Neutron Activation Γ-spectrometry Research Articles

Determination of traces of rare earth elements in high-purity uranium by ion-exchange separation and neutron activation γ-spectrometry

Neutron activation γ-spectrometry is sufficiently sensitive for the determination of traces of rare earth elements but quantitative separation from uranium is essential. The rare earth elements in 0.2 M ammonium carbonate medium are quantitatively retained on Chelex-100, and are quantitatively separated from uranium by recycling the eluate. When 10-g samples are used, neutron activation provides detection limits of 1–20 μg kg −1. Recoveries of rare earths, checked by spiking with radiotracers, are essentially complete.

Preconcentration and speciation of chromium in waters by coprecipitation with lead salts and neutron activation—γ-spectrometry

Chromium species are preconcentrated from water samples by coprecipitation with lead salts and measured in situ after neutron activation. Both chromium(III) and chromium(VI) are coprecipitated with lead phosphate. If only chromium(VI) is collected in a separate sample with lead sulfuate, the individual species can be quantified. The 320-1-keV γ-ray peak of 51Cr ( t 1 2 = 27.7 d) is used for measurement. The procedure has a detection limit of 0.1 μg l −1 for chromium in sea water when 800-ml samples are used.

Determination of gold in natural waters by neutron activationγ-spectrometry preconcentration on active charcoal

A method for the determination of gold at very low levels in waters is presented. The method involves batchwise pre-concentration of gold from 1 l of water at pH 3–4 onto 0.1 g of activated charcoal by shaking 5 min and subsequent treatment of the activated charcoal by instrumental neutron activationγ-spectrometry. Activated charcoal quantitatively adsorbs ionic and colloidal gold from solutions prepared with distilled water and also from natural surface waters spiked and equilibrated with these two forms of gold. Three ion-exchange resins were evaluated for pre-concentration purposes; ionic gold removal was quantitative but colloidal gold removal was incomplete. Electrodeposition at a carbon fibre electrode gave similar results. The charcoal pre-concentration technique was tested on solution containing 198Au tracer and a total concentration of 1 μg l −1. The limit of detection of total gold (ionic and colloidal) for the carbon adsorption/neutron activationγ-spectrometry procedure is 0.3 ng l −1. The method was used to determine gold in surface waters from auriferous regions.

Determination of gold in silicate rocks and ores by coprecipitation with tellurium and neutron activation—γ-spectrometry

The method described for determining ultra-trace levels of gold in geological materials and water samples involves the coprecipitation of gold with elemental tellurium followed by neutron activation of the precipitate. Gold-198 is measured, with detection and determination limits of 0.7 and 2.3 ng Au g −1, respectively. The main interferences in the γ-spectrum are due to tellurium, iodine, and bromine, all of which were significantly reduced by evaporation without the loss of gold. The method also collects palladium and rhodium quantitatively.

Wavelength-dispersive x-ray fluorescence spectrometry of lanthanum and cerium in nodular cast iron

Cerium and lanthanum can be determined in cast iron samples by wavelength-dispersive x-ray fluorescence spectrometry (x.r.f.). Excitation and detection conditions are evaluated, as is the required degree of surface finish of the castings. Standard samples for x.r.f. were obtained by careful determination of the cerium and lanthanum contents of specimen cast iron samples by neutron activation—γ-spectrometry. The calibration graphs obtained with these reference samples and tungsten tube excitation were linear for the ranges 3—30 mg kg −1 lanthanum and 3–60 mg kg −1 cerium. The relativ standard deviations of the determinations, for 400-s counting tims, ranged from 15% for samples containing 4 mg kt −1 La to 4% for samples containing 30 mg kg −1. For cerium, the corresponding numbers were 15% for 3 mg kg −1 and 2% for 60 mg kg −1. For unknown samples, the results obtained with these calibration graphs agreed within 3% with the neutron activation results.

Extraction of gold and mercury from sea water with bismuth diethyldithiocarbamate prior to neutron activation—γ-spectrometry

Gold and mercury in sea water can be selectively extracted by bismuth diethyldithiocarbamate into chloroform at pH ⩽1. The matrix species and many other trace elements in the system are effectively removed during extraction. When neutron activation—γ-spectrometry is used, the detection limits for gold and mercury are 0.001 and 0.01 μg 1 −1, respectively. The relative precision is 9% for gold and 13% for mercury.

Collection of trace metals from sea water by column electrolysis for neutron activation—γ-spectrometry

Electrolysis on a carbon-fiber column electrode is evaluated for the collection of trace metals from sea water as a preliminary step to the simultaneous determination of the metals by neutron activation/γ-spectrometry. The sea-water sample is passed through the carbon-fiber column to which is applied a suitable negative potential. After the electrolysis, the carbon fiber electrode is removed and irradiated in a nuclear reactor, and the induced radioactivity is measured. The effects of the pH of the sample solution on electrolysis are described. Results are reported for gold, cadmium, copper, molybdenum, uranium and zinc. The collection efficiency for uranium and chromium by electrolysis is improved by increasing the pH of the sea-water sample.

Determination of arsenic and antimony in niobium by radiochemical neutron activation—γ-spectrometry

A method for the determination of arsenic and antimony in niobium, with simultaneous determinations of Au, Cu and Mo, is described. The samples are irradiated for 12 h in a thermal neutron flux of 8 × 10 13 n cm -2 s -1 and then dissolved in hydrofluoric —nitric acid. After addition of various masking agents, and reduction with potassium iodide, As(III) and Sb(III) are extracted with diethylammoniumdiethyldithiocarbamate in chloroform. Before reduction, Au, Cu and Mo can be extracted as dithiocarbamates and determined. For samples of about 100 mg, the limits of detection are 10 pg g -1 for As, 20 pg g -1 for Sb, 0.8 pg g -1 for Au, 10 pg g -1 for Cu and 25 ng g -1 for Mo. Results are given for niobium samples of different grades of purity.

Determination of arsenic and antimony in geological materials and natural waters by coprecipitation with selenium and neutron activation—γ-spectrometry

A simple, quantitative method for collecting arsenic and antimony from the digests of geological materials and from salt and fresh waters is described. The procedure involves the addition of selenium(IV) to an acidified sample followed by precipitation of selenium by tin(II) chloride. The precipitate is collected, dried, and irradiated. Arsenic and antimony are quantified directly from the activities of 76As and 122Sb, respectively. The method has detection limits of 9 ng As and 12 ng Sb per gram of rock or 500 g of water, and has been applied to eight new reference standards from the U.S. Geological Survey. Gold is quantitatively collected by the same procedure.