Liquid Hydrogen Moderator Research Articles

Experimental studies on neutronic performance of coupled liquid-hydrogen moderator for pulsed spallation neutron sources

Optimization studies on a coupled liquid-hydrogen moderator system were performed experimentally and the results were compared with those of decoupled liquid-hydrogen and solid-methane moderators. A very large gain factor is obtained in the cold neutron region. Pulse characteristics were also studied and it was found that the pulse broadening by coupling is rather modest.

Comparison between Pulsed Cold Neutron Intensities from Liquid Hydrogen Moderator and from Solid Methane Moderator in Decoupling Type Moderator Assembly

Comparison between Pulsed Cold Neutron Intensities from Liquid Hydrogen Moderator and from Solid Methane Moderator in Decoupling Type Moderator Assembly

Comparison between Pulsed Cold Neutron Intensities from Liquid Hydrogen Moderator and from Solid Methane Moderator in Decoupling Type Moderator Assembly.

Although liquid hydrogen is at present a unique cold moderator applicable to high intensity neutron sources, the reported pulsed cold neutron intensity from a liquid hydrogen moderator is significantly lower than that from a solid methane moderator. In this report, a reflected assembly with a thick hydrogen moderator is used to enhance the pulsed cold neutron intensity and the intensity is compared with that from a solid methane moderator. For comparison, 5 and 15 cm thick moderators were used for liquid hydrogen moderators. The thicker one was used to obtain the saturated intensity of pulsed cold neutrons. The thickness of a solid methane was 5 cm. The cold neutron intensity from the 15 cm thick hydrogen moderator is about 1.6 times as high as that from the 5 cm one, in the case of the graphite reflected moderator assembly with a Cd decoupler. However, even in the case of the reflected assembly, the cold neutron intensities from the liquid hydrogen moderators are much less than that from the solid methan...

The Low-Q Diffractometer at the Los Alamos Neutron Scattering Center

Instrument criteria are presented for the Low-Q Diffractometer (LQD) at the Los Alamos Neutron Scattering Center (LANSCE), and a design is shown to meet these criteria. The collimator consists of multiple-aperture pinhole plates, and incorporates ''dynamic gravity focusing'' to center all wavelengths on the detector. Preliminary test results, making use of the Proton Storage Ring, a liquid hydrogen moderator, and two different position-sensitive detectors are shown.

Power densities in materials in spallation neutron source environments

The intensities and average energies of neutron and gamma fluxes at the center of a moderator have been estimated for the pulsed spallation neutron source IPNS-I (5×10 12 protons per pulse at energy 500 MeV, operating at 30 Hz with a 238U target) presently being constructed at Argonne National Laboratory. The heat deposition rate and the temperature rise without heat flow have been estimated for both polyethylene and liquid hydrogen moderators. Estimates are also made for the heat deposition rates in the boron and gadolinium decouplers. Radiation damage will occur in the outer layer of 0.006 cm of boron carbide decouplers in relatively short irradiation times. Some consideration is given to the thermal characteristics (cooling constant, etc.) of various materials in conjunction with measurements made on a prototype source. The gamma decay factor, the ratio of gamma intensity when proton beam is on to that of just-after-beam-off, has also been calculated.

The liquid hydrogen moderator on the ZING-P′ pulsed spallation neutron source

We describe the liquid hydrogen moderator on the ZING-P′ pulsed spallation neutron source and present results of measurements to assess its performance in several configurations. Measurements were made with the moderator surrounded by a beryllium reflector, with and without a gadolinium decoupler, and also with a room temperature beryllium reflector-filter immediately downstream from the moderator. Results described include neutron beam spectra, pulse widths as a function of neutron energy, absolute neutron beam currents, and the nuclear heating rate. We compare our results with calculations and previous results of others.

Slow neutron scattering and intermolecular excitations in liquid hydrogen

A simple analytical model for inelastic neutron scattering in liquid hydrogen with the effects of delayed diffusion and intermolecular vibrations with a single frequency parameter is proposed. Calculated results show good agreements with experimental results of total and differential scattering cross sections as well as the energy spectra of neutrons in liquid hydrogen moderators, and thus indicate the importance of the consideration of intermolecular excitations in the dynamics of liquid hydrogen.

Monte Carlo comparison of hydrogen cold-neutron sources in radial and tangential beam-tube arrangements

A Monte Carlo comparison of the moderating efficiency of various hydrogen cold-neutron sources in the radial and in the tangential beam-tube arrangements is described. In the calculations performed the length and the relative ortho-para abundance of cooled gaseous- and liquid-hydrogen moderator cylinders were varied. Maximum cold-neutron outputs were obtained by long moderator cylinders rich in parahydrogen in the tangential arrangement. It was found that with a suitable (non-optimal) choice of the moderator length the total cold-neutron output could be almost independent of the ortho-para mixture.

Experimental and theoretical study of cold neutron sources of liquid hydrogen and liquid deuterium

In view of the designing of a cold neutron source for the French-German High Flux Reactor to be built at Grenoble, France, a study of several cold sources of liquid hydrogen and liquid deuterium has been made. By theoretical study a method of calculating the cold neutron flux gain factor of a cold source was discovered, and this was checked by an experimental study in a low power reactor. A significant correspondence between calculations and measurements was obtained. This investigation proved that an optimized cold neutron source of liquid hydrogen could be produced, and also that a liquid deuterium moderator was superior to a liquid hydrogen moderator when D 2 is used in large volumes (about 40:1).