Re-determination of correction factors for primary beta dosimetry

Several correction factors for primary beta dosimetry in radiation protection have been determined by means of measurements and simulations for both the well‑known Böhm primary standard extrapolation chamber developed at PTB (which has been commercially available for a long time) and a new primary standard extrapolation chamber also developed at PTB. The correction factors

• k_el for electrostatic attraction of the entrance window due to the collecting voltage and
• k_sat for ionisation collection losses due to ionic recombination

have been measured.

The following correction factors have been determined by simulations for normal (0°) as well as oblique (15°, 30°, 45° and 60°) radiation incidence:

• k_ba for backscatter from the collecting electrode,
• k_pe for perturbation by the chamber’s side walls, and
• k_ra, k_ac and k_di for inhomogeneity inside the collecting volume. The latter three have been combined to k_ih.

Six more correction factors adopted from the literature have been described to complete the corrections necessary for the primary standards.

The application of the new factors shows improved linearity of the measured signal from primary standard extrapolation chambers. All details as well as a comparison with values given in ISO 6980‑2:2004 (for 0°), all determined at that time by means of measurements, are available in two publications ([1] and [2]). The newly determined correction factors are ready to be implemented in an updated version of ISO 6980‑2.

Literature

[1]        R. Behrens: “Correction factors for primary beta dosimetry”,
Metrologia 57 (2020), 065022, https://doi.org/10.1088/1681-7575/ab6cd6

[2]        R. Behrens: “Correction factors for two new reference beta radiation fields”,
Metrologia 57 (2020), 065005, https://doi.org/10.1088/1681-7575/ab8829

Contact

Rolf Behrens, Department 6.3, Working Group 6.34