Silicon measurement in a lung phantom by neutron inelastic scattering

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Abstract
A study was made to assess the feasibility of determining the S level in human lungs in vivo by measuring the .gamma.-rays arising from the neutron inelastic scattering reaction 28Si(n,n''.gamma.)28Si. Neutron energies in the range 5-8 MeV represented the best compromise between the conflicting requirements of high energy for good detection statistics and low energy to minimize the dose to the subject. The sensitivity of measurement was enhanced by pulsing the neutron beam and counting only during the period of bombardment. This reduced the background counts emanating from thermal neutron reactions in the phantom and from the fast neutron reaction 31P(n,.alpha.)28 Al. In measurements with an anthropomorphic phantom, no interference peaks from other prompt inelastic scattering reactions were observed.With 1 Ge(Li) detector of 19% relative efficiency, a detection limit of 0.6 g S/10 mSv was obtained. Six Ge(Li) detectors of 25% efficiency each would be capable of measuring 0.15 g S in the lungs, the average level found in nonoccupationally exposed adults.

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