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.     

Simultaneous determination of arsenic and antimony in environmental samples by radiochemical neutron activation analysis

A radiochemical separation procedure using an inorganic exchanger, tin dioxide (TDO), for the separation of arsenic from antimony is reported here. This separation avoids the interference of 564 keV gamma-ray of¹²²Sb in the measurement of the 559 keV gamma-ray of⁷⁶As in neutron activation analysis. Environmental samples, after neutron irradiation and digestion, are taken up in 1M HCl–0.1M HF and passed through a TDO column which selectively retains arsenic. The effluent from the TDO column, after proper conditioning, is passed through an anion exchange column for quantitative retention of antimony. The procedure has been utilized for arsenic and antimony determination in NBS Orchard Leaves and NBS Albacore Tuna.     

A radiochemical neutron activation analysis method for the determination of tin,arsenic, copper and antimony for the forensic comparison of bullet lead specimens

Trace element characterization of bullet lead by instrumental neutron activation analysis (INAA) is hampered by the high spectral background due to antimony, normally present in high concentration in bullet lead. Tin is indicated to be a very useful element for characterization purposes. Beta-active¹²¹Sn is a suitable nuclide for quantitation of tin provided it is separated in high radiochemical purity. A radiochemical procedure capable of determining tin down to 10 ppm in bullet lead, a sequential procedure for its determination along with copper, arsenic and antimony and the application of this procedure for the determination of the contents of these elements in various bullet leads are described. This method has been applied to a “Rhinoceros shoot-out” case, referred to our laboratory.     

The determination of235U/238U ratios by activation analysis utilizing high resolution γ-spectrometry

The application of high resolution γ-spectrometry to the direct determination of²³⁵U/²³⁸U isotopic ratios in small uranium samples after neutron activation is reported. The consistency obtained relative to mass spectrometrically determined isotopic ratios is better than 5% for isotopic ratios between 0.06885 and 1.095. The method is not subject to the main disadvantages of the known radiochemical methods for²³⁵U/²³⁸U isotopic ratio determinations, and should be appreciably more rapid compared to the solid-source mass spectrometric method giving the same precision.     

Determination of major and trace elements in iron reference materials using k0-NAA

Major and trace element contents in iron ore reference materials were investigated using k ₀-instrumental neutron activation analysis (k ₀-INAA). To avoid iron interferences, radiochemical separation was developed (k ₀-RNAA). The determination of the investigated elements in the inorganic phase from hydrochloric acid solution was performed after radiochemical separation of iron by diisopropyl ether. It was found that after the Fe elimination, the limit of detection for some elements was much lower that enables their direct determination. The distribution of 39 elements (with intermediate/medium and long half-life radionuclides) after Fe removal was investigated.     

Radiochemical multielement neutron activation analysis of tungsten

A radiochemical neutron activation technique for the detemination of 19 elements in high purity tungsten has been developed. It is based on extraction with diantipyrylmethane (for tantalum and antimony), substoichiometric extraction of molybdophosphate (for phosphorus) and anion-exchange chromatography (other elements) in hydrofluoric acid medium. The results obtained and achievable limits of detection are given. The effects of self-shielding and nuclear interfering reactions are discussed.     

Determination of naturally occurring radionuclides in ultrapure organic liquids

For the determination of trace elements in organic liquids radiochemical neutron activation analysis has been combined with counting methods geared to various decay modes of indicator radionuclides leading to a high sensitivity required for ultrapure samples. The activation parameters such as irradiation time, sample mass and neutron flux have been enlarged to the maximum possible in the available irradiation facility. Separation yields and adsorption losses have been studied in detail for a set of elements in order to rule out losses during the separation process. The attainable limits of detection are 2 · 10^–16g/g for U and Lu, in the 5 · 10^–15g/g range for Th and Sm, in the 1 · 10^–14g/g region for La, 5 · 10^–13g/g for Rb, Cd and 2 · 10^–12g/g for K and In. Although the analysis focused on traces of naturally occurring radioisotopes, results for Cr, Fe, W and Zn are presented as well. Received: 14 May 1997 / Revised: 28 August 1997 / Accepted: 9 September 1997     

Investigations on the preparation and application of some inorganic separators for the removal of the matrix activity in neutron-activated biological samples

For the selective removal of the matrix activity (²⁴Na,³²P and⁴²K) in the neutron activation analysis of biomedical samples the inorganic separators “hydrated antimony pentoxide”, zirconium phosphate, and titanium phosphate were prepared. The sorption parameters of the samples were determined via elution chromatography techniques, with appropriate tracers. The basic principles of the sorption processes were investigated, and the experimental conditions were optimized. These inorganic separators were then applied, combined with a distillation procedure and an ion-exchange separation, for the determination of the following trace elements in animal blood samples: Mn, Co, Cu, Fe and Zn.     

Determination of Macro, Micro and Ultra Micro Concentration of Some Elements in Normal and Diseased Tissues of the Bone by NAA Employing 252Cf and Reactor Neutrons

A method has been developed for the determination of elements in normal and diseased tissues of the bone employing radiochemical and instrumental neutron activation analysis. Elements such as Na, Br, Au, Sb, Sc, Fe, Zn and Cr were subjected to irradiation in ²⁵²Cf or CIRUS reactor followed by measurement of the activity on a HPGe detector coupled to a PC based MCA unit. Elements such as Co, Ca and P were subjected to radiochemical separation prior to the measurement. The statistical evaluation with respect to accuracy and precision is discussed.     

Separation of tantalum from niobium in rock phosphates and its determination through neutron activation analysis

A simple solvent extraction procedure for an effective separation of traces of tantalum from rock phosphate samples has been developed and used in its determination through neutron activation analysis. The tantalum contents in the samples were found to be about 3.10⁻⁷%.     

Determination of metal traces in tantalum by proton activation analysis

Procedures for determining traces of calcium, titanium, vanadium, chromium, iron, copper, niobium, molybdenum and tungsten in tantalum are described utilizing 11 MeV proton activation. The instrumental method of analysis with the use of a Ge(Li) detector and the radiochemical separation of the corresponding fractions are described. The formula for the calculation of the concentration of traces with the use of thick target yields is given. Experimental data on the thick target yields of radioisotopes⁴⁴Sc,⁵²Mn,⁵⁶Co,⁶⁵Zn,^93mMo,⁹⁶Tc are presented. Based on the experimental data, the detection limits are estimated at 1–10 ppb for the above mentioned metal traces in tantalum. The successful solution of the task of the simultaneous determination of nine elements in tantalum confirms the wide applicability of proton activation analysis.     

Activation analysis with cyclotron-produced fast neutrons. Application to instrumental multi-element analysis and to the radiochemical determination of fluorine

Fast neutrons produced by irradiation of a thick beryllium target with 20–50 MeV deuterons are used for activation analysis. The spatial neutron flux distribution around the target is measured. A rotating sample holder is used for the simultaneous irradiation of samples and standards. Instrumental analysis can be applied for a number of elements. As an example, results for calcium and strontium in some reference materials are given. The¹⁹F(n, 2n)¹⁸F reaction is used for the radiochemical determination of fluorine in rocks with a fluorine concentration ranging from 9 to 5400 μg·g⁻¹ Aspirant of the N.F.W.O.     

Computer assisted multielement analysis of terrestrial and extraterrestrial materials and studies on long-lived cosmogenic53Mn by neutron activation

In a large number of alpine rocks and respective mineral separates the beryllium distribution was studied via “non-destructive” photon activation. The detection limit of the assembly was ∼20 ppb. The existence of Be-rich areas was revealed. A selection of individual rocks was analysed by instrumental as well as by radiochemical neutron activation analysis for main and trace elements as: Na, K, Sc, Cr, Mn, Fe, Co, Rb, Cs, La, Eu, Yb, Ta, W, Au, and U. The latter was determined by counting the²³⁵U-fission tracks. The data supply an insight into the complex processes leading to the formation of metamorphic rocks. The hardware and the computer evaluation of the γ-spectra is described in some detail. A further application is the determination of traces of⁵³Mn (in the order of 10⁻¹² g/g) produced by the interaction of cosmic rays with stony meteorites. From a comparison of the²⁶Al- and⁵³Mn-values it is concluded that the depth dependent production of these two radionuclides differs slightly.     

Trace analysis of heavy metals in high purity materials by helium-3 activation analysis

A method is described to determine traces of V, Fe, Ni, Zn, Nb and Mo in high purity matrices of niobium, tantalum and tungsten by non-destructive 14 MeV³He activation analysis. The influence of nuclear and γ-ray interferences in the determination of these elements is discussed.     

Radiochemical activation analysis of arsenic,selenium and antimony in biological samples

A method for the neutron activation analysis of arsenic, selenium and antimony has been developed. A radiochemical separation is performed by distillation followed by precipitation of the individual elements. Selenium and arsenic are precipitated by reduction to the elemental form while antimony is precipitated as sulfide. The chemical yields and detection limits using 0.5 g samples are the following: As 90–100%, 0.4 ppb, Se 80–100%, 8 ppb and Sb 50–70%, 0.2 ppb. Results from the analysis of nine international biological standard samples are given.     

Precise simultaneous determination of zirconium and hafnium in silicate rocks,meteorites and lunar samples

A precise, sensitive and rapid analytical technique has been developed for the simultaneous determination of Zr and Hf in natural silicate matrices. The technique is based on radiochemical neutron activation analysis and employs a rapid fusion dissolution of the sample and simultaneous precipitation of the Zr−Hf pair with p-hydroxybenzene arsonic acid in an acidic medium. The indicator radionuclides,⁹⁵Zr and¹⁸¹Hf, are counted with a pair of high resolution Ge(Li) detectors and the⁹⁵Zr activity is corrected for the contribution from U fission. The chemical yields of the radiochemical separation are based on Hf carrier, which quantitatively carries both Zr and Hf. The yield is determined by reactivation of the processed samples and standards with a²⁵²Cf isotopic neutron source and by counting the 18.6 sec half-life^179mHf. The sensitivity, precision and accuracy of the procedure are demonstrated by replicate analyses of several standard rocks, meteorites and lunar samples which exhibit a wide range of Zr and Hf abundances.     

Radiochemical multielement neutron activation analysis of niobium via medium- and long-lived radionuclides

Two radiochemical neutron activation analysis techniques capable for the determination of Ag, Au, Cd, Co, Cr, Cs, Cu, Fe, Hf, Ir, K, Mn, Mo, Na, Ni, Pd, Pt, Rb, Sc, Se, Ta, Th, Sn, W, Zn, and Zr in niobium via medium- and long-lived indicator radionuclides were developed. They involve two different irradiation and cooling times as well as two different group separation schemes based on extraction and ion exchange. The achievable limits of detection are between 10⁻⁷ g/g and 10⁻¹³ g/g. The techniques were applied to analysis of niobium of different purity grades. For a number of elements, the results of these techniques are compared with those of other techniques. This work was supported by Bundesministerium für Forschung und Technologie, Bonn.     

Instrumental activation analysis for determining the composition of micro-ingots of multi-constituent alloys

A procedure for the instrumental neutron activation analysis of micro-ingots of alloys containing In, Sb, Au, Ga, Ni, Sn and Bi is proposed. The non-destructive analysis of the irradiated samples is performed by γ-spectrometry techniques including one-crystal scintillation detectors, dual-crystal sum-coincidence scintillation detectors and Ge(Li) semiconductor detectors. As a result, the cumbersome operations of radiochemical separation can be eliminated. The sensitivity of quantitative determinations using scintillation detectors in alloys of the above composition is 10⁻¹⁰ g for indium, gold, antimony and gallium and 10⁻⁶ g for nickel and tin. The use of semiconductor detectors yields sensitivities of 10⁻¹⁰ g for indium and gold and 10⁻⁹ g for gallium and antimony.     

Multielement trace analysis of high purity aluminium by neutron activation

Instrumental neutron activation analysis was applied to multielement trace analysis of high purity aluminium samples. In order to reduce the production of²⁴Na from the matrix, samples were activated by thermal neutron flux of high cadmium ratio. Detection limits of various impurity elements were evaluated. So called “five nine” class standard aluminium samples were analyzed and concentrations of various impurity elements were determined. The analytical results obtained on zone refined aluminium samples showed that zone refining is effective against many elements, such as Na, Cr, Fe, Co, Cu, Ga, As, Br, Ba, La, Ce, Sm, Yb, Lu, Hf, W, Th and U, but not very effective against the element Sc.     

Neutronenabsorption Bei der Aktivierungsanalyse von Kadmium und Kadmiumtellurid

A calculation method of self-shielding coefficients of interesting elements in samples of any forms is given for the neutron activation analysis of cadmium and its compounds. The determination of ten elements in cadmium telluride using radiochemical separation and γ spectrometry is described.