A comparison of 252Cf and 238Pu, Be neutron sources for partial-body in vivo activation analysis

A comparison is made of the isotopic neutron sources 252 Cf and 238 Pu, Be for partial-body in vivo neutron activation analysis. Depth distributions of thermal neutron fluences in a water phantom are very similar for the two sources. The peak depth occurs at 5 cm. This value is approximately 2 cm less than the values obtained with uncollimated neutrons produced in broad-beam irradiations. With respect to the fluence-to-dose ratio, the 252 Cf neutrons have an advantage of approximately 1.4 over the 238 Pu, Be source. The use of 252 Cf offers two additional advantages for the investigator. First, it minimizes the on-line fast-neutron damage in Ge(Li) semiconductor detectors. Secondly, it is subject to much less stringent transport regulations that 238 Pu, Be. The latter feature takes on particular importance in view of the increasing usefulness of transportable instruments for in vivo cadmium measurements at the workplace.