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This white paper informs the nuclear astrophysics community and funding agencies about the scientific directions and priorities of the field and provides input from this community for the 2015 Nuclear Science Long Range Plan. It summarizes the outcome of the nuclear astrophysics town meeting that was held on August 21–23, 2014 in College Station at the campus of Texas A&M University in preparation of the NSAC Nuclear Science Long Range Plan. It also reflects the outcome of an earlier town meeting of the nuclear astrophysics community organized by the Joint Institute for Nuclear Astrophysics (JINA) on October 9–10, 2012 Detroit, Michigan, with the purpose of developing a vision for nuclear astrophysics in light of the recent NRC decadal surveys in nuclear physics (NP2010) and astronomy (ASTRO2010). The white paper is furthermore informed by the town meeting of the Association of Research at University Nuclear Accelerators (ARUNA) that took place at the University of Notre Dame on June 12–13, 2014. In summary we find that nuclear astrophysics is a modern and vibrant field addressing fundamental science questions at the intersection of nuclear physics and astrophysics. These questions relate to the origin of the elements, the nuclear engines that drive life and death of stars, and the properties of dense matter. A broad range of nuclear accelerator facilities, astronomical observatories, theory efforts, and computational capabilities are needed. With the developments outlined in this white paper, answers to long standing key questions are well within reach in the coming decade.

The neutron-capture reaction plays a critical role in the synthesis of the elements in stars and is important for societal applications including nuclear power generation and stockpile-stewardship science. However, it is difficult---if not impossible---to directly measure neutron capture cross sections for the exotic, short-lived nuclei that participate in these processes. In this Letter we demonstrate a new technique which can be used to indirectly determine neutron-capture cross sections for exotic systems. This technique makes use of the $(d,p)$ transfer reaction, which has long been used as a tool to study the structure of nuclei. Recent advances in reaction theory, together with data collected using this reaction, enable the determination of neutron-capture cross sections for short-lived nuclei. A benchmark study of the $^{95}\mathrm{Mo}(d,p)$ reaction is presented, which illustrates the approach and provides guidance for future applications of the method with short-lived isotopes produced at rare isotope accelerators.

The need for accurate nuclear reaction data of actinides is well documented and several initiatives from international organizations for improvement have been initiated in the past. This need, particularly in view of method development for non-destructive assay of nuclear waste, has generated a joint effort to use prompt and de- layed neutron activation techniques to enhance nuclear capture data of some long lived actinides such as 237 Np, 242 Pu and 241 Am in the frame of a multilateral cooperation. This research initiative is targeted to lay grounds for the development of a non-destructive active neutron interro- gation technique to quantify actinides in mixed waste and residues from decommissioning of nuclear installations for safe treatment and storage of such materials.

Obtaining reliable data for nuclear reactions on unstable isotopes remains an extremely important task and a formidable challenge. Neutron capture cross sections---crucial ingredients for models of astrophysical processes, national security applications, and simulations of nuclear energy generation---are particularly elusive, as both projectile and target in the reaction are unstable. We demonstrate a new method for determining cross sections for neutron capture on unstable isotopes, using $^{87}\mathrm{Y}(n,\ensuremath{\gamma})$ as a prototype. To validate the method, a benchmark experiment is carried out to obtain the known $^{90}\mathrm{Zr}(n,\ensuremath{\gamma})$ cross section analogously. Our approach, which employs an indirect (``surrogate'') measurement combined with theory, can be generalized to a larger class of nuclear reactions. It can be used both with traditional stable-beam experiments and in inverse kinematics at rare-isotope facilities.

Accurate neutron-capture cross sections on unstable nuclei near the line of beta stability are crucial for understanding the s-process nucleosynthesis. However, neutron-capture cross sections for short-lived radionuclides are difficult to measure due to the fact that the measurements require both highly radioactive samples and intense neutron sources. Essential ingredients for describing the γ decays following neutron capture are the γ-ray strength function and level densities. We will compare different indirect approaches for obtaining the most relevant observables that can constrain Hauser-Feshbach statistical-model calculations of capture cross sections. Specifically, we will consider photon scattering using monoenergetic and 100% linearly polarized photon beams. Challenges that exist on the path to obtaining neutron-capture cross sections for reactions on isotopes near and far from stability will be discussed., SCOPUS: cp.p, ND 2016: International Conference on Nuclear Data for Science and Technology, info:eu-repo/semantics/published

Thermal neutron radiative capture cross sections σ0γ of 155,157Gd are determined by summing the transition cross sections feeding the ground states of the respective product nuclei. The transition ...

The Evaluated Gamma-ray Activation File (EGAF) is the result of a 2000–2007 IAEA Coordinated Research Project to develop a database of thermal, prompt γ-ray cross sections, σ γ , for all elemental and selected radioactive targets. No previous database of this kind had existed. EGAF was originally based on measurements using guided neutron beams from the Budapest Reactor on all elemental targets from Z=1–82, 90 and 92, except for He and Pm. The EGAF σ γ data were published in the Database of Prompt Gamma Rays from Slow Neutron Capture for Elemental Analysis [1]. An international collaboration has formed to continue the EGAF measurements with isotopically enriched targets, derive total radiative thermal neutron cross sections, σ 0 , extend the σ γ data from thermal to 20 MeV neutrons, compile a completed activation data file, improve sections of the Reference Input Parameter Library (RIPL) with more complete and up to date level and γ-ray data, evaluate statistical γ-ray data from reaction studies, and determine recommended neutron separations energies, S n , for atomic mass evaluations. A new guided neutron beam facility has become available at the Garching (Munich) FRM II Reactor, and high energy neutron experimental facilities are being developed by a Berkeley area collaboration where 5–33 MeV neutron beams are available at the LBNL 88” cyclotron, 2.5 and 14 MeV beams at the University of California, Berkeley neutron generator laboratory, and high flux, 10 27 – 33 n⋅cm ⋅ − 2 s − 1 , neutron pulses available from the LLNL National Ignition Facility (NIF).

Neutron capture on unstable nuclei is important in understanding abundances in r-process nucleosynthesis. Previously, the non-elastic breakup of the deuteron in the (d,p) reaction has been shown to provide a neutron that can be captured by the nucleus and the gamma-ray decay of the subsequent compound nucleus can be modelled to predict the gamma-ray decay of the compound nucleus in the (n,γ) reaction. Preliminary results from the 95 Mo(d,pγ) reaction in normal kinematics support the (d,pγ) reaction as a valid surrogate for neutron capture. The techniques to measure the (d,pγ) reaction in inverse kinematics have been developed.

The neutron-capture reaction is fundamental for identifying and analyzing the γ-ray spectrum from an unknown assembly because it provides unambiguous information on the neutron-absorbing isotopes. Nondestructive-assay applications may exploit this phenomenon passively, for example, in the presence of spontaneous-fission neutrons, or actively where an external neutron source is used as a probe. There are known gaps in the Evaluated Nuclear Data File libraries corresponding to neutron-capture γ-ray data that otherwise limit transport-modeling applications. In this work, we describe how new thermal neutron-capture data are being used to improve information in the neutron-data libraries for isotopes relevant to nonproliferation applications. We address this problem by providing new experimentally-deduced partial and total neutron-capture reaction cross sections and then evaluate these data by comparison with statistical-model calculations.

We studied the low-spin structure of odd-odd 88Y via (p,dγ) reactions on an 89Y target. The K150 Cyclotron at the Texas A&M University Cyclotron Institute was employed to provide a 28.5-MeV proton beam, and particle-γ and particle-γ-γ coincidence data were collected with the STARLiTeR array. Moreover, a number of new levels and γ rays have been observed below 2.5 MeV, while level and γ-ray energies as well as spin-parity assignments have been re-evaluated.

The prospects for obtaining neutron capture cross sections indirectly from surrogate measurements are discussed. The surrogate reactions approach has been successfully employed to determine (n,f) cross sections from observed fission decays of compound nuclei created with the help of light-ion inelastic scattering or transfer reactions. The challenges encountered in applications of the method to capture reactions are considered. Case studies are presented that shed light on the accuracy to be expected from this approach, and ideas for improving the resulting cross sections are discussed.

Author(s): Sleaford, B.W. | Abstract: The neutron capture reaction is useful in identifying and analyzing the gamma-ray spectrum from an unknown assembly as it gives unambiguous information on its composition. This can be done passively or actively where an external neutron source is used to probe an unknown assembly. There are known capture gamma-ray data gaps in the ENDF libraries used by transport codes for various nuclear applications. The Evaluated Gamma-ray Activation file (EGAF) is a new thermal neutron capture database of discrete line spectra and cross sections for over 260 isotopes that was developed as part of an IAEA Coordinated Research Project. EGAF has been used to improve the capture gamma production in ENDF libraries. For medium to heavy nuclei the quasi continuum contribution to the gamma cascades is not experimentally resolved. The continuum contains up to 90percent of all the decay energy an is modeled here with the statistical nuclear structure code DICEBOX. This code also provides a consistency check of the level scheme nuclear structure evaluation. The calculated continuum is of sufficient accuracy to include in the ENDF libraries. This analysis also determines new total thermal capture cross sections and provides an improved RIPL database. For higher energy neutron capture there is less experimental data available making benchmarking of the modeling codes more difficult. We use CASINO, a version of DICEBOX that is modified for this purpose. This can be used to simulate the neutron capture at incident neutron energies up to 20 MeV to improve the gamma-ray spectrum in neutron data libraries used for transport modelling of unknown assemblies.

J. T. Burke, ∗ J. J. Ressler, J. E. Escher, N. D. Scielzo, I. J. Thompson, R. Henderson, J. Gostic, L. Bernstein, D. Bluel, M. Weideking, V. Meot, O. Roig, L. W. Phair, R. Hatarik, J. Munson, 4 C. Angell, B. Goldblum, C. W. Beausang, T. Ross, R. Hughes, M. Aiche, G. Barreau, N. Cappelan, S. Czajkowski, B. Hass, B. Jurado, L. Mathieu and I. Companis 8 Physics Division, Lawrence Livermore National Laboratory, Livermore, California 94550, USA Service de Physique Nucleaire, Commissariat a l’Energie Atomique, Bruyeres-le-Chatel, Arpajon, France Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA Department of Nuclear Engineering, University of California, Berkeley, California 94720, USA Nuclear Physics Department, University of Richmond, Richmond, Virginia 23173, USA Centre d’Etudes Nucleaires Bordeaux Gradignan, CNRS/IN2P3, Univ. Bordeaux 1, Chemin du Solarium, 33175 GRADIGNAN, France Centre d’Etudes Nuclaires Bordeaux Gradignan, CNRS/IN2P3, Univ. Bordeaux 1, Chemin du Solarium, 33175 GRADIGNAN, France Horia Hulubei National Institute for Physics and Nuclear Engineering, 077125 Bucharest-Magurele, Romania

We have measured partial γ-ray cross sections following neutron capture in enriched 151Eu and 153Eu targets at the cold-neutron-beam facility of the Budapest Research Reactor. The cross sections were standardized using a stoichiometric natEuCl 3 target with the well-known 1951-keV γ-ray cross section from the 35Cl(n,γ)36Cl reaction at the cold-neutron-beam facility of the Garching Research Reactor. The γ-ray cross sections were corrected for effective g-factors. These data were combined with the structural information of 152Eu and 154Eu given in the Evaluated Nuclear Structure Data File to produce capture γ-ray level schemes. The total radiative capture cross sections of the 151Eu(n,γ) 152 m 1 , g Eu and 153Eu(n,γ)154Eu reactions were determined by summing the experimental transition intensities from known levels with simulated intensities of transitions from higher excitations to the ground- or metastable-state. The individual 151Eu(n,γ) 152 m 1 Eu and 151Eu(n,γ)152gEu reaction cross sections disagree with values in the literature. However, the total cross section of the 151Eu(n,γ)152Eu reaction does agree with those values. Also, our deduced cross section for the 153Eu(n,γ)154Eu reaction closely follows the data in the literature. These results are supported by an earlier standardization experiment done at the Budapest Research Reactor using a target of Eu 2 O 3 solution in H 2 SO 4 .

Semidirect capture, a two-step process that excites a giant-dipole resonance followed by its radiative de-excitation, is a dominant process near giant-dipole resonances, that is, for incoming neutron energies within 5–20 MeV. At lower energies such processes may affect neutron capture rates that are relevant to astrophysical nucleosynthesis models. We implement a semidirect capture model in the coupled-channel reaction code Fresco and validate it by comparing the cross section for direct-semidirect capture 208 Pb(n, γ ) 209 Pb to experimental data. We also investigate the effect of low-energy electric dipole strength in the pygmy resonance. We use a conventional single-particle direct-semidirect capture code Cupido for comparison. Furthermore, we present and discuss our results for direct-semidirect capture reaction 130 Sn(n, γ ) 131 Sn, the cross section of which is known to have a significant effect on nucleosynthesis models.

Cross sections for compound-nuclear reactions involving unstable targets are important for many applications, but can often not be measured directly. Several indi- rect methods have recently been proposed to determine neutron capture cross sections for unstable isotopes. We consider three approaches that aim at constraining statistical calculations of capture cross sections with data obtained from the decay of the compound nucleus relevant to the desired reaction. Each method produces this compound nucleus in ad ifferent manner (via a light-ion reaction, a photon-induced reaction, or β-decay) and requires additional ingredients to yield the sought-after cross section. We give a brief outline of the approaches and employ preliminary results from recent measurements to illustrate the methods. We discuss the main advantages and challenges of each approach.

The work of this collaboration during its existence is summarized. The mission of the TORUS Topical Collaboration was to develop new methods that advance nuclear reaction theory for unstable isotopes by using three-body techniques to improve direct reaction calculations. This multi-institution collaborative effort was and remains directly relevant to three areas of interest: the properties of nuclei far from stability, microscopic studies of nuclear input parameters for astrophysics, and microscopic nuclear reaction theory. The TORUS project focused on understanding the details of (d,p) reactions for neutron transfer to heavier nuclei. The bulk of the work fell into three areas: coupled channel theory, modeling (d,p) reactions with a Faddeev-AGS approach, and capture reactions.

An indirect method for determining cross sections of reactions proceeding through a compound nucleus is presented. Some applications of the Surrogate nuclear reaction approach are considered and challenges that need to be addressed are outlined.

An innovative method for indirectly determining reaction cross sections via Surrogate Nuclear Reactions is presented. Exploring indirect approaches for obtaining reaction cross sections is important since a large number of nuclear reactions relevant to astrophysics cannot be measured with currently available techniques. A program is outlined for developing a comprehensive framework for planing and interpreting experiments that can yield the cross sections of interest. The applications will focus on reactions involving unstable nuclei that play a key role in the production of the elements between iron and uranium.

Neutron-induced reaction cross sections are sometimes difficult to measure due to target or beam limitations. For two-step reactions proceeding through an equilibrated intermediate state, an alternate "surrogate reaction" technique [J.D. Cramer and H.C. Britt, Nucl. Sci. Eng. 41, 177 (1970), H.C. Britt and J.B. Wilhelmy, Nucl. Sci. Eng. 72, 222 (1979), W.Younes and H.C. Britt, Phys. Rev. C 67, 024610 (2003)] can be applicable, and is currently undergoing investigation at LLNL. Measured decay probabilities for the intermediate nucleus formed in a light-ion reaction can be combined with optical-model calculations for the formation of the same intermediate nucleus via the neutron-induced reaction. The result is an estimation for overall (n,γ/n/2n) cross sections. As a bench-mark, the reaction 92Zr(α, α ′ ), surrogate for n+91Zr, was studied at the A.W. Wright Nuclear Structure Laboratory at Yale. Particles were detected in the silicon telescope STARS (Silicon Telescope Array for Reaction Studies) and γ-ray energies measured with germanium clover detectors from the YRAST (Yale Rochester Array for SpecTroscopy) ball. The experiment and preliminary observations will be discussed.

One-nucleon transfer reactions, long used as a tool to study the structure of nuclei, are potentially valuable for determining reaction cross sections indirectly. This is significant, as many reactions of interest to astrophysics and other applications involve short-lived isotopes and cannot be measured directly. We describe a procedure for obtaining constraints for calculations of neutron capture cross sections using observables from experiments with transfer reactions. As a first step toward demonstrating the method, we outline the theory developments used to properly describe the production of the compound nucleus 88Y* via the one-nucleon pickup reaction 89Y(p,d)88Y* and test the description with data from a recent experiment. We indicate how this development can be used to extract the unknown 87Y(n,γ) cross section from 89Y(p,dγ) data. The example illustrates a more generally applicable method for determining unknown cross sections via a combination of theory and transfer (or inelastic scattering) experiments.

The $^{240}\mathrm{Am}(n,f$) cross section has been measured for the first time above 4 MeV, using the surrogate-ratio method over the neutron energy range of 200 keV to 14 MeV. The reactions $^{243}\mathrm{Am}(p,tf$) and $^{238}\mathrm{U}(p,tf$), which proceed through the fissioning excited nuclei $^{241}\mathrm{Am}$* and $^{236}\mathrm{U}$*, were used as surrogates for the desired $^{240}\mathrm{Am}(n,f$) and $^{235}\mathrm{U}(n,f$) reactions. The experiment was fielded using the STARLiTeR detector system with a recently commissioned VME-based data acquisition system. The 38.4-MeV proton beam used in these measurements was provided by the K150 cyclotron at the Texas A Cyclotron Institute. The measured $^{240}\mathrm{Am}(n,f$) cross section disagrees with many of the most recent evaluations, and a reevaluation is recommended.

The pairing-plus-quadrupole model, realized in the framework of the Elliott SU(3) scheme, is used to study the combined effects of the quadrupole-quadrupole, pairing, and spin-orbit interactions on ground state shapes of nuclear systems. Relevant measures for nuclear deformation are reviewed. Representation mixing induced by the symmetry-breaking pairing and spin-orbit forces is shown to soften the deformation. The angular momentum dependence of the results is discussed.

A model system which mimics the shell-model dynamics of strongly deformed nuclei is constructed in order to study the role of particles in the unique parity orbitals of heavy deformed nuclei and to test the validity and applicability of some commonly used truncation procedures. Working in a truncation-free environment and including quadrupole-quadrupole, spin-orbit, orbit-orbit, and pairing forces, we find that for standard nuclear systems the correlations generated among particles in the unique parity space and by the interaction of nucleons in the normal parity orbitals with those in the unique parity orbitals play an important role in driving the many-particle system towards its maximum allowed deformation. The results suggest that nucleons in the unique parity levels contribute significantly to the overall collectivity of a nuclear system and should be taken into account explicitly whenever possible, or at least through renormalization procedures that can be justified in special cases, like for collective states below the backbending region.

The neutron-induced fission cross section of {sup 238}Pu was determined using the surrogate ratio method. The (n,f) cross section over an equivalent neutron energy range 5-20 MeV was deduced from inelastic {alpha}-induced fission reactions on {sup 239}Pu, with {sup 235}U({alpha},{alpha}{sup '}f) and {sup 236}U({alpha},{alpha}{sup '}f) used as references. These reference reactions reflect {sup 234}U(n,f) and {sup 235}U(n,f) yields, respectively. The deduced {sup 238}Pu(n,f) cross section agrees well with standard data libraries up to {approx}10 MeV, although larger values are seen at higher energies. The difference at higher energies is less than 20%.

The neutron-induced fission cross section of $^{238}\mathrm{Pu}$ was determined using the surrogate ratio method. The $(n,f)$ cross section over an equivalent neutron energy range 5--20 MeV was deduced from inelastic $\ensuremath{\alpha}$-induced fission reactions on $^{239}\mathrm{Pu}$, with $^{235}\mathrm{U}$($\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}}f)$ and $^{236}\mathrm{U}$($\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}}f)$ used as references. These reference reactions reflect $^{234}\mathrm{U}$($n,f)$ and $^{235}\mathrm{U}$($n,f)$ yields, respectively. The deduced $^{238}\mathrm{Pu}$$(n,f$) cross section agrees well with standard data libraries up to $~$10 MeV, although larger values are seen at higher energies. The difference at higher energies is less than 20%.

The 75As(d,pγ) reaction in inverse kinematics as a surrogate for neutron capture was performed at Oak Ridge National Laboratory using a deuterated plastic target. The intensity of the 165 keV γ-ray from 76As in coincidence with ejected protons, from exciting 76As above the neutron separation energy populating a compound state, was measured. A tight geometry of four segmented germanium clover γ-ray detectors together with eight ORRUBA-type silicon-strip charged-particle detectors was used to optimize geometric acceptance. The preliminary analysis of the 75As experiment, and the eïňČcacy and future plans of the (d,pγ) surrogate campaign in inverse kinematics, are discussed.

The prospects for determining cross sections for compound-nuclear neutron-capture reactions from Surrogate measurements are investigated. Calculations as well as experimental results are presented that test the Weisskopf-Ewing approximation, which is employed in most analyses of Surrogate data. It is concluded that, in general, one has to go beyond this approximation in order to obtain (n, ) cross sections of su cient accuracy for most astrophysical and nuclear-energy applications. Cross sections for compound-nuclear (n, ) reactions are needed for a variety of applications, including astrophysics and nuclear energy. Modeling astrophysical processes that produce the heavy isotopes beyond iron, simulating nu- clear reactor operations, exploring alternative fuel cycles for energy generation, and studying transmutation options for radioactive waste, requires cross sections for neutron- induced reactions on isotopes from di erent regions of the nuclear chart. As many short-lived species cannot be made into targets for direct cross-section measurements, one has to rely on calculations or explore indirect approaches. The desired accuracies for the cross sections of inter- est, often in the range of 10% or less, can be much smaller than the theoretical uncertainties that exist when the model parameters are insu ciently constrained by data. For in- stance, standard evaluations for the (n, ) reaction on the s-process branch point nucleus 95 Zr (t1=2 = 64 d) vary from each other roughly by a factor of four 1 . Exploiting regional systematics, whenever cross sections or relevant structural data (level densities, -ray strength functions, etc.) for near- by nuclei are known, can provide valuable constraints for the calculations. In this contribution we explore the prospects for de- termining or constraining (n, ) cross sections through Sur- rogate measurements. The Surrogate nuclear reaction tech- nique combines experiment with theory to obtain cross sec- tions for compound-nuclear (CN) reactions, a+A! B ! c+C, involving targets (A) that are di cult or impossible to obtain (1-3). In the Hauser-Feshbach formalism, the cross section for this "desired" reaction takes the form: (Ea) = X

Motivated by the renewed interest in the surrogate nuclear reactions approach, an indirect method for determining compound-nuclear reaction cross sections, the prospects for determining (n, gamma) cross sections for deformed rare-earth and actinide nuclei are investigated. A nuclear-reaction model is employed to simulate physical quantities that are typically measured in surrogate experiments and used to assess the validity of the Weisskopf-Ewing and ratio approximations, which are typically employed in the analysis of surrogate reactions. The expected accuracy of (n,gamma) cross sections extracted from typical surrogate measurements is discussed and limitations of the approximate methods are illustrated. Suggestions for moving beyond presently-employed approximations are made., Comment: 18 pages, 15 figures

Working in a shell‐model framework, I use moments of the nuclear many‐body Hamiltonian to illustrate the importance of the residual interaction to microscopic calculations of the nuclear level density.

Precise gamma‐ray thermal neutron capture cross sections have been measured at the Budapest Reactor for all elements with Z = 1–83,92 except for He and Pm. These measurements and additional data from the literature been compiled to generate the Evaluated Gamma‐ray Activation File (EGAF), which is disseminated by LBNL and the IAEA. These data are nearly complete for most isotopes with Z

The nuclear physics group at the Oslo Cyclotron Laboratory has developed a method to extract nuclear level density and γ‐ray strength function from first‐generation γ‐ray spectra. This method is applied on the nuclei 44,45Sc and 50,51V in this work. The experimental level densities of 44,45Sc are compared to calculated level densities using a microscopic model based on BCS quasiparticles within the Nilsson level scheme. The γ‐ray strength functions are also compared to theoretical expectations, showing an unexpected enhancement of the γ‐ray strength for low γ energies (Eγ⩽3 MeV) in all the isotopes studied here. The physical origin of this enhancement is not yet understood.

To benchmark the validity of using the (d,pγ) reaction as a surrogate for (n,γ), the 171,173Yb(d,pγ) reactions were measured and compared with the neutron capture cross sections measured by Wisshak et al. The (d,pγ) ratios were measured using an 18.5 MeV deuteron beam from the 88‐Inch Cyclotron at LBNL. Preliminary results comparing the surrogate ratios with the known (n,γ) cross sections are discussed.

Because of the non–zero nuclear equilibration time, the compound–nucleus scattering model fails when the incident energy exceeds 10 or 20 MeV, and precompound reactions become important. Basic ideas used in the quantum–statistical approaches to these reactions are described.

We propose a model to describe cluster productions within the framework of the intranuclear cascade (INC) model. In our model, combination of the “surface coalescence” and the “knockout” is implemented to describe cluster productions in intermediate‐energy nuclear reactions. In the present work, the basic ingredients of our INC model are defined and applied to nucleon and cluster productions for the proton‐nucleus reactions. Although our INC model has some difficulties and room for improvement, it gives a good overall agreement with experimental data of not only nucleon productions but also cluster productions at intermediate energies.

Prompt fission neutrons and gamma‐rays emitted by excited primary fission fragments are indirect probes to the nuclear configurations present near the scission point. By studying detailed characteristics of these quantities, it is shown that one can discriminate between various assumptions regarding the sharing of the free energy at scission among the two fragments. The case of low‐energy neutron‐induced fission on 235U is studied and interpreted in terms of fission modes.

The Surrogate nuclear reactions method, an indirect approach for determining cross sections for compound‐nuclear reactions involving difficult‐to‐produce targets, is reviewed. The underlying formalism is outlined, the challenges involved in carrying out a complete Surrogate treatment are detailed, and the present status of the theory is summarized. The approximations employed in the analyses of Surrogate experiments are discussed and their validity is examined.

Some of the most fascinating questions about the limits of nuclear stability are confronted in the heaviest nuclei. How many more new elements can be synthesized? What are the nuclear and chemical properties of these exotic nuclei? Does the 'Island of Stability' exist and can we ever explore the isotopes inhabiting that nuclear region? This paper will focus on the current experimental research on the synthesis and characterization of superheavy nuclei with Z > 112 from the Dubna/Livermore collaboration. Reactions using 48Ca projectiles from the U400 cyclotron and actinide targets ({sup 233,238}U, {sup 237}Np, {sup 242,244}Pu, {sup 243}Am, {sup 245,248}Cm, {sup 249}Cf) have been investigated using the Dubna Gas Filled Recoil Separator in Dubna over the last 8 years. In addition, several experiments have been performed to investigate the chemical properties of some of the observed longer-lived isotopes produced in these reactions. Some comments will be made on nuclear reactions used for the production of the heaviest elements. A summary of the current status of the upper end of the chart of nuclides will be presented.

We have indirectly determined the 237Np(n,f) cross section over an equivalent neutron energy range from 10 to 20 MeV using the surrogate reaction 238U(3He,tf). A self‐supporting ∼761 μg/cm2 metallic 238U foil was bombarded with a 42 MeV 3He2+ beam from the 88‐Inch Cyclotron at Lawrence Berkeley National Laboratory (LBNL). Outgoing charged particles and fission fragments were identified using the Silicon Telescope Array for Reaction Studies (STARS) consisted of two 140 μm and one 1000 μm Micron S2 type silicon detectors. These results were compared with the 237Np(n,f) cross section data from the direct measurements, the Evaluated Nuclear Data File (ENDF/B‐VII.0), and the Japanese Evaluated Nuclear Data Library (JENDL 3.3) and found to closely follow those datasets.

The current status of experimental study of level density and γ‐strength functions is reviewed. Three experimental techniques are used. These are measurements of particle evaporation spectra from compound nuclear reactions, the measurements of particle‐γ coincidences from inelastic scattering and pick‐up reactions and the method of two‐step γ‐cascades following neutron/proton radiative capture. Recent experimental data on level densities from neutron evaporation spectra are shown. The first results on the cascade γ‐spectrum from the 59Co(p,2γ)60Ni reaction are presented.

An overview on phenomena observed in low‐energy fission is presented, including new results from a GSI experiment with relativistic secondary beams. The interpretation of the structural effects in terms of fission channels reveals an astonishing stability of the fission‐channel positions in the heavy fragment in nuclear charge in contrast to the previously assumed constancy in mass. The statistical model is applied to deduce the relevant characteristics of the potential‐energy surface. It is assumed that the different degrees of freedom are frozen at a specific stage each on the descent from saddle to scission due to the fission dynamics. Evidence for the separability of compound‐nucleus and fragment properties in fission is deduced.

We discuss how nuclear reaction theories and experimental data are utilized in many different application fields. The neutron‐induced compound nuclear reactions, which take place from the sub‐eV energy range up to tens of MeV, are the most important mechanisms to analyze the experimental data, to predict unknown reaction cross sections, to evaluate the nuclear data for databases, and to reduce the uncertainties. Improvement of predictive‐power of nuclear reaction theories still requires further development of compound nuclear reaction theories for fission and radiative capture processes, since these reaction cross sections are especially important for nuclear science and technologies. An acceptable accuracy of these cross‐sections has been achieved only if they were experimentally confirmed.

We are developing a novel code that treats induced fission by statistical (or Monte‐Carlo) simulation of individual decay chains. After its initial excitation, the fissionable compound nucleus may either de‐excite by evaporation or undergo binary fission into a large number of fission channels each with different energetics involving both energy dissipation and deformed scission pre‐fragments. After separation and Coulomb acceleration, each fission fragment undergoes a succession of individual (neutron) evaporations, leading to two bound but still excited fission products (that may further decay electromagnetically and, ultimately, weakly), as well as typically several neutrons. (The inclusion of other possible ejectiles is planned.) This kind of approach makes it possible to study more detailed observables than could be addressed with previous treatments which have tended to focus on average quantities. In particular, any type of correlation observable can readily be extracted from a generated set of events. With a view towards making the code practically useful in a variety of applications, emphasis is being put on making it numerically efficient so that large event samples can be generated quickly. In its present form, the code can generate one million full events in about 12 seconds on a MacBook laptop computer. The development of this qualitatively new tool is still at an early stage and quantitative reproduction of existing data should not be expected until a number of detailed refinement have been implemented.

We measured the ratio of the fission probabilities of 234U* relative to 236U* formed via an (α,α′) direct reactions using the STARS array at the 88‐inch cyclotron at the Lawrence Berkeley National Laboratory. This ratio has a shape similar to the ratio of neutron capture probabilities from 233U(n,f) and 235U(n,f), indicating the alpha reactions likely formed a compound nucleus. This result indicates that the ratios of fission exit channel probabilities for two actinide nuclei populated via (α,α′) can be used to determine an unknown fission cross section relative to a known one. The validity of the External Surrogate Ratio Method (ESRM) is tested and the results support the conclusions of Burke et al. [1].

In recent years, the microscopic method has been applied to the notoriously difficult problem of nuclear fission with unprecedented success. In this paper, we discuss some of the achievements and promise of the microscopic method, as embodied in the Hartree‐Fock method using the Gogny finite‐range effective interaction, and beyond‐mean‐field extensions to the theory. The nascent program to describe induced fission observables using this approach at the Lawrence Livermore National Laboratory is presented.