A proposed three-phase counting system for the in vivo measurement of the major elements using pulsed 14 MeV neutrons.

It is proposed to employ a pulsed source of 14 MeV neutrons for in vivo activation analysis. This would permit the differentiation, with time, of the resulting gamma ray emission into three separate spectra, according to the type of nuclear reaction and mode of decay. The three-phase counting has been divided into approximately 10 microseconds during "beam-on," and 200 and 800 microseconds during "beam-off." Measurements of the major elements, C, N, O, Cl, and P, to give nutritionally-important body compartments of total body fat, protein, water, minerals, and extracellular water, thus is expected with a single scan.