Experimental studies of the effect of the ortho/para ratio on the neutronic performance of a liquid hydrogen moderator for a pulsed neutron source

The neutron energy spectra change within 20%, depending on the para hydrogen concentrations. With increasing para hydrogen concentration, the pulse peak intensity increases and the pulse width becomes narrower. Furthermore, for a decoupled moderator, the pulse decay becomes faster with increasing para hydrogen concentration. From a viewpoint of the figure of merit (FOM=I/FWHM2) the para hydrogen moderator showed almost the same performance as that of the solid methane moderator, which is considered to be a high performance moderator for pulsed neutron source.