In-vivo resonant gamma detection

We have been developing the technique of resonant gamma absorption for the in vivo measurement of body nitrogen and calcium. The principle of this technique is the measurement of the degree to which gamma rays that are resonant with a particular nucleus (either nitrogen or calcium) are more attenuated by the body than nonresonant gamma rays of nearly the same energy. We have fabricated a full-size gamma-resonance instrument for measuring body nitrogen, and have demonstrated the operation of this instrument on nitrogen-bearing phantoms at proton currents of 30-50 microamperes on target.