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Determine the dosimetric quality and the planning time reduction when utilizing a template-based automated planning application.A software application integrated through the treatment planning system application programing interface, QuickPlan, was developed to facilitate automated planning using configurable templates for contouring, knowledge-based planning structure matching, field design, and algorithm settings. Validations are performed at various levels of the planning procedure and assist in the evaluation of readiness of the CT image, structure set, and plan layout for automated planning. QuickPlan is evaluated dosimetrically against 22 hippocampal-avoidance whole brain radiotherapy patients. The required times to treatment plan generation are compared for the validations set as well as 10 prospective patients whose plans have been automated by QuickPlan.The generations of 22 automated treatment plans are compared against a manual replanning using an identical process, resulting in dosimetric differences of minor clinical significance. The target dose to 2% volume and homogeneity index result in significantly decreased values for automated plans, whereas other dose metric evaluations are nonsignificant. The time to generate the treatment plans is reduced for all automated plans with a median difference of 9' 50″ ± 4' 33″.Template-based automated planning allows for reduced treatment planning time with consistent optimization structure creation, treatment field creation, plan optimization, and dose calculation with similar dosimetric quality. This process has potential expansion to numerous disease sites.

Purpose Linear accelerator quality assurance (QA) in radiation therapy is a time consuming but fundamental part of ensuring the performance characteristics of radiation delivering machines. The goal of this work is to develop an automated and standardized QA plan generation and analysis system in the Oncology Information System (OIS) to streamline the QA process. Methods Automating the QA process includes two software components: the AutoQA Builder to generate daily, monthly, quarterly, and miscellaneous periodic linear accelerator QA plans within the Treatment Planning System (TPS) and the AutoQA Analysis to analyze images collected on the Electronic Portal Imaging Device (EPID) allowing for a rapid analysis of the acquired QA images. To verify the results of the automated QA analysis, results were compared to the current standard for QA assessment for the jaw junction, light‐radiation coincidence, picket fence, and volumetric modulated arc therapy (VMAT) QA plans across three linacs and over a 6‐month period. Results The AutoQA Builder application has been utilized clinically 322 times to create QA patients, construct phantom images, and deploy common periodic QA tests across multiple institutions, linear accelerators, and physicists. Comparing the AutoQA Analysis results with our current institutional QA standard the mean difference of the ratio of intensity values within the field‐matched junction and ball‐bearing position detection was 0.012 ± 0.053 (P = 0.159) and is 0.011 ± 0.224 mm (P = 0.355), respectively. Analysis of VMAT QA plans resulted in a maximum percentage difference of 0.3%. Conclusion The automated creation and analysis of quality assurance plans using multiple APIs can be of immediate benefit to linear accelerator quality assurance efficiency and standardization. QA plan creation can be done without following tedious procedures through API assistance, and analysis can be performed inside of the clinical OIS in an automated fashion.

An experiment on 235U was performed with a white-spectrum neutron beam at the Los Alamos Neutron Science Center. Gamma rays from the (n, γ) and (n, f) reactions were measured with the DANCE array. We present spectra of γ rays emitted shortly after any of the reactions occurs. A novel method for background estimation was applied. The spectrum of the late fission γ rays is compared with CGMF predictions.

Two measurements of fission γ rays were performed with the DANCE and NEUANCE arrays using the reactions 235 U(n, f) and 252 Cf(sf). Utilizing the fast time response of the detectors and a method for estimating the accidental background, we obtained the energy spectrum of the late prompt fission γ rays as a function of the time since fission. The experimental results are compared with predictions of the code CGMF folded with GEANT4 simulations of the detector response.

We propose a novel method to extract the prompt neutron multiplicity distribution, $P(\nu)$, in fission reactions based on correlations between prompt neutrons, $\gamma$ rays, and fragment kinetic energy arising from energy conservation. In this approach, only event-by-event measurements of the total $\gamma$-ray energy released as a function of the total kinetic energy (TKE) of the fission fragments are performed, and no neutron detection is required. Using the $\texttt{CGMF}$ fission event generator, we illustrate the method and explore the accuracy of extracting the neutron multiplicity distribution when taking into account the energy resolution and calibration of the energy measurements. We find that a TKE resolution of under 2 MeV produces reasonably accurate results, independent of typical $\gamma$-ray energy measurement resolution., Comment: 5 pages, 4 figures, published in PRC

To enhance the capabilities of the DANCE array, a new detector array NEUANCE was developed to enable simultaneous measurements of prompt fission neutrons and γ rays. NEUANCE was designed and constructed using 21 stilbene organic scintillator crystals. It was installed in the central cavity of the DANCE array. Signals from the 160 BaF 2 detectors of DANCE and the 21 detectors of NEUANCE were merged into a newly designed high-density high-throughput data acquisition system. The excellent pulse shape discrimination properties of stilbene enabled detection of neutrons with energy thresholds as low as 30–40 keVee. A fission reaction tagging method was developed using a NEUANCE γ -ray or neutron signal. The probability of detecting a neutron from the spontaneous fission of 252Cf using NEUANCE is ∼ 47%. New correlated data for prompt fission neutrons and prompt fission γ rays were obtained for 252 Cf using this high detection efficiency experimental setup. Average properties of prompt fission neutron emission as a function of prompt fission γ -ray quantities were also obtained, suggesting that neutron and γ -ray emission in fission are correlated.

The 239Pu(n,γ) cross section has been measured from 10 eV to 1.3 MeV as part of an experimental campaign using the Detector for Advanced Neutron Capture Experiments (DANCE). The work represents a significant advance in experimental technique, with improved systematic uncertainties in key regions in the keV to MeV regime. In general the results of prior work are confirmed with improved uncertainties, particularly at the highest incident neutron energies.

We report the measurement of a neutron radiative cross section on a target with a high gamma activity, at the Los Alamos DANCE detector (Detector for Advanced Neutron Capture Experiments) for the first time. The $(n,\ensuremath{\gamma})$ reaction properties of the unstable $^{173}\mathrm{Lu}$ isotope were studied. Two experimental campaigns were needed to determine the $^{173}\mathrm{Lu}(n,\ensuremath{\gamma})$ cross section. They were performed at the Los Alamos Neutron Science Center (LANSCE) spallation neutron source facility. To this end, two targets were produced from an Hf sample using successively proton irradiation and chemical separations. They were composed of $^{173}\mathrm{Lu},^{174}\mathrm{Lu}$, and $^{175}\mathrm{Lu}$ isotopes. The two measurements were conducted at two-year intervals, taking advantage of the difference of the isotopic decay lifetimes in order to identify resonances from the $^{173}\mathrm{Lu}(n,\ensuremath{\gamma})$ and $^{174}\mathrm{Lu}(n,\ensuremath{\gamma})$ reactions. Just over one hundred new resonances were observed, the majority of which come from the $^{173}\mathrm{Lu}(n,\ensuremath{\gamma})$ reaction. Only a few of them were assigned to the $^{174}\mathrm{Lu}(n,\ensuremath{\gamma})$ reaction. As regards the $^{173}\mathrm{Lu}(n,\ensuremath{\gamma})$ reaction, the radiative neutron capture cross section was determined over the energy range from thermal neutron up to 200 eV. The parameters of resonances in the resolved resonance region were extracted with the sammy code while calculations with talys determined the capture cross section in the unresolved resonances region. At the keV region, we performed standard talys calculations as well as other microscopic investigations by substituting the standard talys photon strength function by another one from QRPA models.

A major barrier in the study of neutron-induced nuclear reactions is the impossibility of direct measurements with short-lived radioactive isotopes. For these exotic nuclei, theoretical inputs such as the photon strength function (PSF) are poorly constrained. At Los Alamos National Laboratory, the Detector for Advanced Neutron Capture Experiments (DANCE) provides direct measurements of $\ensuremath{\gamma}$-ray cascades following neutron capture reactions on stable or long-lived radioactive nuclei. While Hauser-Feshbach calculations can provide reasonable predictions for neutron capture on heavy nuclei, their application to neutron-rich light nuclei with low nuclear level densities and low neutron separation energies is questionable. In this paper, we report on the $\ensuremath{\gamma}$-ray spectra from individual neutron resonances from the $^{96}\mathrm{Zr}(n,\ensuremath{\gamma})$ reaction, with an emphasis on the sensitivity of of the $\ensuremath{\gamma}$-ray spectra to different PSF models. The comparison of the measured $\ensuremath{\gamma}$-ray spectra with predicted spectra does not support the addition of a low-energy enhancement of the size reported in many charged-particle reaction measurements, but the sensitivity of the $\ensuremath{\gamma}$-ray spectra to different PSF models is weak.

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. The time is provided by registering the fission fragments in a layer of a thin scintillation film with a signal rise time of 1 ns. The scintillation light output is measured by two silicon photomultipliers with rise time of 0.5 ns. Overall time resolution of the source is 0.3 ns. Design of the source and test measurements using it are described. An example application of the source for determining the neutron/gamma pulse-shape discrimination by a stilbene crystal is given.

A fission-fragment detector based on thin scintillating films 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 4π 4 π detection of the fission fragments. The scintillation photons were registered with silicon photomultipliers. A measurement of the 235 U (n,f) ( 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.

The preparation of 191Ir and 193Ir electrodeposits for neutron capture cross-section measurements at the detector for advanced neutron capture experiments located at the at Los Alamos Neutron Science Center is described. The electrodeposition of iridium in the desired thickness of 0.4–1 mg/cm2 is challenging. Better yields and thicknesses were obtained using electrodeposition from isopropyl alcohol solutions than from ammonium sulfate solutions. 191Ir and 193Ir targets were initially prepared using the standard single-sided electrodeposition cell. Iridium electrodepositions using a double-sided electrodeposition cell were developed and were optimized, resulting in thick, uniform iridium deposits. LA UR 15-22475.

Neutron-induced fission of 235U was studied at the thermal column of the UMass Lowell 1 MW Research Reactor. A collimated, 2.25-inch diameter beam of thermal neutrons with the flux of ~5x105 n/cm2/sec induced fission reaction on a plate of low-enriched uranium with the areal density ~25 mg/cm2 of 235U. We have used the prompt fission-neutron tagging method to identify the fission reaction in the off-line analysis. The method employs the pulse-shape discrimination of neutrons and gamma-ray events in stilbene scintillator and enables identification of coincidence events of prompt fission gamma-rays and prompt fission neutrons in coincidence time intervals less than 20-30 ns. The prompt gamma-ray radiation was detected using two co-linear NaI(Tl) detectors. The measured spectra of prompt-fission gamma rays between 150 keV and 6 MeV are presented. The results from these initial measurements demonstrate the feasibility of the experimental method. Future measurements with extended arrays of detectors are planned.

A single, unifying measurement of the $^{239}\mathrm{Pu}$ capture cross section from 1 keV to 1.3 MeV has been performed for the first time using the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos Neutron Science Center (LANSCE). The experimental method combines a prior experiment's characterization of prompt fission $\ensuremath{\gamma}$ rays in conjunction with a fission tagging detector with a separate experiment using a thick $^{239}\mathrm{Pu}$ sample to extract the neutron capture cross section in ratio to $^{239}\mathrm{Pu}(n,f)$. We have made new predictions of the capture cross section taking into account recent results for the $M1$ scissors mode present in other actinides. The results show deviations from current evaluations which are 30% higher at the highest energies, and will be used to improve calculations relevant for several applications.

New data on the prompt fission neutron spectra (PFNS) from neutron-induced fission with higher accuracies are needed to resolve discrepancies in the literature and to address gaps in the experimental data. The Chi-Nu project, conducted jointly by LANL and LLNL, aims to measure the shape of the PFNS for fission of 239Pu induced by neutrons from 0.5 to 20 MeV with accuracies of 3–5% in the outgoing energy from 0.1 to 9 MeV and 15% from 9 to 12 MeV and to provide detailed experimental uncertainties. Neutrons from the WNR/LANSCE neutron source are being used to induce fission in a Parallel-Plate Avalanche Counter (PPAC). Two arrays of neutron detectors are used to cover the energy range of neutrons emitted promptly in the fission process. Challenges for the present experiment include background reduction, use of 239Pu in a PPAC, and understanding neutron detector response. Achieving the target accuracies requires the understanding of many systematic uncertainties. The status and plans for the future will be presented.

A position-sensitive, high-resolution time-of-flight detector for fission fragments has been developed. The SPectrometer for Ion DEterminiation in fission Research (SPIDER) is a $2E-2v$ spectrometer designed to measure the mass of light fission fragments to a single mass unit. The time pick-off detector pairs to be used in SPIDER have been tested with $\alpha$-particles from $^{229}$Th and its decay chain and $\alpha$-particles and spontaneous fission fragments from $^{252}$Cf. Each detector module is comprised of a thin electron conversion foil, electrostatic mirror, microchannel plates, and delay-line anodes. Particle trajectories on the order of 700 mm are determined accurately to within 0.7 mm. Flight times on the order of 70 ns were measured with 200 ps resolution FWHM. Computed particle velocities are accurate to within 0.06 mm/ns corresponding to precision of 0.5%. An ionization chamber capable of 400 keV energy resolution coupled with the velocity measurements described here will pave the way for modestly efficient measurements of light fission fragments with unit mass resolution., Comment: 15 pages 6 figures

The cross section for neutron capture in the continuum region has been difficult to calculate accurately. Previous results for $^{238}\mathrm{U}$ show that including an $M1$ scissors-mode contribution to the photon strength function resulted in very good agreement between calculation and measurement. This paper extends that analysis to $^{234,236}\mathrm{U}$ by using $\ensuremath{\gamma}$-ray spectra measured with the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos Neutron Science Center to constrain the photon strength function used to calculate the capture cross section. Calculations using a strong scissors-mode contribution reproduced the measured $\ensuremath{\gamma}$-ray spectra and were in excellent agreement with the reported cross sections for all three isotopes.

The $^{236}\mathrm{U}(n,\ensuremath{\gamma})$ reaction cross section has been measured for the incident neutron energy range from 10 eV to 800 keV by using the Detector for Advanced Neutron Capture Experiments (DANCE) $\ensuremath{\gamma}$-ray calorimeter at the Los Alamos Neutron Science Center. The cross section was determined with the ratio method, which is a technique that uses the $^{235}\mathrm{U}(n,f)$ reaction as a reference. The results of the experiment are reported in the resolved and unresolved resonance energy regions. Individual neutron resonance parameters were obtained below 1 keV incident energy by using the $R$-matrix code sammy. The cross section in the unresolved resonance region is determined with improved experimental uncertainty. It agrees with both ENDF/B-VII.1 and JEFF-3.2 nuclear data libraries. The results above 10 keV agree better with the JEFF-3.2 library.

The $^{242}\mathrm{Am}$ metastable isomer's neutron-induced destruction mechanisms were studied at the Los Alamos Neutron Science Center using the Detector for Advanced Neutron-Capture Experiments array with a compact parallel-plate avalanche counter. New $^{242\mathrm{m}}\mathrm{Am}$ neutron-capture cross sections were determined from 100 meV to 10 keV, and the absolute scale was set with respect to a concurrent measurement of the well-known $^{242\mathrm{m}}\mathrm{Am}$ neutron-induced-fission cross section. The new fission cross section spans an energy range from 100 meV to 1 MeV and was normalized to the ENDF/B-VII.1 evaluated cross section to set the absolute scale. Our $^{242\mathrm{m}}\mathrm{Am}(n,f)$ cross section agrees well with the cross section of Browne et al. [Phys. Rev. C 29, 2188 (1984)] over this large energy interval. The new neutron-capture cross section measurement complements and agrees well with our recent results reported below 1 eV in Buckner et al. [Phys. Rev. C 95, 024610 (2017)]. This new work comprises the most comprehensive study of $^{242\mathrm{m}}\mathrm{Am}(n,\ensuremath{\gamma})$ above thermal energy. Neutron-induced resonance energies and parameters were deduced with the sammy $R$-matrix code for incident neutron energies up to 45 eV, and the new average ${\mathrm{\ensuremath{\Gamma}}}_{\ensuremath{\gamma}}$ is $13%$ higher than the evaluated average $\ensuremath{\gamma}$ width.

The neutron-induced reaction cross sections of $^{242m}\mathrm{Am}$ were measured at the Los Alamos Neutron Science Center using the Detector for Advanced Neutron-Capture Experiments array along with a compact parallel-plate avalanche counter for fission-fragment detection. A new neutron-capture cross section was determined, and the absolute scale was set according to a concurrent measurement of the well-known $^{242m}\mathrm{Am}(n,f)$ cross section. The ($n,\ensuremath{\gamma}$) cross section was measured from thermal energy to an incident energy of 1 eV at which point the data quality was limited by the reaction yield in the laboratory. Our new $^{242m}\mathrm{Am}$ fission cross section was normalized to ENDF/B-VII.1 to set the absolute scale, and it agreed well with the ($n,f$) cross section reported by Browne et al. (1984) from thermal energy to 1 keV. The average absolute capture-to-fission ratio was determined from thermal energy to ${E}_{n}=0.1$ eV, and it was found to be 26(4)$%$ as opposed to the ratio of $19%$ from the ENDF/B-VII.1 evaluation.

In the nuclear mass range A≈60 to 90 of the solar abundance distribution the weak s-process component is the dominant contributor. In this scenario, which is related to massive stars, the overall neutron exposure is not sufficient for the s process to reach mass flow equilibrium. Hence, abundances and isotopic ratios are very sensitive to the neutron capture cross sections of single isotopes, and nucleosynthesis models need accurate experimental data. In this work we report on a new measurement of the Cu63(n,γ) cross section for which the existing experimental data show large discrepancies. The Cu63(n,γ) cross section at kBT=25 keV was determined via activation with a quasistellar neutron spectrum at the Joint Research Centre (JRC) in Geel, and the energy dependence was determined with the time-of-flight technique and the calorimetric 4πBaF2 detector array DANCE at the Los Alamos National Laboratory. We provide new cross section data for the whole astrophysically relevant energy range.

The absolute neutron-capture cross section of 242 Pu was measured at the Los Alamos Neutron Science Center using the Detector for Advanced Neutron-Capture Experiments array along with a compact parallel-plate avalanche counter for fission-fragment detection. During target fabrication, a small amount of 239 Pu was added to the active target so that the absolute scale of the 242 Pu(n,γ) cross section could be set according to the known 239 Pu(n,f) resonance at En,R = 7.83 eV. The relative scale of the 242 Pu(n,γ) cross section covers four orders of magnitude for incident neutron energies from thermal to ≈ 40 keV. The cross section reported in ENDF/B-VII.1 for the 242 Pu(n,γ) En,R = 2.68 eV resonance was found to be 2.4% lower than the new absolute 242 Pu(n,γ) cross section.

Detailed information on the fission process can be inferred from the observation, modeling and theoretical understanding of prompt fission neutron and $\gamma$-ray~observables. Beyond simple average quantities, the study of distributions and correlations in prompt data, e.g., multiplicity-dependent neutron and \gray~spectra, angular distributions of the emitted particles, $n$-$n$, $n$-$\gamma$, and $\gamma$-$\gamma$~correlations, can place stringent constraints on fission models and parameters that would otherwise be free to be tuned separately to represent individual fission observables. The FREYA~and CGMF~codes have been developed to follow the sequential emissions of prompt neutrons and $\gamma$-rays~from the initial excited fission fragments produced right after scission. Both codes implement Monte Carlo techniques to sample initial fission fragment configurations in mass, charge and kinetic energy and sample probabilities of neutron and $\gamma$~emission at each stage of the decay. This approach naturally leads to using simple but powerful statistical techniques to infer distributions and correlations among many observables and model parameters. The comparison of model calculations with experimental data provides a rich arena for testing various nuclear physics models such as those related to the nuclear structure and level densities of neutron-rich nuclei, the $\gamma$-ray~strength functions of dipole and quadrupole transitions, the mechanism for dividing the excitation energy between the two nascent fragments near scission, and the mechanisms behind the production of angular momentum in the fragments, etc. Beyond the obvious interest from a fundamental physics point of view, such studies are also important for addressing data needs in various nuclear applications. (See text for full abstract.), Comment: 39 pages, 57 figure files, published in Eur. Phys. J. A, reference added this version

The CIELO collaboration has studied neutron cross sections on nuclides that significantly impact criticality in nuclear technologies – 16 O, 56 Fe, 235,8 U and 239 Pu – with the aim of improving the accuracy of the data and resolving previous discrepancies in our understanding. This multi-laboratory pilot project, coordinated via the OECD/NEA Working Party on Evaluation Cooperation (WPEC) Subgroup 40 with support also from the IAEA, has motivated experimental and theoretical work and led to suites of new evaluated libraries that accurately reflect measured data and also perform well in integral simulations of criticality.

A highly gamma-radioactive target, 3.7 GBq, of 173 Lu isotope was placed inside the DANCE array (Detector for Advanced Neutron Capture Experiments) at Los Alamos to study the radiative neutron capture on an unstable isotope. The 173 Lu element was produced by natural Hf(p,xn) reactions following by beta-decays at the Isotope Production Facility (IPF). Measurements of radiative neutron capture cross section on 173 Lu were achieved at the Los Alamos Neutron Science Center (LANSCE) spallation neutron source facility over the neutron energy range from thermal up to 1 keV. A special configuration was necessary to perform the experiment using the DANCE [1] array due to the high gamma activity of the target. We will report on the target production, the experiment and the results obtained for the radiative neutron capture on 173 Lu. The radiative capture cross section was obtained for the first time on this unstable nucleus. Some resonances have been characterized. A comparison with a recent data evaluation is presented.

The Detector for Advanced Neutron Capture Experiments (DANCE) has been used to measure the 239 Pu(n, γ ) cross section from 10 eV to the keV region. Three experimental run conditions were used to characterize the prompt fission γ -ray spectrum across the entire energy regime, measure the cross section in the resolved resonance region, and obtain necessary count rate well into the keV region. The preliminary cross sections are in good agreement with current evaluations from 10 eV to 80 keV.

The prompt neutron spectrum from neutron-induced fission needs to be known in designing new fast reactors, predicting criticality for safety analyses, and developing techniques for global security application. A program to measure this spectrum for neutron-induced fission of 239 Pu is underway at the Los Alamos Neutron Science Center. The goal is to obtain data on the shape of the spectrum with a small uncertainty over the emitted neutron energy range of 100 keV to 12 MeV with additional data below and above this range. The incident neutron energy range will be from 0.5 to 30 MeV. The status of this program including results of initial experimental measurements is described here.

A new measurement of the 238 U(n, γ ) cross section using a thin 48 mg/cm 2 target was made using the DANCE detector at LANSCE over the energy range from 10 eV to 500 keV. The results confirm earlier measurements. Measurements of the gamma-ray emission spectra were also made for 238 U(n, γ ) as well as 234,236 U(n, γ ). These measurements help to constrain the radiative strength function used in the cross-section calculations.

The prompt γ-ray spectra from 235U(n,f) at incident energies of 1 to 20 MeV and for 235Cf(s.f.) were measured up to 4 MeV in coincidence with two parallel plate avalanche counters and the liquid scintillator array FIGARO. The unfolded γ-ray spectra from 1–4 MeV using the single value decomposition and iterative Bayesian techniques for the incident neutron energy regions corresponding to the first, second and third chance fissions were found to nearly identical and similar to the distribution from the spontaneous fission of 252Cf. General agreement with the γ-ray distributions from fission was also found with previous measurements.

Multi-step cascade γ -ray spectra from neutron capture at isolated resonances of 152 , 154 − 158 Gd nuclei were measured at the LANSCE/DANCE time-of-flight facility in Los Alamos National Laboratory. The main objective of these experiments was to obtain new information on photon strength functions with emphasis on the role of the M 1 scissors mode vibration. An analysis of the data obtained shows that the scissors mode plays a significant role in the ground state transitions, as well as in the transitions populating all excited states of the studied nuclei. The estimates of the scissors mode strength indicate that for 157 , 159 Gd this strength is significantly higher than in neighboring even–even nuclei 156 , 158 Gd. The results are compared with the ( γ , γ ′ ) data for the ground-state scissors mode and the results from 3 He-induced reactions.

Measurements of correlated data on prompt-fission γ-rays (PFG) have been carried out for various actinide isotopes in recent years using the Detector for Advanced Neutron Capture Experiments (DANCE) at Los Alamos National Laboratory (LANL). We have developed a model that conveniently parametrizes the correlated data of γ-ray multiplicity and energy. New results on two- dimensional prompt-fission γ-ray multiplicity versus energy distributions from spontaneous fission on 252 Cf and neutron-induced fission on 242 m Am are presented together with previously obtained results on 233,235 U and 239 Pu. Correlated PFG data from 252 Cf are also compared to results of the detailed theoretical model developed at LANL, for different thresholds of PFG energies. Future plans to measure correlated data on fission fragments, prompt fission neutrons and γ-rays at DANCE are presented.

The isomeric ratios for the neutron capture reaction $^{176}$Lu($n,\gamma$) to the $J^{\pi}=5/2^-$ 761.7 keV, $T_{1/2}$ =32.8 ns and the $J^{\pi}=15/2^+$, 1356.9 keV, $T_{1/2}$=11.1 ns levels of $^{177}$Lu have been measured for the first time. The experiment was carried out with the Detector for Advanced Neutron Capture Experiments (DANCE) at the Los Alamos National Laboratory. Measured isomeric ratios are compared with talys calculations using different models for photon strength functions, level densities, and optical potentials. In order to reproduce the experimental γ-ray spectra, a low-energy resonance must be added in the photon strength function used in our Hauser-Feshbach calculations.

The outgoing neutron energy spectra from neutron-induced fission of various actinides are important for basic understanding of the fission process near the scission point as well as playing a large role in neutron transport codes, which are heavily relied upon in the design of advanced nuclear reactors and simulations of critical assemblies. The reliability of the results of neutron transport models is a strong function of the quality of the nuclear data used as input. Currently, the world's experimental database of fission neutron spectra is severely incomplete (especially for higher incident neutron energies) with large uncertainties in key portions of the outgoing energy spectra. Many transport codes use evaluated data libraries, which are based on the approach of the Los Alamos model. Other theoretical models have been developed, but the available data cannot distinguish the results of different models (as is the case for 239Pu). Better measurements are needed for all incident and outgoing neutron energies, but most urgently in the low-energy (below 1 MeV) and high-energy (above 6 MeV) portions of the outgoing spectra where theoretical model results differ greatly. We present the design considerations (and some characterization results) of the two Chi-Nu neutron detector arrays: one array of 6Li-glass detectors and one array of liquid-scintillator detectors. These detector arrays are being constructed to meet the challenge of measuring the prompt fission neutron spectra (for a few common actinides) to a higher accuracy and precision than achieved previously and over a larger incident energy range than has been covered by previous experimenters. We see a significant reduction in neutron-scattering backgrounds with our new array designs.

Prompt-fission-neutron spectra for neutron-induced fission reactions on uranium and plutonium isotopes are important for nuclear applications. We have used 6 Li-glass scintillation detectors to measure outgoing neutron energies in the range from 10 keV to 1 MeV, where there is currently large uncertainty in nuclear data. To better understand the response of 6 Li-glass detectors in this energy range, measurements of well-known spontaneous-fission neutrons from a 252 Cf source were done in the neutron-beam flight path. Results were compared with Monte Carlo simulations and they show good agreement. Similar measurements with a 7 Li-glass detector were used to assess gamma-ray background yields.

A compact gas-filled avalanche counter for the detection of fission fragments was developed for a highly segmented 4 π γ-ray calorimeter, namely the Detector for Advanced Neutron Capture Experiments located at the Lujan Center of the Los Alamos Neutron Science Center. It has been used successfully for experiments with 235 U, 238 Pu, 239 Pu, and 241 Pu isotopes to provide a unique signature to differentiate the fission from the competing neutron-capture reaction channel. It was also used to study the spontaneous fission in 252 Cf. The design and performance of this avalanche counter for targets with extreme α-decay rate up to ∼2.4×10 8 /s are described.

The distributions of prompt γ rays from the spontaneous fission of 252Cf and neutron-induced fission of 235U were measured up to ∼ 4 MeV using a liquid scintillator array. The unfolding of measured fission γ rays is presented using the Single Value Decomposition and iterative Bayesian methods. General agreement was found with comparisons made with previous measurements. The energy dependence of the prompt γ - ray distributions for the spontaneous fission of 252Cf and the neutron-induced fission of 235U from bombarding energies of 1-2, 5-10, and 10–20 MeV were found to be almost identical in the γ - ray energy region 1–4 MeV.

Conference of 2016 International Conference on Nuclear Data for Science and Technology, ND 2016 ; Conference Date: 11 September 2016 Through 16 September 2016; Conference Code:130583; International audience; In the framework of the OECD/NEA WPEC subgroup 41, ways to improve neutron induced capture cross sections for 241Am and 237Np are being sought. Decay data, energy dependent cross section data and neutron spectrum averaged data are important for that purpose and were investigated. New time-of-flight measurements were performed and analyzed, and considerable effort was put into development of methods for analysis of spectrum averaged data and re-analysis of existing experimental data.

The absolute neutron-capture cross section of $^{242}\mathrm{Pu}$ was measured at the Los Alamos Neutron Science Center using the Detector for Advanced Neutron-Capture Experiments array along with a compact parallel-plate avalanche counter for fission-fragment detection. The first direct measurement of the $^{242}\mathrm{Pu}(n,\ensuremath{\gamma})$ cross section was made over the incident neutron energy range from thermal to $\ensuremath{\approx}6$ keV, and the absolute scale of the $(n,\ensuremath{\gamma})$ cross section was set according to the known $^{239}\mathrm{Pu}(n,f)$ resonance at ${E}_{n,R}=7.83$ eV. This was accomplished by adding a small quantity of $^{239}\mathrm{Pu}$ to the $^{242}\mathrm{Pu}$ sample. The relative scale of the cross section, with a range of four orders of magnitude, was determined for incident neutron energies from thermal to $\ensuremath{\approx}40$ keV. Our data, in general, are in agreement with previous measurements and those reported in ENDF/B-VII.1; the $^{242}\mathrm{Pu}(n,\ensuremath{\gamma})$ cross section at the ${E}_{n,R}=2.68$ eV resonance is within $2.4%$ of the evaluated value. However, discrepancies exist at higher energies; our data are $\ensuremath{\approx}30%$ lower than the evaluated data at ${E}_{n}\ensuremath{\approx}1$ keV and are approximately $2\ensuremath{\sigma}$ away from the previous measurement at ${E}_{n}\ensuremath{\approx}20$ keV.

The cross section of the neutron capture reaction $^{176}\mathrm{Lu}(n,\ensuremath{\gamma})$ has been measured for a wide incident neutron energy range with the Detector for Advanced Neutron Capture Experiments at the Los Alamos Neutron Science Center. The thermal neutron capture cross section was determined to be $(1912\ifmmode\pm\else\textpm\fi{}132)$ b for one of the Lu natural isotopes, $^{176}\mathrm{Lu}$. The resonance part was measured and compared to the Mughabghab's atlas using the $R$-matrix code, sammy. At higher neutron energies the measured cross sections are compared to ENDF/B-VII.1, JEFF-3.2, and BRC evaluated nuclear data. The Maxwellian averaged cross sections in a stellar plasma for thermal energies between 5 keV and 100 keV were extracted using these data.

The isomeric ratio for the neutron capture reaction 176 Lu(n, γ ) on the J π = 5/2 − , 761.7 keV, T 1/2 =32.8 ns level of 177 m Lu, has been determined in the neutron energy range 8.5 eV-100 keV for the first time using the DANCE array at the Los Alamos National Laboratory.

A summary of the current and future experimental program at DANCE is presented. Measurements of neutron capture cross sections are planned for many actinide isotopes with the goal to reduce the present uncertainties in nuclear data libraries. Detailed studies of capture gamma rays in the neutron resonance region will be performed in order to derive correlated data on the de-excitation of the compound nucleus. New approaches on how to remove the DANCE detector response from experimental data and retain the correlations between the cascade gamma rays are presented. Studies on 235U are focused on quantifying the population of short-lived isomeric states in 236U after neutron capture. For this purpose, a new neutron detector array NEUANCE is under construction. It will be installed in the central cavity of the DANCE array and enable the highly efficient tagging of fission and capture events. In addition, developments of fission fragment detectors are also underway to expand DANCE capabilities to measurements of fully correlated data on fission observables.

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 careful new measurement of the {sup 238}U(n,{gamma}) cross section from 10 eV to 100 keV has been made using the DANCE detector at LANSCE. DANCE is a 4{pi} calorimetric scintillator array consisting of 160 BaF{sub 2} crystals. Measurements were made on a 48 mg/cm{sup 2} depleted uranium target. The cross sections are in general good agreement with previous measurements. The gamma-ray emission spectra, as a function of gamma multiplicity, were also measured and compared to model calculations.

The SPectrometer for Ion DEtermination in fission Research (SPIDER) measures both position and time-of-flight (TOF) of charged particles using a system of thin carbon foils, electrostatic mirrors, microchannel plates, delay-line anodes, and a fast TDC. Tests have been conducted using 229Th and the alpha emitters in its decay chain. To date, timing resolution of 200 ps (FWHM) has been achieved corresponding to roughly 0.5% uncertainty in velocity measurements of fission fragments over a flight path of 52.1 cm. This velocity resolution, in combination with demonstrated fragment energy resolution is sufficient for 1 amu resolution of light mass fragments.

The ionization chamber component of the SPIDER detector has been designed to measure energy loss and kinetic energy of fragments produced through neutron-induced fission with energy resolutions of

Latest generation fission experiments provide an excellent testing ground for theoretical models. In this contribution we compare the measurements obtained with the DANCE calorimeter at 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 isomeric ratios as a function of the initial angular momentum of the fission fragments. Comparison with the available experimental data allows us to determine the initial spin distribution. Finally, we study the sensitivity to the discrete spectra input.

The signal of isospin-asymmetric phase transition in the evolution of the chemical potential was observed for hot quasi-projectiles produced in the reactions 40,48Ca + 27Al confirming an analogous observation in the lighter system 28Si + 112,124Sn. With increasing mass, the properties of hot quasi-projectiles become increasingly influenced by the secondary emission. Thermodynamical observables exhibit no sensitivity to the different number of missing neutrons in the two reactions 40,48Ca + 27Al, thus providing a signal of dynamical emission of neutrons, which can be related to formation of a very neutron-rich low-density region (neck) between the projectile and target., Comment: LaTeX, article expanded, 2 figures added, 17 pages, 7 figures