| Abstract | For quality assurance in the realization and transfer of the unit of the absorbed dose rate at 0.07 mm tissue depth for beta radiation by the national standard laboratories, comparison measurements, especially between the primary standard facilities are needed. A corresponding comparison took place from 2004 to 2007 as EUROMET project No. 739. The comparison described in this report took place from 2018 to 2023 with the following extensions:
• instead of only eight laboratories, this time 16 participants from all parts of the world (five continents) were included;
• besides the absorbed dose rate at 0.07 mm tissue depth, 3 mm tissue depth was included for the first time;
• three different types of primary standards and
• radiation sources of four differing design types were used;
• one laboratory participated at an extreme altitude of 3000 m above sea level which required a very significant correction for air density to the dose rate;
• finally, besides the long-established beta reference radiation fields from the three radio nuclides
1. ¹⁴⁷Pm with Ē= 0.07 MeV and Eₘₐₓ = 0.22 MeV,
2. ⁸⁵Kr with Ē= 0.25 MeV and Eₘₐₓ = 0.7 MeV, and
3. ⁹⁰Sr/⁹⁰Y with Ē= 0.8 MeV and Eₘₐₓₘₐₓ = 2.3 MeV, also a fourth, i.e., a high-energy radiation field utilizing
4. ¹⁰⁶Ru/¹⁰⁶Rh with Ē= 1.2 MeV and Eₘₐₓ = 3.5 MeV, was included for the first time;
all four in accordance with the international standard series ISO 6980 from the International Organization for Standardization (ISO).
A flat ionization chamber accompanied by a complete measurement system was used as the transfer instrument for the comparison. The calibration coefficients of this chamber were compared in the reference fields listed above. The 16 participants were from Germany (PTB), Portugal (IST-LPSR), Spain (CIEMAT), Hungary (BFKH), Sweden (SSM), Finland (STUK), France (LNE-LNHB), China (NIM), Republic of Korea (KRISS), Taiwan (INER), Japan (NMIJ), South Africa (NMISA), Mexico (ININ), Canada (NRC), United States of America (NIST), and Cuba (CPHR). The PTB was the pilot laboratory, and the comparison ran under EURAMET Project No. 1398 and BIPM KCDB: EURAMET.RI(I)-S16. The results from 13 of the 16 participants are consistent with the stated uncertainties while one participant's results agree for normal radiation incidence (0°) but not for oblique angles, one participant's results agree for the quantity Hₚ(0.07) but not for Hₚ(3) and one participant's results agree for the ⁹⁰Sr/⁹⁰Y radiation quality but not for ⁸⁵K. |
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