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We tabulate the atomic mass excesses and binding energies, ground-state shell-plus-pairing corrections, ground-state microscopic corrections, and nuclear ground-state deformations of 9318 nuclei ranging from $^{16}$O to $A=339$. The calculations are based on the finite-range droplet macroscopic model and the folded-Yukawa single-particle microscopic model. Relative to our FRDM(1992) mass table in {\sc Atomic Data and Nuclear Data Tables} [{\bf 59} 185 (1995)], the results are obtained in the same model, but with considerably improved treatment of deformation and fewer of the approximations that were necessary earlier, due to limitations in computer power. The more accurate execution of the model and the more extensive and more accurate experimental mass data base now available allows us to determine one additional macroscopic-model parameter, the density-symmetry coefficient $L$, which was not varied in the previous calculation, but set to zero. Because we now realize that the FRDM is inaccurate for some highly deformed shapes occurring in fission, because some effects are derived in terms of perturbations around a sphere, we only adjust its macroscopic parameters to ground-state masses. The values of ten constants are determined directly from an optimization to fit ground-state masses of 2149 nuclei ranging from $^{16}$O to $^{265}_{106}$Sg and $^{264}_{108}$Hs. The error of the mass model is 0.5595~MeV. We also provide masses in the FRLDM, which in the more accurate treatments now has an error of 0.6618 MeV. But in contrast to the FRDM, it is suitable for studies of fission and has been extensively so applied elsewhere, with FRLDM(2002) constants. The FRLDM(2012) fits 31 fission barrier heights from $^{70}$Se to $^{252}$Cf with a root-mean-square deviation of 1.052 MeV., 233 pages, 41 figures. arXiv admin note: text overlap with arXiv:nucl-th/9308022

The SPectrometer for Ion DEtermination in fission Research (SPIDER) has been developed for measuring mass yield distributions of fission products from spontaneous and neutron-induced fission. The 2 E –2 v method of measuring the kinetic energy ( E ) and velocity ( v ) of both outgoing fission products has been utilized, with the goal of measuring the mass of the fission products with an average resolution of 1 atomic mass unit (amu). The SPIDER instrument, consisting of detector components for time-of-flight, trajectory, and energy measurements, has been assembled and tested using 229 Th and 252 Cf radioactive decay sources. For commissioning, the fully assembled system measured fission products from spontaneous fission of 252 Cf. Individual measurement resolutions were met for time-of-flight (250 ps FWHM), spacial resolution (2 mm FHWM), and energy (92 keV FWHM for 8.376 MeV). Mass yield results measured from 252 Cf spontaneous fission products are reported from an E – v measurement.

The ability to describe production of light fragments (LF) is important for many applications, such as cosmic-ray-induced single event upsets (SEUs), radiation protection, and cancer therapy with proton and heavy-ion beams. The cascade-exciton model (CEM) and the Los Alamos version of the quark-gluon string model (LAQGSM) event generators in the LANL transport code MCNP6, describe quite well the spectra of fragments with sizes up to 4 He across a broad range of target masses and incident energies (up to ∼ 5 GeV for CEM and up to ∼ 1 TeV/A for LAQGSM). However, they do not predict the high-energy tails of LF spectra heavier than 4 He well. Most LF with energies above several tens of MeV are emitted during the precompound stage of a reaction. The current versions of our event generators do not account for precompound emission of LF larger than 4 He. The aim of our work is to generalize the precompound model to include such processes, leading to increased predictive power of LF production. Extending the model in this way provides preliminary results that have much better agreement with experimental data.

The liquid-drop model has its origins in the first mainstream model of the binding energy of nuclei, sometimes referred to as the semiempirical mass formula, which emerged in the mid 1930s. It is a beautiful example of a model that fulfills the criteria of what a theoretical model is and what an arbitrary parameterization of some data set is not: (1) it has a simple intuitive interpretation, (2) it was of enormous and immediate practical utility in interpreting nuclear experimental data such as radioactive decay and nuclear reactions, (3) it could predict binding energies of nuclei to which its parameters had not been adjusted, (4) it could be generalized to describe new, unanticipated phenomena such as fission, and (5) deviations of its predictions from experimental data yielded insight into nuclear structure and guided the development of more sophisticated models. Generalized liquid-drop models remain important because of the development of macroscopic–microscopic models which give important quantitative insight into ground-state structure and binding energies (nuclear masses) and many details of nuclear fission. We review these points and some associated historical milestones.

Isotope production cross sections from 112Sn + 112Sn and 124Sn + 124Sn reactions at 1 GeV/nucleon, which were measured recently at GSI using the heavy-ion accelerator SIS18 and the Fragment Separator (FRS), have been analyzed with the latest Los Alamos Monte-Carlo transport code MCNP6 using the LAQGSM03.03 event generator. MCNP6 reproduces reasonably well all the measured cross sections. Comparison of the MCNP6 results with the measured data and with calculations by a modification of the Los Alamos version of the Quark-Gluon String Model allowing for multifragmentation processes in the framework of the Statistical Multifragmentation Model (SMM) by Botvina and coauthors, as realized in the code LAQGSM03.S1, does not suggest unambiguous evidence of a multifragmentation signature.

We describe a new cumulated fission product yield (FPY) evaluation for fission spectrum neutrons on plutonium that updates the ENDF/B-VI evaluation by England and Rider, for the forthcoming ENDF/B-VII.1 database release. We focus on FPs that are needed for high accuracy burnup assessments; that is, for inferring the number of fissions in a neutron environment. Los Alamos conducted an experiment in the 1970s in the Bigten fast critical assembly to determine fission product yields as part of the Interlaboratory Reaction Rate (ILRR) collaboration, and this has defined the Laboratory's fission standard to this day. Our evaluation includes use of the LANL-ILRR measurements (not previously available to evaluators) as well as other Laboratory FPY measurements published in the literature, especially the high-accuracy mass spectrometry data from Maeck and others. Because the measurement database for some of the FPs is small - especially for {sup 99}Mo - we use a meta-analysis that incorporates insights from other accurately-measured benchmark FP data, using R-value ratio measurements. The meta-analysis supports the FP measurements from the LANL-ILRR experiment. Differences between our new evaluations and ENDF/B-VI are small for some FPs (less than 1-2%-relative for {sup 95}Zr, {sup 140}Ba, {sup 144}Ce), but are larger for {sup 99}Momore » (4%-relative) and {sup 147}Nd (5%-relative, at 1.5 MeV) respectively. We present evidence for an incident neutron energy dependence to the {sup 147}Nd fission product yield that accounts for observed differences in the FPY at a few-hundred keV average energy in fast reactors versus measurements made at higher average neutron energies in Los Alamos' fast critical assemblies. Accounting for such FPY neutron energy dependencies is important if one wants to reach a goal of determining the number of fissions to accuracies of 1-2%. An evaluation of the energy-dependence of fission product yields is given for all A values based on systematical trends in the measured data, with a focus on the energy dependence over the fast neutron energy range from 0.2-2 MeV. Based on these trends, we present an evaluation of the FPY data at 0.5 and 2.0 MeV average incident neutron energies. This new set of ENDF/B-VII data will enable users to linearly interpolate between the pooled FPY data at {approx}0.5 MeV and our new data at 2 MeV to obtain FPYs at other energies.« less

We discuss the relation between the fission-fusion potential-energy surfaces of very heavy nuclei and the formation process of these nuclei in cold-fusion reactions. In the potential-energy surfaces, we find a pronounced valley structure, with one valley corresponding to the cold-fusion reaction, the other to fission. As the touching point is approached in the cold-fusion entrance channel, an instability towards dynamical deformation of the projectile occurs, which enhances the fusion cross section. These two 'cluster effects' enhance the production of superheavy nuclei in cold-fusion reactions, in addition to the effect of the low compound-system excitation energy in these reactions. Heavy-ion fusion reactions have been used extensively to synthesize heavy elements beyond actinide nuclei. In order to proceed further in this direction, we need to understand the formation process more precisely, not just the decay process. The dynamics of the formation process are considerably more complex than the dynamics necessary to interpret the spontaneous-fission decay of heavy elements. However, before implementing a full dynamical description it is useful to understand the basic properties of the potential-energy landscape encountered in the initial stages of the collision. The collision process and entrance-channel landscape can conveniently be separated into two parts, namely the early-stage separatedmore » system before touching and the late-stage composite system after touching. The transition between these two stages is particularly important, but not very well understood until now. To understand better the transition between the two stages we analyze here in detail the potential energy landscape or 'collision surface' of the system both outside and inside the touching configuration of the target and projectile. In Sec. 2, we discuss calculated five-dimensional potential-energy landscapes inside touching and identify major features. In Sec. 3, we present calculated 'collision surfaces' for still separated targets and projectiles. Implications for SHE formation are discussed. Section 4 is a short summary of the present analysis.« less

The CEM2k and LAQGSM codes have been recently developed at Los Alamos National Laboratory to simulate nuclear reactions for a number of applications. We have benchmarked our codes against most available measured data at incident particle energies from 10 MeV to 800 GeV and have compared our results with predictions of other current models used by the nuclear community. Here, we present a brief description of our codes and show illustrative results to show that CEM2k and LAQGSM can be used as reliable event generators for space-radiation-shielding, cosmic-ray-propagation, and other astrophysical applications. Finally, we show the use of our calculated cross sections together with experimental data from our LANL T-16 compilation to produce evaluated files which we use in the GALPROP model of galactic particle propagation to better constrain the size of the CR halo., 10 pages, 9 figures, LaTeX, talk given at the World Space Congress 2002, 34th COSPAR Scientific Assembly, Houston, Texas, USA, 10-19 October 2002, to appear in Advances in Space Research

We have used an extended version of the Cascade-Exciton Model (CEM) to analyze more than 600 excitation functions for proton induced reactions on 19 targets ranging from 12C to 197Au, for incident energies ranging from 10 MeV to 5 GeV. We have compared the calculations to available data, to calculations using approximately two dozen other models, and to predictions of several phenomenological systematics. We present here our conclusions concerning the relative roles of different reaction mechanisms in the production of specific final nuclides. We comment on the strengths and weaknesses of the CEM and suggest possible further improvements to the CEM and to other models.

On the basis of a macroscopic dynamical model, we explore the effect of two prototype dissipation mechanisms that represent opposite extremes of small and large dissipation on the formation of a third fragment during the fission of very heavy nuclear systems. With five collective coordinates to describe axially symmetric and reflection-symmetric nuclear shapes, we solve the generalized Hamilton equations of motion numerically to determine the time evolution of the system. The nuclear potential energy of deformation is calculated as the sum of a repulsive Coulomb energy and an attractive Yukawa-plus-exponential potential, the inertia tensor is calculated for incompressible, nearly irrotational flow by use of the Werner-Wheeler method and the dissipation tensor is calculated for both two-body viscosity and one-body dissipation. For light nuclei the dynamical evolution leads to compact binary scission shapes, but for sufficiently heavy nuclei it leads to shapes with long necks that subsequently contract at the extremities to form three fragments. This ternary division, whose onset begins at Z 2 A∼35 for two-body viscosity and much later at Z 2 A∼57 for one-body dissipation, is examined in terms of a neck instability that is analogous to the Plateau-Rayleigh hydrodynamic instability of an uncharged, infinite, initially stationary cylinder. For nuclear systems with mass numbers ranging from 200 to 500, we calculate the mass of the third fragment that forms under certain circumstances, the translational kinetic energy of the two end fragments at infinity, and the time required for the system to descend from its saddle point to scission.

Large fragment (A>4) production at high angular momentum is studied via the reaction, 200 MeV 45 Sc + 65 Cu. Comparisons of the fragment yields from this reaction (high angular momentum) to those from 93 Nb + Be (low angular momentum) are used to verify the strong angular momentum dependence of large fragment production predicted by equilibrium models. Details of the coincident γ-ray distributions not only confirm a rigidly rotating intermediate but also indicate that the widths of the primary L-wave distributions decrease with increasing symmetry in the decay channel. These data are used to test the asymmetry and L-wave dependence of emission barriers calculated from a rotating, finite range corrected, liquid drop model.

By use of semiclassical mean-field methods, we study the dependence of the curvature-energy coefficient and other surface properties of nuclear matter upon the energy-density functional. This is done both by solving the Euler-Lagrange equation with a simplified phenomenological functional and by obtaining a variational solution with a fourth-order extended Thomas-Fermi functional. The calculated curvature-energy coefficient a c decreases with increasing value of the bulk nuclear incompressibility coefficient K for physically relevant values of K , but always remains larger than 3 MeV in either approach when the volume-energy coefficient, saturation density, surface-energy coefficient and surface diffuseness are constrained to their experimental values. The calculated values of the curvature-energy coefficient a c are significantly larger than experimental values obtained from analyses of fission-barrier heights and ground-state masses of nuclei throughout the periodic table. Among possible resolutions of this anomaly, we suggest that relativistic effects or correlations may play a significant role in the nuclear surface, or that the leptodermous expansion may break down in regions of large curvature, such as occurs for highly deformed shapes and for light nuclei.

We discuss recent advances in a unified macroscopic-microscopic description of large-amplitude collective nuclear motion such as occurs in fission and heavy ion reactions. With the goal of finding observable quantities that depend upon the magnitude and mechanism of nuclear dissipation, we consider one-body dissipation and two-body viscosity within the framework of a generalized Fokker-Planck equation for the time dependence of the distribution function in phase space of collective coordinates and momenta. Proceeding in two separate directions, we first solve the generalized Hamilton equations of motion for the first moments of the distribution function with a new shape parametrization and other technical innovations. This yields the mean translational fission-fragment kinetic energy and mass of a third fragment that sometimes forms between the two end fragments, as well as the energy required for fusion in symmetric heavy-ion reactions and the mass transfer and capture cross section in asymmetric heavy-ion reactions. In a second direction, we specialize to an inverted-oscillator fission barrier and use Kramers' stationary solution to calculate the mean time from the saddle point to scission for a heavy-ion-induced fission reaction for which experimental information is becoming available.

Negative-parity excited states of doubly even nuclei have earlier been attributed to vibrational excitations. This paper shows that an interpretation starting from a reflection asymmetric intrinsic state is more appropriate for certain nuclei in the radium region. Theoretical evidence for stable octupole deformation comes from a deformed shell-model calculation in which we use a single-particle potential with a realistic radial shape and a finite-range interaction for the surface energy. The octupole effect systematically improves the agreement between theoretical and experimental masses. The low-lying O + excitations observed in experiment are compatible with the calculated collective octupole potentials. The possibility of obtaining further evidence from the spectroscopy of odd-mass nuclei is considered in an exactly solvable model, which shows that the smaller energy splitting observed in odd- A parity doublets mainly reflects single-particle fragmentation of the collective mode. The systematics of theoretical shell structure and experimental spectroscopy suggests the presence of other regions of octupole collectivity near the limits of stability.