A study of gamma-ray and neutron radiation in the interaction of a 2 MeV proton beam with various materials.
Epithermal neutron source based on a tandem accelerator with vacuum insulation and lithium target has been proposed, developed and operated in Budker Institute of Nuclear Physics. The source is regarded as a prototype of a future compact device suitable for carrying out BNCT in oncology centers. In this work the measurements of gamma-ray and neutron radiation are presented for the interaction of a 2 MeV proton beam with various materials (Li, C, F, Al, V, Ti, Cu, Mo, stainless steel, and Ta). The obtained results enabled the optimization of the neutron-generating target and the high energy beam transportation path.
In situ study of the blistering effect of copper with a thin lithium layer on the neutron yield in the 7Li(p,n)7Be reaction
Abstract A vacuum insulated tandem accelerator was used to study the effect of blistering on the neutron yield under 2-MeV proton bombardment of lithium target. The target is a thin lithium layer evaporated onto an efficiently cooled copper substrate. Targets with lithium thickness from 1 to 84 µm were irradiated by protons up to fluence of 6.3 1020 cm−2 which was significantly greater than the blistering threshold. The state of the targets surface was observed using long-distance microscope, video camera, infrared camera. The neutron dose was measured by dosimeters, the neutron flux density was measured by neutron detector. After irradiation, the targets were analyzed on Raman spectrometer, single crystal diffractometer, electron microscope, scanning profilometer, scanning electron microscope, atomic emission spectrometer. The article describes the experiment, presents the results obtained and notes their significance in the enhancement of a target for the neutron source used in boron neutron capture therapy.
Superpermeability of solid membranes and gas evacuation
Solid membrane permeable for a substantial part of the incident gas flow in one direction and impermeable in the inverse direction might be used as an ideal vacuum pump. In the case where gas is absorbed without dissociation and the gas temperature is equal to that of the membrane, only an infinitesimal part of the incident gas flow can penetrate through the membrane. If, however, the gas is ‘hotter’ than the membrane (on account of excitation, dissociation, heating, etc.) the membrane permeability may become comparable to that of the opening in a thin wall (superpermeability). The condition indispensable for this to take place is the inlet boundary special state hindering the thermal desorption of the absorbed gas. After special boundary processing the membrane becomes superpermeable for non-equilibrium gas while ordinary permeability, small as it is, becomes practically negligible. So when non-equilibrium is maintained only at one side of the membrane, gas would flow only in one direction as is required for pumping, compression and recuperation. In the case where the absorption is accompanied by dissociation (as in the H2-Me systems) superpermeability in principle may be achieved with equal temperatures of gas and the membrane. However, in the temperature and pressure ranges of practical interest this can be achieved only in the H2-Pd system and with a clean membrane surface. Under the non-equilibrium condition superpermeability is possible for various gas-solid combinations over a wide range of the gas pressures, membrane temperatures (low temperatures included) and boundary conditions.