Neutron diffraction and spectroscopy offer unique insight into structures and properties of solids and molecular materials. All neutron instruments located at the various neutron sources are ...distinct, even if their designs are based on similar principles, and thus, they are usually less familiar to the community than commercial X‐ray diffractometers and optical spectrometers. Major neutron instruments in the USA, which are open to scientists around the world, and examples of their use in coordination chemistry research are presented here, along with a list of similar instruments at main neutron facilities in other countries. The reader may easily and quickly find from this minireview an appropriate neutron instrument for research. The instruments include single‐crystal and powder diffractometers to determine structures, inelastic neutron scattering (INS) spectrometers to probe magnetic and vibrational excitations, and quasielastic neutron scattering (QENS) spectrometers to study molecular dynamics such as methyl rotation on ligands. Key and unique features of the diffraction and neutron spectroscopy that are relevant to inorganic chemistry are reviewed.
Major instruments in the USA for (1) single‐crystal and powder neutron diffraction and (2) inelastic neutron scattering (INS) and quasielastic neutron scattering (QENS) spectroscopy are presented with examples of their use in coordination chemistry. Similar instruments at main neutron facilities in other countries are listed for the reader to find a suitable neutron instrument for research.
•Boron based thin-film neutron monitor was developed for the in situ neutron beam monitoring of the KAERI-NDP system.•Neutron transmission ratios of 1 μm thick B and BN thin-film neutron monitors ...were 92.46% and 93.93% for cold neutron beam, respectively.•The optimal RF power and deposition temperature for the B and BN film were (80 W, 550 °C) and (110 W, 350 °C), respectively.•The DPA rates of the B and BN film neutron monitors were estimated to be 1.54–5.15 × 10−14 and 1.52–1.93 × 10−15 DPA/s for cold and fast neutron, respectively.•Based on its performance, the developed neutron monitor can be used for the in situ measurement of neutron beam.
A B-based thin-film neutron monitor is developed for the in situ neutron beam monitoring of the Korea Atomic Energy Research Institute neutron depth profiling system. Thin-film samples are prepared via radio-frequency (RF) sputtering. The RF power, Ar partial pressure, and deposition temperature are varied to optimize the growth and thickness uniformity of the samples. The neutron transmission ratio and collision heating of the designed samples are estimated via Monte Carlo simulation. The neutron transmission ratios of B and BN films prepared in this study are 92.46% and 93.93%, respectively, and the effect of temperature increase is negligible. The displacement per atom (DPA) rates of the B and BN thin films are lower than those of other known B neutron flux monitors, based on the results of DPA calculation for estimating the defect of the sample via neutron irradiation.
We report an improved measurement of the free neutron lifetime τn using the UCN τ apparatus at the Los Alamos Neutron Science Center. We count a total of approximately 38 × 106 surviving ultracold ...neutrons (UCNs) after storing in UCN τ's magnetogravitational trap over two data acquisition campaigns in 2017 and 2018. We extract τn from three blinded, independent analyses by both pairing long and short storage time runs to find a set of replicate τn measurements and by performing a global likelihood fit to all data while self-consistently incorporating the β -decay lifetime. Both techniques achieve consistent results and find a value τn = 877.75 ± 0.2 8stat + 0.22/−0.16syst s. With this sensitivity, neutron lifetime experiments now directly address the impact of recent refinements in our understanding of the standard model for neutron decay.
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Boron neutron capture therapy (BNCT) was first proposed as early as 1936, and research on BNCT has progressed relatively slowly but steadily. BNCT is a potentially useful tool for cancer treatment ...that selectively damages cancer cells while sparing normal tissue. BNCT is based on the nuclear reaction that occurs when
B capture low-energy thermal neutrons to yield high-linear energy transfer (LET) α particles and recoiling
Li nuclei. A large number of
B atoms have to be localized within the tumor cells for BNCT to be effective, and an adequate number of thermal neutrons need to be absorbed by the
B atoms to generate lethal
B (n, α)
Li reactions. Effective boron neutron capture therapy cannot be achieved without appropriate boron carriers. Improvement in boron delivery and the development of the best dosing paradigms for both boronophenylalanine (BPA) and sodium borocaptate (BSH) are of major importance, yet these still have not been optimized. Here, we present a review of this treatment modality from the perspectives of radiation oncology, biology, and physics. This manuscript provides a brief introduction of the mechanism of cancer-cell-selective killing by BNCT, radiobiological factors, and progress in the development of boron carriers and neutron sources as well as the results of clinical study.
General-relativistic simulations of binary neutron star (NS) mergers with viscosity reveal a new outflow mechanism operating in unequal mass binaries on dynamical timescales and enabled by turbulent ...viscosity. These "viscous-dynamical" ejecta are launched during the merger due to the thermalization of mass exchange streams between the secondary and the primary NS. They are characterized by asymptotic velocities extending up to ∼0.8c, and have masses that depend on the efficiency of the viscous mechanism. Depending on the unknown strength of the effective viscosity arising from magnetohydrodynamic instabilities operating during the merger, the overall mass of the dynamical ejecta could be enhanced by a factor of a few and the mass of the fast tail of the ejecta, having asymptotic velocities ≥0.6c, by up to four orders of magnitude. The radioactive decay of the expanding viscous-dynamical ejecta could produce bright kilonova transients with signatures of free neutron decay in the first hour, and enhanced near-infrared flux on a timescale of a few days. The synchrotron remnant produced by the interaction between the ejecta and the interstellar medium could also be significantly enhanced by viscosity. Such a remnant could be detected in the case of GW170817 as a rebrightening of the radio signal in the next months to years.
Highly anisotropic, beam-like neutron emission with peak flux of the order of 109 n/sr was obtained from light nuclei reactions in a pitcher-catcher scenario, by employing MeV ions driven by a ...sub-petawatt laser. The spatial profile of the neutron beam, fully captured for the first time by employing a CR39 nuclear track detector, shows a FWHM divergence angle of ∼ 70 ° , with a peak flux nearly an order of magnitude higher than the isotropic component elsewhere. The observed beamed flux of neutrons is highly favourable for a wide range of applications, and indeed for further transport and moderation to thermal energies. A systematic study employing various combinations of pitcher-catcher materials indicates the dominant reactions being d(p, n+p)1H and d(d,n)3He. Albeit insufficient cross-section data are available for modelling, the observed anisotropy in the neutrons' spatial and spectral profiles is most likely related to the directionality and high energy of the projectile ions.
The joint evaluated fission and fusion nuclear data library 3.3 is described. New evaluations for neutron-induced interactions with the major actinides
235
U
,
238
U
and
239
Pu
, on
241
Am
and
23
Na
...,
59
Ni
, Cr, Cu, Zr, Cd, Hf, W, Au, Pb and Bi are presented. It includes new fission yields, prompt fission neutron spectra and average number of neutrons per fission. In addition, new data for radioactive decay, thermal neutron scattering, gamma-ray emission, neutron activation, delayed neutrons and displacement damage are presented. JEFF-3.3 was complemented by files from the TENDL project. The libraries for photon, proton, deuteron, triton, helion and alpha-particle induced reactions are from TENDL-2017. The demands for uncertainty quantification in modeling led to many new covariance data for the evaluations. A comparison between results from model calculations using the JEFF-3.3 library and those from benchmark experiments for criticality, delayed neutron yields, shielding and decay heat, reveals that JEFF-3.3 performes very well for a wide range of nuclear technology applications, in particular nuclear energy.
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