A measurement of the response to fast neutrons of several materials dosemeters

The measurement of the response to fast neutrons of several materials dosemeters, used in zero energy reactor experiments, is described. They are (a) silicon diodes, (b) beryllia, alumina and calcium fluoride TLDs and (c) C/CO2 and C/Ar ionisation chambers. Silicon diodes are used for measuring fast neutrons whereas the others are used to measure γ exposure where the fast neutron response is typically less than 5% of the total signal. For silicon diodes, γ radiation is irrelevant since they respond only to fast neutrons, but the response must be defined accurately. The response function has several resonances so that the calibration must be with a variable but essentially monoenergetic neutron source. Between 0.3 and 2.3 MeV the requirements for both classes of detector can be met simultaneously by accelerating protons onto a tritium target to produce γ free neutrons in defined energy bands. In addition, a thin lithium target was also used to produce more closely defined neutron energies in the range between 117 and 650 keV to identify the response threshold and principle resonance in the silicon diode response. (author)