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In this paper, we describe the separation chemistry and electrodepositions conducted for the preparation of 241Am, 243Am and 233U targets used for cross-section measurements at DANCE. Thick, adherent deposits were prepared using molecular plating from isopropyl alcohol solutions. Improved yields and thicknesses were observed for 241Am electrodeposition after the material was purified using TRU resin from Eichrom. Similarly, 233U deposits were improved after purification with an anion exchange column in 9 M HBr followed by purification using UTEVA resin from Eichrom.

We describe advances made recently at Los Alamos for ENDF/B-VII, and for future ENDF releases, of actinide cross-section evaluations. Using americium as an illustrative example, we describe recent experiments that have largely confirmed the nuclear theory predictions that were the basis for the ENDF/BVII.0 data for these americium reactions. The goal of this paper is to highlight some of the open issues in our understanding of the actinide nuclear data – especially for fast reactor applications – and show examples of how experiment, theory, and integral data validation has advanced our understanding. We will also describe the usage of these data in MCNP and SN radiation transport simulations of various integral critical systems, for both criticality and for transmutation reaction rates.

An overview of recent efforts to produce and separate neutron-rich rare isotopes in quasielastic and deep-inelastic collisions around and below the Fermi energy is presented. The experiments have been performed at the Cyclotron Institute of Texas A&M University employing beams from the K500 Superconducting Cyclotron. Two magnetic separators were used: the MARS recoil separator and the Superconducting Solenoid Line (BigSol Line). In these efforts we observed an enhanced production of neutron-rich nuclides in comparison with high-energy fragmentation mechanisms. This trend has been attributed to the role of the N/Z ratio and the nuclear periphery of the target. From a practical viewpoint, we conclude that reactions below or around the Fermi energy offer a novel way to access very neutron-rich rare isotopes. The experience obtained in the production of rare isotope beams (RIB) below the Fermi energy will be exploited in the ongoing RIB Upgrade of the Cyclotron Institute that will involve production, stopping and reacceleration of rare isotopes.

The detector for advanced neutron capture experiments (DANCE) at Los Alamos National Laboratory (LANL) is used for neutron capture cross sections measurements. Its high granularity of 160 BaF 2 detectors in a 4 π geometry allows for highly efficient detection of prompt γ-rays following a neutron capture. The performance of the detector was simulated using the GEANT4 Monte Carlo code. The model includes all 160 BaF 2 crystals with realistic dimensions and geometry. The 6 LiH shell, beam pipe, crystal wrapping material, aluminum holders, photomultiplier material and materials of the calibration sources were included in the simulation. Simulated γ-ray energy and total γ-ray energy spectra gated on cluster and crystal multiplicities were compared to measured data using 88 Y, 60 Co, 22 Na calibration sources. Good agreement was achieved. A total efficiency and peak-to-total ratio as a function of γ-ray energy was established for mono-energetic γ-rays.

The process of nuclear multifragmentation leads to thermodynamic conditions akin to those encountered in the collapse/explosion of massive stars. Thus, the knowledge obtained from studying multifragmentation may be applied to describe matter distribution in supernova. Along these lines, the present study focuses on the symmetry energy of hot fragments produced in the multifragmentation of neutron-rich systems following collisions near the Fermi energy. The experiments consist of high-resolution mass spectrometric measurements of the isotopic and velocity distributions of heavy projectile fragments. The data were systematically compared to calculations with the Statistical Multifragmentation Model (SMM). The study indicates a gradual decrease of the symmetry energy coefficient from the standard value of ∼25 MeV in the compound nucleus regime ( E ∗ / A E ∗ / A > 4 MeV). The isotopic distributions of the hot fragments are very wide and extend towards or beyond the neutron drip-line. These findings may have important implications to the composition and evolution of hot astrophysical environments, such as core-collapse supernova and the course of the ensuing nucleosynthesis processes, such as the r-process.

The neutron capture cross section of the $s$-process branch nucleus $^{63}\mathrm{Ni}$ affects the abundances of other nuclei in its region, especially $^{63}\mathrm{Cu}$ and $^{64}\mathrm{Zn}$. In order to determine the energy-dependent neutron capture cross section in the astrophysical energy region, an experiment at the Los Alamos National Laboratory has been performed using the calorimetric $4\ensuremath{\pi}\phantom{\rule{4pt}{0ex}}{\mathrm{BaF}}_{2}$ array DANCE. The ($n,\ensuremath{\gamma}$) cross section of $^{63}\mathrm{Ni}$ has been determined relative to the well-known $^{197}\mathrm{Au}$ standard with uncertainties below 15%. Various $^{63}\mathrm{Ni}$ resonances have been identified based on the $Q$ value. Furthermore, the $s$-process sensitivity of the new values was analyzed with the new network calculation tool NETZ.

A new neutron detector array (NEUANCE) is under development at the Los Alamos Neutron Science Center (LANSCE). After completion, NEUANCE will be installed in the central cavity of the 3.6π Υ-ray detector array DANCE located at the Lujan Center of LANSCE. The detector system, with simultaneous neutron and -ray detection capability, will be used to study neutron-induced capture and session reactions. The response of a EJ-309 scintillation detector to Υ-ray and neutron radiation was measured using the standard Υ-ray and 252Cf sources. The light from the detector was collected using a Hamamatsu photomultiplier tube or a Silicon photomultiplier GEANT4 was used to understand the light output and the optical photon transport in the scintillation. The detector geometry and optimum parameters for the data acquisition system were determined based on the test results and the simulations. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Investigation of prompt fission and neutron-capture Υ rays from fissile actinide samples at the Detector for Advanced Neutron Capture Experiments (DANCE) requires use of a fission-fragment detector to provide a trigger or a veto signal. A fission-fragment detector based on thin scintillating films and silicon photomultipliers has been built to serve as a trigger/veto detector in neutron-induced fission measurements at DANCE. The fissile material is surrounded by scintillating films providing a 4π detection of the fission fragments. The scintillations were registered with silicon photomultipliers. A measurement of the 235 U( n,f ) reaction with this detector at DANCE revealed a correct time-of-flight spectrum and provided an estimate for the efficiency of the prototype detector of 11.6(7)%. Design and test measurements with the detector are described. A neutron source with fast timing has been built to help with detector-response measurements. The source is based on the neutron emission from the spontaneous fission of 252 Cf and the same type of scintillating films and silicon photomultipliers. Overall time resolution of the source is 0.3 ns. Design of the source and test measurements with it are described. An example application of the source for determining the neutron/gamma pulse-shape discrimination by a stilbene crystal is given.

Spectra of $\ensuremath{\gamma}$ rays following the $^{97}\mathrm{Mo}(n,\ensuremath{\gamma})$ reaction were measured as a function of incident neutron energy with the DANCE (Detector for Advanced Neutron Capture Experiments) array of $160 {\mathrm{BaF}}_{2}$ scintillation detectors at the Los Alamos Neutron Science Center using an enriched $^{97}\mathrm{Mo}$ target. These spectra were used for the assignment of spins of the $^{97}\mathrm{Mo}$ resonances up to neutron energy ${E}_{n}=1.7$ keV, as well as in the study of photon strength functions (PSFs) in $^{98}\mathrm{Mo}$. Analysis of the spectra with the nuclear statistical model showed that they can be well reproduced with the same PSF models which well described the $\ensuremath{\gamma}$ decay following slow neutron capture in $^{95}\mathrm{Mo}$. On the other hand, the spectra are inconsistent with PSFs describing some other experimental data in $^{98}\mathrm{Mo}$.

A new measurement of the 237U(n, f) cross section from thermal to ≈ 100 keV is discussed, using one of the flightpaths at the LANSCE Lujan Center. Previous energy-resolved resonance-region measurements have been conducted using weapon test time-of-flight[1] and the LANSCE Lead Slowing Down Spectrometer[2], the former of which is limited in its energy range, and the latter in its energy resolution and range. We present here a proposal, based on simulations of the Lujan Center neutron flux and a hypothetical experiment, that is expected to adequately address both of these issues.

The neutron-capture reaction produces a large variety of γ-ray cascades with different γ-ray multiplicities. A measured spectral distribution of these cascades for each γ-ray multiplicity is of importance to applications and studies of γ-ray statistical properties. The DANCE array, a 4π ball of 160 BaF2 detectors, is an ideal tool for measurement of neutron-capture γ-rays. The high granularity of DANCE enables measurements of high-multiplicity γ-ray cascades. The measured two-dimensional spectra (γ-ray energy, γ-ray multiplicity) have to be corrected for the DANCE detector response in order to compare them with predictions of the statistical model or use them in applications. The detector-response correction problem becomes more difficult for a 4π detection system than for a single detector. A trial and error approach and an iterative decomposition of γ-ray multiplets, have been successfully applied to the detector-response correction. Applications of the decomposition methods are discussed for two-dimensional γ-ray spectra measured at DANCE from γ-ray sources and from the 10B(n, γ) and 113Cd(n, γ) reactions.

An overview of the current experimental program on measurements of neutron capture and neutron induced fission at the Detector for Advanced Neutron Capture Experiments (DANCE) is presented. Three major projects are currently under way: 1) high precision measurements of neutron capture cross sections on Uranium isotopes, 2) research aimed at studies of the short-lived actinide isomer production in neutron capture on 235U and 3) measurements of correlated data of fission observables. New projects include developments of auxiliary detectors to improve the capability of DANCE. We are building a compact, segmented NEUtron detector Array at DANCE (NEUANCE), which will be installed in the central cavity of the DANCE array. It will thus provide experimental information on prompt fission neutrons in coincidence with the prompt fission gamma-rays measured by 160 BaF2 crystals of DANCE. Additionally, unique correlated data will be obtained for neutron capture and neutron-induced fission using the DANCE-NEUANCE experimental set up in the future.

Multi-step cascade γ-ray spectra from the neutron capture at isolated resonances of 161Dy nucleus were measured at the LANSCE/DANCE time-of-flight facility in Los Alamos National Laboratory. The objectives of this experiment were to confirm and possibly extend the spin assignment of s-wave neutron resonances and get new information on photon strength functions with emphasis on the role of the M1 scissors mode vibration. The preliminary results show that the scissors mode plays a significant role in all transitions between accessible states of the studied nucleus. The photon strength functions describing well our data are compared to results from 3He-induced reactions, (n,γ) experiments on Gd isotopes, and (γ,γ’) reactions.

The hot bimodal fission of 252Cf is reexamined with new high-statistics data. We constructed a γ-γ-γ coincidence cube for binary fission and LCP-gated γ-γ matrix for ternary fission. By identifying the secondary fission fragments from their γ-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the “hot mode” corresponding to ≈3.1% of the total yield. In α ternary fission, the first measurements of yields for specific fission splits are presented. The Te-α-Ru and Xe-α-Mo neutron yields fit well with a single mode, but the Ba-α-Zr split shows evidence for an enhanced hot mode with an intensity of ≈13.8% of the normal mode.

In the paper efficient nonlinear fitting algorithms without matrix inversion are described. The algorithms were applied to the analysis of two- and three-fold coincidence γ-ray spectra. They were used to process coincidence matrices from fission data from the multidetector GAMMASPHERE spectrometer.

Ternary fission of 252Cf was studied at Gammasphere using eight ΔE×E particle telescopes. Helium, beryllium, boron, and carbon light charged particles (LCPs) emitted with kinetic energy more than 9, 21, 26, and 32 MeV, respectively, were identified. The 3368-keV γ transition from the first 2+ excited state in 10Be was found and the population probability ratio N(2+)/N(0+) = 0.160 ± 0.025 was estimated. No evidence was found for 3368-keV γ rays emitted from a triple molecular state. For the first time, charge distributions are obtained for ternary fission fragments emitted with helium, beryllium, and carbon LCPs.

The competition between fusion-fission and quasi-fission in the reactions 48 Ca+ 208 Pb and 48 Ca+ 244 Pu(E * = 40MeV) is investigated using the pre-scission neutron multiciplicity distributions ( PSNMD ) obtained with a new analysis protocol.

From multiparameter data obtained at Lawrence Berkeley National Laboratory, the integral characteristics of the prompt γ-ray emission were extracted for tripartition of 252Cf with He, Be and C being the third light charged particle. We used multifold γ-ray coincidence spectra for the determination of γ-ray multiplicities assuming a Gaussian distribution for γ-ray multiplicity. The multiplicity distribution characteristics, i.e. mean multiplicity and its dispersion were obtained by minimizing with respect to the calculated values of probabilities of multifold γ-ray coincidences using a combinatoric method. Comparison with the known experimental data from binary fission was made. Further, we investigated dependencies of the mean γ-ray multiplicity on the kinetic energy of the light charged particle. The mean γ-ray multiplicity for He ternary fission is found to increase rapidly with increasing kinetic energy of He in the region less than 11 MeV and then decrease slowly with increasing kinetic energy of He. The anomalous behaviour of γ-ray emission is discussed. The mean γ-ray multiplicity was determined for the first time for Be and C ternary fission. For Be, the γ-ray multiplicity as a function of kinetic energy was obtained as well.

M. G. Itkis,∗ ,a A. A. Bogatchev,a I. M. Itkis,a M. Jandel,a J. Kliman,a G. N. Kniajeva,a N. A. Kondratiev,a I. V. Korzyukov,a E. M. Kozulin,a L. Krupa,a Yu. Ts. Oganessian,a I. V. Pokrovski,a V. A. Ponomarenko,a E. V. Prokhorova,a A. Ya. Rusanov,a V. M. Voskresenski,a A. A. Goverdovski,b F. Hanappe,c T. Materna,c N. Rowley,d L. Stuttge,d G. Giardina,e and K. J. Moodyf Flerov Laboratory of Nuclear Research, JINR, 141980 Dubna, Russia Institute for Physics & Power Engineering, 249020 Obninsk, Russia Universite Libre de Bruxelles, 1050 Bruxelles, Belgium Institut de Recherches Subatomiques, F-67037 Strasbourg Cedex, France Dipartimento di Fisica dell’ Universita di Messina, 98166 Messina, Italy University of California, Lawrence Livermore National Laboratory, Livermore, California 94551, USA

A great deal of effort has been dedicated to the revision of the standard values in connection with the neutron interaction for some actinides. While standard data compilation are available for decades nuclear data evaluations included in existing nuclear data libraries (ENDF, JEFF, JENDL, etc.) do not follow the standard recommended values. Indeed, the majority of evaluations for major actinides do not conform to the standards whatsoever. In particular, for the n + 235 U interaction the only value in agreement with the standard is the thermal fission cross section. A resonance re-evaluation of the n + 235 U interaction has been performed to address the issues regarding standard values in the energy range from 10−5 eV to 2250 eV. Recently, 235 U fission cross-section measurements have been performed at the CERN Neutron Time-of-Flight facility (TOF), known as n_TOF, in the energy range from 0.7 eV to 10 keV. The data were normalized according to the recommended standard of the fission integral in the energy range 7.8 eV to 11 eV. As a result, the n_TOF averaged fission cross sections above 100 eV are in good agreement with the standard recommended values. The n_TOF data were included in the 235 U resonance analysis that was performed with the code SAMMY. In addition to the average standard values related to the fission cross section, standard thermal values for fission, capture, and elastic cross sections were also included in the evaluation. This paper presents the procedure used for re-evaluating the 235 U resonance parameters including the recommended standard values as well as new cross section measurements.

In a Monte Carlo Hauser-Feshbach statistical framework, we describe spectra, average multiplicities, average energy, and multiplicity distributions of the prompt $\ensuremath{\gamma}$ rays produced in the thermal neutron-induced fission of $^{235}\mathrm{U}$ and $^{239}\mathrm{Pu}$, and the spontaneous fission of $^{252}\mathrm{Cf}$. Comparisons against recent experimental data show reasonable agreement in all cases investigated, after adjustment of the initial spin distribution in the fission fragments. In particular, when we include in the calculation the Doppler broadening we obtain a qualitatively good description of the measured low-energy spectra, where contributions from collective discrete transitions in specific fragments can be identified. At higher energies, both the calculated neutron and $\ensuremath{\gamma}$-ray spectra are softer than experimental data. The impact of selected model parameters on the prompt neutron and $\ensuremath{\gamma}$-ray spectra is analyzed. Finally, we present the prompt $\ensuremath{\gamma}$ spectrum and multiplicity distribution for the neutron-induced fission of $^{235}\mathrm{U}$ for 5.5 MeV neutron incident energy, just below the threshold for second-chance fission.

The experimental spectra of γ rays following radiative neutron capture on iso- lated resonances of stable 152,154−158 Gd targets were measured by the DANCE calorime- ter installed at the Los Alamos Neutron Scattering Center in New Mexico, USA. These spectra were analyzed within the extreme statistical model to get new information on the photon strength functions. Special emphasis was put on study of the scissors vibrational mode present in these isotopes. Our data show that the scissors-mode resonances are built not only on the ground states but also on the excited levels of all studied Gd iso- topes. The scissors mode strength observed in 157,159 Gd products is significantly higher than in neighboring even-even nuclei 156,158 Gd. Such a difference indicates the existence of an odd-even effect in the scissors mode strength. Moreover, there exists no universal parameter-free model of the electric dipole photon strength function describing the ex- perimental data in all of the Gd isotopes studied. The results for the scissors mode are compared with the (γ, γ � ) data for the ground-state transitions and with the results from 3 He-induced reactions.

The Pu($n,\ensuremath{\gamma}$) cross section has been measured over the energy range 10 eV to 1 keV using the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos Neutron Science Center as part of a campaign to produce precision ($n,\ensuremath{\gamma}$) measurements on Pu. Fission coincidences were measured with a parallel-plate avalanche counter and used to measure the prompt fission $\ensuremath{\gamma}$-ray spectrum in this region to accurately characterize background. The resulting ($n,\ensuremath{\gamma}$) cross section is generally in agreement with current evaluations. The experimental method utilizes much more detailed information than past measurements on Pu and can be used to extend the measurement to higher incident neutron energies.

Background: Accurate knowledge of the $^{238}\mathrm{U}$($n$,$\ensuremath{\gamma}$) cross section is important for developing theoretical nuclear reaction models and for applications. However, capture cross sections are difficult to calculate accurately and often must be measured.Purpose: We seek to confirm previous measurements and test cross-section calculations with an emphasis on the unresolved resonance region from 1 to 500 keV.Method: Cross sections were measured from 10 eV to 500 keV using the DANCE detector array at the LANSCE spallation neutron source. The measurements used a thin target, 48 mg/cm${}^{2}$ of depleted uranium. Gamma cascade spectra were also measured to provide an additional constraint on calculations. The data are compared to cross-section calculations using the code CoH${}_{3}$ and cascade spectra calculations made using the code dicebox.Results: This new cross-section measurement confirms the previous data. The measured gamma-ray spectra suggest the need for additional low-lying dipole strength in the radiative strength function. New Hauser-Feshbach calculations including this strength accurately predict the capture cross section without renormalization.Conclusions: The present cross-section data confirm previous measurements. Including additional low-lying dipole strength in the radiative strength function may lead to more accurate cross-section calculations in nuclei where $\ensuremath{\langle}{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}\ensuremath{\rangle}$ has not been measured.

Recent efforts to produce and separate neutron-rich rare isotopes in peripheral collisions below the Fermi energy are presented. The experiments have been performed at the Cyclotron Institute of Texas A&M University employing beams from the K500 Superconducting Cyclotron. Two magnetic separators were used: the MARS recoil separator and the Superconducting Solenoid Line (BigSol Line). An enhanced production of neutron-rich nuclides in comparison with high-energy fragmentation mechanisms has been observed and attributed to the role of the N/Z and the nuclear periphery of the target. From a practical viewpoint, these reactions below or around the Fermi energy offer a novel way to access very neutron-rich rare isotopes. The experience obtained in the production of rare isotope beams (RIB) below the Fermi energy will be exploited in the ongoing RIB upgrade of the Cyclotron Institute that will involve production, stopping and reacceleration of rare isotopes.

CIELO (Collaborative International Evaluated Library Organization) provides a new working paradigm to facilitate evaluated nuclear reaction data advances. It brings together experts from across the international nuclear reaction data community to identify and document discrepancies among existing evaluated data libraries, measured data, and model calculation interpretations, and aims to make rapid progress in reconciling these discrepancies to create more accurate ENDF-formatted files. Our goal is for this first step to be achieved within three years. The focus will initially be on a small number of the highest-priority isotopes, namely 1H, 16O, 56Fe, 235,238U, and 239Pu. The present paper is a first step to identify discrepancies between various evaluations of the highest priority isotopes, which was commissioned by the OECD's Nuclear Energy Agency WPEC (Working Party on International Nuclear Data Evaluation Co-operation) during a meeting held in May 2012. The evaluated data for these materials in the existing nuclear data libraries - ENDF/B-VII.1, JEFF-3.1, JENDL-4.0, CENDL-3.1, ROSFOND, IRDFF 1.0 - are reviewed, disrepancies are identified, and some integral properties are given. The paper summarizes a program of nuclear science and computational work needed to create the new CIELO nuclear data evaluations., JRC.D.4-Standards for Nuclear Safety, Security and Safeguards

Latest generation fission experiments provide an excellent testing ground for theoretical models. In this contribution we compare the measurements for ${}^{235}$U(${n}_{\mathrm{th}}$,f), obtained with the Detector for Advanced Neutron Capture Experiments (DANCE) calorimeter at Los Alamos Neutron Science Center (LANSCE), with our full-scale simulation of the primary fragment de-excitation, using the recently developed cgmf code, based on a Monte Carlo implementation of the Hauser-Feshbach theoretical model. We compute the isomer ratios as a function of the initial angular momentum of the fission fragments, for which no direct information exists. Comparison with the available experimental data allows us to determine the initial spin distribution. We also study the dependence of the isomer ratio on the knowledge of the low-lying discrete spectrum input for nuclear fission reactions, finding a high degree of sensitivity. Finally, in the same Hauser-Feshbach approach, we calculate the isomer production ratio for thermal neutron capture on stable isotopes, where the initial conditions (spin, excitation energy, etc.) are well understood. We find that with the current parameters involved in Hauser-Feshbach calculations, we obtain up to a factor of 2 deviation from the measured isomer ratios.

Radiative neutron capture reaction was measured in the resolved resonance region for ${}^{152,154,156,158}$Gd targets with the Detector for Advanced Neutron Capture Experiments $\ensuremath{\gamma}$-ray calorimeter at the Los Alamos Neutron Science Center. The $\ensuremath{\gamma}$-ray energy spectra for different multiplicities were obtained for several $s$-wave resonances in each nucleus. These spectra were analyzed within the extreme statistical model to provide unique information on the photon strength functions and especially on the scissors mode in odd Gd isotopes. The main result of this analysis is that in all nuclei scissors-mode resonances are built on excited levels and not only on their ground states. The strength of the mode found in ${}^{153}$Gd and ${}^{155}$Gd is comparable to the strength observed in well-deformed even-even Gd isotopes while it is substantially higher in ${}^{157,159}$Gd. The difference in observed strengths of the scissors mode indicates an existence of an even-odd effect in this quantity.

Cascades of $\ensuremath{\gamma}$-ray transitions in ${}^{112}$Cd and ${}^{114}$Cd have been studied in a neutron-capture experiment at the Los Alamos Neutron Science Center using a highly segmented and highly efficient $\ensuremath{\gamma}$-ray calorimeter---Detector for Advanced Neutron Capture Experiments. Intensity distributions of two-, three-, and multifold coincidence $\ensuremath{\gamma}$-ray transitions de-exciting resonances with known angular momenta and terminating at the ground state and at the first excited levels have been obtained. The results are compared with statistical-model calculations using the code dicebox for the two theoretical models of electric-dipole photon-strength functions, the standard Lorentzian and the model of Kadmenskii, Markushev, and Furman. It has been found that a combination of the two models reproduces the data best. Adding resonance structures, such as the scissors mode and the pygmy resonance, to the photon-strength function do not improve the description of the $\ensuremath{\gamma}$-ray spectra.

The DANCE (Detector for Advanced Neutron Capture Experiments) array located at the Los Alamos national laboratory has been used to obtain the neutron capture cross sections for the 175 Lu and 176 Lu isotopes with neutron energies from thermal up to 100 keV. Both isotopes are of current interest for the nucleosyn- thesis s-process in astrophysics and for applications as in reactor phys ics or in nuclear medicine. Three targets were used to perform these measurements. One was nat Lu foil and the other two were isotope-enriched targets of 175 Lu and 176 Lu. The cross sections are obtained for now through a precise neutron flux determination and a normalization at the thermal neutron cross section value. A comparison with the recent experimental data and the evaluated data of ENDF/B-VII.0 will be presented. In addition, resonances parameters and spin assignments for some resonances will be featured.

Background: The prompt gamma-ray spectrum from fission is important for understanding the physics of nuclear fission, and also in applications involving fission. Relatively few measurements of the prompt gamma spectrum from ${}^{239}$Pu($n,f$) have been published.Purpose: This experiment measured the multiplicity, individual gamma energy spectrum, and total gamma energy spectrum of prompt fission gamma rays from ${}^{239}$Pu($n,f$) in the neutron energy range from thermal to 30 keV, to test models of fission and to provide information for applications.Method: Gamma rays from neutron-induced fission of ${}^{239}$Pu were measured using the DANCE gamma-ray calorimeter. Fission events were tagged by detecting fission products in a parallel-plate avalanche counter in the center of DANCE. The measurements were corrected for detector response using a geant4 model of DANCE. A detailed analysis for the gamma rays from the 1${}^{+}$ resonance complex at 10.93 eV is presented.Results: A six-parameter analytical parametrization of the fission gamma-ray spectrum was obtained. A Monte Carlo Hauser-Feshbach calculation provided good general agreement with the data, but some differences remain to be resolved.Conclusions: An analytic parametrization can be made of the gamma-ray multiplicity, energy distribution, and total-energy distribution for the prompt gamma rays following neutron-induced fission of ${}^{239}$Pu. This parametrization may be useful for applications. Modern Monte Carlo Hauser-Feshbach calculations can do a good job of calculating the fission gamma-ray emission spectrum, although some details remain to be understood.

The (n,γ) cross section on the unstable 173Lu(t1/2 = 1.37y) has been measured from thermal energy up to 200 eV at Los Alamos Neutron Science Center (LANSCE) with The Detector for Advanced Neutron Capture Experiements (DANCE). The main aim of this study is to validate and optimize reaction models for unstable nucleus. A preliminary capture yield will be presented in this paper.

Neutron capture experiments on highly enriched 117,119Sn isotopes were performed with the DANCE detector array located at the Los Alamos Neutron Science Center. The DANCE detector provides detailed information about the multi-step γ-ray cascade following neutron capture. Analysis of the experimental data provides important information to improve understanding of the neutron capture reaction, including a test of the statistical model, the assignment of spins and parities of neutron resonances, and information concerning the Photon Strength Function (PSF) and Level Density (LD) below the neutron separation energy. Preliminary results for the (n,γ) reaction on 117,119Sn are presented. Resonance spins of the odd-A tin isotopes were almost completely unknown. Resonance spins and parities have been assigned via analysis of the multi-step γ-ray spectra and directional correlations.

Efficient data storing employing compression methods is described. The algorithm was optimized for on-line analysis and compression with minimal number of mathematical operations needed.

Modular system to acquire, store, analyze and process experimental nuclear data is described. Besides standard methods new developed algorithms also have been included in the system.

The neutron capture cross section of (235)U was measured for the neutron incident energy region between 4 eV and 1 MeV at the DANCE facility at the Los Alamos Neutron Science Center with an unprecedented accuracy of 2-3% at 1 keV. The new methodology combined three independent measurements. In the main experiment, a thick actinide sample was used to determine neutron capture and neutron-induced fission rates simultaneously. In the second measurement, a fission tagging detector was used with a thin actinide sample and detailed characteristics of the prompt-fission gamma rays were obtained. In the third measurement, the neutron scattering background was characterized using a sample of (208)Pb. The relative capture cross section was obtained from the experiment with the thick (235)U sample using a ratio method after the subtraction of the fission and neutron scattering backgrounds. Our result indicates errors that are as large as 30% in the 0.5-2.5 keV region, in the current knowledge of neutron capture as embodied in major nuclear data evaluations. Future modifications of these databases using the improved precision data given herein will have significant impacts in neutronics calculations for a variety of nuclear technologies.

The ${}^{155}$Gd($n$,$\ensuremath{\gamma}$) reaction was measured with the DANCE $\ensuremath{\gamma}$-ray calorimeter at the Los Alamos Neutron Science Center. Spins were determined for the $s$-wave resonances by analysis of the $\ensuremath{\gamma}$-ray multiplicity distributions. The analysis was performed with a pattern recognition method. The resulting level densities for the $J=1$ and 2 resonances are in qualitative agreement with the expected 2$J$ $+$ 1 dependence. The average $s$-wave resonance spacing was determined to be ${D}_{0}=1.62$ $\ifmmode\pm\else\textpm\fi{}$ 0.15 eV. Analysis of the neutron resonances with the code sammy yielded the $s$-wave strength function ${S}_{0}=1.99\ifmmode\pm\else\textpm\fi{}0.28\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and the average total radiative width ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}$ $=$ 120 $\ifmmode\pm\else\textpm\fi{}$ 3 meV.

In recent years we have performed a series of neutron capture experiments with the DANCE detector array located at the Los Alamos Neutron Science Center. The radiative decay spectrum from the compound nucleus contains important information about nuclear structure and the reaction mechanism. The primary goals of the measure- ments are to obtain improved capture cross sections, to determine properties of the photon strength function, to improve neutron level densities and strength functions by determin- ing the spin and parity of the capturing states. We shall present examples of our recent results.