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  • Author or Editor: N. Whitehead x
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Abstract  

A method of detecting inaccessible metallic corrosion is proposed, in which a gamma-emitting radionuclide added in aqueous solution to the contents of a pipe or vessel attaches itself selectively to corrosion products, and then may be detected from outside using a hand-held gamma detector. This was simulated in the laboratory in preliminary studies. Corrosion products studied were oxidised iron, FeS, goethite, magnetite, spinel and oxidised stainless steel.K d values were derived for various radionuclides. Of the radionuclides studied,60Co,152Eu,214Pb,214Bi and226Ra seem potentially useful, but not22Na or137Cs.

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Abstract  

It proved possible to detect the precise location of large geological faults using the amount of40K and220Rn daughter gamma-rays and the amount of222Rn (measured in a scintillation chamber) which could be extracted from the soil using negative pressure. Both40K and228Th appear to be concentrated in fault gouge. The222Rn content extractable from the soil is a measure of permeability and is very low in the region of the fault due to clay-like fault gouge. The method was demonstrated successfully on the large Wellington fault at Upper Hutt, New Zealand.

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Abstract  

Otoliths are bony structures found in the ears of fish and used in the210Pb/226Ra dating method for age determination. This paper checks the assumption that222Rn is not lost from or added to orange roughy fish otoliths by diffusion, which would invalidate the technique. The first method of monitoring diffusion relies on measuring the gamma activity of daughter radionuclides. Otoliths were exposed to an atmosphere enriched in222Rn for 10 days, and the supported gamma activity inside them measured allowing for various decay corrections. The calculated radon addition was (0.5±0.5)% of the activity of the226Ra present. The second method used an alpha spectrometer and attempted to detect222Rn directly outgased from otoliths in the detector vacuum chamber. The results were consistent within errors with those of the first method and showed no loss or gain of222Rn, supporting previous estimates of a long life-span for the orange roughy. In contrast it was found that approximately 10% of222Rn formed in orange roughy fish scales was lost to an evacuated environment, (hence perhaps to an aqueous environment) and that for this species it could be difficult to base a dating method on analysis of scales. Nevertheless a preliminary minimum age of 57 years was obtained. The methods could be used with non-biological samples to determine222Rn diffusion rates.

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Abstract  

Dating rocks using226Ra/230Th isochrons demands radiochemical purification of radium and thorium. This paper presents an improved method. Rocks are solubilised by nitric/nydrofluoric digestion followed by dissolution of insoluble fluorides by boric/nitric acids, and Th is extracted by passing the 8M nitric solution through an anion column in nitrate form. The eluant contains Ra and Ba which are precipitated as sulphate and redissolved in alkaline EDTA. Complete separation of Ba and Ra from sulphate is on an AG 1×8 anion column in EDTA form, which was found better than the chloride form. The Ba+Ra is separated on an AG 50W×8 cation column, and uses CDTA as an eluant for Ba. Careful pH control is essential. Ra elutes later with EDTA or 4M HCl and is precipitated with 125 g barium as sulphate to yield a source suitable for -spectrometry, or further treated to electroplate the Ra. The yield tracers used are228Th and224Ra. Because the sample contains natural224Ra a correction must be applied, calculated from the amount of natural232Th in the Th spectrum. Th may be precipitated with 100 g of ferric iron and gives a spectrometry-quality source, but further purification and electrodeposition was found to be preferable. Variations on the method for the case of analysis of calcium-rich fish otoliths are described.

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Abstract  

The radionuclides222Rn and220Rn are measured by incorporating their daughters214Pb and212Pb in a very thin layer of PbS and accumulating the alpha spectrum of their daughter products214Po and212Po. The median yield was measured as 88% using a known amount of210Pb tracer. A single fumarole and all 23 geothermal wells tested were found to contain220Rn. As isotopes of Th, Bi, Po and Ra, are also absorbed in the PbS layer, the method can be used for determinations of these in tap-water.

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Abstract  

A new method of227Ac determination is based on total sample decomposition, followed by preconcentration as oxalate and hydroxides, and purification from thorium isotopes and rare earths on ion-exchange columns with nitric acid. The actinium is electroplated on stainless-steel discs with near 100% yield from a water/propanol medium and measured by alpha spectrometry.225Ac is used as a yield monitor. An immediate first count gives overall tracer recovery (typically around 80%). A second count two months later gives a sensitive measure of227Ac through its decay products at 5.5–6.1 MeV. Analysis of reference samples gave satisfactory results.

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Abstract  

We give a new general method of separation of the title radionuclides, using ferric hydroxide precipitations, cation exchange chromatography followed by anion exchange for U, further cation exchange for Pa and direct elution for Th. Electrodeposition for all three elements is from sulfate medium. Yields for Pa, Th, Pa, U are mostly about 98%. Matrices analyzed include calcite, dolomite, phosphorite, sediments, organic material, and mineral fractions from rock.

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Abstract  

A new, and non-destructive method of characterising obsidians for archaeological purposes is described. Sodium, fluorine, and aluminium are determined by inelastic scattering of a beam of protons from a 3 MeV Van de Graaff accelerator. Irradiation and counting are simultaneous and take five minutes per sample, while data analysis is automated and requires about 20 sec per sample.

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Abstract  

Evidence for the presence of111Ag in Chernobyl fallout at Monaco is given. This fission radionuclide has not been previously reported in Chernobyl fallout. Peak values were as high as 1.9 Bq m–3. Arguments are presented that the observed110mAg content in the fallout originated from volatilisation of silver neutron flux monitors in the reactor rather than production by other nuclear reactions.

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