Prompt-gamma neutron activation facility for measuring body nitrogen in vivo in small animals.

We have designed a prompt-gamma neutron activation facility for in vivo measurements of total body N in small animals. The facility incorporates a 252C neutron source with an emission rate of 3.2 x 10(8) n s-1 (140 micrograms), and a heavy-water neutron collimator-moderator assembly, together providing an optimum thermal flux-to-dose ratio for a 0.25-0.5 kg animal. Using two NaI(Tl) detectors we can attain a fractional statistical error of measurement of 3.5% for a dose equivalent of approx 50 mSv, sufficiently low that serial measurements can be made on the same animal.