To resolve long-standing differences between LANL and LLNL regarding the correct fission basis for analysis of nuclear test data [M.B. Chadwick et al., Nucl. Data Sheets 111, 2891 (2010); H. Selby et al., Nucl. Data Sheets 111, 2891 (2010)], a collaboration between TUNL/LANL/LLNL has been established to perform high-precision measurements of neutron induced fission product yields. The main goal is to make a definitive statement about the energy dependence of the fission yields to an accuracy better than 2-3% between 1 and 15 MeV, where experimental data are very scarce. At TUNL, we have completed the design, fabrication and testing of three dual-fission chambers dedicated to 235U, 238U, and 239Pu. The dual-fission chambers were used to make measurements of the fission product activity relative to the total fission rate, as well as for high-precision absolute fission yield measurements. The activation method was employed, utilizing the mono-energetic neutron beams available at TUNL. Neutrons of 4.6, 9.0, and 14.5 MeV were produced via the 2H(d,n)3He reaction, and for neutrons at 14.8 MeV, the 3H(d,n)4He reaction was used. After activation, the induced γ-ray activity of the fission products was measured for two months using high-resolution HPGe detectors in a low-background environment. Results for the yield of seven fission fragments of 235U, 238U, and 239Pu and a comparison to available data at other energies are reported. For the first time results are available for neutron energies between 2 and 14 MeV.

The gamma-ray cascades following the Mo-95(n,gamma)Mo-96 reaction were studied with the gamma calorimeter DANCE (Detector for Advanced Neutron Capture Experiments) consisting of 160 BaF2 scintillation detectors at the Los Alamos Neutron Science Center. The gamma-ray energy spectra for different multiplicities were measured for s- and p-wave resonances below 2 keV. The shapes of these spectra were found to be in very good agreement with simulations using the DICEBOX statistical model code. The relevant model parameters used for the level density and photon strength functions were identical with those that provided the best fit of the data from a recent measurement of the thermal Mo-95(n,gamma)Mo-96 reaction with the two-step-cascade method. The reported results strongly suggest that the extreme statistical model works very well in the mass region near A=100.

The capture process is a nuclear reaction in which a target atom captures an incident projectile, e.g. a neutron. The excited-state compound nucleus de-excites by emitting photons. This process creates an atom that has one more neutron than the target atom, so it is a different isotope of the same element. With low energy (slow) neutron projectiles, capture is the dominant reaction, other than elastic scattering. However, with very heavy nuclei, fission competes with capture as a method of de-excitation of the compound nucleus. With higher energy (faster) incident neutrons, additional reactions are also possible, such as emission of protons or emission of multiple neutrons. The probability of a particular reaction occurring (such as capture) is referred to as the cross section for that reaction. Cross sections are very dependent on the incoming neutron's energy. Capture reactions can be studied either using monoenergetic neutron sources or 'white' neutron sources. A 'white' neutron source has a wide range of neutron energies in one neutron beam. The advantage to the white neutron source is that it allows the study of cross sections as they depend on neutron energies. The Los Alamos Neutron Science Center, located at Los Alamos National Laboratory, provides an intense white neutron source. Neutrons there are created by a high-energy proton beam from a linear accelerator striking a heavy metal (tungsten) target. The neutrons range in energy from subthermal up to very fast - over 100 MeV in energy. Low-energy neutron reaction cross sections fluctuate dramatically from one target to another, and they are very difficult to predict by theoretical modeling. The cross sections for particular capture reactions are important for defense sciences, advanced reactor concepts, transmutation of radioactive wastes and nuclear astrophysics. We now have a strong collaboration between Lawrence Livermore National Laboratory, Los Alamos National Laboratory, North Carolina State University and Charles University in Prague. In this paper, we report neutron capture studies that are of particular interest to Lawrence Livermore National Laboratory. In addition to determining neutron capture cross sections, we are also interested in the nuclear properties of the excited state compound nuclei created in the capture reactions. One model that describes the behavior of the nucleus is the statistical model. Our statistical studies included measuring the photon strength function, resonance parameters, level density and gamma-ray ({gamma}-ray) cascade multiplicity. The DANCE array allows the separation of cascades by the number of transitions (multiplicity) in the cascade, and this makes it possible to study detailed properties of the statistical cascade such as the relationship between multiplicity and energy distributions. The work reported here includes reaction on molybdenum targets, europium targets, gadolinium targets and the first americium-242m target. Our goal is to improve the accuracy and provide new measurements for stable and radioactive targets. We are especially interested in energy-dependent neutron capture cross sections. In all of our experiments, the photons emitted in the capture reactions are gamma rays, and they are detected by the barium fluoride crystal array named the Detector for Advanced Neutron Capture Experiments (DANCE) shown in Fig. 1. The detector array is made of 160 crystals arranged in a sphere around the target. There are four different crystal shapes, each of which covers an equal solid angle. This array was specifically designed to measure neutron capture cross sections with targets that were milligram sized or smaller, including radioactive targets. The barium fluoride crystals are scintillation (light generating) detectors with very fast response time, and are therefore suitable for high count rate experiments. Actual neutron capture events must be reliably distinguished from background {gamma}-rays, which are always present in neutron induced reactions. To reduce the background of scattered neutrons, a lithium hydride shell is placed inside the array. The purpose of using the spherical array of detectors is to cover all possible directions of emitted {gamma} rays, so we will come as close as possible to complete detection of all the prompt {gamma}-ray cascades emitted in a capture reaction. The sum of the energy of the {gamma} cascades is a measure of the binding energy of the capture neutron. The binding energy is the energy required to remove a bound neutron from the nucleus. The measured mass of the nucleus is smaller than the masses of the target nucleus plus the captured neutron, and the difference (converted to energy) is the binding energy of the capture neutron. Because the detector is segmented into a large number of independent detectors, additional information on event multiplicities (number of {gamma} rays emitted) and other properties can be determined.

{gamma}-ray excitation functions have been measured for the interaction of fast neutrons with {sup 48}Ti (neutron energy from 1 MeV to 250 MeV). The Los Alamos National Laboratory spallation neutron source, at the LANSCE/WNR facility, provided a ''white'' neutron beam which is produced by bombarding a natural W target with a pulsed proton beam. The prompt-reaction {gamma} rays were measured with the large-scale Compton-suppressed Ge spectrometer, GEANIE. Neutron energies were determined by the time-of-flight technique. Excitation functions were converted to partial {gamma}-ray cross sections, taking into account the dead-time correction, the target thickness, the detector efficiency, and neutron flux (monitored with an in-line fission chamber). The data analysis is presented here for neutron energies between 1 to 20 MeV. Partial {gamma}-ray cross sections for transitions in {sup 47,48}Ti, {sup 48}Sc, and {sup 45}Ca have been determined. These results are compared to Hauser-Feshbach predictions calculated using the STAPRE code, which includes compound nuclear and pre-equilibrium emission. The partial cross sections for {gamma} rays, whose discrete {gamma}-ray cascade path leads to the ground state in {sup 48}Ti, {sup 47}Ti, {sup 48}Sc, and {sup 45}Ca have been summed to obtain estimates of the lower limits for reaction cross sections. Partial cross sections for unobserved {gamma}-rays are predicted from the STAPRE code. These lower limits are combined with Hauser-Feshbach calculations to deduce {sup 48}Ti(n,n'){sup 48}Ti, {sup 48}Ti(n,2n){sup 47}Ti, {sup 48}Ti(n,p){sup 48}Sc, and {sup 48}Ti(n,{alpha}){sup 45}Ca reaction channel cross sections.

The level structure of Au-197 has been studied using the (n,n'gamma) reaction. A germanium detector array (GEANIE) for gamma-ray detection and the "white" neutron source at LANSCE/WNR were used for the measurement. The energy of the incident neutrons was determined using the time-of-flight technique. Partial gamma-ray cross sections were measured for a total of 90 transitions of Au-197. A total of 52 new gamma rays were assigned to Au-197 and placed on the level scheme based on the partial gamma-ray excitation functions and the gamma-gamma coincidence data. The level scheme of Au-197 is now more complete up to similar to 2 MeV excitation energy. The first excited states of the decoupled band built on the proton-hole h(11/2) configuration were established.

Absolute partial {gamma}-ray cross sections for the production of discrete {gamma}-rays from the reaction {sup 150}Sm(n,2n{gamma}{sub i}){sup 149}Sm were measured using the GEANIE {gamma}-ray spectrometer coupled with the intense white neutron source at WNR/LANSCE. The measurements were made for incident neutron energies between threshold (8.04 MeV) and 20 MeV. The partial cross sections for 21 {gamma}-rays were extracted from the data. Of these, 17 were compared to calculations performed using the enhanced Hauser-Feshbach code STAPRE. The partial {gamma}-ray cross sections of the observed parallel decay paths to the ground state were summed, forming a lower bound for the (n,2n) reaction channel. A combination of theory and experiment was then used to deduce the (n,2n) reaction channel cross section.

We evaluate new n+{sup 89}Y radchem cross sections using recent LANSCE/GEANIE measurements and GNASH nuclear model calculations, together with previous measurements at Livermore by Dietrich et al. A quantification of margins and uncertainties (QMU) analysis leads to evaluated cross sections for the (n,2n) population of the {sup 88}Y ground state and m1, m2 isomers, together with uncertainties. Our new results agree with historic radchem database cross sections within a few percent below 15 MeV (with larger differences above 15 MeV) and they therefore provide a validation of the historic Arthur work that is used in LANL simulation codes. Since the (n,2n) cross sections to the {sup 88}Y g.s. and m1, m2 isomers impact the average {sup 88}Y(n,2n){sup 87}Y cross section at leading-order, we determine the new 14.1 MeV average {sup 88}Y(n,2n){sup 87}Y cross section (crucially important for radchem). Our new 14 MeV average {sup 88}Y(n,2n){sup 87}Y cross section is 1107 mb ({+-} 4%) which agrees with the value obtained from the historic Arthur cross section data to 0.7%.

States in Zr have been observed with the ( n,n8g) reaction using both spallation and monoenergetic accelerator-produced neutrons. A scheme comprised of 81 levels and 157 transitions was constructed concentrating on levels below 5.6 MeV in excitation energy. Spins have been determined by considering data from all experimental studies performed for Zr. Lifetimes have been deduced using the Doppler-shift attenuation method for many of the states, and transition rates have been obtained. A spherical shell-model interpretation in terms of particle-hole excitations assuming a Sr closed core is given. In some cases, enhancements in B(M1) andB(E2) values are observed that cannot be explained by assuming simple particle-hole excitations. Shell-model calculations using an extended f pg-shell-model space reproduce the spectrum of excited states very well, and the gross features of the B(M1) andB(E2) transition rates. Transition rates for individual levels show discrepancies between calculations and experimental values.

The level structures of Rh-106,Rh-108,Rh-110,Rh-112 have been studied in the fission of the compound system formed in three different heavy-ion induced reactions. Sequences of five transitions, together with weak crossover transitions, have been assigned to each isotope based on coincidences with known transitions in the complementary fragments. Comparison with the lighter odd-odd Rh isotopes supports assignment of these sequences as the yrast bands built on the pig(9/2)xnuh(11/2) configuration.

The level structure of several Zr isotopes near A=94 (Zr-92,Zr-93,Zr-94,Zr-95) has been studied in the fission of the compound nucleus Pb-197, formed in the Mg-24+Yb-173 reaction at E(Mg-24)=134.5 MeV. Sequences of gamma-ray transitions, observed in coincidence with known transitions in the complementary Mo fragments, have been newly assigned to Zr-93,Zr-95. The previously known level scheme of Zr-94 has been considerably extended to higher excitations, and exhibits structural similarities to the level scheme of Zr-92 up to spin 10 (h) over bar. The level schemes of Zr-93 and Zr-95 can be generally interpreted as the coupling of a d(5/2) neutron to the levels of Zr-92,Zr-94 and Zr-96, respectively. The observed experimental states are compared with theoretical shell-model calculations.

The level structures of odd A similar to 110 Ru, Pd, and Cd isotopes have been investigated following the fission of compound nuclei formed in heavy-ion fusion reactions. New sequences have been assigned to Ru-107, and to Cd-113,Cd-115,Cd-117,Cd-119 isotopes using the complementary fission fragment technique. A comparison with neighboring neutron-deficient and neutron-rich odd-A Ru, Pd, and Cd isotopes supports an interpretation of these sequences as originating from the neutron h(11/2) orbital. The occupation of this orbital polarizes the nucleus to a nonaxial shape in odd-A Ru, Pd and Cd isotopes over a wide range of neutron numbers. The yrast bands in the Cd-114,Cd-116,Cd-118,Cd-120 cores have been extended to higher spins and excitation energies.

States in Mo-92 have been observed with the (n,n' gamma) reaction with spallation neutrons produced at the LANSCE-WNR facility. Gamma rays were detected with the GEANIE spectrometer, and the neutron energies were determined by the time-of-flight method. Combining excitation function and gamma gamma coincidence analysis, 13 new levels have been deduced. The level scheme has been extended considerably for low- to medium-spin levels below 5 MeV in excitation energy.

The yrast superdeformed band in Pb-194 has been populated using the Yb-174(Mg-25,5n)Pb-194 reaction at E-beam = 130 MeV. Decay gamma rays were detected using the GAMMASPHERE array at the 88-Inch Cyclotron. Twelve gamma-ray transitions have been observed directly linking three members of the Pb-194 yrast superdeformed band to low-lying normal deformed levels. Anisotropy measurements indicate that these linking decays include E1, M1, and mixed M1/E2 multipolarities. The radiative widths deduced are very inhibited, typically B(E1)similar to 10(-8) Weisskopf units (W.u.) and B(M1)similar to 10(-5) W.u. Without recourse to a priori assumptions J(pi) = 6(+) and E-x = 4878.4(3) keV have been unambiguously assigned to the lowest-lying observed superdeformed state (the state populated by the 170-keV intraband transition). The intensity of the observed primaries accounts for 21(2)% of the superdeformed band population.

Ten new transitions in Mo-107 have been observed and levels in Mo-109 are identified for the first time in a gamma-gamma-gamma coincidence study from the spontaneous fission of Cf-252 with 72 Compton suppressed Ge detectors in Gammasphere. Two sets of bands, each set intertwined by E1 transitions are observed in Mo-107 and one such set in Mo-109. The observed level schemes are interpreted in terms of possible octupole deformation originating from the strong interaction of the h(11/2) and d(5/2) neutron shells.

Four bands of enhanced dipole transitions, with weak crossovers, have been observed in Pb-195. Three of these bands are connected to the spherical levels. in addition, the spherical level scheme has been extended. The nuclear spectroscopy was done with the early implementation of GAMMASPHERE and HERA arrays of Get detectors. The nucleus Pb-193 was populated in the Yb-174(Mg-24,5n) reaction at beam energies of 129, 131, and 134 MeV. The experimental results are compared to tilted-axis cranking calculations. The systematical behavior of the dipole bands in the heavier odd-A Pb isotopes, Pb-195,Pb-197,Pb-199,Pb-201, is also discussed.

The gamma rays associated with the decay of Ga-68 in equilibrium with Ge-68 have been studied using the 20-element High Energy Resolution Array (HERA) facility. Five new transitions were observed along with the known ones from earlier works. The E2/M1 mixing ratios for two of these new transitions were obtained by gamma-gamma(theta) techniques.

The nucleus 193Hg was populated in the reaction Yb-176(Ne-22,5n) at the incident energy E(Ne-22) = 110 MeV. Reaction gamma rays were detected with a Ge-detector array. A new ''collective'' structure was observed at E(x) > 5.7 MeV. The states of the structure extend from I greater-than-or-equal-to 47/2 to I + 10, and they decay with competing dipole and quadrupole transitions. The structure is populated very strongly in this reaction: the lowest member is produced with approximately 20% of the 193Hg cross section.

Lifetimes of states in two DELTA-I = 1 bands in 198Pb have been measured using the Doppler-shift attenuation method. The in-band reduced transition probabilities are approximately 1-2 Weisskopf units, assuming magnetic dipole transitions. The measured lifetimes in conjunction with the partial level scheme support an oblate collective interpretation for these structures.