An improved pneumatic sample transport system for measurement of activation cross-sections with d-D neutrons in the energy range between 2.1 and 3.1 MeV

摘要

We have improved a pneumatic sample transport system that enables activation cross-sections to be measured by producing short-lived nuclei on the order of sub-millibarns. The irradiation distances between the d-D neutron source and the samples ranged from 20 to 65 mm at six angles of between 0° and 155°. The neutron fluence rates were between 1 x 10~8 and 5 x 10~6 n/cm~2/s in the 2.1-3.1 MeV range, and these values were between 24 and 3 times higher than those of the previous system, which used a distance of 100 mm, at the Fusion Neutronics Source at the Japan Atomic Energy Research Institute. The energy spreads at the irradiation positions were calculated by taking into account the slowing of incident 350-keV deuterons, the self-loaded deuteron distribution in the Ti-target and the solid angle subtended by the irradiated sample. At each angle, the acceptable close distance was found to be about 20 mm under the condition of an energy spread of less than about 300 keV. The spreads at about 0° and 180° were determined mainly by the slowing of deuterons in the target, while those at about 90° were determined by the finite solid angle. The activation cross-sections of ~(27)Al (n, p) ~(27)Mg and ~(61)Ni (n, p) ~(61)Co reactions were obtained for test measurements. This was undertaken with the prospect of using the present system to systematically measure the activation cross-sections down to a sub-millibarn level.