Journal of Radioanalytical anclNuclear Chemistry, Articles, Vol. 114, No. 1 (1987) 165-172 A SYSTEM FOR THE DETERMINATION OF SILICON IN THE HUMAN LUNG USING NEUTRONS FROM A 2MV VAN DE GRAAFF GENERATOR A, KACPEREK,* C. J. EVANS,* J. DUTTON,* W. D. MORGAN,** A. SIVYER** *Department of Physics, University "Collegeof Swansea, University of Wales,Singleton Park, Swansea SA2 8PP(UK) **Department of Medical Physics and Clinical Engineering, Singleton Hospital, Swansea SA2 8QA (UK) (Received December 12, 1986) Neutron activation analysis, using inelastic scattering, provides a quantitative, nondnvasive technique of studying silica burdens and is potentially useful ,as a screening procedure for occupationally exposed workers. In this method, silicon is measured using the fast neutron inelastic scattering reaction 2 s Si(n,n' ?)28Si which emits 1779 keV 7-rays. The method requires a source of fast neutrons (> 2MeV'). A 2MV Van de Graaff generator has been developed to produce a pulsed beam of 5.2 MeV neutrons. The pulsed beam has the advantage of improving measurement sensitivity by separating in time the inelastic scattering v-rays from those due to thermal-neutron capture reactions. The incident neutron energy was chosen to maximise the silicon ?-ray count rate, while keeping the signal from the competing reaction s l P(n,a)2s AI negligible. Introduction Exposure to silicon, in the form of silica, is hazardous to lung tissue, causing fibrosing and leading to silicosis. This condition is mainly due to occupational exposure in such places as mines and quarries, where silica dust is prevalent. Normal diagnosis based on patient history and X-radiography is d~fficult. The quantitative measurement of Si lung burden would be useful in order to study its relationship to observable patient symptoms and to provide a possible screening technique for exposed personnel. While Si lung burdens of 2 to 3 g are typical in silicotic individuals, non-exposed people have levels of about 0.1 g /I/. This paper describes the use of in vivo neutron activation analysis that would permit non-invasive quantitative measurements to be performed with a detection limit lower than the lung burdens of exposed individuals. Previous work /2/ has shown that the fast neutron inelastic scattering reaction 28Si(n,n'y)28Si, emitting 1779 keV y-rays, offers the most promise for silicon measurement, having a higher cross-section than the fast reaction 28Si(n,p)28A1 and the Elsevier Sequoia S. A., Lausanne Akaddmiai Kiad6, Budapest