Use of delayed neutrons in activation analysis

Most of the radionuclides formed by activation decay by beta and gamma emission. However, in a few cases, neutron emitters are formed. Usually in nuclear reaction, the neutrons are emitted promptly, but in these few cases, the neutron-emitting nuclides are formed not by the direct activation but rather from beta decay of a directly formed radionuclide and hence the neutron emission is delayed by the beta emission; consequently the neutrons are called delayed neutrons. Due to the scarcity of neutron emission and the possibility of neutron detection without interferences from other emissions, this method is a very selective one and consequently may be also a sensitive one but can be used only in few cases, i.e., only for few elements. Up to now the activation analysis followed by delayed-neutron detection was used mainly and almost only to determine fissionable material, i.e., U, Th, and Pu and mainly by neutron activation. However, in principle also other elements can be determined in this method, e.g., neutron activation can be used to determine 9Be and 17O since their reactions with fast neutrons lead to the delayed neutron precursors 9Li and 17N by the reactions 9Be(n,p)9Li and 17O(n,p)17N. For 9Li, the half-life is quite short - 178.3 ms, but still it can be determined by using the double reaction 6Li(n,α)T, 18O(t,α)17N and detecting the delayed neutrons due to 17N. These two reactions can be used also for the determination of 18O by adding a known amount of 6Li