Radiation protection for particle accelerators: new testing option for dosimeters

A medical linear accelerator is aimed at a concrete wall. The radiation field penetrates the wall and is attenuated. Source: PTB

Modern particle accelerators that generate high-energy pulsed X-rays are increasingly being used in tumour therapy as well as in science and technology. This expands the opportunities in medicine and research but also represents a challenge in terms of radiation protection. Namely, although the radiation dose for people operating the devices can be monitored using "passive personal dosimeters", there is still only limited scope for supplementary monitoring using directly readable electronic measuring devices, as is standard practice in other radiation applications.

The pulsed X-ray radiation from accelerator systems is made up of many individual radiation pulses, each of which is extremely intense but only lasts about a millionth of a second. Conventional electronic personal dosimeters cannot detect this radiation correctly, and there is no facility where measuring devices of this kind can be tested according to recognised standards. To fill this gap and enable the testing and development of suitable measuring devices, the Federal Office for Radiation Protection (BfS) has commissioned the Physikalisch-Technische Bundesanstalt (PTB), the National Metrology Institute of Germany, to develop what is known as a reference field.

On the other side of the wall, the radiation field emerges from the wall in the area marked in yellow. The reference measuring instrument is mounted on a sliding track, and the distance from the wall can be varied. Source: PTB

Special test setup at PTB

In a reference field, measuring devices can be specifically exposed to radiation of known intensity and other properties. This approach allows testers to determine a device's basic suitability for an area of application and its measurement accuracy.

For this purpose, PTB has set up a specific experimental design at one of its medical particle accelerators in Braunschweig. With this setup, it is possible to generate radiation such as that occurring outside the irradiation field of an accelerator or in adjacent rooms in spite of shielding. The resulting radiation field was measured precisely, and a flexible measuring station was set up at which electronic personal dosimeters and hand-held measuring devices could be tested to see how well they respond to high-energy pulsed X-rays.

Electronic personal dosimeters

Contribution to the further development of radiation protection

The BfS supports the Federal Environment Ministry (BMUV) in ensuring and further developing comprehensive radiation protection in research, technology and medicine. The establishment of a reference field provides an important basis for the development and testing of electronic personal dosimeters and hand-held measuring devices that can be used on accelerator systems. In the future, this should contribute to better radiation protection for personnel and to the simplification and quality assurance of technical inspections of such systems by experts.

The project's final report can be found in the BfS's Digital Online Repository and Information System (DORIS) at http://nbn-resolving.de/urn:nbn:de:0221-2024040842847. The reference field can be used at PTB by research and development for a fee. Further information is available from PTB.