Thoron standard source.

Thoron (220Rn) has been identified as a possible health concern in specific places such as monazite processing plants and (rare-earth) mines. The short half-life of thoron (55.8 s) makes thoron calibration sources and thoron chambers less common than the corresponding radon (222Rn) ones. In this paper an inexpensive and straight forward but accurate thoron source is described that can easily be set up in typical nuclear environmental laboratories. The source of thoron is a solution of Th(NO3)4 in water. Thoron is extracted by bubbling air through the solution using an aerator. The gamma rays from the solution are measured at the same time. The thoron activity concentration in the exit stream follows from the reduction in the intensity of the gamma rays from the progeny of thoron over time.

Radon transfer velocity at the water-air interface.

Radon is a radionuclide that is one of the most commonly used natural tracers, for example in groundwater. The transport of radon at the water-air interface is investigated in this work at very low turbulence such as when water samples are taken for radon measurements. This very important process for the accurate measurement of radon in water has, surprisingly, not been investigated very often. By using a mathematical model and an experiment the radon transfer velocity coefficient (k) from the water-air interface was found to be (1.4±0.2)×10(-6)ms(-1). This radon transfer velocity indicates that the escape is a relatively slow process which justifies the use of radon in water measurements.

Determining the radon exhalation rate from a gold mine tailings dump by measuring the gamma radiation.

The mining activities taking place in Gauteng province, South Africa have caused millions of tons of rocks to be taken from underground to be milled and processed to extract gold. The uranium bearing tailings are placed in an estimated 250 dumps covering a total area of about 7000 ha. These tailings dumps contain considerable amounts of radium and have therefore been identified as large sources of radon. The size of these dumps make traditional radon exhalation measurements time consuming and it is difficult to get representative measurements for the whole dump. In this work radon exhalation measurements from the non-operational Kloof mine dump have been performed by measuring the gamma radiation from the dump fairly accurately over an area of more than 1 km(2). Radon exhalation from the mine dump have been inferred from this by laboratory-based and in-situ gamma measurements. Thirty four soil samples were collected at depths of 30 cm and 50 cm. The weighted average activity concentrations in the soil samples were 308 ± 7 Bq kg(-1), 255 ± 5 Bq kg(-1) and 18 ± 1 Bq kg(-1) for (238)U, (40)K and (232)Th, respectively. The MEDUSA (Multi-Element Detector for Underwater Sediment Activity) γ-ray detection system was used for field measurements. The radium concentrations were then used with soil parameters to obtain the radon flux using different approaches such as the IAEA (International Atomic Energy Agency) formula. Another technique the MEDUSA Laboratory Technique (MELT) was developed to map radon exhalation based on (1) recognising that radon exhalation does not affect (40)K and (232)Th activity concentrations and (2) that the ratio of the activity concentration of the field (MEDUSA) to the laboratory (HPGe) for (238)U and (40)K or (238)U and (232)Th will give a measure of the radon exhalation at a particular location in the dump. The average, normalised radon flux was found to be 0.12 ± 0.02 Bq m(-2) s(-1) for the mine dump.