Simulation of the radiation fields of 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, is in worldwide use to irradiate devices with calibrated beta sources. In this work the electron and photon particle spectra of the BSS 2 radiation fields are made available as data files, in addition angular distributions and the depth dose profiles are given. The spectra were determined using the Monte Carlo particle transport code BEAMnrc and are provided as electronic files. In order to verify the simulations, from the same simulations the depth dose curves in a phantom were deduced and compared with corresponding measurements -the agreement is quite good -proving the correctness of the particle spectra.

Monte Carlo-Based Spencer–attix and Bragg–gray Tissue-to-Air Stopping Power Ratios for Iso Beta Sources

“…The authors used the EGSnrc-based (9) BEAMnrc (10) user-code for this purpose. More recently, Behrens carried out EGSnrc Monte Carlo simulation of radiation fields of beta secondary standard BSS-2 (11) .…”

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

“…The phantoms consist of 4element ICRU tissue (ρ = 1.0 g/cm 3 ; 10.12 % H, 11.1 % C, 2.6 % N, and 76.18 % O -percentages per weight) surrounded by dry air (ρ = 1.1974·10 −3 g/cm 3 ; 0.01 % C, 75.53 % N, 23.18 % O, and 1.28 % Ar -again percentages per weight). As shown earlier, at least up to 50 % air humidity has no significant effect on the results [17]. The dimensions of the surrounding air are 1.2 m x 1.2 m x 1.2 m with the surface of the phantom in the geometrical centre of the air volume.…”

“…To make the simulations efficient, the sources were not simulated directly but phase space files produced in earlier simulations were used as input [17]. These files contain the full information of a radiation ?eld in a certain cross-sectional plane, e.g.…”

“…However, the depth dose curve, T (d) which is the transmission at a depth d in tissue, suggests a value of T (6 mm) / T (3 mm) ≈ 0.1 [17] which is less than 0.23. (The transmission of 0.23 is present at d ≈ 5 mm: T (5 mm) / T (3 mm) ≈ 0.23.)…”

“…Therefore, measured and calculated angular dependence factors for the slab phantom, R(d; α) slab , are compared in figures 2 and 3 for the quantities H p (0.07) slab and H p (3) slab , respectively. The angular factor is given by Rh the absorption dominates (decrease of the corresponding depth dose curve for α = 0˚) [17].…”