Setting up and characterizing high-energy and pulsed reference fields to ensure radiation protection at accelerator facilities in medicine and in research

High-energy, pulsed reference radiation fields (energy: up to 20 MeV; pulse duration: a few microseconds) are currently being set up. This is taking place within the scope of a departmental research project (reference number: 3619S2236) funded by the BMU/BfS (Federal Ministry for the Environment, Nature Conservation and Nuclear Safety/Federal Office for Radiation Protection). Once the project has been completed, such fields will be available for the first time to check the correct operation and determine the operation limitations of area dosemeters and personal dose equivalent meters.

There is reason to assume that dosemeters may, under certain circumstances, not provide correct measurement values at high energies, in particular in pulsed radiation fields [1,2]. Due to a lack of reference radiation fields, this range of parameters cannot be checked at present. This can be problematic, in particular for external experts using dosemeters when checking accelerators for their commissioning. There is a need for reference fields whose parameters are similar to those of radiation fields behind the shields of electron accelerators (energy: up to 20 MeV; pulse duration: a few microseconds). Such reference fields are currently being set up at PTB Braunschweig within the scope of a project funded by the BMU/BfS. Medical linacs and a research accelerator are being used for this purpose. In this way, the important parameters (photon energy and dose rate) can be varied both by the accelerators’ high voltage and by the shieldings used, thus allowing several reference fields/reference field conditions to be realized. The photon spectra to be expected and other parameters (such as the influence of scattering) are determined and optimized by means of Monte Carlo simulation. After the field has been characterized, commercially available dosemeters as well as dosemeter prototypes can be tested in this radiation field under defined conditions. It is planned that these new reference fields be integrated in the corresponding ISO standard in the long run to ensure test conditions that are also internationally harmonized in this field. The test methods still have to be developed. They will subsequently be standardized in the form of IEC standards.

This project is supported by the BfS. Its reference number is 3619S2236, and it is titled “Setting up and characterizing a reference field to ensure radiation protection at accelerator facilities in medicine and research and to test and calibrate the corresponding measuring instruments”.

Fig.: Schematic representation of the setup of some reference fields for the testing and calibration of dosemeters. A medical accelerator is used to generate beams. The PTB secondary standard is located behind a structural protective barrier. This standard is used to characterize the radiation field as well as the DUT (i.e. the dosemeter).

Literature

[1]        H. Zutz and O. Hupe, “Ambient dose and dose rate measurements in the vicinity of elekta precise accelerators for radiation therapy”, Radiation Protection Dosimetry, vol. 162, no. 4, pp. 431–437, 2014, doi: 10.1093/rpd/nct356

[2]        S. Friedrich and O. Hupe, “Testing Different Area Dosemeters Concerning Their Behaviour in Pulsed Radiation Fields”, Radiation Protection Dosimetry, vol. 182, no. 4, pp. 480–487, Jul. 2018, doi: 10.1093/rpd/ncy105

Contact

J. Busse, Department 6.3, Working Group 6.31

H. Zutz, Department 6.3, Working Group 6.31