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Calibration of beta sources

Source types

The beta radiation sources of the Pm-147, Kr-85 and Sr-90/Y-90 nuclides of the BSS2 beta secondary standard Opens internal link in current windowBSS2 are calibrated at the specified distances, with and/or without beam flattening filter, in an irradiation facility equivalent to that of the BSS2. Source adapters (source in a shielding of its own with beam shutter) and the nuclide-specific beam flattening filters are concerned. Assignment of source and beam flattening filter is ensured by suitable codes applied to source and filter. The exchange of filters makes recalibration necessary.

Other sealed beta radiation sources of the C-14, Pm-147, TI-204, Kr-85, Sr-90/Y-90 and Ru-106/Rh-106 nuclides can be calibrated at any distance from the source surface if the dose rates lie in the range from 50 µGy/h to 2 Gy/h. Fixation and adjustment of these sources in front of the PTB's measuring system is to be facilitated by appropriate accessories. Radiation protection during handling and transport of these sources must be ensured by the applicant (manufacturer or user of these sources).

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Contacts:

phone: +49 (0) 531-592-6340

phone: +49 (0) 531-592-6352

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Measuring facility:

The absorbed dose rate is measured with high accuracy at the primary standard measuring facility for the unit of the absorbed dose rate of beta radiation in tissue, which comprises a semi-automatic measuring assembly with a volume extrapolation ionization chamber, a highly sensitive charge measuring system, a highly precise voltage source for the chamber voltage, a distance meter for measuring the chamber depth and instruments for measuring the parameters of the environment (temperature, atmospheric pressure, humidity of the air). Control of the measuring assembly and data acquisition are ensured by a software program installed on a PC. The test room is air-conditioned. A flat ionization chamber with fixed volume, which was calibrated by comparison with the primary standard measuring facility, serves as the secondary standard. This chamber allows beta radiation sources to be calibrated with lower accuracy.

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Quantities:

Beta radiation sources can be calibrated for the following quantities:
directional dose equivalent rate, d[H'(0,07)]/dt,
personal dose equivalent rate, d[Hp(0,07)]/dt,
absorbed dose rate to tissue surface, d[Dg(0)]/dt.
Determination of all depth dose curves is also possible.

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Details of calibration:

Calibration covers extrapolation measurements (chamber current as a function of chamber depth) and depth dose measurements (measurements at different depths) in tissue substitute (Hostaphan, PMMA) as well as spectrum measurements for other sealed beta radiation sources. The spectral purity of the BSS2 sources is guaranteed by the manufacturer.

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