Development of reference database for gamma dose assessment in retrospective luminescence dosimetry

Abstract

A reference database is described that converts values of cumulative absorbed dose due to radioactive fallout, determined with samples of brick from buildings using the luminescence method, to be converted to kerma in air in a form suitable for use in dose reconstruction. This avoids the need to resort to specialised Monte Carlo (MC) programming techniques for each application. A simple model, used as the basis for MC simulations, comprised a brick building with one wall facing ground contaminated with radioactive fallout where the soil below ground level was divided into 409 source volume elements, extending in total up to 200 m from the wall and to a depth of 30 cm. MC simulations of the transport of gamma rays from sources of energy 662 keV ( 137Cs) in the soil were performed using the code MCNP 5 to obtain the values of coefficients that quantify the relationship between the specific activity within each source volume and the absorbed dose in a selected ‘detector’ volume of brick within the wall, referred to as the dose coefficient. A program, operating in conjunction with Microsoft Excel, employs additional code to control the movement of data stored in the database and the Excel user interface, enabling the coefficients to be calculated for a specified pattern of sources within the ground. Using these coefficients, the program calculates conversion and correction factors for the user-specified distribution of source activity. Examples of application are presented.