Instrumental neutron activation analysis and inductively coupled plasma mass spectrometry on atmospheric biomonitors

Sensitivities for detecting fluorine, distributed uniformly in elements with atomic numbers 8, 13, 20, 28, 34, 42, 50, 60, 68 and 79, through the F(p,αγ)O reaction, have been calculated using experimentally measured excitation functions and the available energy-range data. Thick target yields of the prompt 6.13 MeV gammas, as well as of the three gamma-lines of 6.13, 6.92 and 7.12 MeV combined, have been plotted as a function of the incident energy of up to 4.16 MeV. From these yield curves the sensitivity of detecting fluorine in thick or thin samples, and even in a layer of known thickness at a particular depth within a thick target, can be directly read for known bombarding and detecting conditions. The curves should also be valid, to a certain approximation, for neighbouring elements and for mixtures or compounds with similar average atomic numbers. Furthermore, it is explained as to how these yield curves can also be used in non-destructive profile analysis of fluorine to much greater depths than can be achieved by the well-known resonance-shift method.     

Proton microprobe determination of fluorine depth distributions and surface multielement characterization in dental enamel

Particle induced X-ray emission analysis (PIXE) and nuclear reaction analysis have been applied to multielemental analysis of human dental enamel in a proton microprobe. The PIXE technique was excercised for the characterization of multielemental lateral distributions on and just below the sample surface. For the assessment of depth distributions of fluorine the resonant nuclear reaction¹⁹F(p,aλ)¹⁶O was used. The combination of two analytical techniques comprising both atomic and nuclear interactions in a microprobe was applied to enamel samples of different origins. One sample constituted a healthy enamel and the other one enamel from a restored tooth. The microprobe in the combined mode was demonstrated to permit the establishment of lateral, concentration gradients of elements heavier than phosphorus with a resolution of 15 μm in enamel and simultaneously of depth distributions of fluorine better than 0.7 μm. The detection limits approached, 10–25 ppm for most of the elements considered. Supported by the Swedish Natural Science Research Council     

Fluorine analysis by activation with an isotopic fast-neutron source and counting Nitrogen-16

A rapid, nondestructive method has been developed for determination of fluorine by activation with fast neutrons from a²⁴¹Am-²⁴²Cm-Be source and counting the 6–7 MeV γ rays of the product nitrogen-16. The total neutron output of the source is 4.8·10⁹ unmoderated neutrons per second and the flux is 1.4·10⁸ fast n·cm⁻²· sec⁻¹. The γ-ray detectors consist of two opposing, matched cylindrical NaI(Tl) crystals 10 cm long and 10 cm in diameter. The sample is irradiated for 30 seconds, cooled for 4 seconds, and then counted for 30 seconds. The sensitivity is 4.8·10⁴ counts nitrogen-16 per gram fluorine, and the limit of detection is 0.4 mg fluorine in a 10-gram sample. A reproducibility of 0.24% is achieved. The relative standard deviation of the specific count rate of nitrogen-16 for 11 fluorine compounds is 1.31%.     

A method for charged-particle activation analysis and its application to fluorine determination by the19F(p, αγ)16O reaction

A simple method for calculating the sensitivity for detecting a nuclide distributed uniformly in any given matrix through charged particle activation is described. This method takes into account the actual values of the reaction cross section at different energies as the beam traverses through a thick target and the corresponding stopping power values. The detection sensitivity for fluorine in a number of matrices through the¹⁹F(p, αγ)¹⁶O reaction have been calculated as a function of the energy from threshold to 4.16 MeV using this method and the sensitivity curves plotted. The sensitivity values (dps/ppm/μA) for a thick or thin target and even for a layer of known thickness at a particular depth within a sample can be directly read from these curves for known bombarding conditions. The comparator methods for charged particle activation analysis of RICCI¹ and of CHAUDHRI,² especially when the matrices of the sample and standard are different, have been compared in the case of F determination through the¹⁹F(p, αγ)¹⁶O reaction. It has been found that the errors are reduced by almost a factor of two when the latter method is used compared to the former one. The fluorine concentration in animal bones and teeth, apatite crystal, and rocks have been determined through the¹⁹F(p, αγ)¹⁶O reaction using the Melbourne University Pelletron.     

Performance comparison of 2.8 MeV and <Superscript>241</Superscript>Am-Be neutrons based moisture measurement setups

Performance of a ²⁴¹Am-Be neutron source-based and 2.8 MeV neutrons-based moisture measurement setups have been compared using Monte Carlo simulation. In the setup fast neutrons transmitted through the sample were detected by a fast neutron detector, which was placed behind a massive long double truncated collimator. The setup geometry was optimized to detect maximum effect of 1–7 wt.% moisture on the neutron intensity transmitted through the sample. The yield of neutrons transmitted through concrete, coal, wood and soil samples containing 1–7 wt.% moisture was calculated for 2.8 MeV neutrons and neutrons from an ²⁴¹Am-Be source. The slopes of the fast neutron intensities transmitted through the samples vs. their moisture contents are very sensitive to the neutron energy and the sample composition. Higher slopes have been observed for the samples with larger bulk density. The slopes of fast neutron yield show dependence on the incident neutron energy. Larger slopes have been observed for neutrons with samller energy. Due to the overall large slopes of the transmitted intensity data of the samples for 2.8 MeV neutrons, it is expected to achieve better sensitivity in moisture measurements for a 2.8 MeV neutrons based moisture setup.     

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.     

Photo-neutron cross-section of 100Mo

The ¹⁰⁰Mo(γ, n) reaction cross-section was experimentally determined at end point bremsstrahlung energy of 10 and 12.5 MeV using off-line γ-ray spectrometric technique. It was also found that ¹⁰⁰Mo(γ, n) reaction cross-section increases sharply from the end point bremsstrahlung energy of 10 MeV to 12.5 MeV, which may be because of GDR around the energy region of 12–16 MeV. The ¹⁰⁰Mo(γ, n) reaction cross-section as a function of photon energy was calculated theoretically using TALYS 1.2 computer code. The flux-weighted average values of ¹⁰⁰Mo(γ, n) reaction cross-section for bremsstrahlung having end point energy of 10 and 12.5 MeV were also calculated using the experimental and theoretical data of mono-energetic photon. The present experimental ¹⁰⁰Mo(γ, n) reaction cross-sections were compared with the bremsstrahlung flux-weighted average values of experimental and theoretical data and found to be in the lower side for 10 MeV and in the higher side for 12.5 MeV.     

Fluorine concentration profile determination in MAGNOX reactor fuel canning material

The role of fluorine, as a corrosion inhibitant was investigated by determining fluorine concentration profiles in corroded MAGNOX reactor fuel cladding material. A nuclear convolution method was employed, based on the¹⁹F(p, αγ)¹⁶O resonant reaction and prompt gamma detection. The investigation was carried out for scale thicknesses of 3.5 and 4.5 μm as determined using 4.5 MeV protons and a broad resonance in¹⁶O(p, p)¹⁶O back-scattering cross-section. The results indicate the presence of thin fluorine concentration layers near to the scale surface on both etched and pre-oxidized magnesium alloy samples. Furthermore, an additional lower concentration distribution was also observed throughout the scale of the pre-oxidized sample.     

Extraction of yttrium with molten monocarboxyl acids

A method has been developed for the determination the fluorine content from the induced activity of the short-lived nuclide²⁰F (T-11.4 s; E_λ=1.63 MeV) formed by the reaction¹⁹F(d,p)²⁰F. The method has been employed to determine fluorine in zirconium using a small-size 3 MeV deuteron accelerator for activation. The lower limit of fluorine detection is 0.5 ppm at the average deteron current of 0.3 μA.     

Production possibility of <Superscript>186</Superscript>Re via the <Superscript>192</Superscript>Os(p,α3n)<Superscript>186</Superscript>Re nuclear reaction

Experimentally measured cross-sections are presented for the first time for the ¹⁹²Os(p,α3n)¹⁸⁶Re nuclear reaction up to 67 MeV. Highly enriched thin ¹⁹²Os targets (15 pcs), prepared by electro-deposition onto Cu backings, were irradiated with an external proton beam delivered by the SSC cyclotron of iThemba LABS. The excitation function curve of the ¹⁹²Os(p,α3n)¹⁸⁶Re reaction shows a maximum cross-section of ~82 mb at about 24 MeV. According to the yield calculations based on the present results, the available cumulative no-carrier-added ¹⁸⁶Re yield is 7.76 MBq/μAh (0.21 mCi/μAh) over the energy region 13.4 → 27.3 MeV.     

Structural and impedance analysis of LiBiP2O7

A new material LiBiP₂O₇ was prepared by solid-state reaction method. The XRD analysis confirms the formation of the sample. The Raman analysis indicates the presence of characteristic bands for a (P₂O₇)⁴⁻ group in the sample. The electrical characterization was carried out using the impedance spectroscopy method in the frequency range of 1 KHz–5 MHz. The bulk conductivity of the material was extracted from the impedance analysis and was found to be in the order of 10⁻⁷ Ω ⁻¹ cm⁻¹ at 473 K. The activation energy was calculated from the Arrhenius plot and was found to be 0.37 eV. The modulus peak maximum shifts to higher frequencies with an increase in temperature and the broad nature of the peaks indicates the non-debye nature of the material. The high value for the activation energy calculated from the conductance spectrum indicates that some energy has been utilized in the creation of charge carriers.     

Fast and precise determination of fluorine in geological samples by 14 MeV neutron activation analysis

A fast and precise method of determining fluorine in geological matrices is proposed. The 0.20 MeV photopeak of¹⁹O, induced by the¹⁹F(n, p)¹⁹O reaction, was used for this assay. Neutron flux monitoring was achieved by adding an internal standard monitor (20 mg Ce) to each sample and counting the activity due to the 0.74 MeV photopeak of^139m Ce, produced in the¹⁴⁰Ce(n, 2n)^139m Ce reaction. This activity was considered to be proportional to the neutron flux during the sample irradiation. This method of fluorine determination was checked on two fluorine geological standards, mica and apatite, containing 1.50 and 2.90% fluorine, respectively. The sensitivity of the method, obviously depending upon the matrix composition, was 1.46 mg for the mica standard.     

Ab initio study of the ground state and conformational stability of peroxyacetyl nitrate in internal rotation about the peroxide bond

The molecular and electronic structure of the ground state of peroxyacetyl nitrate (PAN) was calculated by the unrestricted Hartree-Fock-Roothaan method with the use of the standard 3–21G and 6–31G basis set. The potential curve of the internal rotation about the peroxide bond of PAN was calculated with the 6–31G basis set. The curve contains two maxima. The ground state of PAN is characterized by a structure in which groups of atoms adjacent to the peroxide bond lie in planes that are perpendicular to each other (the dihedral angle ϱ(COON) is 89.9°). The calculated barriers to rotation are 19.6 and 66.8 kJ mol⁻¹. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 600–604, April, 1998.     

Errors in activation analysis by nuclear recoil

The recoil energies of up to several MeV developed during nuclear reactions involving particle emission lead to the radionuclides used in the analysis being redistributed between adjacent materials. In aluminum irradiated by reactor neutrons,²⁴Na losses were observed up to a depth of 8·10⁻⁶ m; in the adjacent silicon, a²⁴Na penetration depth was observed up to 4·10⁻⁶ m. Similar results were obtained from reaction products deriving from irradiation of Ti, Ni, N, S and Cl. This means that the results of activation analysis investigations performed for the purpose of evaluating this type of reaction might contain significant errors if thin layers, boundary zones of very small sample volumes are examined. In the analysis of surface layers on silicon devices, completely erroneous results have been obtained in some cases due to the recoil phenomena described.     

Neutron induced reactions at the Athens Tandem Accelerator NCSR “Demokritos”

The neutron facility at the 5.5 MV tandem T11/25 Accelerator of NCSR “Demokritos” can deliver monoenergetic neutron beams in the energy range from thermal to 450 keV, 4–11.5 MeV and 16–20.5 MeV via the ⁷Li(p,n), ²H(d,n) and ³H(d,n) reactions, respectively. The flux variation of the neutron beam is monitored by using a BF₃ counter and a liquid scintillator BC501A detector. The ²³²Th(n,2n)²³¹Th and ²⁴¹Am(n,2n)²⁴⁰Am as well as (n,2n), (n,p) and (n,α) reactions on natural Ge and Hf isotopes, have been investigated from threshold up to 11.5 MeV, by using the activation method. The cross section values have been determined relative to the ¹⁹⁷Au(n,2n)¹⁹⁶Au, ²⁷Al(n,α)²⁴Na and ⁹³Nb(n,2n) reference reaction cross sections.     

Determination of silicon dioxide in iron and steel-making slags and fluorspars by 14 MeV neutron activation and high-resolution gamma-ray spectrometry

Silicon as silicon dioxide in iron and steel-making slags and fluorspars was analyzed by 14 MeV neutron activation high-resolution γ-ray spectrometry. Silicon was detected by measuring the 1.78 MeV γ-ray of²⁸Al, the product of the²⁸Si(n, p) reaction, using a 30 cm³ coaxial Ge(Li) detector. A modified TPA method was used for the calculation.²⁸Al is also produced from phosphorus by the³¹P(n,α) reaction, and from aluminium by the²⁷Al(n,γ) reaction. The contribution from the former reaction could be corrected experimentally when the P₂O₅ content of the sample was known, while the latter reaction could be neglected in this neutron energy region. The experimental correction coefficient for phosphorus agreed well with the theoretical value calculated from the nuclear properties of silicon and phosphorus. Yields of²⁸Al from SiO₂, P₂O₅ and Al₂O₃ of the same weight percentages were calculated as 1, 0.426 (experimentally 0.44) and 0.0022, respectively. The results of this method agreed well with the results of the usual chemical methods. The limit of detection of SiO₂ in iron and steel-making slags and fluorspars was calculated as 0.07%. The coefficient of variation of repeated experiments was compared with the statistical one.     

Flow injection chemiluminescence determination of isoniazid with electrogenerated hypochlorite

A flow-injection chemiluminescence method for the determination of isoniazid based on the sensitizing effect of isoniazid on the chemiluminescence generating luminol-hypochlorite reaction is described. The hypochlorite was electrogenerated on-line by constant current electrolysis, thus, eliminating instability of hypochlorite solution prepared from commercially available sodium hypochlorite. The calibration graph is linear in the range 1 × 10^–8 to 1 × 10^–6 g mL^–1, and the detection limit is 6 × 10^–9 g mL^–1. The relative standard deviation for determination of 5 × 10^–8 g mL^–1 is 2.8%. The proposed method has been successfully applied to the determination of isoniazid in pharmaceutical preparations. Reveived: 2 May 1998 / Revised: 27 July 1998 / Accepted: 7 August 1998     

Determination of silicon in cast iron by 14 MeV neutron activation

Silicon in cast iron was analyzed by 14 MeV neutron activation—high-resolution γ-ray spectrometry. Silicon was detected as²⁸Al, the product of the²⁸Si(n, p)²⁸Al reaction. Interference of⁵⁶Mn was separated using a Ge(Li) detector and a biased amplifying system. The 1. 81 MeV gamma-radiation of⁵⁶Mn, which is the product of the⁵⁶Fe(n, p)⁵⁶Mn reaction of the matrix of cast iron, was used as an internal standard and for correction of the self-absorption of the 1. 78 MeV gamma-radiation of²⁸Al by the sample. The interferences of aluminum, phosphorus and manganese could be neglected according to the results calculated from their nuclear properties and contents in the cast iron of this experiment. The results of this method agreed well with the results of the usual chemical method, with errors less than 5% of the results, and the precision of the method was satisfactory with a C. V. of less than almost 6% for rapid analysis of silicon in cast iron. The analytical line through the origin with a slope of the mean value of the repetition experiments could be used as the analytical line with almost the same precision and accuracy of the results as for the analytical line calculated by the least squares method.     

Gamma-ray absorption using rubber—lead mixtures as radiation protection shields

In the present study five samples of special rubber–lead were fabricated each of them consists of lead and rubber with different weight ratios. The fabrication was carried out through the process of mixing under compression pressure. Gamma-ray transmission method was employed to determine the linear attenuation coefficient for narrow collimated mono-energetic beams of gamma-rays emitted from ²⁴¹Am 0.059, ¹⁵²Eu 0.13 and ¹³⁷Cs 0.662 MeV. The linear attenuation coefficient of standard rubber–lead shield was also experimentally determined. The percentage of lead in standard rubber–lead shield was determined through the calibration curve or by a simple computer program written in MATLAB. All prepared samples are characterized as flexible and gives a good homogeneity. samples no. 4 & 5 offers the best performance as a radiation protection shields. The results showed an inverse proportionality between the linear attenuation coefficient μ_{l and E}, and μ_l has a direct proportionality with mixing ratios (sample density). The results showed an inverse proportional between the half value layers and the average linear attenuation coefficients of the various samples.     

Spectrophotometric flow injection determination of trace iodide in table salt and laver through the reaction of iodate with 3,5-Br2-PADAP and thiocyanate

A new simple, rapid and sensitive spectrophotometric flow injection method for the determination of trace iodide is described based on an ion associate of iodate (IO₃ ^–) with 2- (3,5-dibromo-2-pyridylazo)-5-diethylamino-phenol (3,5-Br₂-PADAP) and thiocyanate (SCN^–). In a strongly acidic medium, this unstable violet product was formed with an absorption maximum at 605 nm. Flow injection is an ideal method to reproducibly monitor the transient signal. Various parameters were optimized using the Super Modified Controlled Weighted Centroid Simplex Method (SMCWC). Under the optimum experimental conditions, iodide could be determined in the range of 1.00 × 10^–6 and 2.4 × 10^–5 mol l^–1. The correlation coefficient of the calibration curve is 0.9991. With a sampling frequency of 80 h^–1, the detection limit for iodide is 5.0 × 10^–7 mol l^–1. The proposed method has been applied to the determination of trace iodide after oxidizing I^– in table salt or laver to IO₃ ^–. In addition, the mechanisms of the ion association reaction was studied. Received: 15 August 1996 / Revised: 10 October 1996 / Accepted: 16 October 1996