Letter to the editor.

Abstract

Sir, The metrology of high-energy neutron fields is important because of the increase in the number of high-energy accelerators in research and medicine in Europe, where high-energy neutrons are the dominant component of the radiation field present outside the shielding; high-energy neutrons can also be a secondary component of the fields in the beam delivery system and in the patient's body in hadrontherapy and the occupational exposure to cosmic radiation where high-energy neutrons are a significant component of the total cosmic radiation field in aircraft and in spacecraft. The energy range of neutrons in these fields extends from thermal energies to several gigaelectron volts. In order to make measurements of high-energy neutron fields or for benchmark measurements of calculated fields, it is necessary to characterise and to calibrate instruments in reference fields at energies from 20 MeV up to an energy approaching 1 GeV. Although there are ISO reference fields of <20 MeV, there are none at higher energies. High-energy quasi-monoenergetic neutron (QMN) fields allow for the detailed determination of the energy- and direction-dependent responses of active and passive neutron devices and also the neutron responses of those instruments designed to measure other types of radiation.