Latest Neutron Research Articles

Benchmark tests for the MATXS-formatted XMAP libraries based on ENDF/B-VIII.0 and ENDF/B-VII.1

The new ENDF/B-VIII.0 evaluated nuclear reaction data library is improved relative to the previous ENDF/B-VII.1 library because of using new evaluated data for neutron and photon reactions on certain nuclides. To get a more comprehensive impression for shielding calculations on the latest neutron and photon data library, and to provide reference for the selection of the evaluated nuclear data libraries for the science and engineering applications, we have developed MATXS libraries using the NJOY2016 code for shielding calculations based on ENDF/B-VIII0 and ENDF/B-VII.1, named XMAP-B80 and XMAP-B71 respectively. The performance of the XMAP-B80 and the XMAP-B71 libraries for shielding and criticality calculations was verified by several benchmarks. TRANSX2.15/ANISN system was used to calculate the results of the benchmarks. In addition, we added the calculation results of the Monte Carlo N-particle code as a reference to further verify the correctness of the calculation results of the TRANSX/ANISN code system based on the XMAP libraries.

Structural, dynamical, and transport properties of the hydrated halides: How do At(-) bulk properties compare with those of the other halides, from F(-) to I(-)?

The properties of halides from the lightest, fluoride (F(-)), to the heaviest, astatide (At(-)), have been studied in water using a polarizable force-field approach based on molecular dynamics (MD) simulations at the 10 ns scale. The selected force-field explicitly treats the cooperativity within the halide-water hydrogen bond networks. The force-field parameters have been adjusted to ab initio data on anion/water clusters computed at the relativistic Möller-Plesset second-order perturbation theory level of theory. The anion static polarizabilities of the two heaviest halides, I(-) and At(-), were computed in the gas phase using large and diffuse atomic basis sets, and taking into account both electron correlation and spin-orbit coupling within a four-component framework. Our MD simulation results show the solvation properties of I(-) and At(-) in aqueous phase to be very close. For instance, their first hydration shells are structured and encompass 9.2 and 9.1 water molecules at about 3.70 ± 0.05 Å, respectively. These values have to be compared to the F(-), Cl(-), and Br(-) ones, i.e., 6.3, 8.4, and 9.0 water molecules at 2.74, 3.38, and 3.55 Å, respectively. Moreover our computations predict the solvation free energy of At(-) in liquid water at ambient conditions to be 68 kcal mol(-1), a value also close the I(-) one, about 70 kcal mol(-1). In all, our simulation results for I(-) are in excellent agreement with the latest neutron- and X-ray diffraction studies. Those for the At(-) ion are predictive, as no theoretical or experimental data are available to date.

Modeling the hydration of mono-atomic anions from the gas phase to the bulk phase: The case of the halide ions F−, Cl−, and Br−

In this work, we investigate the hydration of the halide ions fluoride, chloride, and bromide using classical molecular dynamics simulations at the 10 ns scale and based on a polarizable force-field approach, which treats explicitly the cooperative bond character of strong hydrogen bond networks. We have carried out a thorough analysis of the ab initio data at the MP2 or CCSD(T) level concerning anion/water clusters in gas phase to adjust the force-field parameters. In particular, we consider the anion static polarizabilities computed in gas phase using large atomic basis sets including additional diffuse functions. The information extracted from trajectories in solution shows well structured first hydration shells formed of 6.7, 7.0, and 7.6 water molecules at about 2.78 Å, 3.15 Å, and 3.36 Å for fluoride, chloride, and bromide, respectively. These results are in excellent agreement with the latest neutron- and x-ray diffraction studies. In addition, our model reproduces several other properties of halide ions in solution, such as diffusion coefficients, description of hydration processes, and exchange reactions. Moreover, it is also able to reproduce the electrostatic properties of the anions in solution (in terms of anion dipole moment) as reported by recent ab initio quantum simulations. All the results show the ability of the proposed model in predicting data, as well as the need of accounting explicitly for the cooperative character of strong hydrogen bonds to reproduce ab initio potential energy surfaces in a mean square sense and to build up a reliable force field.

NEUTRON SCATTERING IN MAGNETIC FIELDS UP TO 17 T

Neutron scattering in magnetic fields can provide important imformation regarding the magnetism of a system under study on microcsopic scale. Although pulse magnets are capable to reach very high fields, for neutron scattering mostly superconducting magnets are used. At present, a split-pair 14.5 T superconducting magnet used for user-program experiments at HMI offers the highest magnetic field for neutron scattering. With Dy-pole tips placed symmetrically around the sample position a 2.5 T enhancement is achieved. The temperature range accessible with such an insert is between 1.8 and 100 K. Temperatures down to 30 mK can be achieved with a dilution stick, which can be inserted into the 14.5 T cryomagnet. In the contribution we report on the latest neutron scattering achievements in magnetic fields obtained at HMI.

Neutron magnetic resonance experiments

Abstract Neutron magnetic resonance experiments are reviewed from the first experiments of Alvarez and Bloch on the neutron magnetic moment published in 1940 to the most recent neutron electric dipole moment measurements with bottled neutrons. The first measurements on the neutron magnetic moment were accurate to 1 part per 100 whereas the latest neutron beam magnetic resonance experiment at the ILL in Grenoble gives μn = 1.04066884(26) × 10-3μB where μB is the Bohr magne ton, a result good to 0.25 parts per million. Early neutron beam magnetic resonance experiments setting a low upper limit tot he neutron electric dipole moment are also described. The latest and most sensitive electric dipole measurements are with neutrons stored for up to 80 s in a beryllium oxide cylindrical bottle with Be lids. With such an apparatus a value of (0.3±4.8) × 10-25e cm has been measured at Grenoble and with a somewhat different apparatus at Leningrad a value of (2.3±2.3) × 10-25e cm has been found. Plans for even more sensitive measurements are described. Finally, experiments are described for measuring parity non-conserving rotations of the neutron spin on passage through Sn, Pb and La.