Determination of sodium in high purity silica by activation analysis

High purity fused silica samples and NBS standards were irradiated in the Sandia Reactor Facility for 2 hr at a thermal flux of 10(10) neutrons/cm(2)/sec. (24)Na was produced by the reaction (23)Na(n, gamma)(24)Na (14.9 hr half-life, alpha = 0.5 barn), and decayed with emission of 1.37 and 2.75 MeV gamma-rays. With the stated flux and irradiation time, sodium at the 3 ppm level has been determined with a standard deviation of 0.2 ppm. Values obtained by thermal neutron-activation analysis agree well with results obtained by emission spectrography and flame spectrophotometric methods.     

Determination of rare earth elements in rice by INAA and ICP-MS

In order to improve the accuracy of reactor neutron activation analysis, flux gradients and spectrum changes in the irradiation capsule have been studied at the Kyoto University Reactor (KUR). The flux and spectrum monitoring samples of Fe, Co, Au, Sb, U and Ni were placed at several positions in a polyethylene irradiation capsule of 24 mm inner diameter and 98 mm length, and were irradiated in a pneumatic irradiation facility (Pn-2). The flux gradients were found to be rather negligible in the vertical (axial) direction while they were considerable in the radial one. The flux gradient was around 5%/cm for thermal neutrons and 10%/cm for epithermal and fast neutrons. The spectrum changes were dependent on the materials (polyethylene and silica) filled in the capsule. Based on these observations, the effect of the flux gradients and spectrum changes on the accuracy of reactor neutron activation analysis was discussed.     

A group separation based on anion- and cation-exchange from hydrofluoric acid medium Application to multielement neutron-activation analysis of niobium

A group separation procedure for the determination of 33 elements has been developed and applied to the neutron-activation analysis of niobium. It is based on cation- and anion-exchange chromatography in HF media and separates the elements into five groups suitable for gamma spectrometry. The recoveries and their reproducibilities have been studied by the radiotracer technique. Recovery 95% (mean deviation 3%) was obtained for all the elements tested. For a 12-hr irradiation at a thermal neutron flux of 8 x 10(13) n.cm(-2).sec(-1), the limits of detection for a niobium matrix vary between 0.6 pg (for Mn) and 0.6 mug (for Fe).     

Determination of multielements in a typical Japanese diet certified reference material by instrumental neutron activation analysis.

Multielements in a typical Japanese diet certified reference material prepared at the National Institute for Environmental Studies (NIES) of Japan, in collaboration with the National Institute of Radiological Sciences (NIRS) of Japan were determined by instrumental neutron activation analysis (INAA). Five samples (ca. 510-1000 mg) and comparative standards were irradiated for a short time (10 s) at a thermal neutron flux of 1.5 x 10(12) n cm(-2) s(-1) (pneumatic transfer) and for a long time (6 h) at a thermal neutron flux of 3.7 x 10(12) n cm(-2) s(-1) (central thimble) in the Rikkyo University Research Reactor (TRIGA Mark-II, 100 kW). The irradiated samples were measured by conventional gama-ray spectrometry using a coaxial Ge detector, and by anti-coincidence and coincidence gamma-ray spectrometry with a coaxial Ge detector and a well-type NaI(Tl) detector. The concentrations of 38 elements were determined by these methods.     

Neutron-activation analysis of manganese in polysulphide materials

A fast non-destructive neutron-activation analysis method has been developed for manganese in polysulphide adhesives. Samples are irradiated for 20 min at a thermal flux of 2 x 10(10) n cm(-2) sec(-1). The net activity in the 0.845-MeV gamma peak of (56)Mn produced by the (n, gamma) reaction in the sample is compared with the activity obtained from a weighed amount of pure manganese irradiated at the same time. Samples containing 2-3% of manganese have been analysed with a relative standard deviation of 2.9%.     

Photoinitiated gold sol generation in aqueous Triton X-100 and its analytical application for spectrophotometric determination of gold

Gold complex, HAuCl(4) has been transformed into pink-coloured stable gold sol having lambda(max) at 523 nm (in=3.06x10(3)1.mol(-1)cm(-1)) at room temperature in aqueous Triton X-100 (TX-100) upon photoirradiation. It is a very rapid and simple process and the absorbance at 523 nm is a direct measure of gold concentration. Beer's law is obeyed in the range of 0-150 ppm of gold. The relative standard deviation for 22.7 and 90.9 ppm of gold are 2.8 and 2.5% respectively. The 95% confidence limit (ten determinations) for 22.7 ppm of gold is 23.6+/-0.5 ppm. Sandell sensitivity is 6.44x10(-2) mug cm(-2). TX-100 acts both as a reducing agent and a stabilizer here. Statistical parameters, effects of TX-100 concentration, irradiation time and interferents are studied. The method is applicable for ore and synthetic mixture analysis.     

Compounds of 6Li and natural Li for EPR dosimetry in photon/neutron mixed radiation fields

Formates and dithionates of 6Li, enriched and 7Li in natural composition of Li offer a possibility to measure the absorbed dose from photons and thermal neutrons in a mixed radiation field for instance at a boron neutron capture therapy (BNCT) facility. Tests with formates and dithionates of enriched 6Li and lithium compounds with natural composition have been performed at the BNCT facility at Studsvik, Sweden. Irradiations have been performed at 3 cm depth in a Perspex phantom in a fluence rate of thermal neutrons 1.8 x 10(9) n cm(-2) s(-1). The compounds were also irradiated in a pure X-ray field from a 4MV linear accelerator at 5 cm depth in a phantom with accurately determined absorbed doses. The signal intensity and shape was investigated within 3 h after the irradiation. A single line spectrum attributed to the CO2- radical was observed after irradiation of lithium formate. An increase in line width occurring after neutron irradiation in comparison with photon irradiation of the 6Li sample was attributed to dipolar broadening between CO2- radicals trapped in the tracks of the alpha particles. A spectrum due to the SO3- radical anion was observed after irradiation of lithium dithionate. The signal amplitude increased using the 6Li in place of the Li with natural composition of isotopes, in studies with low energy X-ray irradiation. Due to the decreased line width, caused by the difference in g(N) and I between the isotopes, the sensitivity with 6Li dithionate may be enhanced by an order of magnitude compared to alanine dosimetry. After comprehensive examination of the different combinations of compounds with different amounts of 6Li and 7Li regarding dosimetry, radiation chemistry and EPR properties these dosimeter material might be used for dose determinations at BNCT treatments and for biomedical experiments. Interesting properties of the radical formation might be visible due to the large difference in ionization density of neutrons compared to photons.     

Second-order interference in the neutron activation analysis of arsenic in a germanium matrix

The second-order interference ⁷⁴Ge(n, γ; β^-, n, γ)⁷⁶ As can occur in the activation analysis of arsenic in a germanium matrix, using thermal neutrons. As the literature data show poor agreement, this interference was determined experimentally. A practical formula was derived, for irradiation times longer than 2 h, which showed that the interference, expressed as an apparent arsenic concentration, is proportional to the neutron flux. Experiments were performed for irradiation times of 10, 15 and 20 h at a neutron flux of 10¹⁴ n/cm²/sec, yielding apparent arsenic concentrations in the germanium matrix of respectively 223, 408 and 597 p.p.b. From these results a value of 0.48 ±0.06 barn could be calculated for the activation cross-section of ⁷⁴Ge for neutron capture.     

Determination of inorganic impurities in vinyl chloride by activation analysis

Trace impurities in vinyl chloride have been determined by activation analysis in a reactor thermal neutron flux of 1.2 x 10(9)n mm (2)sec . Irradiations were carried out on liquid and solid samples at the same time as a standard. Gamma-spectrometry was used to reveal the presence of arsenic and bromine, the quantitative estimation being based on two calculus methods., The impurities determined were: arsenic 8.0 +/- 0.6 x 10(-4)%, bromine 3.07 +/- 0.2 x 10(-3)% and phosphorus 2.0 +/- 0.15 x 10(-2)%.     

Interference by neutron induced second order nuclear reaction in activation analysis of rare earths

In determining the trace impurities existing in high-purity rare earth samples by the neutron activation analysis, there are much interference due to nuclides induced from neutron induced second order nuclear reaction. This paper presents the degree of interference calculated over the ranges of irradiation time from 10⁵ to 10⁷ sec and of thermal-neutron flux from 1·10¹² to 1·10¹⁵ n·cm⁻²·sec⁻¹. According to the results of these calculations, degree of interference under the neutron irradiation condition for 288 hrs in the thermal-neutron flux of 3·10¹³n·cm⁻²·sec⁻¹ is concluded to be 6.4·10⁶ ppm Gd in Eu, 2.2·10⁴ ppm Sm in Eu, 1.9·10⁴ ppm Ho in Dy, 1.1·10³ ppm Eu in Sm, 1.1·10² ppm Ce in La and 1.1·10 ppm Tb in Gd, respectively. Especially, the Gd determination in the Eu target is extremely affected by¹⁵³Gd formed from the¹⁵¹Eu (n, γ) reaction. On the contrary, this reaction is effective in producing¹⁵³Gd activity.     

Neutron activation analysis of microgram amounts of thorium in uranium ores and process liquors by means of thorium-233

A method is described for neutron activation analysis of thorium by employing thorium-233. Decontamination steps include anion exchange in 12.5 N HCL, precipitation of fluoride, extraction with mesityl oxide and thorium oxalate precipitation. The time spent is less than 1 h; spurious activities in counting samples amount only to 2% and can easily be corrected for. The sensitivity of the method is ca. 0.02 μg of thorium in a neutron flux of 10¹²n/cm²/sec with an irradiation time of 5 min.     

Instrumental neutron activation analysis of silicon wafers using the silicon matrix as the comparator

For the instrumental neutron activation analysis of trace impurities in high purity silicon wafer, a modified single comparator method has been applied. The energy distribution of the neutrons at the irradiation position was measured using the two flux monitors, Au and Co, and elemental contents were calculated using the silicon matrix in the wafer as a comparator. This has advantage of reducing the cross contamination from an external monitor during sample preparation and irradiation, the uncertainties from the non-homogeneity of the neutron flux and the error on the weight of comparators. Determination limits for 49 elements were presented under the condition of 72 hours irradiation at a neutron flux of 3.7·10¹³ n·cm^-2·s^-1 and 4000 s measurement. The analytical results obtained by this method and the conventional single comparator method were compared and were found to agree well within 5%.     

Two-photon excited fluorescence of nitrogen-vacancy centers in proton-irradiated type Ib diamond

Two-photon fluorescence spectroscopy of negatively charged nitrogen-vacancy [(N-V)-] centers in type Ib diamond single crystals have been studied with a picosecond (7.5 ps) mode-locked Nd:YVO(4) laser operating at 1064 nm. The (N-V)- centers were produced by radiation damage of diamond using a 3 MeV proton beam, followed by thermal annealing at 800 degrees C. Prior to the irradiation treatment, infrared spectroscopy of the C-N vibrational modes at 1344 cm(-1) suggested a nitrogen content of 109 +/- 10 ppm. Irradiation and annealing of the specimen led to the emergence of a new absorption band peaking at approximately 560 nm. From a measurement of the integrated absorption intensity of the sharp zero-phonon line (637 nm) at liquid nitrogen temperature, we determined a (N-V)- density of (4.5 +/- 1.1) x 10(18) centers/cm3 (or 25 +/- 6 ppm) for the substrate irradiated at a dose of 1 x 1016) H(+)/cm(2). Such a high defect density allowed us to observe two-photon excited fluorescence and measure the corresponding fluorescence decay time. No significant difference in the spectral feature and fluorescence lifetime was observed between one-photon and two-photon excitations. Assuming that the fluorescence quantum yields are the same for both processes, a two-photon absorption cross section of sigma(TPA) = (0.45 +/- 0.23) x 10(-50) cm(4).s/photon at 1064 nm was determined for the (N-V)- center based on its one-photon absorption cross section of sigma(OPA) = (3.1 +/- 0.8) x 10(-17) cm2 at 532 nm. The material is highly photostable and shows no sign of photobleaching even under continuous two-photon excitation at a peak power density of 3 GW/cm(2) for 5 min.     

Determination of palladium in gasoline by neutron activation analysis and automated column extraction

Palladium in gasoline was determined by means of neutron activation analysis (NAA) and selective sorbent extraction. Unleaded gasoline consistent with DIN EN 228, RON 95 was irradiated at a thermal neutron flux of phith = 1.68 x 10(13)s(-1)cm(-2) and an epithermal neutron flux of 3.32 x 10(11)s(-1)cm(-2) for t(irr) = 12 h. The irradiated gasoline was digested with nitric acid and palladium was then separated as N,N-diethyl-N'-benzoylthiourea complex by an automated column pre-concentration procedure. The eluate of 50 microL was dried on a filter paper and the 88.03 keV photons resulting from the decay of 109Pd were detected in a low level HPGe spectrometer with an efficiency of 35.5%. Severe interferences with other matrix constituents, especially 82Br could be overcome and the detection limit for palladium was improved to 3.4 ng/L at a confidence level of 90%. Although the analytical procedure applied yielded the lowest detection limit for palladium obtained in gasoline up to now, no indications for the presence of palladium were found.     

Investigation on thermal-neutron sensitivity of commercial BeO(Na) thermoluminescence dosimeter and development of thermal-neutron insensitive BeO(Na) phosphors encapsulated in quartz-capillary

BeO(Na) TLD on the market, UD-170 L, gives thermoluminescence response equivalent to irradiation with 3.2 +/- 0.5 cGy of 60Co gamma-rays after irradiation with 10(10) thermal neutrons per cm2. Because of this neutron sensitivity, UD-170 L is not suitable for measurement of gamma-rays in gamma-neutron mixed radiation from a nuclear reactor of Kinki University when we use it for radiobiological research. To reduce this troublesome sensitivity, we replaced the glass capillary used for UD-170 L with a quartz capillary. Quartz tube encapsulated BeO(Na) showed a markedly reduced response to thermal neutrons.     

Monitoring of neutron flux changes in short-lived neutron activation analysis

It is well known variations in neutron fluxes can adversely affect the final result in neutron activation analysis. The monitoring of neutron flux changes are usually described for medium and long-lived NAA using foils of cobalt, gold, zirconium, etc. However, for short-lived neutron activation analysis there appears to be no systematic study of the variations of the neutron flux. With our new automatic pneumatic system, where irradiation timing, decay and counting and position are very reproducible, we have performed a series of experiments using thermal and epithermal neutrons using aluminum wire as a monitor to monitor the neutron fluxes. Our experiments confirm that neutron flux fluctuations in the worst case can be up to ±12 % with a SD of 2–3 %. This effect can be seen regardless of the irradiation time and must be taken into consideration to achieve the best result.     

The Characterization of a Neutron Radiography Triga Reactor for NAA of Chlorine in an Iron Oxide Matrix

An irradiation position in the 250 kW Triga reactor was characterized for instrumental neutron activation analysis of chlorine in an iron oxide matrix. Factors that affect the accuracy of the determination include variations in the reactor neutron spectrum and flux as a function of spatial position and the presence of chlorine impurities. Gold wire and foils were used to determine the neutron flux and cadmium ratio as a function of height in an air-filled irradiation tube.     

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.     

Estimation of the possibilities of a neutron generator-based source of thermalized neutrons for activation analysis

Characteristics of a source of thermal neutrons based on an evacuated NG-400 neutron generator with the maximum flux (Φ_f) 2 × 10¹¹ neutron/s for 14 MeV neutrons and 2 × 10⁹ neutrons/s for 3 meV neutrons have been investigated. The possibilities of its application for neutron activation analysis have been estimated. The distribution, composition, and density (φ_T) values of the thermal neutron flux have been measured in the inner cavity of the moderator using activation detectors. φ_T was 2 × 10⁸ and 2 × 10⁶ neutrons/cm² s for thermalized neutrons with energies of 14 and 3 MeV, respectively. The possibilities of the apparatus have been estimated theoretically and experimentally for the cases of thermalized neutrons of 14 MeV and 3 MeV.     

Solvent extraction and photometric determination of molybdenum (VI) with 2-aminobenzenethiol

A new extractive photometric method is described for estimation of molybdenum with 2-aminobenzenethiol. The green complex in chloroform has its absorbance maximum at 700 nm and is stable for 2 hr when extracted from a solution of optimum pH range 1.4-2.8. The extraction is quantitative. The sensitivity is 0.0075 microg cm (2). Beer's law is obeyed over the range 0.25-10 ppm with optimum range 0.5-4.5 ppm. The molar absorptivity is 7.08 x 10(4) 1.mole(-1). cm(-1). The overall stability constant is 2.0 x 10(8) at 25 +/- 0.1 degrees.