An improved method for99Tc analysis and application to human tissues

Zircon separated from samples of monazite in beach sand have been analyzed for Zr, Hf, U, Th, Sc and REE concentration by the neutron activation analysis technique. After irradiation, the rare earth elements were separated from Zr and Hf by oxalate precipitation, using La as a carrier, from²³⁹Np/U/ by ion-exchange chromatographic method and from²³³Pa/Th/ by co-precipitation with MnO₂. The chondritic normalized REE pattern of two zircon samples show negative Eu anomalies with a slope increasing at the heavy rare earths.     

Simultaneous determination of trace uranium and thorium by radiochemical neutron activation analysis

A method for the simultaneous, radiochemical neutron activation analysis of uranium and thorium at trace levels in biological materials is described, based on a technique known as LICSIR, in which a double neutron irradiation is employed. In the first, long irradiation²³³Pa (27.0 d) is induced by neutron capture on²³²Th and then the sample is cooled for several weeks. A second short irradiation to induce²³⁹U (23.5 m) is followed by a rapid sequential radiochemical separation by solvent extraction of²³⁹U with TBP and²³³Pa with TOPO. Chemical yields of²³⁹U and²³³Pa were measured for each sample aliquot using added²³⁵U and²³¹Pa tracers from the -spectra of the separated fractions. The technique was validated by quality control analyses.     

Simultaneous determination of tantalum,niobium, thorium and uranium in placer columbite-tantalite deposits from the Akim Oda District of Ghana by epithermal instrumental neutron activation analysis

Summary Tantalum, niobium, thorium and uranium contents of 21 columbite-tantalite minerals from the Akim Oda District of Ghana have been determined using epithermal instrumental neutron activation analysis (ENAA) with a conventional counting system. As thermal neutron filters, boron carbide was encapsulated in the irradiation vials during irradiation. The samples were irradiated at one of the outer irradiation channels in the Ghana Research Reactor-1 facility, and counted directly. Various elements were identified and quantified using 172 keV of ^182mTa, 871 keV of ^94mNb, 86.5 keV of ²³³ Th and 74.7 keV of ²³⁹U. The precision and accuracy of the method were evaluated using standard reference materials and the precision was found to be within 5% with comparable accuracy. The composition of columbite-tantalite minerals ranged from 33.1% to 59.2% Ta₂O₅ and 19.2% to 44.6% Nb₂O₅, ThO₂ and U₃O₈ the levels were 0.024-0.045% and 0.014-0.048%, respectively.     

Verunreinigunsprofile Unterschiedlich Bearbeiteter Siliziumproben

Impurity profiles of selected samples are determined by neutron activation analysis. After irradiation and cleaning with a mixture of hydrochloric and nitric acid a layer of 20 μm was etched with hydrofluoric and nitric acid. In the layer 0.5 ng/cm² Cu and 3 ng/cm² Fe were found. In cutted slides of zonefloated silicon we found a deep profile expressed by the equation c=c_o·exp-(x/a)², c_o=2 ppm, a=190 μm.      

Use of k0 concept to corrections for interferences from fissionable nuclides in reactor NAA

A neutron spectrum-independent compound nuclear constant, Ik_o, is proposed for fission interference corrections in reactor NAA by parametric method. Ik₀ values for eight major fission interference cases, belonging to three different types, have been determined in six irradiation positions (with _th/ _e 13,7–134) of three research reactors in our Institute. The general agreement among experimental Ik₀ 's from different irradiation positions and between experimental and calculated Ik₀ values for the same interference case verifies the validity of the method. Calculated Ik₀ values for all the possible fission interferences are tabulated. Interferences from²³⁸U(n,) and²³²Th(n,) reactions and reactor fast neutron induced²³⁸U(n, f) and²³²Th(n, f) reactions are discussed.     

A pre-concentration neutron activation analysis method for the determination of 232Th utilizing a dry-tube irradiation facility

A revized method for determining ²³²Th using a pre-concentration neutron activation analysis (PCNAA) procedure was developed to accommodate irradiation in a dry irradiation tube environment. ²³²Th extracted by ion-exchange from a sample was electrodeposited onto 5/8″ diameter vanadium planchets, which are arranged in a stack and irradiated in the dry tube central irradiation facility (CIF) of the reactor. The higher neutron fluence of this facility improved sensitivity by approximately 37%, however, the higher temperatures required modifications to the irradiation procedure. Because the heat in the CIF would melt the plastic spacers used in the original method, a tube of high-purity quartz was used to contain samples, and high purity quartz spacers were used to separate the vanadium planchets during the irradiation. Test irradiations have determined that no significant transfer occurred from the disks to the silica disks and no significant variation in the neutron flux was observed. Finally, a thin film barrier was tested for its ability to reduce recoil contamination from ²²⁹Th onto the detector during alpha spectroscopy. The film was shown to reduce contamination to levels indistinguishable from normal background.     

Radiochemical separation of thorium by isotope ion exchange

The aim of the present work is to obtain the separation of²³³Th from the radioisotopes formed in the irradiation of Mn, U, Ba, Cs, Co and the lanthanide elements with thermal neutrons, because they may interfere in the neutron activation analysis of Th, when the activity of²³³Th is used. The experiments were performed with the resin Bio-Rad AG 50W X-4 and X-8 (100–200 mesh) in the thorium form. The separation of²³³Th from the interfering radioisotopes is based on the retention of²³³Th by the resin (isotope exchange) and the elution of the interfering radioisotopes with a dilute solution of Th in 0.5M HCl. Batch experiments were made in order to determine the equilibrium time for the isotopic ion exchange of thorium and also the distribution coefficients of the interfering elements between the solution and the resin. Column experiments were carried out with the purpose of establishing the conditions that allow the maximum isotope exchange of²³³Th and the minimum retention of the interfering radioisotopes in the resin. With this purpose, a statistical interpretation of a four variable experimental design is presented.From a thesis submitted by C. Sepúlveda Munita to the Instituto de Pesquisas Energéticas e Nucleares (CNEN/SP) University of São Paulo, in partial fulfillment of a Doctor of Science's Degree. Work supported by the Brazilian Atomic Energy Commission.     

The reaction117Sn (n,n′)117mSn as a primary interference in (n, γ) neutron activation analysis

The¹¹⁶Sn (n, γ)^117mSn reaction commonly used in reactor-neutron activation analysis (RNAA) turned out to be seriously interfered by the¹¹⁷Sn (n, n′)^117mSn reaction, as observed from irradiation in channels with largely different neutron thermalization. To estimate the magnitude of this primary interference an attempt was made to determine the relevant fission neutron averaged cross-section, yielding approximately σ_{n, n}, (¹¹⁷Sn)==0.09±0.01 barn. This value—believed to be the first measured and published—is remarkably high especially when compared to the 2200 m·s^?1 cross-section σ_o[¹¹⁶Sn(n, γ)^117mSn]=0.006 barn.     

The leachability of some natural and man-made radionuclides from soil and sediments on acid attack

A radiotracer study was made of the leachability of some natural and man-made radionuclides from soils and sediments subjected to attack by various acid mixtures. Particular attention was paid to the nuclides²³⁸U,²³²Th, Pa (as²³³Pa) and Np (as²³⁹Np), since for these neutron activation can be used to study recoveries and/or to induce in situ radionuclides in samples. Thus conventional NAA allowed determination of total²³⁸U and²³²Th instrumentally, and also enabled analysis of leachates and residues by radiochemical or instrumental NAA. Activation of these nuclides produced samples endogenously labelled with²³³Pa and²³⁹Np whose behaviour on acid dissolution/leaching could be examined. Furthermore, comparison of neutron irradiated and non-irradiated samples allowed us to investigate the possibility of increased leachability induced by nuclear recoil reactions; however, this effect was negligible. We also investigated the acid leaching of americium adsorbed on the surface of sediment. In general, unsatisfactory leaching recoveries were found for²³³Pa,²³⁹Np and²³²Th for most materials, indicating the need for total dissolution procedures.     

A neutron activation analysis procedure for the determination of uranium,thorium and potassium in geologic samples

A neutron activation analysis procedure was developed for the determination of uranium, thorium and potassium in basic and ultrabasic rocks. The three elements are determined in the same 0.5-g sample following a 30-min irradiation in a thermal neutron flux of 2·10¹² n·cm^?2·sec^?1. Following radiochemical separation, the nuclides²³⁹U (T=23.5 m),²³³Th (T=22.2 m) and⁴²K (T=12.36 h) are measured by β-counting. A computer program is used to resolve the decay curves which are complex owing to contamination and the growth of daughter activities. The method was used to determine uranium, throium and potassium in the U. S. Geological Survey standard rocks DTS-1, PCC-1 and BCR-1. For 0.5-g samples the limits of detection for uranium, throium and potassium are 0.7, 1.0 and 10 ppb, respectively.     

Neutron activation analysis of Th via233Pa

A method is described for the analysis of thorium by neutron activation. The sample is brought into solution and quantitative extraction of²³³Pa is carried out in 1M HNO₃ using 0.5M HTTA in benzene. Extraction mechanisms are discussed. The use of a low-power reactor (100 kW_th) enables determination of thorium at a lower concentration limit of 50 ng for periods of irradiation, cooling and measurement of 3 hours, 24 hours and 300 seconds, respectively.     

Fine structure of mass and charge distribution in low energy fission

Studies of finer details in mass and charge distribution fission leads to a better understanding of the fission process. Experimental determination of independent and cumulative yields using radiochemical techniques as well as mass spectrometers and fission product recoil separators form the basis of such studies. It has been established that closed shells as well as an even number of nucleons influence both mass and charge distributions. The magnitudes of these effects may be estimated from existing experimental yield data and various fission models. Using our measurements of several fission yields and those existing in the literature we have calculated even-odd proton and neutron effects for various low energy fissioning systems. Where enough data existed, direct calculations were made, whereas for other cases the Z_p-model of WAHL has been used. It is found that the even-odd proton effect is well established and pronounced in thermal neutron fission of²³⁵U and²³³U. Lesser effects were found for reactor neutron induced fission of²³²Th, thermal neutron fission of²³⁹Pu and spontaneous fission of²⁴⁵Cm and²⁴⁹Cf. No effect seems to exist in the thermal neutron fission of²⁴¹Pu and the spontaneous fission of²⁵²Cf. The even-odd neutron effect is found to be much lower than the corresponding proton effect in²³⁵U and²³³U fissions and is nonexistent in the rest of the fissioning systems.     

Neutron flux variability at the TRIGA MARK II reactor,Ljubljana, as a parameter with applying the ko-method of NAA

Neutron-flux behaviour during irradiation should be known when applying the k_o-method of neutron activation analysis /NAA/. During two 100-hour operating periods of the TRIGA MARK II reactor, Ljubljana, the flux was measured by means of a¹⁹⁷Au/n,/¹⁹⁸Au monitor /E=411.8 keV/. Cadmium-covered irradiations were also performed to obtain the epithermal flux and thermal-to-epithermal flux ratio variations. Consistency was found between these results and the reactor operators' logbook record.     

A performance comparison of k<Subscript>0</Subscript>-based ENAA and NAA in the (K,Th, U) radiation dose rate assessment for the luminescence dating of sediments

Summary Recently, in our laboratory an intercomparison was made of methods for the annual radiation dose determination (assessed from direct radiation counting and/or from the measurement of the K, Th and U contents) applied to luminescence dating of loess and sand sediment, whereby the emphasis was put on their precision and accuracy. Although these properties are important, the duration of the measurement is also a practically relevant aspect. Indeed, direct alpha, beta and gamma-counting can last a week or more, and the determination of K, Th and U via NAA can take up to three weeks to enable proper gamma-ray spectrometry of the long-lived ²³³ Th/²³³Pa. Therefore, in the present work the performance of k₀-based epiCd-NAA (ENAA, with irradiation under a cadmium cover) when applied to sediments is compared to k₀-NAA. As concluded, with the use of k₀-ENAA the analysis turnaround time could be considerably reduced from ~3 weeks to ~ 2.5days, while maintaining satisfactory accuracy, precision and determination sensitivity.     

Determination of232Th in human tissues by pre-concentration neutron activation analysis with yield determination using227Th

The accurate and precise determination of²³²Th in biological samples is very important for the development of biokinetic models for thorium and for improving our knowledge on its distribution in human tissues. Radiochemical neutron activation analysis has long been one of the most sensitive methods for the determination of²³²Th. However, these determinations suffer in reliability because recovery information following the separation is not typically available. This information is particularly important for difficult matrices such as human bone where recoveries may be significantly less than unity. Also, the separation of difficult matrices following neutron activation may involve relatively high personal dose from the co-activated matrix. A novel approach for the determination of radiochemical yield has been developed which employs the use of a readily available, gamma-emitting isotope of thorium,²²⁷Th.²²⁷Th, obtained by radiochemical separation from²²⁷Ac, is added to each, dissolved sample prior to separation and the chemical yield determined by gamma-ray spectrometry following the separation. This pre-concentration step is then followed by neutron activation and the²³²Th determined via²³³Pa using gamma-ray spectrometry. Detection limits were approximately an order of magnitude lower than obtained by alpha-spectrometry.     

Utilization ofk o-factors for quality assurance in neutron activation analysis

Multielement certification analysis by instrumental neutron activation analysis requires simultaneous irradiation of several elemental comparator standards in order to ascertain traceability. Internal consistency of different comparators may be checked by calculation ofk _o-ratios, which show large deviations from unity in case of stoichiometric or other gross errors. Quality assurance based on the Analysis of Precision ofk _o-ratios from replicate analyses detects unexpected variability associated with inaccurate comparator standards. In two actual cases of cerification lack of statistical control amongk _o-ratios led to biased analytical results.     

Reactor neutrons irradiation effect on the photocatalytic activity of SnO<Subscript>2</Subscript> thin films

SnO₂ thin films synthesized by sol-gel are irradiated with reactor neutrons up to fast neutron fluence of 9.6 × 10¹⁷ neutrons cm^–2 at 40°C. The influence of defects generated by neutrons irradiation, through the properties modification, on the photo-catalytic activity of SnO₂ films is investigated. It is found that the photoactivity of the irradiated films is enhanced after reactor neutrons irradiation. An improvement of 41% is observed for the sample irradiated at a neutron fluence of 9.6 × 10¹⁷ neutrons cm^–2. This is attributed to several parameters modified by the reactor neutron irradiation principally the crystallite size and space charge region which are closely related to the photocatalytic performance.     

ko-measurements and related nuclear data compilation for (n, γ) reactor neutron activation analysis

k_o-factors of 35 isotopes used in reactor neutron activation analysis were measured with a high degree of accuracy (1–2%). To minimize systematic errors, measurements were carried out using different reactor types, irradiation conditions (18 < Φ_s/Φ_e), Ge(Li) detectors, sample detector geometry, etc. Analyst-oriented tabulations including all necessary nuclear data, “best values”, as well as recommended k_o-values are given to facilitate analytical work with the new method. Some practical aspects as well as limitations of the k_o-method are also outlined together with the applied neutron flux and cross-section conventions. Research associate of the National Fonds voor Wetenschappelijk Onderzoek, Belgium     

The dependence of build-up233U,232U,233Pa and fission products from ThO2 irradiated in HFETR on integral thermal neutron fluxes and neutron spectra

In this paper the dependence of build-up²³³U,²³²U,²³³Pa and fission products from ThO₂ irradiated in HFETR on integral thermal neutron fluxes and neutron spectra have been investigated. The yields of all above nuclides in ThO₂ increase with the increase of integral thermal neutron fluxes at different neutron spectra. The values of²³³U/²³²Th increase with the increases of _th and decreases with the increase of fast/thermal neutron ratios (_f/_th). The values of²³²U/²³³U increase with the increase of both _th and _f/_th ratio. The amount of fission products relative to original irradiated thorium decreases with the increase of _f/_th ratios. These results could be used to evaluate the behaviour of thorium-based nuclear fuel in reactor.     

Determination of thorium and uranium at the nanogram per gram level in semiconductor potting plastics by neutron activation analysis

A method was developed to determine thorium and uranium in semiconductor potting plastics. The method is based on neutron activation and subsequent radiochemical separation to isolate and permit measurement of the daughter products²³³Pa and²³⁹Np of the induced²³³Th and²³⁹U. These plastics typically contain macro amounts of silicon, bromine and antimony and nanogram per gram amounts of thorium and uranium. The radiochemical method provides the necessary sensitivity and makes it possible to easily attain adequate decontamination of the tiny amounts of²³³Pa and²³⁹Np from the high levels of radioactive bromine and antimony.Deceased