A very limited number of field experiments have been performed to assess the relative radiation detection sensitivities of commercially available equipment used to detect radioactive sources in recycled metal scrap. Such experiments require the cooperation and commitment of considerable resources on the part of vendors of the radiation detection systems and the cooperation of a steel mill or scrap processing facility. The results will unavoidably be specific to the equipment tested at the time, the characteristics of the scrap metal involved in the tests, and to the specific configurations of the scrap containers. Given these limitations, the use of computer simulation for this purpose would be a desirable alternative. With this in mind, this study sought to determine whether Monte Carlo simulation of photon flux energy distributions resulting from a radiation source in metal scrap would be realistic. In the present work, experimental and simulated photon flux energy distributions in the outer part of a truck due to the presence of embedded radioactive sources in the scrap metal load are compared. The experimental photon fluxes are deduced by in situ gamma spectrometry measurements with portable Ge detector and the calculated ones by Monte Carlo simulations with the MCNP code. The good agreement between simulated and measured photon flux energy distributions indicate that the results obtained by the Monte Carlo simulations are realistic.
Indoor radon concentrations were measured in 77 schools of the prefecture of Xanthi in northern Greece. The arithmetic mean radon concentration is 231 Bq m(-3) with a range between 45 and 958 Bq m(-3). Thirty five schools have mean radon concentration above 200 Bq m(-3) and nine schools have mean radon concentration above 400 Bq m(-3). From continuous radon gas measurements in the school with a relative higher radon concentration (958 Bq m(-3)) was deduced the 'true' radon concentration, defined as the radon concentration in the school during the hours of the presence of teachers and scholars. The mean 'true' radon concentration for a time period of about 2 weeks was 104 Bq m(-3). The mean radon concentration for the same 2 weeks was seven times higher (700 Bq m(-3)). Greek and International regulations for radon in workplaces refer to only the mean annual radon concentration. It would be preferable for schools to replace the mean annual radon concentration with the 'true' radon concentration.
The profile of (137)Cs present in undisturbed soil due to the Chernobyl accident was measured repeatedly for approximately 20 y. The vertical migration of (137)Cs in soil is a very slow process. The mean vertical migration velocity is estimated at approximately 0.1-0.2 cm y(-1). A method based on in situ gamma spectrometry measurements and Monte Carlo computations, aimed at estimating the profile of (137)Cs without performing any soil sampling, is investigated.
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