With the Beta Secondary Standard (BSS), an important basis was created thirty years ago for the dissemination of the unit of the absorbed dose rate of beta radiation to tissue, which has proven its worth in practice. The main reasons for the popularity of the BSS are the traceability of its calibration to the primary standard measuring device of PTB and its conformity with the recommendations of the international standard ISO 6980. In 1996, an extensive modification of the BSS was started with the aim of improving its ease of operation, achieving a greater variety in practical use, assuring the quality when performing irradiations and optimizing radiation protection. In the following report, the result of this optimization, the new Beta Secondary Standard type 2 (BSS 2), will be presented. To this end, we will report on the investigations carried out on the BSS 2 and on the experiences gained in the work with of the BSS 2 and the calibration of -so far -32 sets of radiation sources.
An comparison of absorbed dose rates,). (D 07 0 t & , in tissue at radiation protection levels for beta dosimetry was performed between two national laboratories, the D. I. Mendeleyev Institute for Metrology (VNIIM) in St. Petersburg (Russia) and the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig (Germany), in 1999 and 2001 using flat ionisation chambers as transfer standards. The dose rates were determined at the calibration distances by measurements with the primary standard measuring devices of VNIIM and PTB with extrapolation chambers to realise the unit of absorbed dose rate to tissue for beta radiation. In the two steps reported on here, transfer chambers of VNIIM and PTB were calibrated in beta radiation reference fields at VNIIM and at PTB. The values of the calibration factors for the flat ionisation chambers agreed within ± 2 % for 90 Sr/ 90 Y, 85 Kr and 204 Tl and ± 4 % for 147 Pm beta radiation.
Beta dosimetry, especially at the extremities, is gaining in importance due to the increasing use of beta particle sources, e.g. in brachytherapy. The dosimetric properties of personal dosemeters to be worn on the extremities and capable of measuring the personal dose equivalent, Hp(0.07), in beta and/or photon radiation fields were investigated within the scope of intercomparison measurements organised by the PTB in two steps. The results were evaluated on the basis of recommendations from the German Commission on Radiological Protection (SSK). In the first step 10 types of dosemeter were investigated in beta particle fields in a range of mean energies from 0.06 MeV to 0.8 MeV. In the second step, five selected beta dosemeter types were exposed to beta particles and, in addition, to photons and to mixtures of both. Three dosemeters fulfill the requirements for the whole range of mean beta energy used for the intercomparison and meet the requirements for photon radiation from 8 keV to 662 keV.
For quality assurance in the realization and transfer by the national standard laboratories of the unit of the absorbed dose rate at 0.07 mm tissue depth for beta radiation, comparison measurements among the primary standard facilities are needed. Although some bilateral comparisons have taken place for this quantity, the CCRI decided in May 2003 that a EUROMET supplementary comparison would be appropriate if inclusive of primary standards laboratories of other regional metrology organizations. The operation and results of such a comparison are reported here. A flat ionization chamber and measurement system was used as the transfer instrument. A comparison was made of the calibration coefficients of this transfer instrument in various beta-particle laboratory reference fields (Pm-147, Kr-85, Tl-204 and Sr-90/Y-90) measured by each of the eight participants from France, Italy, Finland, Germany, Russian Federation, USA, Canada and Japan. The PTB was the pilot laboratory and the comparison ran from January 2004 until April 2007 under EUROMET project No 739 and EUROMET.RI(I)-S2. The results for most of the participants are consistent with the stated uncertainties although an extreme deviation is apparent for Pm-147 beta radiation for one participant.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by EUROMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).
In January 2004, two EUROMET supplementary comparisons started, coordinated by Physikalisch-Technische Bundesanstalt (PTB): one for the radiation protection quantity 'personal dose equivalent' Hp(10) using X-radiation, and one for the quantity 'absorbed dose in tissue' Dt(0.07) using beta reference fields. The focus of both comparisons lies on calibrations using radiation qualities at which the dissemination of the quantities considered here is difficult. Within the scope of the two comparisons, an ionisation chamber shall be calibrated. Together with a transfer chamber optimised to measure Hp(10) and Dt(0.07), respectively, for each comparison a complete electronic measuring system is circulated. These transfer devices, as well as, a specially developed test procedure, which has to be carried out by each participant to check the instruments, are described. For both comparisons, the results of those participants who had finished their measurements and delivered the measuring protocol until February 2005 were evaluated. As the comparisons are still running these first results are shown in an anonymous form. A first assessment of the data will be given.
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