Development of high pressure deuterium gas targets for the generation of intense mono-energetic fast neutron beams

Two different technical solutions to the problem of generation of mono-ener getic fast neutron beams on the gaseous targets are presented here. A simpl e and cost-effective design of a cooled windowed gas target system is descr ibed in the first part of this paper. It utilises a thin metallic foil wind ow and circulating deuterium gas cooled down to 100 K. The ultimate beam ha ndling capability of such target is determined by the properties of the win dow. Reliable performance of this gas target system was achieved at 1 bar o f deuterium gas, when exposed to a 45 mu A beam of 5 MeV deuterons, for per iods in excess of 6 h, Cooling of the target gas resulted in increased fast neutron output and improved neutron to gamma-ray ratio. The second part of this paper discusses the design of a high pressure, windowless gas target for use with pulsed, low duty cycle accelerators. A rotating seal concept w as applied to reduce the gas load in a differentially pumped system. This a llows operation at 1.23 bar of deuterium gas pressure in the gas cell regio n. Such a gas target system is free from the limitations of the windowed ta rget but special attention has to be paid to the heat dissipation capabilit y of the beam dump, due to the use of a thin target. The rotating seal conc ept is particularly suitable for use with accelerators such as radio-freque ncy quadrupole (RFQ) linacs that operate with a very high peak current at l ow duty cycle. The performance of both target systems was comprehensively c haracterized using the time-of-flight (TOF) technique. This demonstrated th at very good quality mono-energetic fast neutron beams were produced with t he slow neutron and gamma-ray component below 10% of the total target outpu t. (C) 1999 Elsevier Science B.V. All rights reserved.