Effective dose and organ doses due to gas bremsstrahlung from electron storage rings

Abstract

Bremsstrahlung on residual gas is an important source of beam losses in electron–positron storage rings. The bremsstrahlung photons are emitted in a narrow cone in the forward direction, which produces a “hot spot” of dose at the end of a straight section. Estimates of radiation hazard due to gas bremsstrahlung have so far been performed by calculating the maximum dose equivalent (MADE) or similar quantities. However, the use of quantities conceived for broad parallel beams in the case of very narrow beams significantly overestimates the organ doses and effective dose. In this paper a more sophisticated computational model was used to calculate the values of effective dose and absorbed doses in various organs due to gas bremsstrahlung X-rays generated by 0.1–10 GeV electrons. The bremsstrahlung photons generated by the interaction of a monoenergetic electron beam in a 1 m long air target were made to impinge on a selected organ of an hermaphrodite anthropomorphic mathematical model placed at 1 and 10 m distances from the end of the target. Organ dose and effective dose were calculated for five representative organs, namely right eye, ovaries, breast, testes and thyroid. Fits to the calculated values are given, as well as the dependence of photon fluence and dosimetric quantities on various parameters. The results are compared with previous estimates based on MADE and with values of ambient dose equivalent.