The importance of natural radiation has gained a large concern all over the world from the viewpoint of radiation protection. In this paper, the Hungarian studies in the environmental radioactivity are summarized, including external gamma dose rate measurements, radon surveys, dose contribution of building materials with high concentration of radioisotopes and water investigations in aspect of natural radioactivity.
The concept of exemption has been widely used in radiological protection. It is part of the regulator's arsenal for applying legislative requirements in a graded fashion, to avoid the expenditure of effort on situations where the return in terms of improvement in protection would otherwise be trivial. Nevertheless, it still remains a controversial matter. Perhaps somewhat surprisingly, it is not so much the dosimetric criteria for exemption that cause debate; it is more the way in which the concept is used; the scenarios employed to calculate derived activity concentrations, and its relationship to the somewhat analogous concept of exclusion. Much of the debate regarding the use of the concept and its relationship with exclusion finds its origin in the national legislative culture that has developed over the years in various countries and the inevitable resistance to keep pace with the evolution of the system of radiological protection as recommended by the International Commission on Radiological Protection and implemented through the International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources. A particular problem has been the full integration into the legislative system of protection of exposures to radiation from sources of natural origin and the degree to which exemption is a relevant concept for dealing with such situations. The purpose of this paper is to attempt to provide some clarity on the two concepts and their practical implementation with a view to encouraging international harmonization and avoiding further unnecessary debate.
Neutron dose to radiotherapy patients treated with 10MV x-ray beams was evaluated based on the spectrometry of incident photoneutrons. Neutron energy spectra could be obtained by unfolding measured responses of neutron capture rates of indium activation foils in a polyethylene phantom with response functions calculated by Monte Carlo simulation. Unfolded neutron spectra inside and outside the x-ray beam indicated that photoneutrons distributed in the energy region of less than 1MeV with the maximum fluence per unit lethargy at around 0.1MeV. Effective dose to the patient was adopted as a fundamental protection quantity since photoneutrons from the accelerator head were found to enter the whole body of the patient with approximately flat intensity. Outside the X-ray beam, the dose was evaluated to be 59μSv/photon Gy from the neutron energy fluence to the effective dose conversion-coefficients tabulated by the ICRP for anterior-posterior irradiation geometry. Since total effective dose received by the patient during the treatment period corresponding to an integral photon dose of 60Gy was estimated to be as small as 3.5mSv, no additional shield would be required for contaminant photoneutrons generated by 10MV therapeutic x-rays.