Abstract
Personal dosimetry for underground workers mainly concerns measurement of the concentration of radon (and its daughters) and the correct application of the data in dose calculation, using a biokinetic model for lung dosimetry. A conservative approach for estimating the potential dose in caves (or underground) is based on solid state alpha track detector measurements. The obtained dataset is converted into an annual effective dose in agreement with the ICRP recommendations using the “cave factor”, the value of which depends on the spectrum of aerosol particles, or on the proportional representation of the unattached and the attached fraction and on the equilibrium factor. The main difference between apartments and caves is the absence of aerosol sources, high humidity, low ventilation rate and the uneven surface in caves. A more precisely determined dose value would have a significant impact on radon remedies or on restricting the time workers stay underground. In order to determine how the effective dose is calculated, it is necessary to divide these areas into distinct categories by the following measuring procedures: continual radon measurement (to capture the differences in EERC between working hours and night-time, and also between daily and seasonal radon concentration variations); regular measurements of radon and its daughters to estimate the equilibrium factor and the presence of 218Po; regular indoor air flow measurements to study the location of the radon supply and its transfer among individual areas of the cave; natural radioactive element content evaluation in subsoils and in water inside/outside, a study of the radon sources in the cave; aerosol particle-size spectrum measurements to determine the free fraction; monitoring the behaviour of guides and workers to record the actual time spent in the cave, in relation to the continuously monitored levels of Rn concentration.
Highlights
One of the more interesting type of underground spaces, in terms of personal dosimetry, are karst caves, which are found in regions with exceptionally high radon concentrations, due to minimal airflow and negligible air exchange
The new approach presumes that the entire effective dose that a person receives from radon daughters should be calculated as the sum of all effective doses obtained from the individual sizes of the aerosols, using the following assumptions: only 222Rn and its daughters occur in the caves (if this assumption is incorrect, it would be difficult to determine the conversion factors between the exposure to products of radon decay (WLM) a EERC, because the radon daughters are differentiated by their latency energy); the mutual ratio of radon daughters and the equilibrium factor and the spectrum of aerosols in a given place is constant [2]
The enhancement of personal dosimetry for underground work places includes a study of the given questions from three main points of view: 1. A classification of underground areas, and of the main characteristics and differences that have an influence on individual irradiation from radon and on measuring the concentration of radon and radon daughters
Summary
One of the more interesting type of underground spaces, in terms of personal dosimetry, are karst caves, which are found in regions with exceptionally high radon concentrations, (despite the very low uranium content in limestone) due to minimal airflow and negligible air exchange. Exact effective dose estimation is required, in view of the potential health hazards caused by inhaling radon and its daughters, in order to categorize such unsafe work areas In this respect, the main differences between apartments and caves is the absence of aerosol sources All of the obtained data was used for a discussion of the location-related value of “cave factor” and for effective dose calculation
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