Neutron activation analysis

In a method of simultaneously analysing the aluminium and silicon content of a sample, the material is irradiated with fast neutrons from a single neutron source and the following measurements are made: a) thermal neutron flux; b) 1.78 MeV gamma radiation and c) 1.015 MeV, 0.844 MeV or both 1.015 and 0.844 MeV gamma radiation. The last measurement is used to estimate the aluminium content of the sample. Silicon content is estimated using the 1.78 MeV measurement compensated by the gamma radiation at 1.78 MeV due to the thermal neutron reaction with the estimated aluminium in the sample. The nuclear reactions providing the basis of the invention are: 27Al(n,p)27Mg and 28Si(n,p)28Al. In the decay of 27Mg 0.844 MeV and 1.055 MeV gamma rays are emitted. A third nuclear reaction is important with samples having significant water content. This reaction, 27Al(n,γ)28Al, which entails the capture of slow neutrons in aluminium, results in the emission of 1.78 MeV gamma radiation additional to the 1.78 MeV gamma radiation from the fast neutron reaction with silicon