摘要: A comparison was made between MCNP calculations and experimental measurements of the neutron spectrum from the liquid hydrogen moderator on ISIS. The calculations were performed for varying ortho/para concentrations, and demonstra... 展开 A comparison was made between MCNP calculations and experimental measurements of the neutron spectrum from the liquid hydrogen moderator on ISIS. The calculations were performed for varying ortho/para concentrations, and demonstrated a best fit for 100% para-hydrogen. The agreement between the measured and calculated results was good below 2? (i.e. for energies above 20 meV) but significant deviations were seen for longer wavelengths. A second study used the MCNP code for a detailed comparison of the time distributions and neutron spectra from poisoned liquid hydrogen and liquid methane moderators. The results indicate that the replacement of a liquid methane moderator with liquid hydrogen, in order to eliminate radiation damage effects, is an option which can be seriously considered. (auth) 收起