Mohsen Abou Mandour

Improved representation of scattering and straggling in Monte Carlo simulations of electron beam absorption

Abstract The accuracy of the Monte Carlo simulation of electron beam absorption in matter depends on fine details of the representation of multiple angular scattering and energy loss straggling. The paper refers to a technique of “grouping” the electron history in relatively short track length bins, which technique permits to work with Moliere and Landau distributions. Corrections to these distributions - a modified screening angle and the inclusion of small radiative energy losses in the Landau distribution are introduced and the theoretical reasons for these corrections discussed. The results calculated for carbon absorbers are in very good agreement with experimental data on energy deposition, transmission coefficient, mean-square scattering angle and energy loss spectra.

Electron fluence perturbation by cylindrical gas-filled ionization chambers with axes parallel to the beam

Abstract A systematic imperfection of charged particle beam dosimetry performed with cavity ionization chambers according to the Bragg-Gray principle is theoretically evaluated. Due to differences in multiple scattering of the particles in the gas-filled cavity and in the solid or liquid medium replaced by the gas, the particle fluence in the gas exceeds the undisturbed fluence existing in the absence of the cavity. For cylindrical cavities with their axes parallel to the beam, three separable mechanisms contributing to this disturbance are evaluated by application of multiple scattering theory. The range of validity of the calculations is extended over that of a previous study, and a revised “perturbation correction factor” is derived. The accuracy of the results is confirmed by comparison with Monte Carlo calculations for 10 MeV electrons in carbon.

Towards a methodology for bulk sample neutron activation analysis

Abstract The main challenge in large sample neutron activation analysis (LSNAA) is the determination of neutron self-shielding and gamma ray self-attenuation corrections. After these corrections are determined, the analysis proceeds as in normal neutron activation analysis (NAA), as if the sample were infinitely small. In this paper, these corrections are calculated using the MCNP code for different standard sample geometries with different diameters. Modelling studies for LSNAA using an external neutron beam were performed. An analytical formula for the correction factors for neutron self-shielding and gamma ray self-attenuation is derived. The correction factors as well as flux parameters are calculated analytically. The analytical formula is verified using the MCNP code. All of the calculated parameters were tabulated and graphed. From the calculated data, other unknown material parameters could be obtained based on tabulated data or graphs. This method is a direct and easy method to perform large sample neutron activation analysis without complex calculations. In addition, for the user who does not have good experience with codes such as MCNP, she/he can use the chart or the tabulated information to define their unknown sample with the required information for the LSNAA experiment.

The influence of cylindrical air cavities on fluence distributions of high energy electrons

Abstract The perturbation of dose distribution caused by air cavities in electron-irradiated media can be appreciable. A Monte Carlo program is developed to determine the effect of a cylindrical air cavity embedded in a homogeneous medium on the fluence distribution. The axis of the cylindrical cavity is assumed normal to the incident electron beam. The case of 10 MeV electrons and carbon as a homogeneous medium is considered. A study of the fluence and current distributions showed that close to and behind the cavity there is a focusing effect on the particles along the central axis of the beam. The characteristic hot spots in the fluence and current profiles beneath the cavity at its shadow edges are not observed.

Application of k 0 -INAA for the determination of essential and toxic elements in medicinal plants from West Pokot County, Kenya

The k0-INAA has been applied for determining nineteen elements in six medicinal plants used to cure various diseases in West Pokot, Kenya. It was observed that some elements are accumulated in excessive amount by the tested plants. Care has to be taken to control the daily dose of these herbs. Reference materials (IAEA-155 and IAEA-V-10) were analyzed simultaneously with the samples to evaluate the accuracy of the analysis protocol. It was found that the measured elemental concentrations were in a good agreement with the reported values with a maximum deviation of 20%.

Quantitative analysis of the mean square radial displacement of high energy electron beams

Abstract It is well known that a key characteristic of the pencil beam method of electron beam treatment planning, the mean square radial displacement, increases with absorber depth. In calculating this slope from multiple scattering theory, the mean energy loss with increasing depth has been taken into account, but it is shown that some discrepancy compared to measured values persists. The remaining influences of electron path detours and of the spectral width can be accounted for by starting the calculation from measured values of mean square scattering angle. The relations thus established can be used for the purposes of treatment planning in homogeneous and inhomogeneous absorbers.

Electron fluence perturbation by gap-shaped and by cylindrical gas-filled ionization chambers with axes normal to the beam

Abstract For electron beam absorbed dose measurements using gas-ionization chamber, a perturbation correction factor has been defined to correct for the disturbance of the fluence. For a gap-shaped cavity, a revised perturbation factor is derived. The range of validity of the calculations is extended over that of a previous study. The direct calculations for cylindrical cavities are very difficult. Instead, the form of the cylinder is approximated by a square parallelepiped. Comparison with Monte Carlo calculations showed good agreement.