An intercomparison of the D2O-moderated 252Cf reference neutron sources at PTB and NPL

The Physikalisch-Technische Bundesanstalt (PTB) and the National Physical Laboratory (NPL) have compared the neutron leakage spectra of their D2O-moderator assemblies using their own 252Cf sources. This was achieved by means of two transfer devices having very different neutron responses as a function of neutron energy. The fluence rate responses of the transfer instruments were evaluated from measurements of the count rate at several distances. The results indicate that the irradiation assemblies of the two laboratories produce the same fluence rate, normalised to the source strength of the bare californium source, and that the neutron leakage spectra from the two assemblies are practically identical over the intermediate and fast neutron energy ranges. (author)