Effective depth of spermatogonia in man II. Calculations for external high-energy beta rays

An important criterion for dosemeter design for male gonad dosimetry in mixed beta-gamma fields is the effective spermatogonial depth. A detector set at this depth will register mean dose to the spermatogonia: this is the quantity of interest for genetic risk, which is proportional to the mean dose to the spermatogonia, averaged over the whole testicular volume. Factors affecting mean spermatogonial dose and effective depth of the spermatogonia were examined by computer using a simple mathematical model. Depth dose data were input from tables of beta dose. Mean spermatogonial dose shows a moderate dependence upon beta maximum energy, and a moderate inverse dependence upon scrotal thickness and source distance in air. Effective spermatogonial depth, while largely independent of source distance, shows strong dependence upon beta maximum energy: hence dosemeters designed for a given beta maximum energy will over-respond when exposed to betas of higher energy. Values of effective spermatogonial depth are given for two isotopes. In fields of mixed isotopes, weighting of the depths is essential for averaging.