Abstract
In this work, we present the results of the first part of a research project aimed at offering a complete response to dosimeters providers and nuclear physicists’ demands for high-energy (6 – 9 MeV) photon beams for radiation protection purposes. Classical facilities allowing the production of high-energy photonic radiation (proton accelerators, nuclear reactors) are very rare and need large investment for development and use. A novel solution is proposed, consisting in the use of a medical linear accelerator, allowing a significant decrease of all costs.Using Monte Carlo simulations (MCNP5 and PENELOPE codes), a specifically designed electron-photon conversion target allowing for obtaining a high energy photon beam (with an average energy weighted by fluence of about 6 MeV) has been built for radiation protection purposes. Due to the specific design of the target, this “realistic” radiation protection high-energy photon beam presents a uniform distribution of air kerma rate at a distance of 1 m, over a 30 × 30 cm2 surface. Two graphite cavity ionizing chambers for ionometric measurements have been built. For one of these chambers, the charge collection volume has been measured allowing for its use as a primary standard. The second ionizing chamber is used as a transfer standard; as such it has been calibrated in a 60Co beam, and in the high energy photon beam for radiation protection.The measurements with these ionizing chambers allowed for an evaluation of the air kerma rate in the LINAC based high-energy photon beam for radiation protection: the values cover a range between 36 mGy/h and 210 mGy/h, compatible with radiation protection purposes.Finally, using Monte Carlo simulations, conversion coefficients from air kerma to dose equivalent quantities have been calculated in the range between 10 keV and 22.4 MeV, for the spectral distribution of the fluence corresponding to the beam produced by the linear accelerator of the LNE-LNHB.
Highlights
Radiation protection of workers susceptible to be exposed to ionizing radiation requires the use of dosimeters type tested and calibrated in radiation fields covering all the encountered situations at one’s workplace
In the great majority of cases, a good agreement was obtained between MCNP5 and PENELOPE 2008: the difference between values obtained by the two codes is generally smaller than 0.5%
The values of the coefficients presented in these three tables are mean values of coefficients calculated by MCNP5 and by PENELOPE 2008 calculation
Summary
Radiation protection of workers susceptible to be exposed to ionizing radiation requires the use of dosimeters type tested and calibrated in radiation fields covering all the encountered situations at one’s workplace. The radiation qualities to be used for type tests and calibrations are described in the international standard series ISO 4037. In nuclear industry, dosimeters must be tested in high energy photon fields (mean energy of spectrum of 6 to 7 MeV). A LNE-LNHB project was launched in order to design, construct and characterize a high energy photon field in order to meet the dosimeters manufacturers and users needs (Project Review 2014). The international standard ISO 4037-1 [1] presents the production modes and the technical characteristics of radiation fields that are necessary for the characterization of these dosimeters for high-energy photons. There are few facilities providing high-energy photon fields for radiation protection standards and calibration purposes. The current work presents a new practical solution of setting such fields using a conventional radiotherapy linear accelerator (LINAC)
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