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Accurate nuclear data provide an essential foundation for advances in a wide range of fields, including nuclear energy, nuclear safety and security, safeguards, nuclear medicine, and planetary and space exploration. In these and other critical domains, outdated, imprecise, and incomplete nuclear data can hinder progress, limit precision, and compromise safety. Similar nuclear data needs are shared by many applications, thus prioritizing these needs is especially important and urgently needed. Many levels of analysis are required to prepare nuclear measurements for employment in end-user applications. Because research expertise is typically limited to one level, collaboration across organizations and international borders is essential. This perspective piece provides the latest advances in nuclear data for applications and describes an outlook for both near- and long-term progress in the field.

This paper provides a template of expected uncertainties and correlations for measurements of total neutron cross-section observables by transmission. Measurements with time-of-flight and mono-energetic neutron sources are covered. The information required for evaluations in the resonance region and high energy region is detailed, along with the template of uncertainties and correlations that can be used in the absence of other information.

This paper provides a template of expected uncertainties and correlations for measurements of neutron-induced capture and charged-particle production cross sections. Measurements performed in-beam include total absorption spectroscopy, total energy detection, γ-ray spectroscopy, and direct charged-particle detection. Offline measurements include activation analysis and accelerator mass spectrometry. The information needed for proper use of the datasets in resonance region and high energy region evaluations is described, and recommended uncertainties are provided when specific values are not available for a dataset.

A new experiment configuration was designed, developed, and implemented to measure photoneutron yields using the Rensselaer Polytechnic Institute (RPI) electron linear accelerator (LINAC) at the RPI Gaerttner LINAC Center. The experiment configuration includes a new target assembly that converts the LINAC electron beam into a high energy bremsstrahlung photon flux incident upon a sample material of interest. The photons excite nuclei in the sample of interest, which can subsequently emit neutrons (photoneutrons). The photoneutrons emitted in the direction of the detector system travel through a series of collimated vacuum pipes before reaching a pair of proton-recoil high-energy neutron detectors. The signals generated by the neutron detectors are processed using a digital data acquisition system and subsequently analyzed to determine the energy-dependent photoneutron yield from the sample of interest. The new experiment configuration was used to perform proof-of-concept experiments to measure the photoneutron yields from samples of tantalum and beryllium. The measured results were then compared against the results from Monte Carlo simulations of the detailed experiment configurations to perform preliminary assessments of evaluated photoneutron data libraries.

A novel method was developed to separate the 238U fission contribution measured in quasi-differential time-of-flight scattering experiments in order to isolate the elastic and inelastic events. Pulse height distributions from in-beam measurements were used to generate response functions, which were used to reconstruct the 238U prompt fission neutron spectra. This method was validated by reconstructing the measured 252Cf spontaneous fission pulse height distribution. Monte Carlo calculations were used to model the experiment. Good agreement was observed between the measured and calculated 238U fission contribution.

Recently, a cold moderator was designed and developed for use at the Rensselaer Polytechnic Institute Linear Accelerator (RPI LINAC). This cold moderator proved to easily and safely couple to an existing neutron producing target, while enhancing neutron flux below 0.02 eV by up to a factor of 8 by cooling polyethylene down to 29 K. This cold moderator capability allowed for significantly improved counting statistics below 0.02 eV not previously possible due to a poor signal to background ratio. Additionally, testing was performed to characterize the energy resolution of the new cold moderator system and found the system easily capable of resolving resonances in Ta-181 at 4 and 10 eV, while also clearly resolving the Bragg edges found in Be metal below 0.01 eV. Following the design and development of a cold polyethylene moderator, a series of thermal total cross section measurements were performed for polyethylene, polystyrene, Plexiglas and yttrium hydride in the thermal region. These measurements serve to help validate thermal scattering law (TSL) evaluations in the 0.0005 – 1 eV energy range. For polyethylene and polystyrene, two sets of experiments were performed – one with the Enhanced Thermal Target (ETT) and another with the ETT plus the new cold moderator capability (ETTC). The yttrium hydride and Plexiglas measurements were only performed with the ETTC. The measurements for polyethylene help to validate the data processing methodology when using the ETTC, while extending the measured range of polyethylene down to 0.0005 eV. Two different Plexiglas, Plexiglas G and Plexiglas G-UVT, and two different concentrations of yttrium hydride, H/Y = 1.85 and 1.68, were measured. Overall, all materials had generally good agreement with their ENDF/B-VIII.0 TSL evaluations, though some discrepancies were noticed. In the case of the yttrium hydride, the high energy oscillations in the hydrogen cross section and the low energy Bragg edges in the yttrium cross section were clearly seen. These measurements represent the first total cross section measurements that encompass the entire thermal region from 0.0005 – 1 eV for polystyrene and yttrium hydride.

54Fe radiative capture cross section and transmission measurements were conducted at the Rensselaer Polytechnic Institute (RPI) Gaerttner Linear Accelerator (LINAC) Center using an enriched 54Fe sample in the keV energy region. 54Fe is a constituent of natural iron, which is present in a large variety of nuclear grade materials. Therefore, it is important to have an accurate understanding of the cross sections of 54Fe, which can be measured experimentally. In the time-of-flight measurements conducted at the LINAC, an array of four C6D6 detectors surrounded the sample and radiative capture data were collected using a digital data acquisition system. Additionally, a Li-glass detector was used to collect transmission data using an analog data acquisition system. The radiative capture yield of the 54Fe measurements were normalized to saturated resonances observed in Au and Ta to obtain an absolute capture yield. The preliminary capture yield and preliminary transmission obtained can be compared to evaluations and existing experimental data. Some disagreements were observed in prominent d-wave capture resonances observed in 54Fe in the low-keV neutron energy region. Both sets of experimental data along with pre-existing datasets will greatly enhance RPI’s ability to perform resonance evaluation for 54Fe up to roughly 1 MeV.

R-matrix formalism is extended beyond compound nuclear (CN) resonant reactions to include parameterization of direct as well as doorway processes. Direct processes in the R-matrix exterior are parameterized by a unitary matrix that introduces mixing among wave function coefficients of the incoming and outgoing wave function components at the R-matrix channel surface. Doorway processes are parameterized by separating the Hilbert space of the interior R-matrix region into its doorway and CN subspaces, from which doorway state eigenenergies, reduced width amplitudes, and the strengths of their coupling to CN levels appear as new R-matrix parameters. Parameterization of generalized as well as the conventional Reich–Moore approximation for eliminated capture channels in the presence of direct, doorway, and CN processes is presented along with a complex-valued scattering length with contributions from direct, doorway, and CN capture processes. Derivation of Brune’s alternative R-matrix parameters is extended to include doorway states. This work suggests how R-matrix formalism could be extended further by adopting the concepts from related reaction formalisms.

A neutron induced neutron emission experiment was conducted as the Los Alamos Neutron Science Center (LANSCE) facility at Los Alamos National Laboratory (LANL). In this experiment, a sample was placed in a well collimated neutron beam and was surrounded by an array of 28 fast neutron detectors (EJ-309). The experiment was performed with a neutron flight path of 21.5 m from the source to the sample, and 1 m from the sample to the detectors. The neutron emission from the sample was measured as a function of neutron time of flight covering an incident energy range from 0.7- 20 MeV. The samples included U-235, Pu-239, carbon (graphite), and blanks that matched the encapsulation of the sample. The measured samples were constantly cycled in and out of the neutron beam. This type of experiment measures neutron emission from all reactions occurring in the sample such as fission and elastic and inelastic scattering. Similar to the methodology previously developed at RPI [1], the measurements were compared with detailed simulations of the experiment using different cross section evaluations for the sample. The observed differences can be attributed to the evaluated neutron cross section and angular distributions. The carbon sample was used as a reference to validate both the experiment and simulation methodology and showed good agreement between experiments and simulations. A review of the experimental setup, analysis methods, and some of the results will be presented.