Abstract
Body fat is measured by detecting C and O in vivo through fast neutron inelastic scattering. A sealed DT neutron generator is used for the pulsed (4–10 kHz) production of fast neutrons. Carbon and oxygen are detected by counting the 4.44 and 6.13 MeV gamma rays resulting from the inelastic scattering of the fast neutrons from 12C and 16O. Large Bi 4Ge 3O 12 (BGO) crystal detectors (127 × 76 mm) are used for the gamma ray detection during the 10 μs neutron burst. BGO detectors improved the signal to background ratio for the carbon detection by a factor of six compared to 152 × 152 mm NaI (Tl) detectors. Exposure to scattered neutrons did not affect the gain stability of the BGOs. Thermal neutrons from a moderated 238PuBe source are used for the measurement of total body nitrogen (and thus protein). The resulting high energy prompt gamma rays from nitrogen (10.83 MeV) are detected simultaneously with the irradiation. BGO detectors have superior stability operating in an environment of variable neutron exposure and high counting rates. However, the presence of neutrons creates a 10.2 MeV gamma ray peak from 73Ge in the BGO detector which interferes with the nitrogen peak. Whole body gamma ray counters, consisting of NaI(Tl) crystal detectors in a shielded room, are used to measure the natural radioactivity of the body due to 40K. They are also used to measure body Ca, P, Na and Cl, following total body exposure to thermal neutrons.
Published Version
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