Optimisation of a secondary standard chamber for the measurement of the ambient dose equivalent, H*(10), for low photon energies.
A secondary standard ionisation chamber for photon radiation for measuring an ionisation current, which is directly proportional to the conventionally true value of the ambient dose equivalent, H*(10), was optimised. The chamber was developed in the Austrian Research Centers Seibersdorf and is used successfully worldwide by dosimetry laboratories. The chamber response with respect to H*(10) for photon energies from 40 to 1,250 keV is nearly constant. For lower photon energies the response is strongly energy-dependent and does not fulfil the requirements concerning the quality of a secondary standard given in ISO 4,037-2, i.e. for energies for which the determination of the conventionally true value of H*(10) is very difficult. Considering the dose limits defined in the Directive 96/29/Euratom, in the case of whole-body irradiation the knowledge of the personal dose equivalent is of importance down to energies of approximately 12 keV. For area dosimetry, this means that the knowledge of H*(10) for energies approximately >or=12 keV is necessary. To get one secondary standard chamber for H*(10) for the whole photon energy range and to close the gap for low energies in the dissemination of the conventionally true value of H*(10), the chamber was optimised for a flat response for energies from approximately 12 to 1,250 keV.
Ankerhold
U
U
Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany. ulrike.ankerhold@ptb.de
D002138:Calibration; D004867:Equipment Design; D005062:European Union; D006801:Humans; D018499:Linear Energy Transfer; D017785:Photons; D011829:Radiation Dosage; D011835:Radiation Protection / Q000592:standards; D011874:Radiometry / Q000295:instrumentation*