The determination of 129I in milk and vegetation using neutron activation analysis.

A new method has been developed to measure 129I in the environment with detection limits below 10 mBq/kg of vegetation and 10 mBq/l of cows' milk. The method is based on extraction of 129I from the milk or vegetation sample, onto an ion exchange resin. An inactive carrier of 127I is added to the sample before separation, to monitor losses throughout the entire procedure. The ion exchange resin is irradiated for 7.5 h in a neutron flux of 10(16) n m-2 s-1 to induce the 129I(n, gamma) 130I reaction with thermal neutrons. The 127I carrier undergoes a (n,2n) reaction with fast neutrons to produce 126I. Iodine is extracted from the ion exchange resin after irradiation with an elution scheme which removes contamination from the radionuclide 82Br, the main interference in the analysis. Finally iodine is precipitated as AgI for gamma ray analysis. The sample is counted for 3 h on a Ge semiconductor detector to measure the radionuclide 130I, which has a half life of 12.4 h and 126I, which has a half life of 13.0 days. The measured 130I activity is compared to a known standard to deduce the amount of 129I in the sample, and the concentrations are corrected for losses during processing using the measured activity of 126I. The detection limits for 129I by this method are below 10 mBq/l for milk samples and 10 mBq/kg for vegetation. In addition to routine monitoring of milk and grass samples the method has been used to measure 129I deposition on grass and soils in a field near the Sellafield plant. Results of these analyses, along with measurements of 129I in air and rainfall using the same methodology, have been used to determine deposition velocity and retention coefficients of 129I to grass.

The determination of tritium, 14C and 35S in milk and crop samples using a combustion technique.

The use of a combustion technique for the determination of low energy beta-emitting radionuclides in solid and liquid samples has been in widespread use for a number of years. However, the sensitivity of measurements by existing commercially available combustion apparatus has been limited by the amount of sample that can be combusted before incorporating the combustion products into a liquid scintillator for subsequent counting. Consequently the determination of tritium, 14C and 35S at environmental levels has not been possible using commercially available equipment. This paper describes the apparatus and method that was developed at the Central Veterinary Laboratory for the determination of these low energy beta-emitters in milk and crop samples. A typical sample size of 20-50 g is routinely measured, although the apparatus is designed to be able to make several sequential combustions before measurement of the oxidation products by liquid scintillation counting.

Intercomparison exercise on the determination of plutonium in biological material.

This paper gives the results of an intercomparison exercise on the determination of plutonium-238 in urine. The urine, containing metabolised plutonium, was analysed by 6 laboratories in the United Kingdom and 5 in France. Three solutions were provided, a high and low level solution and a blank solution comprising the diluent urine. Several different methods were used by the various laboratories and the results showed good agreement between them.

The radioactivity content of United Kingdom coal.

Twenty samples of coal representing each of the seven major regions of the National Coal Board have been analysed for their natural radioactivity content. A variety of methods have been used to verify the results, but the major technique used was radiation spectrometry of 3 kg samples. The results indicate a mean value for uranium and radium activity in British coals of 14.5 Bq/kg, for thorium 12.5 Bq/kg and for potassium 150 Bq/kg. These are significantly lower levels of actinides than have been previously reported and represent only two thirds of those previously used as source terms for assessment of the radiological impact of fossil fuel burning in the U.K.. The content of potassium in U.K. coal is twice the accepted global mean but the radiological significance of this element is negligible. A subsidiary finding is that uranium and its daughter radium are in secular radioactive equilibrium in coal within the experimental error of the analysis.

The development and application of alpha-particle spectrometry for low-level-radioactivity measurements in biological and environmental materials.

The design, construction and use of a purpose-built alpha-particle spectrometer is presented. The application of the spectrometer in the determination of low levels of radioactivity in biological and environmental materials is also discussed.

The uptake by man of cadmium ingested in crab meat.

Seven male volunteers with normal iron stores ate the brown meat from crabs whose diet had contained radioactive cadmium-115m. Systemic uptake of cadmium by the volunteers, derived from measurements of their residual body radioactivity several weeks after intake, averaged 2.7 +/- 0.9 (se)%, essentially as found by others in studies with extrinsically labelled food.