reference Input
Parameter Library (RIPL) (Capoteetal., 2009;Capote, 2023). e
product of an international eort, RIPL is a valuable collection
of model calculations of nuclear information needed for reaction
calculations and nuclear data evaluations. RIPL includes eight
sub-libraries: masses, nuclear levels, resonance spacing, optical
model, level densities, giant dipole resonances, ssion barriers, and
computer codes. RIPL has seen wide utilization through the nuclear
data community and contains valuable information for nuclear
astrophysics research.
A series of global theoretical model predictions have been
published by Mölleretal. (1995),Mölleretal. (1997),Mölleretal.
(2016),Mölleretal.(2019) and are available online at Möller (1997).
ese collections contain ground-state masses, deformations,
alpha-decay Q values, half-lives, beta-decay Q-values for beta-
minus and electron capture decays, beta-delayed neutron-emission
probabilities, potential-energy surfaces, ssion-potential-energy
surfaces, and (for ground states) odd-proton and odd-neutron spins,
proton and neutron pairing gaps, and proton and neutron separation
energies. ese quantities are calculated for nearly 9,000 nuclides
starting at 16O and ranging from the proton-to neutron-drip line
up to Z= 136. e 2012 version of the Finite Range Drop Model
(FRDM) (Möller, 1997) is a central component of these models.
e site also has single-particle level diagrams and other graphical
information.
A separate, smaller collection of global structure model
predictions were produced together with cross section predictions
from the NON-SMOKER code (Rauscher, 2023a); these are posted
online at Rauscher (2023b). e available structure quantities
include nuclear partition functions, nuclear levels, and ground state
contributions to nuclear rates. In similar fashion, the BRUSLIB
(Goriely,2023b) library, discussed below in Section2.3, supplements
its collection of thermonuclear reaction rates with theoretical
structure data, including ground state and single-particle level
properties, densities and potentials, nuclear level densities, partition
functions, E1 strength functions, and ssion properties. e
importance of the properties of bound levels for direct capture on
neutron-rich unstable nuclei was pointed out in Goriely (1998a) and
remains a challenge to this day.
Finally, a number of structure datasets are posted the
Nuclear Computational Low Energy Initiative (NUCLEI) site
(NUCLEICollaboration, 2023). is collaboration is using high
performance computing and advanced theoretical techniques to
model the properties of nuclei. e data posted at their site includes
mass tables, global mass model predictions, tables of 2+level
energies, ssion barriers, giant dipole resonance parameters, and
more. ey also have a repository of nuclear codes available for
download.
2.2.4 Nuclear masses
e latest evaluated nuclear mass datasets from the AME
eort, as well as their NUBASE structure properties dataset,
are available online at the Atomic Mass Data Center (AMDC)
(AtomicMassDataCenter, 2023), hosted at the IAEA Nuclear
Data Service (InternationalAtomicEnergyAgency, 2023a); the
masses are also published online in Huangetal. (2021) and
Wangetal. (2021). e evaluated masses in the AME are critical
for determining the energy release of thermonuclear reactions and
for calculating cross sections of unmeasured reactions. ere is
also a longstanding (2008–2022) independent eort by B. Singh to
compile nuclear mass measurements. ose compilations are posted
online at the nuclearmasses.org service (SmithMS.etal., 2023),
which enables customized visualization and rapid comparisons (e.g.,
RMS dierences) between theoretical, experimental, and evaluated
nuclear masses (SmithMS., 2011).
2.3 Thermonuclear reaction rates
Research in nuclear astrophysics has always relied heavily
on libraries of thermonuclear reaction rates. Collections of rates
of charged-particle induced reactions, neutron-induced reactions,
weak nuclear reactions, and other collections are briey described
below. Descriptions of processing tools required to produce these
libraries from reaction and structure data les are given in
Section2.4.
e rate libraries described below contain rates from
assessments of individual reactions, from large-scale reaction model
calculations, from other rate libraries, or from a combination of
these sources. Most libraries are general purpose, valid over the
temperature range of 107K–1010K that covers most astrophysical
phenomenon. However, some individual assessments are made
over truncated temperature ranges corresponding to the energies
measured in particular laboratory experiments, and care must be
taken to extrapolate such rates for extended temperature ranges to
avoid any problematic behavior. An example of this can be found in
Smithetal. (1993) wherein a solar energy-based 3H (α,γ)7Li rate is
modied to be valid at Big Bang temperatures.
ree dierent formats are used for reaction rate libraries. In
one format, rate values are provided on a temperature grid. Once
the tabulated (temperature, rate) ordered pairs are read into an
astrophysical simulation code for each reaction, these “pointwise”
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rates must be interpolated at each time step because the simulations
require rates on a dynamically-adjusted set of temperatures. In
another format, a single functional form is chosen as an analytical
expression (of rate versus temperature) for all rates, with each
reaction having a dierent set of parameters for that function; the
parameters are generated by a t to the rate values. Once the t
parameters are read in for all reactions, the value of any rate at
any temperature (i.e., at any timestep) is calculated with that single
functional form and its respective parameters; no interpolation is
needed. e third format utilizes a dierent analytical functional
form for each reaction rate. In that scheme, these functions, resulting
from ts, are incorporated in the simulation code and each rate is
calculated at any temperature with its respective function, again with
no interpolation. ere are advantages and disadvantages of each of
these formats, based on the convenience to prepare the library, the
accuracy of the resulting rate values, the speed of execution, and the
complexity of the required coding. e choice of rate library formats,
however, does not limit the simulation execution speed; rather, the
execution is limited by the time to invert a large matrix at each time
step. is matrix is used to solve a linearized system of abundance
changes over small time steps (Hix and Meyer, 2006).
2.3.1 Charged particle-induced reactions
Early eorts to generate charged particle reaction rates for
studies of stellar burning were carried out by W. Fowler and his
collaborators, resulting in ve published collections from 1967
to 1988 (Fowleretal., 1967;Fowleretal., 1975;Harrisetal., 1983;
Caughlanetal., 1985;Caughlan and Fowler, 1988). e last of
these libraries (Caughlan and Fowler, 1988;SmithM.etal., 2023)
contains 159 rates and served as a standard for well over a
decade. at collection provides a dierent analytical function of
temperature for each rate, as well as pointwise rate values. Other
smaller charged-particle reaction rate collections were subsequently
created, specialized for solar burning [e.g.,Adelbergeretal. (1998);
Adelbergeretal. (2011)], for nuclei in the mass range 20–40
(Iliadisetal., 2001), for nova nucleosynthesis [e.g.,Politanoetal.
(1995);Starreldetal. (1998);Iliadisetal. (2001);Starreldetal.
(2001)], for X-ray bursts [e.g.,vanWormeretal. (1994);Schatzetal.
(1998)], and for Big Bang nucleosynthesis [e.g.,Wagoneretal.
(1967);Wagoner (1969);Smithetal. (1993);Descouvemontetal.
(2004)].
e NACRE (Anguloetal., 1999) rate collection was assembled
by the rst large, international, multi-institution eort to assess
charged-particle induced rates for stellar burning. is library,
published in 1999, contained 86 rates on mostly stable nuclei, many
of them updated from rates in the CF88 collection (Caughlan and
Fowler, 1988). e eort utilized a methodology of streamlined
assessments directed at determining the total cross section [or
astrophysical S-factor (Rolfs and Rodney, 1988)] at low energies,
with a focus on the resonant contributions from single-particle
levels near a particle threshold. NACRE contains analytical
expressions for S-factors, while the rates are given pointwise on
a temperature grid. NACRE-II (Xuetal., 2013a;Goriely, 2013), a
2013 update, featured new rates for 34 reactions and the use of
potential models for extrapolating measured cross sections to lower
energies.
Rates from the NACRE collections form the core of the
Brussels nuclear reaction rate library (BRUSLIB) (Goriely, 2004;
Aikawaetal., 2005;Xuetal., 2013b;Goriely, 2023b). e early
versions of BRUSLIB also included theoretical rates calculated
from the MOST statistical reaction code (Goriely, 1998b), while
later BRUSLIB versions (Goriely, 2023b) use statistical model
rates calculated from TALYS (Koning, 2023a) cross sections. As
mentioned above, BRUSLIB includes a large collection of theoretical
structure properties, and (as discussed below) it also includes rate
of neutron-induced reactions. e Nuclear Network Generator
NETGEN (Aikawaetal., 2005;Jorissen, 2023) is a companion
soware tool that generates pointwise reaction rates from BRUSLIB
for subsequent use in nucleosynthesis calculations.
e JINA REACLIB library (Cyburtetal., 2010;
JointInstituteforNuclearAstrophysics, 2023a) is one of the most
widely utilized rate libraries in astrophysical simulations. It is the
default library for many of the nucleosynthesis codes discussed in
Section2.4. REACLIB had its origin in 1987 (ielemannetal.,
1987) as a set of statistical model calculations using the SMOKER
Hauser-Feshbach reaction model code, the precursor code to
NON-SMOKER (Rauscher and ielemann, 2000). REACLIB
features one functional form [described in Cyburtetal. (2010)]
to t (parameterize) all reaction rates, and the library itself is a
table of the parameter values for each rate. REACLIB has since
had many upgrades and expansions, including the addition of
approximately 200 rates based on assessments performed by
the nuclear astrophysics community [e.g.,Schatzetal. (1998);
Anguloetal. (1999);Iliadisetal. (2001);Xuetal. (2013a) and many
more]. Approximately 48,000 of the total 55,000 rates in JINA
REACLIB are based on statistical model calculations, specically the
2008 version of NON-SMOKER code (Rauscher and ielemann,
2000;Rauscher, 2023a). It should be noted that JINA REACLIB also
contains rates for neutron-induced reactions, as discussed below.
An important advance in the methodology of reaction rate
determinations was made with the STARLIB reaction rate library
(Iliadisetal., 2010a;Iliadisetal., 2010b;Iliadisetal., 2010c;
Longlandetal., 2010;Sallaskaetal., 2013;Iliadis, 2023). STARLIB
features rate determinations, upper and lower limits, and probability
distribution functions based on Monte Carlo propagations of
nuclear level uncertainties through the reaction rate calculation.
STARLIB contains 62 charged particle-induced reactions on nuclei
in the mass range of 14–40 that are treated with this method.
is library provides pointwise rates (no analytical formulae),
and adds a large number (over 47,000) of rates determined from
TALYS (Koning, 2023a) cross section calculations and additional
rates from other sources (e.g., NACRE, decays from ENSDF, and
more) (Sallaskaetal., 2013) to produce a rate library useful for
astrophysical simulations of proton-rich environments.
2.3.2 Neutron-induced reactions
For neutron-induced reactions, many collections do not provide
thermonuclear reaction rates; rather, they feature Maxwellian-
averaged Cross Sections (MACS) [see, forexample, Käppeler (2012)]
calculated at an average temperature characteristic of s-process
nucleosynthesis. A MACS is obtained by folding the energy-
dependent dierential cross section with the thermal velocity
distribution of neutrons in the stellar plasma, and is proportional
to the thermonuclear rate divided by the mean thermal velocity.
Many collections of MACS provided values only at kT = 25keV
[e.g.,Kaeppeleretal. (1982);Käppeler (2012)], in part because many
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neutron-induced reaction measurements are made using the 7Li
(p,n) reaction as a source of neutrons; this reaction produces a
Maxwellian-like distribution of neutrons peaked at that energy
(Beeretal., 1980). It should be noted that some authors prefer
to provide MACS at kT = 30keV [e.g.,Baoetal. (2000)]. e
approach of providing MACS at one average temperature is,
however, problematic for simulations that feature thermonuclear
burning at other temperatures. Examples of other important
temperatures for stellar neutron-induced reactions include 8keV for
the 13C pocket formation aer the third dredge up in AGB stars
(Bisterzoetal., 2015), 90keV for shell carbon burning in AGB stars
(Käppeler, 2012), and up to 1MeV for r-process nucleosynthesis
(Horowitzetal., 2019).
Early eorts to generate collections of MACS for neutron-
induced reactions—primarily for neutron captures—were made in
the 1960s and 1970s by Macklin and Gibbons (1965) and Allenetal.
(1971). ese libraries formed the basis for early quantitative studies
of s-process nucleosynthesis by W. Fowler and others. It should be
noted that these collections included MACS on a grid of kT values
from 5 to 90keV, making them suitable for a wider range of studies
than some later collections.
As experimental measurements improved, rate collections were
revised and expanded. e collections of Kaeppeleretal. (1982),Bao
and Kaeppeler (1987), and Baoetal. (2000) signicantly advanced
the quality of neutron capture data processed for s-process studies.
A 2005 update of Baoetal. (2000) forms the core of the Karlsruhe
Astrophysical Database of Nucleosynthesis in Stars (KADONIS)
(Dillmannetal., 2006;Dillman, 2023), which is supplemented from
rates from other sources as well. is is a web-based collection
of experimental (n, γ) MACS relevant for studies of s-process
nucleosynthesis. KADONIS was subsequently extended in 2013 to
contain neutron capture rates on 32 p-rich unstablenuclei for studies
of the p-process (Szucsetal., 2014).
In the nuclear data community, MACS have been calculated
(Pritychenkoetal., 2010;Pritychenko and Mughaghab, 2012;
Pritychenko, 2020;National Nuclear Data Center, 2023d) for
neutron capture reactions from cross sections in the ENDF
(National Nuclear Data Center, 2023a), JEFF (Nuclear Energy
Agency, 2023), JENDL (Japan Atomic Energy Agency, 2023),
ROSFOND (Inst Phys Power Engr, 2023), and CENDL (Chinese
Institute of Atomic Energy, 2023) libraries. Comparisons [e.g.,
Zhangetal. (2022)] between these MACS and those generated from
experiments [e.g., (Dillman (2023)] or from nuclear models [e.g.,
(Rauscher (2023a)] originating from nuclear astrophysics studies
may improve the overall quality of all MACS collections.
For studies of the astrophysical r-process, it is critical to
have reaction rates rather than MACS because of the wide
range of temperatures present in neutron star mergers and
core-collapse supernovae. It is also necessary to have neutron
capture rates on thousands of neutron-rich unstable nuclei,
which necessitates the use of nuclear models. NON-SMOKER
(Rauscher, 2023a) was used to generate such rates for the JINA
REACLIB library (JointInstituteforNuclearAstrophysics, 2023a);
TALYS (Koning, 2023a) was similarly used to generate rates for
BRUSLIB (Goriely, 2023b). Recently, TALYS was used to generate
the TENDL-Astrophysics database (Koning, 2023c), which contains
neutron capture reaction rates on 8,892 isotopes with uncertainties
generated from 288 models that combine dierent choices of input
parameters—gamma strength functions, level densities, optical
models, collective enhancements, width uctuations, and mass
models. e incorporation of uncertainties and the complete
coverage of neutron-induced reactions on stable and neutron-rich
isotopes make this library useful for quantitative investigations of
s-process and r-process nucleosynthesis.
2.3.3 Weak nuclear reactions
Weak nuclear reactions such as beta decays are very important
for thermonuclear burning processes. For the r-process, these decays
are critical input as they set the timescale of the burning and the
nal abundances [see, e.g.,Langanke and Martínez-Pinedo (2003);
Cowanetal. (2021)]. Beta-delayed single and multiple neutron
emissions are also important as they alter the mass distribution of
r-process abundances. Electron (positron) capture reactions are also
needed for neutron-rich (proton-rich) nuclei. Where measurements
of the beta- and positron-decay lifetimes of nucleinear stability exist,
they are included in ENSDF (NationalNuclearDataCenter, 2023b);
these values are oen incorporated into thermonuclear rate libraries.
For r-process simulations, however, thousands of weak rates on very
neutron-rich nuclei are needed, and theoretical models are required
to provide the needed data.
Important early theoretical studies of weak reactions in the
nuclear astrophysics community were made by Fulleretal. (1980);
Fulleretal. (1982a);Fulleretal. (1982b);Fulleretal. (1985). ese
collections included stellar weak interaction rates for intermediate-
mass nuclei (up to mass 60) and are still used by some
astrophysical simulation codes today (Timmes, 2023). Temperature
dependences were soon added to tables of weak rates (Takahashi
and Yokoi, 1987). Many other advances have followed, using a wide
variety of theoretical approaches including microscopic models,
shell-model Monte-Carlo, random phase approximation (RPA),
quasiparticle RPA, relativistic RPA, nite-temperature relativistic
nuclear eld theory, and many more [see, e.g.,Ferreiraetal.
(2014);Litvinovaetal. (2020);Suzuki (2022);Goriely (2023a);
Suzukietal. (2023)]. While some tables of weak rates have been
published in the literature [see, e.g.,Takahashi and Yokoi (1987);
Mölleretal. (1997)], others have been folded into the major
thermonuclear reaction rate libraries (described above) including
JINA REACLIB (JointInstituteforNuclearAstrophysics, 2023a),
BRUSLIB (Goriely, 2023b), and others. e most recent global
calculation, in Neyetal. (2020), employs a nite-amplitude method
and quasiparticle RPA to calculate beta decays of nearly 4,000
neutron-rich nuclei; the beta decays and strength functions are
available as a Supporting Material to the journal article (Neyetal.,
2023).
2.4 Astrophysics simulation codes,
processing tools, and software systems
2.4.1 Simulation codes
Astrophysics simulations play a pivotal role in enabling
studies of the cosmic creation of elements and the evolution
and explosion of stellar systems. e two major aspects of these
simulations, the hydrodynamics and the thermonuclear burning,
are closely coupled: energy generated by thermonuclear burning
alters the hydrodynamics (i.e., temperature and density), and
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updated hydrodynamics alters the reaction rates and subsequent
thermonuclear burning. While the ideal simulation would fully
couple these two aspects—a high resolution three-dimensional
(3D) numerical hydrodynamical treatment coupled to a complete
thermonuclear reaction network—this is not yet possible (even in
2D) due to the extreme computational resources required. For this
reason, simulations emphasizing the hydrodynamic aspects utilize
a truncated reaction network (e.g., an alpha-nuclei network); this
provides, in a computationally possible manner, an approximation
to the nuclear energy generation that dynamically modies the
hydrodynamic conditions at each time step. e current state-
of-the-art in core-collapse supernova modeling has, notably, now
reached high resolution 3D numerical hydrodynamics simulations
with a 160 nuclide network (Sandovaletal., 2021). With computing
power now reaching the exaop (1018 oating point operations per
second) scale (ORNL, 2023), it is exciting to imagine that coupling
3D hydrodynamics and full thermonuclear burning will perhaps be
achieved for some systems within a decade.
In contrast, there are two categories of simulations with modest
computational requirements: those that combine an approximate
1D analytical hydrodynamics calculation with a full thermonuclear
burn simulation, and “post-processing” codes that calculate a
full thermonuclear burn over an static (imported) hydrodynamics
prole. ese simulations can routinely track compositional changes
over thousands of nuclear species.
For each of these three categories of simulations, thermonuclear
reaction rate libraries provide critical nuclear physics input. Most
codes having a preferred rate library format of either pointwise rates
or analytical rate formulae. Additionally, some codes have a default
rate library that is hardwired, others enable rate library substitutions
aer a fair amount of eort, and still others make it easy to rapidly
change rate libraries. Below, we describe a variety of astrophysical
simulation codes that are available to the community.
e Modules for Experiments in Stellar Astrophysics (MESA)
(Paxtonetal., 2011;MESACollaboration, 2023) is a widely used set
of open source libraries for computational stellar astrophysics. It
features a 1D stellar evolution module that couples hydrodynamics
and nucleosynthesis using adaptive mesh renement, and has
separate modules for nuclear reaction rates, equations of state, and
more. e default thermonuclear reaction rate library for MESA is
a custom combination of 300 rates from CF88, NACRE, and others;
there is an option to use rates from the JINA REACLIB collection as
well.
e NUGRID post-processing nucleosynthesis code
(Denissenkovetal., 2014;NUGRIDCollaboration, 2023) has the
capability of processing the multi-zone output of 1D stellar evolution
codes such as MESA (Paxtonetal., 2011;MESACollaboration,
2023), and enables a dynamical adjustment of the size of the network
depending on the composition. NUGRID has a reaction library that
combines pointwise reaction ratesf rom numerous sources including
NACRE (Anguloetal., 1999), CF88 (Caughlan and Fowler, 1988),
BRUSLIB (Goriely, 2023b), an early version of JINA REACLIB
(JointInstituteforNuclearAstrophysics, 2023a), and other
sources. NUGRID also has an associated jupyter-based platform
and python scripts.
XNet (Hix, 2023) is a fully-implicit post-processing
nucleosynthesis code. It can be run in standalone mode or
coupled to a hydrodynamics package. For the latter, XNet has
been coupled to FLASH (Fryxelletal., 2000;Dubeyetal., 2009)
and CHIMERA (Bruennetal., 2020) for studies of core collapse
supernova simulations [see, e.g.,Sandovaletal. (2021) mentioned
above], as well as to other codes to study other phenomena. XNet
uses thermonuclear rates from JINA REACLIB as a default, and can
track ∼5,000 nuclide abundances for r-process studies. As described
below, XNet has also been integrated into the Computational
Infrastructure for Nuclear Astrophysics (CINA) (Smith, 2023) in
a manner that enables rapid customization of input reaction rate
libraries.
e Portable Routines for Integrated nucleoSynthesis Modeling
(PRISM) nucleosynthesis code (Sprouseetal., 2020;Sprouseetal.,
2021) is a modern code used for a novel “nucleosynthesis tracing”
technique. PRISM relies primarily on theoretical reaction rates of r-
process nuclei calculated with the statistical Hauser-Feshbach code
CoH (Kawanoetal., 2016).
SkyNet (Lippuner and Roberts, 2017) is another new nuclear
reaction network code. It is written in a modular fashion and
features signicant attention to neutrino-induced nucleosynthesis.
is code uses as default reactions from JINA REACLIB
(JointInstituteforNuclearAstrophysics, 2023a) and from other
sources.
Torch (Timmes, 1999;Timmes, 2023) is an older general
reaction network that is set for a 513 isotope network by default;
this network can be expanded to include more species as needed.
e default nuclear reactions are from a combination of an
early version of REACLIB (JointInstituteforNuclearAstrophysics,
2023a), NON-SMOKER (Rauscher, 2023a), and other sources.
e WinNet (Winteler, 2013) code is an updated version of
the BasNet (ielemannetal., 2011) reaction network; neither of
these two codes are publicly distributed. WinNet can track over
5,800 nuclides, contains reactions from NON-SMOKER and many
other sources, and has been used for studies of the r-process
in core-collapse supernovae and in neutron star mergers [e.g.,
Korobkinetal. (2012)].
e Webnucleo nuclear reaction network (Meyer, 2012;Meyer,
2023) is a modular system for nucleosynthesis calculations available
both in jupyter notebooks and in downloadable source code. is
system accepts user-specied pointwise reaction rates as default
inputs. e pynucastro library (SmithAI.etal., 2023) is a new
open-source python library that enables interactive creation and
exploration of nuclear reaction networks. e networks built with
this system can be exported for use in large-scale simulation codes.
2.4.2 Processing Tools and software systems
Signicant eort is required to prepare the thermonuclear
reaction libraries that are the key nuclear input for all the
simulations discussed above. Of all the necessary steps, the most
critical are the calculation of resonant cross sections from the
properties of near-threshold levels and the numerical integration
of energy-dependent cross sections to form temperature-dependent
thermonuclear reaction rates. ese processing steps are well known
and are discussed in books [e.g.,Clayton (1984);Rolfs and Rodney
(1988);Iliadis (2015)] as well as in many journal articles. For this
reason, many nuclear astrophysics research groups have built, but
rarely distribute, their own codes for such calculations. It should
be noted, however, that some details (e.g., numerical integration
routines) can produce dierences in outputs from dierent codes.
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Another important processing step is the tting of temperature-
dependent rates to analytical formulae. Such ts are challenging
because reaction rates can vary by up to 30 orders of magnitude
or more over astrophysical temperature ranges (see, e.g.,Figure2).
Fits of rates to the REACLIB analytical formulation are, for example,
discussed in Cyburtetal. (2010). Other important processing
steps include creating inverse reaction rates from forward rates
and checking that they obey the principle of detailed balance,
converting cross sections to S-factors, numerically interpolating
codes to generate thermonuclear rates at any temperature from
pointwise rate tables, downloading and extracting data from
standard databases [e.g., ENDF (NationalNuclearDataCenter,
2023a), ENSDF (NationalNuclearDataCenter, 2023b)], and more.
A number of these processing steps are contained within
CINA (Nesarajaetal., 2005a;Nesarajaetal., 2005b;Smith, 2005;
Smithetal., 2006;Smith, 2023). is soware system is a unique
online cloud-computing data “pipeline” that provides a simple
graphical user interface (GUI) to guide users step-by-step in
processing and using nuclear data in astrophysical simulations.
Operating since 2004, CINA enables users to work with nuclear
data, with thermonuclear reaction rates, and with nucleosynthesis
simulations. For nuclear data, users can upload, manipulate, and
save reaction cross sections. For thermonuclear rates, users can:
convert cross sections or S-factors into thermonuclear reaction
rates via numerical integration; modify, parameterize (i.e., t
to the REACLIB analytic formula), and save rates into rate
libraries; and combine libraries to form custom collections that
can run in nucleosynthesis simulations. For simulations, users can:
upload custom hydrodynamic proles; set up and execute post-
processing nucleosynthesis simulations with the XNet code (Hix,
2023); run multi-zone simulations and compute zone-weighted
nal abundances; set up batch modes of runs over multiple rate
libraries and hydrodynamic proles; rapidly change nuclear physics
inputs (i.e., reaction rates) and determine astrophysical impacts;
run automated sensitivity studies for determining input (rate) vs
output (abundance) correlations; save and visualize simulations
with customizable plots and animations; analyze and annotate
simulations; quantify uncertainties in predicted nal abundances;
and compare multiple simulation results. Information in CINA,
including large custom rate libraries and simulation outputs,
can easily be shared between users within the system as well
as exported. CINA’s GUI is platform independent and runs on
any machine with Java installed; the system is free to use and
all users receive free disk space to store their runs. Since it
is a remotely-executed cloud computing service, CINA requires
users to have an active internet connection, but does not require
any compilation, libraries, licenses, special environments, or user
updates in order to operate. CINA utilizes the JINA REACLIB
(JointInstituteforNuclearAstrophysics, 2023a) database as the
default rate library, but enables users to quickly create, save, share,
and use customized rate libraries from within the GUI.
2.5 Bibliographic data
Bibliographic data is also critical for progress in nuclear
astrophysics research. e three most valuable resources are
described below, created by the astrophysics, nuclear data, and
nuclear astrophysics communities, respectively. First, the NASA
Astrophysical Data System ADS (NASA, 2023) is a widely used
service that contains references from hundreds of journals in
astrophysics and related elds, including those not accessed in
other services like Monthly Notices of the Royal Astronomical
Society (MNRAS) (OxfordAcademic, 2023) and Publications of the
Astronomical Society of the Pacic (PASP) (IOPScience, 2023).
ADS also, for example, contains direct links to many articles (in
HTML or PDF formats) published in the Astrophysical Journal
(American Astronomical Society, 2023).
In the nuclear data community, the Nuclear Science References
(NSR) (Pritychenkoetal., 2011) bibliographic database is the
standard source for reference material. NSR, which contains
references to over 250,000 papers in nuclear physics going back
over 100years, includes a DOI number and a unique accession
number for each entry; ENSDF nuclear structure evaluations list
these accession numbers directly in their bibliographic database
eld. NSR entries also contain keywords which facilitates evaluation
work as well as general searches. Finally, from the nuclear
astrophysics community, the JINA Virtual Journal of Nuclear
Astrophysics (JointInstituteofNuclearAstrophysics, 2023b) is a
valuable resource for research. e editors of this source scan 42
nuclear science and astrophysics journals for articles in nuclear
astrophysics.
2.6 Dissemination services
Data dissemination refers to the distribution of datasets
via downloads, access to datasets and their data by
browsing/searching/ltering, and visualization. e two major
dissemination services in the nuclear data community are the
National Nuclear Data Center (NNDC) (Brookhaven National
Laboratory, 2023) in the US and the Nuclear Data Services
(International Atomic Energy Agency, 2023a) at the International
Atomic Energy Agency (International Atomic Energy Agency,
2023b) in Vienna. ese provide access to the unevaluated databases
XUNDL (Brookhaven National Lab, 2023) and EXFOR (IAEA
Nuclear Data Services, 2023a), the evaluated databases ENSDF
(National Nuclear Data Center, 2023b) and ENDF (National Nuclear
Data Center, 2023a), and many more datasets and services for
basic and applied nuclear science. For any given dataset, there
is no single dissemination method that satises the needs of the
entire community. It is therefore common that dierent approaches
are used at dierent nuclear data centers to access certain critical
databases. For example, NuDAT (National Nuclear Data Center,
2023c) is used to access XUNDL and ENSDF at the NNDC,
while LiveChart (IAEA Nuclear Data Services, 2023b) is used for
similar purposes at the IAEA NDS. Because new dissemination
tools are routinely added to the NNDC and IAEA NDS sites,
it is recommended to regularly browse their websites for new
resources.
In the nuclear astrophysics community, databases are usually
disseminated via a website at the institution where the database
is hosted. Many of these websites were referenced in the sections
above. For example, rate libraries including JINA REACLIB
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(JointInstituteforNuclearAstrophysics, 2023a), STARLIB (Iliadis,
2023), TENDL (Koning, 2023b), NACRE-II (Goriely, 2013), and
KADONIS (Dillman, 2023) all have their own webpage for
dissemination. In some cases, libraries can also be accessed through
services that incorporate or manipulate them. For example, the
JINA REACLIB library can be accessed through CINA (Smith,
2023), and NACRE and NACRE-II can be accessed through
BRUSLIB (Goriely, 2023b). It is not uncommon for website
addresses to change, however, as well as for web hosting to
be discontinued. For example, the original web posting of the
NACRE collection is no longer online. ere are also examples
of certain libraries being manually entered into websites, such as
the CF88 library (SmithM.etal., 2023), while other datasets are
posted as individual journal articles [e.g.,Rauscher and ielemann
(2001)] or as the Supporting Material of an article [e.g.,Neyetal.
(2023)].
2.7 Other data
2.7.1 Nuclear equation of state
e nuclear equation of state (EOS) describes the characteristics
(e.g., compressibility) and the dynamics of nuclear matter in ultra-
dense systems such as neutron stars, core-collapse supernovae,
and neutron star mergers (Oerteletal., 2017). In Sumiyoshietal.
(2020), considerations of the inuence of neutron-rich matter,
hyperons and quark matter, and hadron-to-quark transitions in
EOS studies are reviewed. Because the EOS is needed, especially
for supernova simulations, at nite temperature and various lepton
fractions, the results are usually presented in a tabular fashion, and
many studies [e.g.,Shen (2014);Shenetal. (2020)] have produced,
analyzed, and compared the impact of dierent EOS tables on
neutron stars and related systems. While not all EOS reported in
the literature are publicly distributed, an online archive of many
EOS tables may be found at Shen (2023a). e EOS tables for some
particular studies are also posted online [e.g.,Shen (2023b);Lattimer
(2023)].
2.7.2 Fission yields
In the synthesis of the heaviest elements in core-collapse
supernovae and neutron star mergers, the series of neutron captures
on n-rich unstable nuclei, the r-process, leads to the formation of
nuclei that undergo ssion[se e,e.g.,C ôtéetal.(2018)]. When ssion
causes these heavy nuclei break apart, this eectively prevents even
more massive nuclei from being formed; it therefore helpsdetermine
the “endpoint” of the r-process. From as early as the 1930s [e.g.,
Bohr and Wheeler (1939)], the ssion process has been a focus of
a segment of the nuclear physics community. Despite much eort,
the complex mechanism of ssion has made it very challenging to
model (Schunck and Robledo, 2016). For this reason, ssion has
rarely been incorporated in astrophysical simulations even though
it plays a critical role in the decay of heavy nuclei. In Goriely (2015),
the eects of ssion recycling (where ssion products undergo
subsequent neutron captures leading to ssion), ssion fragment
distributions, and the capture of prompt ssion neutrons were
investigated. e results of some ssion models relevant for nuclear
astrophysics are posted online: BRUSLIB (Goriely, 2023b) provides
ssion information for 1,000 isotopes with Zranging from 90 to
110, and Goriely (2009) provides similar information. More recently,
the Fission In R-process Elements (FIRE) collaboration (Côtéetal.,
2018;FIRECollaboration, 2023) was formed to focus on integrating
advanced models of spontaneous, neutron-induced, and β-delayed
ssion into rapid neutron capture (r-process) nucleosynthesis
codes and examining the subsequent astrophysical impacts. A
set of their ssion yields are distributed at FIRECollaboration
(2022).
3 Challenges
e section above details both the specialized steps prepare
nuclear data for use in astrophysical simulations, and the wide
variety of data resources that help can help with this important
work. While some of these resources were specically developed
for nuclear astrophysics data, others are more general purpose
databases and tools developed for basic and applied nuclear
science that nonetheless have signicant utility for astrophysical
simulations.
Despite the impressive list of available resources, the current
status of nuclear data for nuclear astrophysics is problematic. Below
we discuss some major challenges that constrain the scientic impact
of current work and may impede future eorts.
3.1 Outdated reaction rate libraries
e most critical challenge is that the major reaction rate
libraries discussed in Section2 above do not contain the latest
measurements and theoretical calculations. Because of the time
required to compile, assess, and process datasets, some lag
(perhaps ∼3years) is expected between the publication of new
results and their incorporation into databases. e current
delays are, however, much longer. e JINA REACLIB database
(JointInstituteforNuclearAstrophysics, 2023b), for example,
added no new rates for nearly a decade (2012–2021), then none since
the addition of 46 new rates in 2021. Many measurements made in
that decade are missing from this critical library. Also troubling is the
48,000 rates in JINA REACLIB based on NON-SMOKER (Rauscher,
2023a) cross sections have not been updated since 2009, and those
particular cross sections utilized nuclear masses from the 2003
Atomic Mass Evaluation (Audietal., 2003;Wapstraetal., 2003),
which are nearly two decades out of step with the latest AME2020
values (Huangetal., 2021;Wangetal., 2021). Furthermore, the
NON-SMOKER rates themselves have not been updated since 2011
(Rauscher, 2023b).
Regarding other major libraries, BRUSLIB (Goriely, 2023b) and
NETGEN (Jorissen, 2023) were last updated in 2015, while STARLIB
(Iliadis, 2023) has only added a few rates since 2015. Additionally,
both BRUSLIB and STARLIB use rates from TALYS (Koning, 2023a)
statistical model cross sections generated before 2015, and therefore
do not take advantage of the signicant progress in TALYS since that
time (Koningetal., 2019). e NACRE eort (Anguloetal., 1999)
ended in 1999, while NACRE-II (Xuetal., 2013a;Goriely, 2013)
ended in 2013. KADONIS (Dillman, 2023) was completed in 2005
(with some updates in 2013), while the RIPL eort (Capote, 2023)
ended in 2013.
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Smith 10.3389/fspas.2023.1243615
e lack of assessment eorts and resulting time delay
from measurements and theory calculations to incorporation into
databases have a signicant scientic impact: many astrophysics
modelers are utilizing nuclear information that is many years out
of date, which calls into question the reliability and accuracy
of their model predictions, as well as the consistency of these
predictions with other studies that have used more updated
data. Actions that may reduce this time lag are discussed in
Sections4 and 5.
3.2 Growing demands, stagnant
productivity
As mentioned in Section1, this is an incredibly exciting
time in the eld of nuclear astrophysics. e number of new
nuclear datasets will jump dramatically as new accelerator facilities
[e.g., FRIB (Weietal., 2019), RIBF (Motobayashi and Sakurai,
2012), FAIR (Scheidenberge, 2017), RAON (Hong, 2023)] begin
measurements with unstable beams. Rapid progress in astrophysical
simulations, including more realistic treatments of thermonuclear
burning in multi-dimensional simulations and going beyond
Sandovaletal. (2021) and into the exascale computing regime,
will place more stringent demands on nuclear data than ever
before. Additionally, a new generation of space observatories [e.g.,
the Origins Space Telescope (OriginsSpaceTelescopeStudyTeam,
2023a;OriginsSpaceTelescopeStudyTeam, 2023b) and the Lynx
X-ray Observatory (Lynx X-ray Observatory Team, 2023)] promise
decades of new discoveries that will likely push all aspects of
astrophysical modeling—including the nuclear data input—to new
directions and new extremes.
To ensure that this growing demand for nuclear data can be
met, the productivity of eorts to compile, assess, and process data
must increase. is increase could come from a combination of a
larger workforce, a workforce with new capabilities, and advances
in methodology. Presently, however, there is stagnation in all three
areas. First, the workforce that has long pursued nuclear data work
for nuclear astrophysics is subcritical and is not being readily
replaced by new recruits, based on the number of publications and
the authorship in the eld as well as on anecdotal information.
Secondly, the adoption of the latest advances in this eld is lagging
behind that in nuclear theory and other areas of nuclear science.
Examples of this can be seen in, for example, Boehnleinetal.
(2022) for progress in machine learning in nuclear physics, and
Kolosetal. (2022) for nuclear applications. ird, with a number
of important and valuable exceptions [e.g.,Anguloetal. (1999);
Sprouseetal. (2021);Iliadisetal. (2022);Mumpoweretal. (2022);
SmithAI.etal. (2023);Iliadis (2023);Smith (2023)], there have been
limited methodology innovations in this eld. As an example, no
new methods of accessing thermonuclear reaction rates have been
developed in nearly 40years: the innovation of a single analytical
functional form for all reaction rates (ielemannetal., 1987) was
in the mid-1980s, at about the same time that pointwise rates became
popular (Caughlanetal., 1985), and this was 20years aer the
introduction of using dierent formulae for each rate (Fowleretal.,
1967).
By recognizing this coming “perfect storm” of growing demand
and excitement in nuclear astrophysics coupled to stagnant
productivity in the associated data eort, it may be possible to
lessen the impact with prudent planning and new initiatives. Some
possibilities are listed below in Sections4 and 5.
4 Data needs and initiatives
By recasting the challenges discussed above in Section3 into
prioritized nuclear data needs, initiatives can be devised that may
help ensure the longevity of eorts to best prepare nuclear data
for use in astrophysical simulations. First, for the crisis of outdated
reaction rate libraries, it is clear that [1] assessments of low-energy
cross sections and near-threshold level properties are needed, along
with [2] enhanced eorts in global nuclear structure and reaction
calculations. To address the crisis of stagnant productivity in an
era of growing demand, a solution may be found by [3] advancing
the methodology in nuclear astrophysics data. ese are all high
priority needs for the nuclear astrophysics community. Below we
discuss initiatives to meet these needs, then give suggestions for
implementation in Section5 below.
4.1 Enhanced cross section and level
property assessments
Assessments of cross sections and level properties are the
most time-consuming step in bringing lab results into astrophysics
models. Unfortunately, the community is currently lacks a steady
source of these assessments. In the U.S., for example, only 1% of
the eort of the national nuclear data program (NNDC, 2023c)
is directed at nuclear astrophysics topics, while at the same time
the previous eorts in assessments (see Section3) have been
concluded. e few ongoing eorts in this area are primarily
small projects in individual research groups that tend to be under-
and haphazardly-funded, driven by specic short-term research
goals, and pursued independently of others. As a result, these
lack continuity, completeness, and a coordinated vision for the
future. Establishing an eort in cross section and level property
assessments for nuclear astrophysics is the critical step to initiate
updates of the outdated thermonuclear rate libraries discussed in
Section3. While the particular choice of reactions and nuclear
levels to assess may depend on many factors—sensitivity studies
[e.g.,SmithMS. (2011);Zhuetal. (2021)], recent experimental
activities, the quality of existing datasets, requests by astrophysical
modelers, the complexity of the evaluation, the interests of the
evaluators, and the connections to astrophysical observations—it
is clear that the problem of outdated thermonuclear rate libraries
is most directly addressed by establishing a new assessment
eort.
4.2 Enhanced global nuclear model
calculations
Despite signicant progress of recent eorts to provide
theoretical cross sections and level properties across the nuclear
chart (discussed in Sections2.1 and 2.2), enhanced eorts in this
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Smith 10.3389/fspas.2023.1243615
work are needed—for nuclear astrophysics as well as for many
related research areas. For cross sections, eorts with TALYS are
advancing the eld, but more work is needed with that code
to calculate charged-particle induced reactions—and then to
include the results in TENDL-Astro (Koning, 2023c). It is also
important to increase the energy delity of low-energy TALYS
cross sections on low-mass target nuclei. e use of other reactions
codes like CoH (Kawanoetal., 2016) and EMPIRE (Hermanetal.,
2007) for global calculations is also essential, to ensure that
TALYS is not the sole source for this valuable information.
Regarding work with global structure models, eorts are needed
for comprehensive calculations of bound and near-threshold level
properties, because of the non-negligible contributions of direct
and resonant capture to the total capture cross section (Goriely,
1998a). It is possible that combining high performance computing
techniques [e.g.,NUCLEICollaboration (2023)] with a variety of
theoretical approaches [e.g., those described in Goriely (2023a)]
could signicantly improve structure property estimates that are
essential for global reaction rate calculations. Overall, boosting eort
in global model calculations of cross sections and level properties will
be of tremendous benet in nuclear astrophysics, as well as in basic
and applied nuclear science.
4.3 Improved methodologies
As mentioned above in Section3, expanding and evolving
the workforce would certainly be an eective way to address the
stagnant productivity of this work in an era of growing demand.
In this review, however, we will focus on technical solutions to
help productivity, specically on [3] advancing the methodology
in nuclear astrophysics data. Because some current codes in this
community have their roots in outdated techniques (e.g., numerical
approaches and approximations, poor documentation, lack of
benchmarks), there may be opportunities for very cost-eective
methodology improvements that “do more with less”. Changes
in methodology can be inspired by advances in the underlying
physics and by advances in other elds (e.g., machine learning, data
science, high performance computing, and (see below) high energy
physics), as well as by unexpected and innovative [“disruptive”
(Williams, 2011)] ideas. In addition to boosting eciency, new
methodologies could result in improved quality, reproducibility,
reliability, longevity, and provenance (i.e., tracing of data sources).
Finally, given the recent emphasis on uncertainty quantication
(UQ) eorts [e.g.,Barnesetal. (2021);Kolosetal. (2022)], adding
UQ where it is missing would be a signicant methodology
improvement.
One way to improve methodologies is to enhance development
eorts of the soware tools described in Section2.4. As mentioned
therein, many research groups have their own basic or specialized
tools, and there is an established online data pipeline found in
CINA (Smith, 2023) that processes cross sections into astrophysical
simulations with a point and click GUI. Investments in expanding
current capabilities, including folding in more advanced UQ
and machine learning approaches, could signicantly boost
overall productivity in a very cost-eective manner. Some new
features to develop include: batch processing of complete cross
section libraries into rate libraries; quick transformation of rate
libraries between formats used by leading simulation codes;
toolkits (with templates, guides, Frequently Asked Questions,
smart agents, and more) to speed reaction and level assessments;
automated comparisons of rate libraries [e.g.,Homanetal. (1999);
Zhangetal. (2022)] downloading and extracting data from standard
databases [e.g., ENDF (NationalNuclearDataCenter, 2023a),
ENSDF (NationalNuclearDataCenter, 2023b)]; and benchmarks
and validation/verication tools for datasets, processing codes, and
simulation codes. Because dierent researchers have dierent needs,
it is unlikely that any single processing service can meet the needs
of the entire community, so such tools need not necessarily be
centralized.
Inspiration for a new generation of soware tools in
nuclear astrophysics, however, could possibly be found by
adopting approaches followed by large physics collaborations
with vetted analysis soware stacks [e.g., at RHIC (Potekhin,
1467 2023)] and roadmaps for future developments [e.g., the
HEP Soware Foundation (HEPSowareFoundation, 2018)].
Aspects favored in such approaches include: developing modular,
shared, community resources; ensuring resources can be scaled
up, swapped, and customized; developing for longevity and
sustainability; including robust documentation, debugging, and
benchmarking; managing developments with soware experts;
minimizing duplication of eort; encouraging collaborations in
data science and machine learning; and exploring new paradigms.
Ultimately, whether incremental or next-generation in nature,
methodology improvements have tremendous potential to improve
the productivity—and many other aspects—of nuclear astrophysics
data eorts.
5 Discussion
e priorities discussed above in Section4 are to establish eorts
to assess cross sections and level properties, to boost eorts in
global model calculations, and to improve the methodologies used
in nuclear astrophysics data work. Together, these initiatives would
bring thermonuclear rate libraries more up-to-date and prepare
the community to handle an onslaught of new measurements,
theory calculations, and observations that may push the eld
in new directions. If executed well, additional benets from
these eorts may include improving their overall quality and
longevity, forging stronger ties within the community and to
related elds, attracting new recruits, and enabling more of
the full scientic potential of measurements and theories to be
explored.
While the science case for these initiatives was discussed above,
in this section we briey describe issues with their launching and
implementation. First, it is critical to note that these are not risky
concepts. More specically, success of these proposed initiatives for
nuclear astrophysics data do not rst require an eortto demonstrate
proof of principle, as there are successful exemplars of similar eorts
from the past. erefore, the success of these recommended eorts
will hinge upon the well known challenges of obtaining funding,
successful recruiting, and nding principle investigators with the
needed technical background, motivation, and resolve.
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Smith 10.3389/fspas.2023.1243615
Of these three initiatives, the rst is undoubtedly the most
challenging to implement: in contrast to global calculations that
calculate thousands of rates at once, for example, each individual
reaction must be assessed one at a time. To discuss the launch an
assessment eort, it is critical to rst specify the desired output
and duration. A reasonable eort may have a goal of assessing
approximately 100 reactions—enough to make a sizable impact
on the eld—in a time frame (∼5years) typical of long topical
collaborations. Assuming part-time collaborators (pursuing both
research and assessments) who complete 2 assessments each per
year, a group of 15 such collaborators could likely complete 100
assessments in 5years, if year-long periods for initial training
and coordination for nal writing are included. ese numbers
are roughly consistent with the NACRE (Anguloetal., 1999)
collaboration led by C. Angulo from 1993–1999, which had 28
collaborators from 8 countries who assessed 86 reactions. NACRE
has, to date, been the only large, coordinated, international, multi-
institutional collaboration for nuclear astrophysics assessments. It
featured a standardized methodology, a thorough documentation,
and internal peer reviews resulting in a high quality of work. For
these reasons, NACRE is the successful exemplar of the proposed
new assessment eort.
Of course, the output of any eort depends on the commitment
and experience of the collaborators, the complexity of the
assessments, whether the assessments are updates of previous
work, and many other factors. is can be seen from the wide
range of metrics of other past eorts: in 1991, 12 reactions
were assessed in 1year (Smithetal., 1993); the eort led by
W. Fowler from 1967–1988 (Fowleretal., 1967;Fowleretal.,
1975;Harrisetal., 1983;Caughlanetal., 1985;Caughlan and
Fowler, 1988) had 2 to 4 collaborators who assessed and updated
between 36 and 159 reactions; and the eort led by Iliadisetal.
(2001) had 5 collaborators who assessed 55 reactions. It should
be noted that while there are a number of obstacles—funding,
recruiting, sociological—that could hamper the launch of such a
large initiative, there are also a number of advantages—extensive
experience with virtual meetings, more previous eorts to learn
from—that a modern eort has over the past. Most importantly,
it has been 30years since NACRE was formed, and it seems
long overdue that a segment of the community came together to
assess critical reactions and level properties and drive the eld
forward.
e challenges facing the launch of boosted eorts in
global model calculations are more modest by comparison.
For example, there are far fewer global reaction codes to
develop than individual reactions to assess, and there are
multiple potential funding sources and workforce pools to
draw from because of overlaps with basic and applied nuclear
science. Since this initiative is a boost (hopefully signicant) to
ongoing eorts, a key challenge would be to distinguish it from
“business as usual”. By delineating and completing a strong set
of deliverables, such as generating three global thermonuclear
rate libraries along with a study comparing both the results
and the codes, this challenge could be readily handled. In fact,
there are many instances of theoretical collaborations that have
successfully overcome this issue [e.g., for the theory of jets in
relativistic heavy ion collisions (Gyulassyetal., 2015)], as well as
successful theory comparison eorts [e.g., with statistical model
codes (Homanetal., 1999) and R-matrix codes (Leebetal.,
2023)].
Finally, there are many dierent ways to congure an
initiative to improve nuclear astrophysics data methodologies;
this mirrors the range of possible activities and approaches
mentioned above in Section4. A low-cost approach would be
to form a working group that regularly met to propose and
discuss collaborative projects, new concepts, coding obstacles,
connections with other elds, and short- and long-term planning. It
would be advantageous if such a working group would strongly
advocate a common conceptual and soware framework—one
that included dening the elements of a data pipeline and their
characteristics with shared base code templates. In that way,
disparate projects run independently by collaborators could
work together in a virtual data pipeline that could be used by
all.
Alternatively, a large scale, centrally managed initiative
modeled aer those in other elds (e.g., high energy physics
(HEPSowareFoundation, 2018)) could combine large, medium,
and small scale projects to form a robust, benchmarked, vetted,
cohesive soware ecosystem for nuclear astrophysics research.
e challenge of launching and sustaining such an eort would
be oset by its technical advantages (described in Section4) as
well as by the achievement of building a system that could set
the standard—for not just nuclear astrophysics, but also for the
low energy nuclear science and astrophysics theory communities.
Such an eort would require a combination of researchers,
professional coders, project integration management experts, and
students. It should be noted that an eort of this scale would
be immensely valuable for recruiting a new generation into the
eld, and even more so if ties to machine learning and data
science communities—and a commitment to community wide
ideals [e.g., OPEN Data (CenterforOpenScience, 2023), FAIR
(Wilkinsonetal., 2016)]—were established as core components
of the system.
6 Summary
e study of the cosmic synthesis of elements, the evolution
and explosion of stars, the nature of the early Universe,
and other important topics in nuclear astrophysics are now
central to nuclear science. Studies of these puzzles motivate
a wide range of laboratory measurements and theoretical
calculations, but the latest results must be processed before
they can be used in astrophysical simulations to advance
the eld. Highly specialized resources are required, and
have been developed, for this processing, including nuclear
reaction and nuclear structure data sets, thermonuclear reaction
rate libraries, processing codes, and simulation codes and
services. Unfortunately, many of these resources are out
of date, lack an update plan, and do not utilize advanced
approaches in data science. By establishing an eort to assess
cross sections and level properties, boosting eorts in global
model calculations, and improving nuclear astrophysics data
methodologies, the latest nuclear data could be more rapidly
incorporated into the astrophysical simulations that improve
our understanding of the cosmos. ese initiatives also have the
Frontiers in Astronomy and Space Sciences 14 frontiersin.org
Smith 10.3389/fspas.2023.1243615
potential to strengthen and expand the nuclear astrophysics
community.
Author contributions
e author conrms being the sole contributor of this work and
has approved it for publication.
Funding
is work was supported by the U.S. Department of Energy
Oce of Science, Oce of Nuclear Physics, under Contract Number
DE-AC05-00OR22725 at ORNL.
Acknowledgments
e author wishes to thank Caroline Nesaraja and Larry
Zhang for helpful discussions, and the late Richard Meyer for
encouraging the author to collaborate with the nuclear data
community.
Conict of interest
e author declares that the research was conducted in the
absence of any commercial or nancial relationships that could be
construed as a potential conict of interest.
Publisher’s note
All claims expressed in this article are solely those of the
authors and do not necessarily represent those of their aliated
organizations, or those of the publisher, the editors and the
reviewers. Any product that may be evaluated in this article, or claim
that may be made by its manufacturer, is not guaranteed or endorsed
by the publisher.
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