Measurement method of activation cross-sections of reactions producing short-lived nuclei with 14 MeV neutrons

We describe a method for obtaining reliable activation cross-sections in the neutron energy range between 13.4 and 14.9 MeV for the reactions producing short-lived nuclei with half-lives between 0.5 and 30 min. We noted neutron irradiation fields and measured induced activities, including (1) the contribution of scattered low-energy neutrons, (2) the fluctuation of the neutron fluence rate during the irradiation, (3) the true coincidence sum effect, (4) the random coincidence sum effect, (5) the deviation in the measuring position due to finite sample thickness, (6) the self-absorption of the γ-ray in the sample material and (7) the interference reactions producing the same radionuclides or the ones emitting the γ-ray with the same energy of interest. The cross-sections can be obtained within a total error of 3.6%, when good counting statistics are achieved, including an error of 3.0% for the standard cross-section of 27Al (n, α) 24Na. We propose here simple methods for measuring γ-rays efficiently at a close source-to-detector distance and for measuring β+ activities emitting almost no γ-rays.