Evaluation of skin absorbed doses during manipulation of radioactive sources: a comparison between the VARSKIN code and Monte Carlo simulations
The evaluation of skin doses during manipulation of radioactive sources can be a critical issue for which the most accurate calculation strategies available should be used. The aim of this work was to compare the results of the analytical approach used in VARSKIN with the simulation of radiation transport and interaction by Monte Carlo calculations in GAMOS (GEANT4-based Architecture for Medicine-Oriented Simulations), and to provide an accurate and versatile tool for the evaluation of skin doses from radionuclide sources of any realistic shape (e.g. cylindrical, parallelepiped), even in the presence of multiple interposed absorber layers. A set of 20 radionuclides (pure β, β–γ, Auger and γ emitters) from among the most frequently employed in nuclear medicine and laboratory practices were selected for comparison. We studied a point-like and a cylindrical source, in the presence of varying thicknesses of absorbing layers. We found a general agreement for most nuclides when the source was directly in contact with skin or in the presence of a thin layer of absorbing material. However, when the thickness of the absorber increased, significant differences were found for several nuclides. In these cases, the proposed method based on a dedicated Monte Carlo simulation could give more accurate results in a reasonable time, which could optimise accuracy when assessing skin doses in routine as well as incidental exposure scenarios.
GAMOS: An easy and flexible way to use GEANT4
The wide range of physics models available in GEANT4, as well as its outstanding geometry and visualization tools, has made it gain widespread use in several fields of physics, like high energy, medical, space, etc. Nevertheless the use of GEANT4 often requires a long learning-curve, which implies a good knowledge of C++ and the GEANT4 code itself. GAMOS facilitates the use of GEANT4 by avoiding the need to use C++, providing instead a set of user commands. One of the novelties of GAMOS with respect to similar simulation codes lies in its flexibility, which makes it appropriate for simulation in many physics fields. This flexibility is sustained by the wide range of geometrical configurations, primary generators and physics lists supported and by the comprehensive set of tools that help the user in extracting detailed information from the simulation through user commands. The use of the plug-in technology contributes to this flexibility, as it facilitates the extension of the framework to include extra functionality not foreseen by the framework authors. GAMOS counts already with several hundreds registered users in the five continents; while it is more frequently used in the medical physics field, its use has also been extended to other fields, like high energy physics, space physics, neutron shielding, etc.
Spectral shapes for atomic-field bremsstrahlung produced by beta particles of yttrium-90 in thick targets of Cu. Cd, Ta and Pb
Experimental results are presented for the spectral shapes for atomic-field bremsstrahlung produced by complete absorption of beta electrons from the decay of 90Y in targets of Cu, Cd, Ta and Pb over the photon energy range from 600 keV to 2 MeV. The experimental data are compared with numerical calculations based on the formulation of Pratt et al., the Born approximation theory of Bethe-Heitler and with the classical theory of Kramers. Although small discrepancies exist at some spectral points scattered throughout the energy region studied, the overall agreement between the theory of Pratt et al. and experiment is good. The experimental data agree with the Elwert-corrected Bethe-Heitler theory within experimental uncertainties for Cu, and a systematic positive deviation is found for Cd, Ta and Pb. The overall agreement between the classical theory of Kramers and experiment is very poor. Agreement between Kramers' theory and experiment is only seen within experimental uncertainties in certain restricted energy regions for Cd, Ta and Pb.