Disintegration of Nitrogen by Fast Neutrons

Abstract

THE reactions ¹⁴₇N (np) ¹⁴₆C and ¹⁴₇N (nα) ¹¹₅B have been investigated using the mono-energetic neutrons, obtained by bombarding a thin heavy-ice target by deuterons (D+D neutrons). With a deuteron energy of 400 keV. and a variation of the angle between the direction of the neutrons used and the beam of impinging deuterons from 34° to 138°, the neutron energy is varied between 3.2 and 2.1 MeV. This method was suggested to me by Dr. H1. de Vries. The number of (np) and (nα) reactions is measured in a nitrogen-filled proportional counter, which is placed in various positions in the above-mentioned interval, with respect to the target. In order to eliminate fluctuations in the yield of the neutron source, the number of kicks from this counter is divided by the number of counts given in the same time by a proportional counter filled with boron fluoride which is kept in a fixed position. For the calculation of the cross-sections, the absolute number of neutrons getting into the nitrogen counter must be known. Therefore the number of neutrons per unit of solid angle in the direction of the boron fluoride counter for a given number of counts was determined from the response of this counter to a source consisting of 90 mgm. radium + beryllium, placed close to the target. For other directions this number was calculated, assuming the (1 + A cos² θ)-law in the centre of gravity co-ordinate system, with A = 1.5 in this case¹.