Dosimetry in radiation fields around high-energy proton accelerators

Abstract

Radiation dosimetry at high-energy proton accelerators is a difficult task because of the complexity of the stray radiation field. A good knowledge of this mixed radiation field is very important to be able to select the type of detectors (active and/or passive) to be employed for routine area monitoring and to choose the personal dosimeter legally required for estimating the effective dose received by individuals. At the same time, the response function of the detectors to the mixed field must be thoroughly understood. A proper calibration of a device, which may involve a complex series of measurements in various reference fields, is needed. Monte Carlo simulations provide a complementary—and sometimes the principal—mean of determining the response function. The ambient dose equivalent rates during operation range from a few hundreds of μ Sv per year to a few mSv per year. To measure such rates one needs detectors of high sensitivity and/or capable of integrating over long periods. The main challenges to be met by a radiation monitoring system are the capability of discriminating the various radiation types, of correctly measuring the high-energy part of the neutron energy distribution—often responsible for a large fraction of the total ambient dose equivalent—and of operating in the pulsed field sometimes encountered around high-energy accelerators. The paper first briefly reviews the most relevant techniques and then concentrates on a few devices pointing to some recent results and developments: the tissue equivalent proportional counter, the silicon-based microdosimeter, the superheated drop detector and high-pressure argon- and hydrogen-filled ionization chambers to be employed for the radiological surveillance of the Large Hadron Collider at CERN. Examples and comparisons between measurements and Monte Carlo predictions are given.