Neutron Irradiation Techniques
Abstract: The He-3 “crisis” has become a fact in the last decade and large scale neutron detectors based on He-3 technologies have become unaffordable. This new He-3 reality has resulted in a major effort worldwide to develop replacement neutron-detector technologies. Many of these technologies are in their infancy and need to be thoroughly tested before becoming mainstream, while others are approaching commercialization and need to be certified. Still others which are commercially available today need to be tested before being installed in, for example, the instruments at the European Spallation Source ERIC. Detector technologies in all three stages of development need neutrons for controlled irradiations. Sources of neutrons for controlled irradiations include accelerators, nuclear reactors and radioactive sources. Neutrons produced in nuclear reactors and at accelerators have a very high cost of entry and a very high cost per neutron. In contrast, radioactive sources produce neutrons with a significantly lower cost of entry and lower cost per neutron. A drawback associated with radioactive sources is the associated isotropic mixed neutron/gamma-ray field. The Source Testing Facility has been established at the Division of Nuclear Physics at Lund University to provide a source-based neutron irradiation facility to local academic users and industry. This work presents the development of a cost-efficient test bed for the production of 2-6 MeV neutrons, an integral part of the Source Testing Facility. The test bed is based on actinide/9Be sources and lowers the barrier for local groups for precision neutron testing of detector technologies and shielding studies. Well-understood nuclear physics coincidence and time-of-flight measurement techniques are applied to unfold the mixed neutron/gamma-ray field and unambiguously identify the energies of the neutrons on an event-by-event basis. The Source Testing Facility thus developed is then used in conjunction with Arktis Radiation Detectors of Zurich, Switzerland for benchmarking the response of next generation He-4 based neutron detectors against standard NE-213 liquid scintillator detectors. The response of these standard NE-213 liquid scintillator detectors is then carefully unfolded and various models of the response of the scintillator itself are tested. The outputs of different actinide/Be-9 sources are then precisely compared in an effort to identify preferred actinides. And lastly, a complementary facility for the tagging of neutrons from the spontaneous-fission source Cf-252 is developed as a first step towards providing users the capability to measure the absolute, fast-neutron detection efficiency of their devices.
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