Preparatory investigations of fast separation for heavy ion reaction products

A method for separation and chemical identification of products formed in nuclear reactions or nuclear decay is to slow down the recoil products in a gas and to transport them to a trap, where a detecting system is arranged. The sources for the recoil products are²⁵²Cf and²²⁴Ra. As transport phase we used nitrogen or argon and added chemical reagents such as methyl and ethyl radicals, chlorine, oxygen, carbon monoxide or methane. The chemical additives lead to selective and fast separation of certain elements. As examples the results of two experiments are presented:²²⁴Ra with ethyl radicals, and²⁵²Cf with chlorine-oxygen-nitrogen mixtures. The registration of the recoil products at the trap was measured as a function of temperature, pressure and composition of the reactive gas.     

Specific activities of radioactive elements from fission product mixtures

Specific activities of radioactive elements at the time of chemical separation from fission product mixtures produced by thermal neutron fission of²³⁵U were computed byBateman's and other equations on an electronic computer. Computations were made for two fission times: fission was assumed to be complete in a few minutes in one case, and over a period of a year in the other case. It was also assumed that each element was separated instantly after allowing the fission products to decay for 1∼10 000 000 hrs (1 140 years). The computations were applied to 12 important elements: Ru, Zr, Nb, Cs, Sr, Pm, Tc, Ba, La, Ce, Kr and Y. Results are given as a diagram for each element. The diagrams are intended to be helpful in the chemical processing of a large quantity of fission products, and industrial or tracer application of these elements.     

Determination of radioisotopes of Ce,Eu, Pu,Am and Cm in low-level-wastes from power reactors

Long-lived isotopes of lanthanides and actinides are very important for the disposal of low-level radioactive wastes. These nuclides serve for risk calculations of accidents. Their determination requires radiochemical separation from high activity main nuclides. Supervision of waste vessels is done by direct non-destructive -spectrometry of the key nuclides:⁶⁰Co for corrosion products and¹³⁷Cs as for fission products as for transuranic elements. The activity ratios of the long-lived nuclides to the key nuclides are called scaling factors. They have to be determined radiochemically in the laboratory in representative samples of each waste type. They are used for activity calculations of long-lived nuclides in the waste vessels. The scaling factors determined are of the order of magnitude of 10^–6 and due to the fact that we have used low-level measurement techniques, we could performe the necessary chemical separations in a laboratory not exceeding the 10-fold free-level limit.     

Verbundverfahren zur Multielement-Spurenbestimmung in hochreinem Chrom nach Spuren—Matrix-Trennung

(Simultaneous determination of trace elements in high-purity chromium by inductively-coupled plasma/atomic emission spectrometry after matrix separation.) The production of high-purity metals requires routine determinations of elements in the ng g^?1 range. Procedures based on wet chemical separation of matrix and trace elements followed by inductively-coupled plasma/atomic emission spectrometry are suitable. The separation of 19 trace metals (Be, Bi, Ca, Cd, Co, Cu, Fe, La, Mg, Mn, Nb, Ni, Pb, Ta, Ti, Th, U, Zn and Zr) from high-purity chromium powder is described. The powder is dissolved in hydrochloric acid and oxidized with perchloric acid or alkaline hydrogen peroxide, and the trace elements are precipitated at pH 11–13 and collected on cellulose loaded with indium hydroxide or on cellulose-Hyphan. The detection limits of the total procedure vary from 10 ng g^?1 for cadmium to 600 ng g^?1 for zinc.     

Characterization of solar grade silicon by Neutron Activation Analysis

An analytical method using neutron activation was developed in order to orientate and check different silicon elaboration processes either as solid ingots or ribbon shaped. This method without chemical separation after irradiation implies the use of a high efficiency semiconductor detector. A particular attention was paid to different causes of error and to the detection limits really obtained. These limits range from 10⁹ to 10¹⁵ at.cm^–3 for about 30 elements systematically locked for after a 72-h irradiation.     

Radiochemical neutron activation analysis of trace impurities in high purity aluminum

Rapid radiochemical neutron activation analysis (RNAA) procedures were developed and employed for the determination of 32 trace impurities in high purity aluminum thin foils. Anion exchange column chromatography was developed for the sequential group chemical separation of various elements which helped in reducing the spectral interferences and improving the sensitivity of the method. The procedure is simple and requires a very short time to separate the elements in three groups for radiometric assay. To determine very low contents of uranium and thorium,²³⁹Np and²³³Pa as activation products were separated using anion exchange and coprecipitation methods. The impurity contents were found to be low, therefore, their adverse effects on microelectronic devices would be negligible. Our data could partially be compared with the data reported in literature.     

Procedures for a fast separation of berkelium from complex mixtures of reaction products

Two procedures are described for fast separations of berkelium from complex mixtures of reaction products arising from heavy ion reactions, such as¹⁸O+²⁴⁸Cm. The first procedure uses a combination of several extraction steps with a final separation on a cation exchanger, the second procedure starts with an anion exchange column which is followed by multiple extractions in different media. The elements separated in the different steps were analyzed and overall decontamination factors are given.     

Charged particle activation analysis applied to the detection of heavy elements

Trace analysis methods have been developed for determining thallium, lead and bismuth. Proton or deuteron activation is used followed by a radiochemical separation of the reaction products:²⁰³Pb from thallium,²⁰⁶Bi from lead, and²⁰⁷Po from bismuth. Activation curves are presented for different nuclear reactions occuring on the elements studied. Determinations have been carried out on high purity samples containing varying amounts of thallium, lead, and bismuth. Based on experimental data, the detection limits are estimated at 0.01 ppm for lead, and 0.001 ppm for thallium and bismuth, respectively.     

Determination of traces of uranium in tungsten and molybdenum by radiochemical neutron activation analysis via the fission product140Ba

A radiochemical separation procedure has been developed to determine traces of uranium in tungsten and molybdenum. In this procedure the fission product¹⁴⁰Ba, as indicator nuclide for uranium, is selectively separated from the matrix activities and from all other long-lived activation and fission products and obtained at high purity. The radionuclide in the final fraction is sufficiently pure so that it can be measured with high counting efficiency by -counting. The separation procedure consists of two steps: a cation-exchange separation to separate barium from the anionic matrix tungste or molybdate, and many other elements. In the second step the Ba-fraction is further purified by precipitation of barium as barium chloride in 8M hydrochloric acid. The precipitate is then dissolved in water for -counting via the Cerenkov effect. The chemical yield for barium is 94.6±2.6%. When samples of 0.1 g, a thermal neutron flux of 2·10¹³ n·cm^–2·s^–1, an irradiation time of 10 hours and a measuring time of 2 hours were applied, then the detection limit of uranium was 4 ng/g.Presented at the 3rd Intern. Conf. on Nuclear and Radiochemistry, Vienna, September 7–11, 1992.     

The determination of boron in zirconium and zircaloy by proton activation analysis based on the 10B(p, α)7Be reaction

The determination of boron in zirconium and zircaloy based on the ¹⁰B(p, α)⁷Be reaction is described. At the 100 and 20 μg g^-1 concentration level (doped samples), instrumental analysis is feasible. At lower concentrations, ⁷Be is separated from the activities formed from zirconium and its alloying elements or impurities, by anion-exchange in hydrofluoric acid medium followed by precipitation of YF₃ and of BaBeF₄. The chemical yield of the separation was determined in several ways. The sensitivity of the method was 15 ng g^-1. For concentrations ranging from 100 to 0.15 μg g^-1, the precision ranged from 3.5 to 10.7%. The results are compared with results obtained by other methods.     

Determination du bore dans le zirconium,par activation au moyen de deutons

The determination of boron in zirconium by activation analysis using the¹⁰B(d, n)¹²C reaction with the chemical separation of¹¹C is described. The method was applied to industrial zirconium samples as zircalloy.

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Collaborateur temporaire de thèse au CEA.     

Neutron activation analysis of pure uranium: Preconcentration of impurity elements

We have developed a radiochemical neutron activation analysis technique (RNAA) of pure uranium with using extraction chromatographic separation of ²³⁹Np from impurity elements in TBP-6M HNO₃ media. The estimation of influence of fission products of ²³⁵U on the results by radiochemical neutron activation analysis has been carried out. For it we have performed NAA with preconcentration of impurity elements. Experiments show that in this case the apparent concentration of Y, Zr, Mo, Cs, La, Ce, Pr, Nd exceeds the true concentration by 2500–3000 times. Therefore, determination of these elements is not possible by RNAA. This technique allowed to use the determination of 26 impurity elements with detection limit 10⁻⁵–10⁻⁹% by mass. This developed technique may be used for the determination of impurities in uranium and its compounds.     

Rapid isolation of plutonium in environmental solid samples using sequential injection anion exchange chromatography followed by detection with inductively coupled plasma mass spectrometry

This paper reports an automated analytical method for rapid determination of plutonium isotopes (²³⁹Pu and ²⁴⁰Pu) in environmental solid extracts. Anion exchange chromatographic columns were incorporated in a sequential injection (SI) system to undertake the automated separation of plutonium from matrix and interfering elements. The analytical results most distinctly demonstrated that the crosslinkage of the anion exchanger is a key parameter controlling the separation efficiency. AG 1-×4 type resin was selected as the most suitable sorbent material for analyte separation. Investigation of column size effect upon the separation efficiency revealed that small-sized (2 mL) columns sufficed to handle up to 50 g of environmental soil samples. Under the optimum conditions, chemical yields of plutonium exceeded 90% and the decontamination factors for uranium, thorium and lead ranged from 10³ to 10⁴. The determination of plutonium isotopes in three standard/certified reference materials (IAEA-375 soil, IAEA-135 sediment and NIST-4359 seaweed) and two reference samples (Irish Sea sediment and Danish soil) revealed a good agreement with reference/certified values. The SI column-separation method is straightforward and less labor intensive as compared with batch-wise anion exchange chromatographic procedures. Besides, the automated method features low consumption of ion-exchanger and reagents for column washing and elution, with the consequent decrease in the generation of acidic waste, thus bearing green chemical credentials.     

Multielement trace analysis by atomic absorption spectrometry and neutron activation analysis in biological matrices

According to calculations of NIX and others, the formation of superheavy elements might occur in heavy-ion reaction systems such as the one under investigation in the present work i.e.,²³⁸U+^63,65Cu at 9.6 MeV/nucleon. Since previous experiments have indicated that upper limits to the production cross-section for superheavy elements are extremely low, we have carried out two rather long irradiations of 27 hrs and 42 hrs, respectively, at the University of Manchester LINAC. The first run has already been reported on in the literature. In the case of the second run, after chemical separation into HgS, CdS, and La(OH)₃ fractions, the samples were assayed simultaneously and continuously over a period of 6 months for alpha-and spontaneous-fission activity, using Si surface-barrier detector. Each sample was at the same time mounted on mice, for the purpose of scanning for fission tracks at a later date. No indications from the data have so far been found that superheavy elements were produced.     

Multi-element analysis of biological samples after intense neutron irradiation an fast chemical separation

For the simultaneous determination of many elements in small biological samples, a multi-element analysis has been developed using neutron activation. After a 24-hr irradiation in a neutron flux of 2.5·10¹⁴ n·cm⁻²·sec⁻¹ and after immediate chemical separation without cooling, it was possible to analyse 24 elements in bovine liver (NBS-SRM 1577). The separation apparatus, set up in a shielded cell can work four samples simultaneously, and its operation is fast enough to allow the detection of radioisotopes with a half-life of about 2 hrs (¹⁶⁵Dy,^57mSr,⁵⁶Mn). Amounts lower than 10⁻³ μg of Dy, Eu, Pr, Sm and Yb were determined.     

Multielement radiochemical neutron activation analysis of high purity aluminium

Summary A radiochemical neutron activation analysis technique for the determination of 51 elements in high purity aluminium via medium- and long-lived indicator radionuclides has been developed. It is based on a separation procedure involving the removal of ²⁴Na, produced via the reaction ²⁷Al(n,), on a hydrated antimony pentoxide column and further separation of the radionuclide mixture into 11 groups on two Dowex 1X8 columns and one Dowex 50X8 column from HCl/HF and HCl media as well as the extraction of copper with APDTC in chloroform. The indicator radionuclides for the significant impurities thorium and uranium, ²³³Pa and ²³⁹Np, were separated with satisfactory selectivity in one fraction. For 43 elements, the limits of detection are <10 ng/g, for thorium and uranium, they are 50 pg/g. The method was applied to the analysis of different high purity aluminium samples. For a number of elements, the results of this technique are compared with those of other techniques.

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Radiochemische Multielement-Neutronenaktivierungsanalyse von hochreinem Aluminium

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Dedicated to Prof. Dr. W. Fresenius on the occasion of his 75th birthday     

Characterization of C8H10 alkylbenzenes by negative ion mass spectrometry

The O^?˙ chemical ionization mass spectrri of the C₈H₁₀ alkylbenzenes, o-, m-. andp -xylene and ethylbenzene, show formation of [M ? H + O]^?, [M ? H]^?, [M ? H₂]^?˙ and, for the xylenes, [M ? CH₃ + O]^? as primary reaction products; the relative importance of these products depends on the isomer. However, [OH]^? is a primary product from reaction of O^?˙ with both the C₈H₁₀ isomers and hydrogen-containing impurities; [OH]^? reacts further with the alkylbenzenes to produce [M ? H]^? with the result that the chemical ionization mass spectra depend on experimental conditions such as sample size and the presence of impurities. The collision-induced charge inversion mass spectra of the [M ? H + O]^? and [M ? H]^? products allow only distinction of ethylbenzene from the xylenes. However, the collision-induced charge inversion mass spectra of the [M ? H₂]^?˙ ions show differences which allow identification of each isomer.     

Sequential determination of Am, Cm, Pu, Np and U by extraction chromatography

Environmental contamination by artificial radionuclides and the evaluation of their sources require precise isotopic analysis and accurate determination of actinide elements above all plutonium and americium. These can be achieved by alpha spectrometry or by inductively coupled plasma mass spectrometry (ICP-MS) after chemical separation. In the present work, a simple, rapid method has been developed for the sequential separation of actinide elements from aqueous solutions and their determination by alpha spectrometry. Extraction chromatography was applied to the separation of ²⁴¹Am, ²⁴⁴Cm, ^{239 + 240,238}Pu, ²³⁷Np and ^238,235,234U using microporous polyethylene supporting tri-n-octylamine as the stationary phase and hydrochloric acid with and without reducing agents as the mobile phase. Actinide in 9 M HCl solution is introduced into the anion exchange column; Pu (IV), Np (IV) and U(VI) are retained on the column while Am (III) and Cm passed through. Pu is eluted first, reductively, after which, Np and then U are eluted. The method can be applied to all aqueous solutions which do not contain strong complexing or precipitation agents for the elements considered.     

A fast separation for antimony produced in heavy-ion induced fission

Fission fragments from heavy ion induced fission were stopped in thin magnesium foils. A fast procedure based on evolution of stibine was developed to separate the antimony isotopes embedded in the foil. A separation system, and a glass pressure filtration system was constructed for this purpose. The chemical yield measured by three independent methods was 80–90%. The degree of decontamination from other fission products was >10². The whole separation took eight minutes.     

Investigation of the behaviour of nuclear reaction products at their volatilization from irradiated Ag and Au targets in dynamic vacuum (10−2–10−3 torr O2 or H2O)

Volatilization of ultramicroamounts of spallogenic products (Mo, Tc, Ru, Re and Os) from the melts of irradiated Ag and Au metals under dynamic vacuum conditions at 10⁻³–10⁻² torr O₂ and H₂O vapours and their separation in a thermochromatographic column are studied. The influence of the time of sublimation, the gas phase parameters and the materials of the crucible and the column are investigated. Possible reactions and chemical forms of volatile spallogenic products are discussed. Diffusion coefficients are defined for an Ag-melt case. The conditions of Re/Os and Mo/Tc/Ru separation are found. The possibility of using the Ag and Au melts in the ISOL-system is considered.