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Abstract  

Studies on the behavior of 129I in the environment are greatly enhanced when the concentration of the radioiodine can be related to stable 127I. The background ratios of 129I/127I of 10-10 and lower, found in uncontaminated areas, are best measured using accelerator mass spectrometry. However, there are many examples of studies where ratios higher than 10-8 have been measured, even in places located remotely from nuclear reprocessing activities. In the vicinity of reprocessing plants it is possible to find ratios between 100 and 10-7, which can be detected easily using neutron activation analysis (NAA). Stable iodine is readily determined at concentrations below 1 mg/kg in environmental materials with instrumental NAA and radiochemical techniques can be used to measure 129I to below mBq concentrations. Therefore, where there are elevated concentrations of 129I it is possible to use a combination of neutron activation techniques to determine 129I/127I ratios. This paper describes how NAA is used to measure 129I/127I ratios in milk, vegetation, and atmospheric samples. Instrumental NAA is used to measure both 129I and 127I where the ratio is between 100 and 10-3. A radiochemical procedure is used to measure 129I at ratios between 10-3 and 10-7, with a thermal neutron flux of 1016 m-2·s-1.

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Abstract  

Recycling of wastepaper has been shown to increase the concentration of metals in the product. Although it is generally assumed that there is no risk of migration of chemical contaminants from recycled paper and board into food, the UK Food Standards Agency has identified limited evidence of such migration. Therefore, it is important to carry out research to establish the concentration of metals in recycled paper and board in contact with food. A previous study at Imperial College had resulted in the development of a neutron activation analysis method to determine trace metals in plastic packaging. This paper describes an initial study to establish whether the same methodology could be applied to paper and board and to carry out a preliminary investigation into a small range of recycled paper and board products. The study was made on 22 elements in 17 products including pizza boxes, fries boxes, kitchen towel, table napkins, greaseproof paper, tea bags and cake cases. This work has shown elevated levels of some elements including barium (69 mg/kg in pizza bases) and chromium (5 mg/kg in napkins, 50 mg/kg in greaseproof paper, 2 mg/kg in cake cases, 90 mg/kg in baking parchment, 5 mg/kg in fries boxes and 5 mg/kg in pizza bases).

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Abstract  

The value of boron, in addition to cadmium, as a thermal neutron filter for the epithermal neutron activation of short-lived radionuclides is shown to depend on sample matrix. Activation ratios of fifty nuclides are measured and the improvement in sensitivity is calculated for geological and biological matrices. The addition of boron, in the case of geological samples where the major interference is Al, improved detection for only F, Y, Sn, Ba, Er, W and Pt. In biological samples where Na is a problem the detection limits for F, Br, Rb, Y, Mo, Pd, Sn, Sb, I, Ba, Nd, Sm, Gd, Er, Hf, W, Re, Pt, Au, Th and U are all theoretically improved.

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Abstract  

The cadmium ratios of 52 short-lived nuclides have been measured. Epithermal neutron irradiation reduces the activities of20F,27Mg,28Al,38Cl,49Ca,46mSc,51Ti,56Mn and66Cu by factors of 20–30. The calculated improvements in detection limits for Ga, Br, Rb, Y, Mo, Rh, Pd, Ag, In, Sn, Sb, I, Ba, Nd, Sm, Gd, Dy, Er, Yb, Hf, W, Re, Pt, Au, Th and U are in the range 1–6. Hafnium was measured in USGS rocks: AGV-1 (4.9 μg g−1), G-2 (7.5 μg g−1) and GSP-1 (14.7 μg g−1) and IAEA standards: SOIL-5 (6.3 μg g−1 and SL-1 (4.6 μg g−1). CCRMP reference concentrates PTC and PTM were analysed for rhodium (1.1 and 0.75 μg g−1, respectively) and silver (69 and 5.8 μg g−1, respectively).

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Abstract  

The detection limit and precision of the determination of a short-lived nuclide by neutron activation analysis are improved by a factor of n1/2 when the gamma-ray spectra of n replicates are added together. This improvement was demonstrated for the measurement of rhodium and silver in two reference sulphide concentrates, by adding 20 replicates (total weight: 10 g). The resulting improvement of 4.5 lowered the detection limit for both rhodium and silver to 0.2 μg/g of sample. The method was applied to the analysis of pyroxenite, sulphide and granite samples from the Bushveld Complex, S. Africa.

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Abstract  

The improvement of detection limits for trace elements in geological samples by epithermal neutron activation analysis is examined. The relative merits of cadmium, boron and composite cadmium+boron filters are compared for trace elements Ni, As, Pd, Cd, Sb, W, Ir, Pt and Au, and interfering elements Na, K, Sc, Cr, Fe, Co and Cu. A boron filter gives optimum sensitivity for the trace elements based on interference from46Sc, but the detection limits are only improved 2–5 times. Ma imum possible improvement, which is shown by Ni, gives sensitivities 5 times better under cadmium and 15 times under boron.

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Abstract  

Cumulative neutron activation is used to determine mg/kg concentrations of gold in rock samples, weighing 10 g. Twenty 0.5 g replicates are irradiated in an epithermal-neutron flux for 5 s and counted for 14 s. The twenty spectra are summed, and gold is measured with the 279 keV gamma-ray of197mAu (7.2 s). Total analysis time for a 10 g sample is 400 s and detection limits around 2 mg/kg are achieved in gold ores, sulfides and silicates.

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Abstract  

Density metering instruments, based on the attenuation of gamma-rays, are used for non-intrusive monitoring of fluids, solids and gases. Applications include thickness gauging, fluid level indicators and determining the composition of two phase systems. This paper describes a study to investigate how the technology can be developed for environmental monitoring and control. Environmental pollutants, Zn and Pb, were selected for the initial study. A 3.7 GBq241 Am source was used to measure the sensitivity of the technique at 17, 20, 26 and 59.5 keV with a Ge planar semiconductor detector for optimum resolution of the photon energies. The optimum thickness for measurements using these four energies was 4 cm. The equipment was calibrated with a 2000 mg/l solution of zinc chloride and a 1000 mg/l solution of lead nitrate. A series of lower concentration solutions were measured to test the accuracy of the method, and demonstrated agreement with the actual concentrations within statistics. The sensitivity of the equipment was 100 mg/l for zinc and 50 mg/l for lead. The limitation to accuracy and precision was the stability of the counting equipment and theoretical detection limits of around 20–50 mg/l should be achieved if the stability of the electronics is improved.

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Abstract  

A rapid neutron activation method was developed to determine very low levels of uranium (gl–1) in groundwater from the Palmyrides region, Central Syria. The239U -ray at 74.7 keV energy was used in the measurements. Results of this technique were compared against the conventional neutron activation analysis (INAA) with239Np and the laser-induced fluoremetry (LIF). In general, the three data sets showed a very good agreement. The described method provides good accuracy, precision and low detection limit, particularly when the total dissolved solids (TDS) of the samples is low.

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Abstract  

A new radiotracer method has been developed to measure the migration of trace elements from food contact packaging into four standard food simulants; acetic acid, ethanol, olive oil, deionised water. A sample of material is irradiated in a thermal neutron flux of 1016n·m–2·s–1 to activate the trace elements and produce a range of radionuclides. The sample is then placed in the food simulant and the migration of the radionuclides is monitored by performing -ray spectrometry on a sample of the simulant. Any radionuclides measured must be due entirely to the migration of the elements present in the plastic, since the simulant itself is not radioactive. Preliminary studies have shown that detection limits of around 0.2g·dm–2 (0.002 mg/kg) can be achieved for antimony in a sample of polyethylene terephthalate. This method can now been extended to measure migration into real foods. This will highlight any differences between the standard simulants currently used and real foods. Since the method only involves irradiation of the packaging material, any food matrix can be studied.

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