Solid thoron source preparation in a porous mineral matrix.

Thoron and progeny are decay products of (232)Th with a great impact on human health. The release of thoron gas from the mining and milling of thorite, monazite and other major thorium ores has been recognised as a potential radiological health hazard. For precise measurements, calibration is a very important factor. This paper describes a cheap and easy way of producing a stable thoron source made of thorium nitrate packed in a porous clay mineral matrix used as (220)Rn generator. The source should have a small spherical shape and be fired at 600°C; this will lead to a great pore volume, necessary for the thoron gas. High importance should be given to the water uptake. The exhalation power of (220)Rn was measured using a Lucas scintillation cell. Experimental efficiency values obtained ranged between 0.16 and 1.44 %.

Determination of the specific alpha activity of thick sources with a large area ZnS(Ag) scintillation detector.

A method for determining the specific alpha activity of thick sources using a large area ZnS(Ag) scintillation detector is presented. In this method a quadratic relationship between the detector response and window thickness is assumed. This method provides a quick estimation of alpha activity in the sample, so it is an indicative method. The aim of this experimental work is to approve theoretical assumption and to develop a standard routine method for absolute alpha measurements of thick contaminated environmental sources. For this purpose reference material U(3)O(8) and spiked standards of soil were used. Measurements of contaminated soil samples from south Serbia showed the practical application of this method.

Investigation in thorium phosphate by NMR II-phosphorus dipolar networks.

With through space and through bond experiments in two-dimensional NMR we analyze the transformation from the thorium phosphate-hydrogen phosphate hydrate (TPHPH) to the beta form of the thorium phosphate diphosphate (beta-TPD) in relation with the phosphorus networks. These techniques are complementary: the through space coupling gives an insight on the dipolar phosphorus networks while the through bond coupling is particularly efficient in the detection of the P2O7 groups. With these experiments we show that in a first step, by heating the precursor TPHPH above 250 degrees C, it transforms into an alpha form of TPD. This transformation is due to the complete condensation of hydrogen phosphate groups HPO4 into P2O7 entities. By heating alpha-TPD above 950 degrees C it transforms into its well-known beta form. The alpha form is characterized by a hygroscopic behavior: some water molecules are present near the P2O7 groups that makes non-equivalent their phosphorus nuclei. PO4 dipolar networks are always present in the alpha form. The main effect of these PO4 and P2O7 units is to give the system a channel structure and the water enters in them.

Analysis of thorium and its progeny by gamma ray spectrometry and alpha track methods.

Samples originating from an EU sponsored intercomparison exercise were analysed by gamma ray spectrometry (a thorium solution sample, a zircon sand sample and a thorium ore sample). An alpha track method was also used to analyse the solution sample. The detection efficiency calibration for the gamma ray spectrometry measurements on the solid samples was established using an in-house standard of thorium nitrate. A GESPECOR Monte Carlo simulation program was utilised in the analysis of the solution sample. The in-house thorium nitrate standard was also used to prepare standards for the alpha track method. The relative differences between the 232Th activity concentration values determined in these intercomparison samples and values supplied by the NPL, UK, were found to be less than 5% when determined by the gamma ray spectrometry method and less than 8% when determined by the alpha track method.