On the energy behaviour of fast d-T neutrons generated by hollow-cylindrical deuteron beams accelerated onto plane tritium targets

Abstract

There exist considerable requirements for the comprehensive characterisation of fast neutron fields produced by extended sources. These needs are driven in part by fusion research, neutron damage studies and efforts towards defining the efficiency of nuclear reaction production. The work contained herein concerns the spatial dependency of neutron energy in the vicinity of homogeneous targets. The study also examines the d-T exoergic nuclear reaction generated in nondispersive media by uniform hollow-cylindrical accelerated particle beams. In particular circumstances, the elementary neutron emission process can be considered to be omnidirectional (due consideration being paid to collision kinetics, which depend upon mass and kinetic energy of the particles involved in nuclear collision and to nuclear reaction energy, etc.) and consequently, analytical expressions can be considerably simplified. Examination is made of an ln-type functional dependence for fast neutron energies, this being typical of, for instance, ring-shaped d-T neutron sources. The spatial distribution of the energy of neutrons produced by this particular type of source passes through maximum values at points whose locus is described by circles with radii depending upon the ratio of the fast neutron source emitting ring (inner and outer) radii. The consequent fast neutron iso-doses can be analytically described by quartic equations, with the ring radii ratio as a parameter and the emitter axis as the axis of symmetry. The description of spatial neutron energy distribution as well as exoergic reaction production and neutron dosimetry described by these expressions is supported by empirical data obtained using 14.1 MeV d-T neutron generators.