Radiation Quantities: Significance of the Angular and Energy Distribution of the Radiation Field

British Committee on Radiation Units and Measurements: Advice on the Implications of the Conversion Coefficients for External Radiations Published in ICRP Publication 74 and in ICRU 57

“…However, the Joint Task Group report concludes that, in practice, irradiation by mono-energetic neutrons rarely occurs and that the ambient dose equivalent is usually a conservative estimate of the effective dose. It has been shown that, in a wide range of working environments, the energy and angular distribution of neutrons is such that E/H * (10) extends from 0.2 to 1.1 [10][11][12][13] but typically lies between 0.88 and 1.05. In environments where high-energy neutrons (>10 MeV) predominate, principally around high energy accelerators and in high altitude flight, calculations and measurements indicate that the values of E/H * (10) lie in the range 0.45 to 1.1 [14,15].…”

“…For neutrons, the ratio of the effective dose to the personal dose equivalent at a depth of 10 mm, E/H p (10), can significantly exceed unity at some energies, even in the rotational (ROT) geometry. For AP geometry, the situation is very similar to that described above for H * (10) but in other geometries, a measurement of H p (10) could seriously underestimate E ([1] figure 57).…”

“…For AP geometry, the situation is very similar to that described above for H * (10) but in other geometries, a measurement of H p (10) could seriously underestimate E ([1] figure 57). However, under typical working conditions, where there is a broad range of neutron energies and directions of incidence, E/H p (10) typically lies between 0.6 and 1.8 for AP and ROT geometries [10][11][12][13]. The value of 1.8 corresponds to a scandium-filtered neutron beam but, although an underestimate of as much as 1.8 is undesirable, it is rarely as large as this value and stems from the artificially high value of E at intermediate neutron energies because of the over weighting of photons generated by neutrons in body tissues.…”