A prototype ionisation chamber as a secondary standard for the measurement of personal dose equivalent, Hp(10), on a slab phantom

The construction and technical characteristics of a secondary standard chamber for measuring the conventionally true value of the personal dose equivalent, H-p(10), on a slab phantom are presented. The chamber was optimised to get a nearly constant response with respect to H-p(10) for photon energies from about 10 keV to 1400 keV and for angles of incidence, or, from 0 degrees to 75 degrees. Thus, once calibrated at the facility of the calibration laboratory, the H-p(10) chamber can be used at other facilities without any need to consider the spectral differences of radiation fields of the same nominal radiation quality but generated by two different facilities. This is a great advantage over the procedure recommended in ISO/FDIS 4037-3, according to which these differences have to be considered for low energy photon radiation and may lead to differences of the conversion coefficients from air kerma, K-a, to H-p(10) of up to several tens of per cent.