Absorbed dose delivered by alpha particles calculated in cylindrical geometry

Abstract

The present work aims to develop a semi-analytical method to calculate the absorbed dose delivered by alpha particles in a cylindrical geometry. This method will be employed to reproduce the dose conversion coefficients or absorbed fraction of alpha particles in sensitive cells of the tracheobronchial tree obtained by NRC and ICRP, respectively. The difference caused by using water stopping power and tissue stopping power will also be investigated. Linear stopping powers for alpha particles in tissue and air were calculated, and the dependences of stopping powers on the traveled distance were established. A geometry model is set up for our calculations, and two different cases have been considered, namely the near-wall and far-wall cases. The total energy imparted to a unit-diameter sphere around a point is shown to be obtainable from a triple integral, which can be solved numerically. The absorbed dose is found to be independent of the diameter of the sphere being considered and additional assumptions about its diameter were not needed. The results obtained are in good agreement with those obtained previously by NRC and ICRP66. Using the semi-analytical method developed in the present work, the dose conversion coefficients or absorbed fraction previously obtained by NRC and ICRP, respectively, have been satisfactorily reproduced. Using the tissue stopping power instead of the water stopping power can slightly lower the values for dose conversion coefficients in the bronchial region.