Radiation Protection Dosimetry Advance Access originally published online on August 9, 2005
Radiation Protection Dosimetry 2006 118(1):16-21; doi:10.1093/rpd/nci334
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Optimisation of a secondary standard chamber for the measurement of the ambient dose equivalent, H*(10), for low photon energies
Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany
* Corresponding author: ulrike.ankerhold{at}ptb.de
Received May 4, 2005, amended July 12, 2005, accepted July 17, 2005
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 1250 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 4037-2, 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 
12 keV. For area dosimetry, this means that the knowledge of H*(10) for energies approximately 
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 12 to 1250 keV.