Extensions to the Beta Secondary Standard BSS 2

Abstract

Since several years, the irradiation facility for beta radiation, the Beta Secondary Standard BSS 2 developed at PTB, has been in worldwide use for the performance of irradiations with calibrated beta sources. Due to recent developments in eye tumor therapy, in eye lens dosimetry, and in soft-and hardware technology, several extensions have been added to the BSS 2.These extensions are described in this paper:1. The possibility of using a 106 Ru/ 106 Rh beta source was added as this radionuclide is often used in tumor therapy. 2. The (small) contribution due to photon radiation was included in the dose (rate) reported by the BSS 2, as this was missing in the past. 3. The quantity personal dose equivalent at a depth of 3 mm, H p (3), was implemented due to recent findings on the radio sensitivity of the eye lens regarding cataract induction and the subsequent lowering of the dose limit from 150 mSv down to 20 mSv per year; 4. The correction for ambient conditions (air temperature, pressure, and relative humidity) was improved in order to adequately handle the quantity H p (3) and in order to extend the range of use beyond 25 • C. 5. A checksum test was added to the software to secure the calibration data against (un)intended changes. 6. The connection of the PC and the BSS 2 has been changed to a network interface (TCP/IP) in order to be able to use up-to-date computers not containing a parallel and a serial port. 7. A rod phantom was added in order to make sure the mechanical set-up is of high quality.All these extensions have been implemented in the PTB's BSS 2 model. The routine implementation of extension 1 is still under investigation by the manufacturer. The commercially available BSS 2 will contain extensions 2 to 6 starting approximately in 2012, while extension 7 has already been incorporated since 2011. Extensions 2 to 4 will also be available for old BSS 2 versions via a software update, starting approximately at the beginning of 2012. Extension 6 will be available via hardware change by the manufacturer.

Correction factors for the ISO rod phantom, a cylinder phantom, and the ICRU sphere for reference beta radiation fields of the BSS 2

“…In those cases where the calculated values did not statistically significantly deviate from 1.0, the correction factors are stated to be 1.0 with their respective standard uncertainty. The values for k rod (α) for α 60˚given in table 2 replace the former one of 1.00 ± 0.03 stated earlier [8]. As can be seen, the old value of 1.00 with its quite large uncertainty of 0.03 was consistent with the new ones.…”

“…3 For the sake of completeness, tables 11 and 12 contain values for T (3; 0˚) slab and R(3; α) slab which have been measured previously [8]. Table 6.…”

“…The depth dependence factor is given by T (3; 0˚) slab = H p (3; 0˚) slab / H p (0.07; 0˚) slab and the angular dependence factor is given by R(3; α) slab = H p (3; α) slab / H p (3; 0˚) slab , all to be measured in the slab phantom; data are available [8].…”

“…The conversion coefficients h D for these quantities are implemented in the software via the ini file "BetaFakt.ini", version 7.4 [8]. According to ISO 6980-3, the phantom dependence was assumed to be negligible for angles of incidence α 60˚, see section 1.…”

“…According to ISO 6980-3, the phantom dependence was assumed to be negligible for angles of incidence α 60˚, see section 1. Thus, values for h p,D (0.07; α) rod and h D (0.07; α) were contained in "BetaFakt.ini" only up to α = 60å nd assumed to be equal to h p,D (0.07; α) slab with a rather large standard uncertainty of 3 % for the rod [8]. The reason was the lack of knowledge of the correction factors k rod (α) and k (0.07; α).…”