Agata Grygier

Radon (²²²Rn) is a naturally occurring radioactive noble gas that is a major source of ionising radiation in the environment. Many measurement techniques can be used to monitor ²²²Rn concentrations in the workplace. The main purpose of conducting such measurements is to identify locations of exposure, determine the effective dose for workers and, if necessary, define actions for reducing the exposure. As part of this study, a series of measurements were conducted in the underground tourist route at Książ Castle in Poland. The route has been open to visitors since late 2018. The measurements included long- and short-term tests. Passive and active methods were used to measure the ²²²Rn activity concentration. Additionally, the potential alpha energy concentration and ambient and radioactive aerosol size distributions were measured. Finally, the annual effective dose for workers was estimated. The dose was calculated while factoring in the legal regulations in the Czech Republic and Poland to demonstrate their effect on the final results. The obtained values were low—they did not exceed 0.218 mSv (for the specified exposure time)—indicating the effectiveness of natural ventilation and a low radiation risk to personnel.

This paper presents the results of a two-year radon risk study conducted at the Historic Silver Mine in Tarnowskie Góry. During this period, continuous measurements of radon activity concentration were carried out in three-month cycles at 30 points distributed along the tourist route. The average radon activity concentration was 1160 Bq/m³ for the first year of measurements and 1210 Bq/m³ in the second year. Based on the collected data, seasonal correction factors considering seasonal variations in radon activity concentration (SCF) were determined. The obtained factors are in the range of 0.8–1.4. In addition, the spatial variation of radon activity concentration was studied at selected locations of the mine at different heights of the location of the detectors and their distribution on opposite sides of the excavation. Based on the collected data, effective doses were calculated. Assuming annual working time of 300 h, which was specified for workers, the average annual dose is 0.6 and 1.3 mSv for the conversion factor of 1.4 mSv/(mJ/m³⋅h) indicated in Polish law and 3.1 mSv/(mJ/m³⋅h) as recommended in the ICRP report no 137 for underground mines respectively. For the annual working time of 1800 h, the corresponding doses would be 3.4 mSv and 7.4 mSv.

The equilibrium factor F is one of the parameters that should be considered when assessing the effective dose based on radon activity concentration. Since the equilibrium factor in various environments ranges theoretically from a value close to 0 to 1, it is expected that dose assessment based on one recommended coefficient value may lead to an underestimation or overestimation of the dose. That is why it is essential to measure this quantity if the basis for dose assessment is the radon concentration and not the concentration of radon decay products. The equilibrium factors were determined based on measurements of radon activity concentration and potential alpha energy concentration and varied from 0.15 to 0.94, with an arithmetic mean of 0.55. The average effective dose calculated for the employee taking into account these values was 31 mSv, assuming an annual working time of 1800 h. In turn, the average effective dose calculated for the equilibrium factor of 0.2 as recommended by the International Commission on Radiological Protection (ICRP) was equal to 13 mSv.

This paper compares the results of measurements taken in the underground workings of active and tourist mines. In these facilities, the aerosol size distributions of ambient aerosols at key workplaces and the distributions of radioactive aerosols containing radon decay products were determined. Based on these studies, dose conversions used for dose assessment and unattached fractions were determined. In addition, radon activity concentrations and potential alpha energy concentrations of short-lived progeny were also measured in the mines to determine the equilibrium factor. The dose conversions varied between 2–7 mSv/(mJ × h × m⁻³). The unattached fraction measured in active coal mines ranged from 0.01–0.23, in tourist mines from 0.09–0.44, and in the tourist cave it was 0.43. The results showed significant discrepancies between the effective doses determined from current recommendations and legal regulations and those determined from direct measurements of parameters affecting exposure.

The objective of this work was to perform a series of measurements of radon and thoron exhalation in the underground workings of an experimental coal mine. In the years 2012–2015, experiments on underground coal gasification were carried out in a coal mine, which caused, among other effects, damage to rock mass. Afterward, periodic increases in the concentration of potential alpha energy (PAEC) of radon decay products in the air were found, which could pose a hazard to miners. The question posed was whether the gasification experiment resulted in the increased migration of radon and thoron. If so, did it increase the radiation hazard to miners? The adaptation of the existing instrumentation to the specific conditions was conducted, and a series of measurements were made. It was found that the measured values of radon and thoron exhalation rates ranged from 3.0 up to 38 Bq·m⁻²·h⁻¹ for radon and from 500 up to 2000 Bq·m⁻²·h⁻¹ for thoron.

Many laboratories around the world work on the issue of protection against ionising radiation. It is a very broad topic, covering both the protection of members of the public and workers exposed to ionising radiation, based on personal or environmental monitoring. Thermoluminescence detectors are commonly used for this purpose, which is accepted in most countries. The entire process of dose evaluation with such dosimeters can be divided into several steps. Undoubtedly, one of the most important steps is the calibration procedure. The calibration should be performed in conditions as similar as possible to those experienced during the exposure. Moreover, the calibration is performed using only the Cs-137 source. This article presents results of Panasonic UD-802 irradiation dosimeters in different radiation fields generated by Cs-137, Kr-85, Sr-90/Y-90 and an x-ray tube, series N, and at different angles such as 0°, 30°, 60°, 90°. On the basis of the obtained results, the calibration coefficients and correction factors were determined in relation to calibration based on Cs-137 or Sr-90/Y-90 irradiated at 0°.