The response of a neutron rem counter to thermal, to intermediate-energy, and to fast neutrons

A neutron rem counter (Studsvik type 2202D) was calibrated at a number of neutron energies during a technical seminar on neutron dosimetry in radiation protection sponsored by the Commission of the European Communities and held at the Physikalisch-Technische Bundesanstalt in Braunschweig. The rem counter was calibrated using 1) monoenergetic neutrons of eight different energies between 100 keV and 19 MeV produced by means of an accelerator, 2) neutrons from three radioactive neutron sources (Ra-Be, Am-Be and 252Cf), and 3) a thermal-neutron beam and two filtered neutron beams (2 and 24.5 keV, respectively) from a reactor. The results show that the sensitivity of the rem counter follows the ''ICRP rem curve'' within about plus minus 20% at neutron energies between 250 keV anf 5 MeV. However, at neutron energies below 100 keV and above 10 MeV, the sensitivity deviates significantly from the ''ICRP rem curve''. When calibrated at, say, 1 MeV, the rem counter will overestimate the dose equivalent in radiation fields where a significant portion of the dose equivalent is due to neutrons of energies between 100 eV and 100 keV, and it will underestimate the dose equivalent from thermal neutrons and from neutrons of energies above 10 MeV. (author)