USE OF THE SI-28(N,P)AL-28 REACTION FOR THE MEASUREMENT OF 14 MEV NEUTRONS FROM FUSION PLASMAS

The 28Si(n, p)28Al reaction is shown to be ideal for monitoring the emission of 14 MeV neutrons from d-t fusion plasmas. The daughter nuclide, 28Al, has a 2.246 min half-life and so is suitable for studying discharges of up to 1 min duration; the decay gamma radiation has an energy of 1.779 MeV and is easily detected with a NaI(Tl) detector. The same sample can be recycled for successive JET discharges and the data taking is fully automatic. Absolute neutron yields are obtained by calibrating with the standard 63Cu(n, 2n) 62Cu reaction. The effective threshold energy of 5 MeV completely discriminates against 2.5 MeV d-d neutrons, making this reaction also highly appropriate for the study of the 14 MeV neutrons emitted during the burnup of the 1.0 MeV tritons produced in the second branch of the d-d reaction. Some results from this application will be presented.