Moderators using liquid and solid methane and liquid hydrogen are currently in use at major spallation neutron sources. Los Alamos Neutron Scattering Center (LANSCE) is planning the use of liquid methane as part of a major update program planned in about three years time. This report presents a general overview of some of these devices and outlines the general engineering design of the proposed LANSCE moderator, including some suggested solutions to the radiation damage problems of methane. Also included is a brief overview of a possible combined H2/Ch4 moderator for high intensity proton beams. 15 figs.

We report the calculated results of neutronic performance of cold moderators in a reference target-moderator-reflector system at the projected 5 MW pulsed spallation neutron source in Japan Atomic Energy Research Institute (JAERI). The cold neutron intensities in present reference model are about 2.3-2.5 times higher than that from the decoupled solid methane (S-CH4) and close to the values obtained at other facilities (LANSCE Upgrade, NSNS, etc.). The H2O premoderator (PM) reduces the energy deposition in a liquid-hydrogen (L-H2) moderator by about a factor of 2 compared with that in a decoupled L-H2 moderator. The dependence of reflector on the neutron intensity and the energy deposition in the cryogenic moderators is also discussed. Although the pulse shapes were not obtained because of time consuming Monte Carlo calculations, we will discuss the pulse shapes based on experiments. (auth).

The Advanced Neutron Source (ANS) cold moderators were not an 'Oak Ridge first', but would have been the largest both physically and in terms of cold neutron flux. Two cold moderators were planned each 410 mm in diameter and containing about 30L of liquid deuterium. They were to be completely independent of each other. A modular system design was used to provide greater reliability and serviceability. When the ANS was terminated, up-grading of the resident High Flux Isotope Reactor (HFIR) was examined and an initial study was made into the feasibility of adding a cold source. Because the ANS design was modular, it was possible to use many identical design features. Sub-cooled liquid at 4 bar abs was initially chosen for the HFIR design concept, but this was subsequently changed to 15 bar abs to operate above the critical pressure. As in the ANS, the hydrogen will operate at a constant pressure throughout the temperature range and a completely closed loop with secondary containment was adopted. The heat load of 2 kW made the heat flux comparable with that of the ANS. Subsequent studies into the construction of cryogenic moderators for the proposed new Synchrotron Neutron source indicated that again many of the same design concepts could be used. By connecting the two cold sources together in series, the total heat load of 2 kW is very close to that of the HFIR allowing a very similar supercritical hydrogen system to be configured. The two hydrogen moderators of the SNS provide a comparable heat load to the HFIR moderator. It is subsequently planned to connect the two in series and operate from a single cold loop system, once again using supercritical hydrogen. The spallation source also provided an opportunity to re-examine a cold pellet solid methane moderator operating at 20K.

Intense beams of cold neutrons are produced at several DOE facilities and are used by researchers to study the microscopic structure of materials. Energetic neutrons are produced by a high energy proton beam impacting a target. The fast neutrons are converted to the desired cold neutrons passing through a cryogenic moderator vessel, presently filled with dense cold hydrogen gas. Moderators made from solid methane have demonstrated superior performance to the hydrogen moderators but cannot be implemented on high power sources such as the SNS due to the difficulty of removing heat from the solid blocks of methane. Cryogenic Applications F, Inc has developed the methane pellet formation and transport technologies needed to produce a hydrogen cooled solid methane pellet moderator, potentially capable of being used in a high power spallation neutron facility. Such a methane pellet moderator could double the brightness of the neutron beam. Prior to this work a methane pellet moderator had not been produced or studied. The Indiana University LENS facility is a small pulsed neutron source used in part to study and develop cold neutron moderators. In this project cold neutrons were produced in a solid methane pellet moderator and analyzed with the LENS facility diagnostics. The results indicated that the neutron beam formed by the pellet moderator was similar to that of a solid methane block moderator.

This book provides a comprehensive and up-to-date introduction to the fundamental theory and applications of slow-neutron scattering.

ISIS is a pulsed spallation neutron source where neutrons are produced by the interaction of a 160 kW proton beam of energy 800 MeV in a water-cooled Tantalum Target. The fast neutrons produced are thermalized in four moderators: two ambient water, one liquid methane operating at 100K and a liquid hydrogen moderator at 20 K. This paper gives a description of the construction of both cold moderator systems, details of the operating experience and a description of the current development program.