The thermal column: A new irradiation position for fission-track dating in the University of Pavia Triga Mark II nuclear reactor

In the present paper a new irradiation position arranged for fission-track dating in the Triga Mark II reactor of the University of Pavia is described. Fluence values determined using the NIST glass standard SRM 962a for fission-track dating and the traditional metal foils are compared. Relatively high neutron thermalization (cadmium ratio of 85.3 for gold and 643 for cobalt) and lack of significant fluence spatial gradients are very favorable factors for fission-track dating. Finally, international age standards (or putative age standards) irradiated in this new position yielded results consistent with independent reference ages.     

Characterisation of Armenian Obsidians: Implications for Raw Material Supply for Prehistoric Artifacts

Obsidians from occurrences located in Armenia have been analysed using neutron activation analysis, both instrumental and epithermal, in order to enhance the knowledge of characteristics of potential sources of raw material exploited during prehistory. An alternative characterization technique, the fission-track dating method, was also applied. Results contribute to increase the data-set for provenance studies of prehistoric obsidian artifacts in the Mediterranean and adjacent regions.     

Characterization of two irradiation positions for fission track dating at the Lena Triga Mark II reactor

In the present paper the use of two natural uranium dosimeters is described. Data are compared with fluence values obtained by using NIST glass standards and the traditional activation of metal foils. Finally an example is reported for application of neutron dosimetry to the dating of the Fish Canyon Tuff age standard.     

Uranium and thorium thin film calibrations by particle track techniques

Particle track techniques, which enable estimation of the uranium and thorium contents in films where energy self-absorption is negligible, are presented. These techniques allow calibration of uranium and thorium thin films with adequate precision to be used in neutron fluence determinations for fission-track dating. Calibration via a particles is relatively simple for the case of uranium films, whereas for thorium films it is necessary to use the spectrometric characteristics of the employed track detector. Besides those based on a particles, calibration procedures via fission fragments are presented both for uranium as well as for thorium films. This revised version was published online in July 2006 with corrections to the Cover Date.     

Activation Constants for Slowpoke and MNS Reactors Calculated from the Neutron Spectrum and k0 and Q0 Values

The relative thermal, epithermal and fast neutron fluxes were measured in the inner and outer irradiation sites of three Slowpoke reactors and one Miniature Neutron Source (MNS) reactor by the bare triple monitor method. Using the measured neutron spectrum parameters and a compilation of published k ₀ and Q ₀ values, activation constants were calculated for the most intense gamma-rays of all nuclides commonly used in NAA. The resulting table of constants can be used to standardize NAA measurements for all elements when combined with relative efficiency measurements and the measurement of the thermal neutron flux with one standard. The observed constancy of the neutron spectra suggests that these activation constants are valid for all 14 Slowpoke and MNS reactors.     

Design and construction of a facility for neutron activation analysis using the 14 MeV neutron generator at HMS Sultan

The potential for using a small, sealed tube, DT neutron generator for neutron activation analysis has been well documented but not well demonstrated, except for 14 MeV activation analysis. This paper describes the design, construction and characterization of a neutron irradiation facility incorporating a small sealed tube DT neutron generator producing 14 MeV neutrons with fluence rates of 2·10⁸ s⁻¹ in 4π (steady state) and 10¹¹ s⁻¹ in 4π (pulsed). Monte Carlo modeling using MCNP4c and McBend9 has been used to optimize the design of this facility, including the location of a thermal irradiation facility for conventional neutron activation analysis. A significant factor in designing the facility has been the requirement to conform with Ionising Radiation Regulations and the design has been optimized to keep potential radiation doses to less that 1 μSv/h at the external walls of the facility. Activation of gold foils has been used for flux characterization and the experimental results agree well with the modeling.     

Simultaneous determination of antimony and chlorine in synthetic rubbers by 14 MeV neutron activation analysis

A nondestructive method for the analysis of Sb and Cl in synthetic rubbers by 14 MeV neutron activation analysis has been developed and evaluated by comparisons with microanalytical and thermal neutron activation analysis results. The method is most precise when a rubber with known amounts of Sb and Cl is used as a standard. Samples containing 0.07 to 2.5 wt.% Sb and 2.5 to 15.9 wt.% Cl have been analyzed and precision for the method is 10% or better. Antimony and Cl detection limits are 0.02 and 0.5 wt.% respectively. Agreement among the three methods is excellent; the thermal activation analysis method is more precise and simpler to apply if only Sb needs to be determined in a sample. This work was supported by the U.S. Department of Energy (DOE) under Contract DE-AC04-76-DP00789. A U.S. DOE facility.     

Variation of selenium concentration in toenails following long-term storage, washing and reactor irradiation

Summary Neutron activation analysis of toenails is often used to monitor body selenium in studies looking for an association between selenium deficiency and an increased cancer risk. In this study, 87 toenail samples were analyzed for Se four times, using neutron activation with 17.4-second ^77mSe, to determine the possible systematic effects of long-term storage, the washing procedure, and irradiation in a nuclear reactor. The mean Se concentration found was 0.92 mg/g, standard deviation 0.14 mg/g. The results showed that the Se concentrations are unaffected by washing and neutron irradiation, but the samples lost moisture during storage causing a 2% increase in the mean Se concentration.     

Measurement of thermal neutron capture cross sections of 237Np and 242Pu using prompt gamma neutron activation

Several samples of ²³⁷Np and ²⁴²Pu were irradiated in the guided cold neutron beam of the prompt gamma activation analysis facility at the Budapest Research Reactor. The thermal neutron capture cross sections of ²³⁷ Np and ²⁴²Pu were evaluated from the obtained prompt and delayed gamma ray data. The thermal neutron capture cross sections for ²³⁷Np(n,γ)²³⁸Np was found to be $ \sigma_{0} ({}^{237}{\text{Np}}) = 170.4 \pm 7.4\,{\text{b}} $ and for ²⁴²Pu(n,γ)²⁴³Pu to be $ \sigma_{0} ({}^{242}{\text{Pu}}) = 19.6 \pm 3.9\,{\text{b}} $ .     

Large sample neutron activation analysis of municipal solid waste using shutdown MNSR photoneutrons

Waste material in many cases may contain hazardous substances. Therefore, it requires appropriate classification. Large sample neutron activation analysis (LSNAA) can be adapted for the screening of such materials. LSNAA of municipal solid waste utilizing shutdown MNSR photoneutrons was performed in this work using internal monostandard technique. Good agreement was obtained between the results of this method and that of standard comparative one. This work allows extending the reactor utilization period by using its irradiation sites during shutdown state as low neutron flux irradiation facility for LSNAA.     

Application of neutron activation analysis in the field of silicon technology for the modern electronic industry

The specific application of neutron activation analysis in the research on the preparation of silicon integrated circuits is discussed. The high flux irradiation facility for large silicon wafers (up to 15 cm diameter) was used, the analytical procedure, and some typical results will be described.     

Determination of carbon,nitrogen and phosphorus in cattail using cold neutron prompt-gamma activation analysis

Summary A method for the determination of carbon, nitrogen, and phosphorus in cattail using cold neutron prompt-gamma activation analysis (CNPGAA) has been developed and evaluated through the analysis of standard reference materials (SRM). After extensive preparation, approximately 400 mg cattail samples from the lower Apalachicola River floodplain were irradiated in the CNPGAA facility at the National Institute of Standards and Technology (NIST). The results of numerous field samples and two standard reference materials using the nuclear method show favorable comparison to results obtained by a CHNS/O analyzer.     

Determination of Uranium and Thorium in Zircon,Apatite, and Fluorite: Application to Laser (U-Th)/He Thermochronology

We have developed a methodology for (U-Th)/He thermochronology on a variety of mineral species. With many laboratories initiating research in the area of (U-Th)/He thermochronology, we recognize that there may be interest in a review of analytical procedures for uranium and thorium determination in single crystals of apatite, zircon, rutile, and fluorite. Uranium and thorium are both determined by inductively coupled plasma mass-spectrometry using an isotope dilution method. While standard and spike solutions can be purchased, their isotopic composition and the concentration of the standard solution need to be verified. Digestion procedures for apatite and fluorite are relatively straightforward, but zircon decomposition requires the use of pressure vessels or fusion. Matrix effects are shown to have an insignificant effect on isotope ratios, although isobaric interferences, particularly of PtAr⁺ on U isotopes, can be a problem. We include complete thermochronology datasets for replicate analysis of Durango apatite, Yucca Mountain fluorite, and an Australian megacryst zircon.     

The determination of ko factors and their application to the neutron activation analysis of pure zirconium metal by the single-comparator method

The procedures followed for the determination of standardization factors and their use in the single-comparator method for multi-element reactor neutron activation analysis are described. The method is applied to the determination of Cr, Mn, Fe, Ni and Mo in pure zirconium metal. The matrix could serve as the single comparator and as a bi-isotopic thermal-to-epithermal neutron flux ratio monitor.     

The determination of uranium and thorium in rocks by neutron activation analysis

A neutron activation method is described for the determination of thorium and uranium in rocks at the microgram and submicrogram levels. Radiochemical separations are carried out using the alpha-active nuclides protactinium-231 and neptunium-237 as tracers. The method is applied to the Standard granite XXX and the standard diabase XXX.     

Determination of carbon, nitrogen, and phosphorus in cattail using thermal neutron prompt gamma activation analysis

A previous study on the determination of carbon, nitrogen, and phosphorus in cattail using cold neutron prompt gamma activation analysis (CNPGAA) demonstrates that the results of numerous cattail samples showed favorable comparison to results from an elemental analyzer (EA) for C and N. However, the results for P overestimated the results from a UV-VIS spectrophotometer because of the interference of chlorine existing in cattail collected from an estuarine environment. To compare to CNPGAA, a method for the determination of C, N, and P in cattail using thermal neutron prompt gamma activation analysis (TNPGAA) has been developed in the TNPGAA facility at the National Institute of Standards and Technology (NIST) and evaluated through the analysis of standard reference materials (SRMs).     

Instrumental neutron activation analysis of hafnium in zirconium metal using internal standardization

Instrumental neutron activation analysis with the internal standard correction was applied to determination Hf in high purity Zr metal. Zirconium, which was a matrix element, was used as an internal standard to compensate for inhomogeneity of the neutron flux through an irradiation capsule and to improve the gamma ray measurement uncertainty. It was found that the linearity of the calibration curves of Hf was improved with using an internal standard. The analytical result of Hf in Zr metal was in good agreement with that obtained by ICP-SFMS. The relative expanded uncertainty (k = 2) was 2.1%, and it was comparable to that of ICP-SFMS.     

Determination of silicon in rocks by fast-neutron activation analysis using internal standards

A technique for using internal standards in the determination of Si in rocks using fast neutron activation is presented. Different weights of barium acetate were irradiated for 30 seconds then cooled for 10 seconds before counting for one minute. A peak area, at 0.662 MeV due to^137mBa, versus weight of barium calibration curve (I) was made. Similarly, barium acetate, which served as the neutron flux monitor, was mixed with known weights of standard rocks, BCR-1 and G-2. Then a peak area (at 1.78 MeV due to²⁸Al) versus weight of silicon (present in the standard rocks) calibration curve (II) was constructed which was corrected for flux variations. Flux corrections were made possible using curve (I). Utilizing curve (I) and curve (II) the percentage Si in granite samples obtained from Llano, Texas, was determined. This technique avoids any external neutron monitor or sample rotation system. The applicability of this approach may be limited to samples in which the internal flux monitor can be dispersed. On assignment from the Philippine Atomic Energy Commission, Manila, NAS-IAEA Fellow.     

BCR certified reference materials for reactor neutron dosimetry

A series of reference materials intended for use as activation or fission monitors for neutron fluence rate measurements has been prepared by the Joint Research Centre of the European Commission. Certification has been carried out by expert European laboratories and distribution of the certified reference materials (CRMs) is through the BCR programme of the Commission. The list (18 CRMs) includes materials to cover the complete energy spectrum, and suitable for different irradiation times. Fission monitors are ²³⁸UO₂ or ²³⁷NpO₂ in the form of microspheres. Activation monitors are high purity metals (Ni, Cu, Al, Fe, Nb, Rh, or Ti), certified for interfering trace impurities, or dilute aluminium-based alloys, where aluminium is chosen as a suitable matrix for reducing the neutron self-shielding effect. Newly certified materials are IRMM-530R Al-0.1%Au, replacing the exhausted IRMM-530 material, used as comparator for k ₀-standardization, and three new Al-Co alloys (0.01-1%Co). Two others, in the process of certification are Al-0.1%Ag and Al-2%Sc for thermal and epithermal fluence rate measurements. Other candidate reference materials currently being certified are two uranium-doped glass intended for dosimetry by the fission-track technique.