Experimental estimation of conversion factors between air kerma free-in-air and individual dose equivalent penetrating for 4-7 MeV photons

The conversion factor for 4-7 MeV photons for conversion from the air kerma free-in-air to the ambient dose equivalent is 1.11-1.10 according to ICRP publication 51. For normal incidence the ambient dose equivalent corresponds to the directional dose equivalent at 10 mm depth in the ICRU sphere. The directional dose equivalent at 10 mm depth is considered as a good approximation of the individual dose equivalent, penetrating. Measurements with TL dosemeters on and in a PMMA slab phantom are compared with air kerma for 4-7 MeV photons. The measurements show that the conversion factor for 4-7 MeV photons for conversion from the air kerma free-in-air to the dose equivalent at 8 mm in a PMMA slab phantom is in the range 1.12-1.08. This is in good agreement with the conversion factors reported in ICRP publication 51. The tested personal dosemeters on the phantom under-respond by up to 6 per cent, relative to the directional dose equivalent at 10 mm depth, for normal incidence and up to 13% at 30o and 60o from normal incidence. This is mainly due to the fact that the dosemeters are not covered with enough build-up material. (author)