Determination du fluor dans les milieux aqueux par activation au moyen de photons gamma

An apparatus ensuring identitical irradiation conditions for three samples and a standard of large volumes is reported. The interference caused by the protons originating from the¹⁶O(γ, p)¹⁵N reaction is determined. Results show that the secondary rection¹⁸O(p, n)¹⁸F induced by the protons of the former reaction gives an apparent fluorine content in natural waters of 0.015 μg/g for a maximum gamma photon beam energy of 21 MeV.      

Determination de L’oxygene et du fluor au moyen de l’activation par les photons γ et le comptage des neutrons retardes emis par17N

The activation of¹⁸O and¹⁹F by the reactions¹⁸O(γ, p)¹⁷N and¹⁹F(γ, 2p)¹⁷N was determined as a function of the maximum energy of the bremsstrahlung beam. By the use of this method it is possible to measure oxygen or fluorine by counting the delayed neutrons emitted by¹⁷N with a half-life of 4.2 sec.      

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.     

Determination de C,N, O,F et de quelques autres elements par activation au moyen des photons gamma

The (γ, n) activation curves for 17 elements were determined as a function of energy between 25 and 42 MeV. From these are deduced the detection sensitivities intrinsically possible for an average beam intensity of 100 μA. Our experimental results are compared with values calculated byG. J. Lutz. The activation curves relative to certain competitive nuclear reactions on N, O and Na, liable to interfere in the measurements of C, N and F, were also determined. It is shown that the relative importance of these competitive nuclear reactions decreases rapidly for energies below 30 MeV and becomes practically negligible at 25 MeV.      

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.     

New gamma-ray intensities for the <Superscript>14</Superscript>N(n,γ)<Superscript>15</Superscript>N high energy standard and its influence on PGAA and on nuclear quantities

The ¹⁴N(n,γ)¹⁵N reaction is a primary γ-ray source for high energy calibration of detectors. The relative γ-ray-intensities of ¹⁵N and the relative γ-ray detection efficiency function have been simultaneously determined up to 10 MeV from γ-peak areas alone. Absolute γ-ray-intensities were obtained with proper renormalization to known absolute intensity. The influence of these new intensity values are assessed for use in PGAA. Any consistently used set of calibration intensities applied in the creation of library values and for analysis do not influence the concentrations. Contrary to this, quantities based on sums of γ-ray cross sections may provide different answers with the new ¹⁵N intensities and they give means to validate them.     

Production of18F with an18O enriched water target

A target system for the production of nucleophilic 110-min¹⁸F from isotopically enriched /¹⁸O/H₂O is described. The process occurs via the nuclear reaction¹⁸O/p,n/¹⁸F, the available proton beam of 72 MeV must be degraded to the entrance energy of 15 MeV. This process is in regular use for the batch production of 0.8–1 Ci¹⁸F.     

Etude de la reaction 14N(d.n)15O a basse energie et application au dosage de l'azote dans le zirconium

Study of the ¹⁴N(d,n)¹⁵O reaction at low energy and application to the determination of nitrogen in zirconiumThe thick target yield for the ¹⁴N(d,n)¹⁵O reaction weis determined between 1 MeV and 5.5 MeV; the “average energy” and the sensitivity of the analysis for nitrogen are calculated. Nitrogen can be determined in zirconium samples at the level of 35 μg g^?1, by irradiating at 4 MeV and 5.5 MeV in a deuteron beam from a Van de Graaff accelerator. After irradiation, the samples are subjected to reducing fusion in a graphite crucible, to separate ¹⁵O. The results are compared with those obtained by other methods on identical samples; there is a difference of 3–17%.     

The state of metals in the Pt/Al2O3 and (Pt-Cu)/Al2O3 catalysts as indicated by IR spectroscopy with isotope dilution of 12C16O with 13C18O molecules

Adsorption of ¹³C¹⁸O+¹²C¹⁶O mixtures on the Pt(2.9%)/γ-Al₂O₃, (Pt(2.6%)+Cu(2.7%))/γ-Al₂O₃, and (Pt(2.6%)+Cu(5.1%))/γ-Al₂O₃ catalysts was studied by FTIR spectroscopy. On the metallic Pt surface at coverages close to saturation, CO is adsorbed both strongly and weakly to form linear species for which the vibrational frequencies of the isolated ¹³C¹⁸O molecules adsorbed on Pt are ∼1940 and ∼1970 cm⁻¹, respectively. The redistribution of intensities of the high-and low-frequency absorption bands in the spectra of adsorbed ¹³C¹⁸O indicates that these linear forms are present on the adjacent metal sites. The weak adsorption is responsible for the fast isotope exchange between the gaseous CO and CO molecules adsorbed on metal. The Pt-Cu alloys, in which the electronic state of the surface Pt atoms characteristic of monometallic Pt remains unchanged, are formed on the surface of the reduced Pt-Cu bimetallic catalysts. The decrease in the vibrational frequencies of the isolated C=O bonds in the isolated Pt-CO complexes suggests that the CO molecules adsorbed on the Cu atoms affect the electronic properties of Pt. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 831–836, May, 2007.     

Determination of relative and absolute abundance of stable nitrogen isotopes by proton induced nuclear reactions

Thick-target yield of γ-rays emitted in the reactions¹⁴N(p,p′γ₁)¹⁴N and¹⁵N(p,αγ₁)¹²C were measured as a function of bombarding energy in order to select the conditions favoring the employment of these reactions in nitrogen isotopic analysis. The applicability of these reactions in the determination of relative as well as absolute nitrogen isotopic abundances was demonstrated at 4.3 MeV bombarding energy. Supported in part by the International Atomic Energy Agency, Vienna, Austria.     

Determination of nitrogen and fluorine in air-dust samples by photon activation

Summary Air-dust samples with masses of 12 mg each were analysed instrumentally for their nitrogen and fluorine content by photon activation. The samples were irradiated with photons of maximum energy,E _max=15MeV. The nuclear reactions¹⁴N(, n)¹³N and¹⁹F(, n)¹⁸F give two positron emitters. The positrons react with electrons, emitting annihilation radiation. The 511-keV peak of the annihilation radiation of¹³N and¹⁸F is measured simultaneously and the decay curve is taken. The half-lives of 9.96 and 109.7 min allow a quantitative separation. By choosingE _max=15 MeV for the activation we eliminate interference from carbon and oxygen. The activation threshold for the n,-reaction of carbon is 18.72 MeV and for oxygen 15.67 MeV, while the activation threshold for N is 10.55 MeV and for F 10.44 MeV. The detection limit for the instrumental method is 4g for both nitrogen and fluorine.

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Die Analyse von Stickstoff und fluor in Luftstaubproben durch Photonenaktivierung

Zusammenfassung An Luftstaubproben von 12 mg Masse konnte der Gehalt an Stickstoff und Fluor durch Photonenaktivierung zerstörungsfrei bestimmt werden. Die Proben wurden mit Photonen einer Energie von E_max=15 MeV bestrahlt. Die 511-keV-Linie der nach¹⁴N (, n)¹³N und¹⁹F (, n)¹⁸F entstandenen Nuklide wurde simultan gemessen und die Zerfallskurve aufgenommen. Die Halbwertszeiten 9,96 und 109,7 min liegen so weit auseinander, daß eine quantitative Trennung möglich ist. Durch Wahl der Aktivierungsenergie treten keine Störungen durch Sauerstoff und Kohlenstoff auf, da die Aktivierungsschwellen für die, n-Reaktionen von C bei 18,72 MeV und von O bei 15,67 liegen, während sie für N bei 10,55 MeV und für F bei 10,44 MeV liegen. Die Nachweisgrenzen liegen beim zerstörungsfreien Verfahren bei 4g für N und für F.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Non-destructive profiling of fluorine in teeth to large depths

A new method for non-destructive depth profiling of fluorine has been developed which extends the profiling range to much larger depths than hitherto possible. In this method the thick-target yield of 6–7 MeV gammas from the reaction of ¹⁹F(p,αγ) ¹⁶O in the tooth sample, was measured as a function of the incident energy from threshold to up to 2.7 MeV and the yield curve plotted. This curve was compared to the calculated yield curve of 6–7 MeV gammas from the same reaction but on an enamel matrix containing uniformly distributed fluorine. The difference in the shape of the two curves was only due to the non-uniform distribution of fluorine in the tooth sample, which could then be calculated. By making use of this method F-depth profiles in teeth of monkeys were determined non-destructively to a depth of 14 μm. This method is also applicable for profiling other elements through appropriate resonant or non-resonant nuclear reactions.     

Determination of nitrogen in steels by alpha-induced prompt gamma-ray spectrometry

The prompt gamma-ray of 871 keV emitted during the bombardment of steels by 5 MeV alpha particles were used to determine nitrogen by means of the reaction¹⁴N(α, pγ)¹⁷O. The method is non-destructive, rapid and experimentally simple. It has a sensitivity of about 7 μg·g⁻¹. In the nitrogen concentration range of 10¹–10² μg·g⁻¹ the relative precision of the method is about 3%. The accuracy of the method compares with that of other nuclear methods. Presented at the 5th Symposium on Recent Developments in Activation Analysis, Oxford, 17–21 July, 1978.     

Stopping power effects in the determination of14N by a resonance reaction

The applicability of the¹⁴N(p,p’ γ₁)¹⁴N nuclear reaction in the determination of the absolute abundance of¹⁴N, with a 2% uncertainty, was demonstrated at 4.3 MeV bombarding energy. The fact that almost all of the thick target γ-ray yield resulted from a resonance at Ep=4.0 MeV allowed to consider the necessary stopping-power corrections only at the energy of that resonance. Alternatively, the method was used to obtain the stopping power of 4.0 MeV protons in complex biological materials. Supported in part by the International Atomic Energy Agency, Vienna, Austria.     

Determination of fluorine by the spectrometry of prompt gamma-rays

The use, for analysis, of prompt gamma-rays excited by 5 MeV alpha-particles from the reactions¹⁹F(α,α′γ)¹⁹F,¹⁹F(α, nγ)²²Na and¹⁹F(α, pγ)²²NE, was studied. The precision of the analyses depended on the gamma-ray energy used for the measurement. Relative standard deviations were ±1.8, ±0.9 and ±1.3% using the 110-, 197- or 1275 keV gamma-rays. The method was tested with N. I. M. standard materials of calcium fluoride and fluorspar, and was used as a rapid method for the determination of fluorine in cements.     

Determination des fonctions d'excitation des reactions19F(p, α0)16O et7Li(p, α0)4He entre 150 et 1800 keV

The experimental device used is described. Excitation functions are given for an angle of observation 150° with respect to the incident beam. The possibilities of applying these reactions to the measurement of surface lithium and fluorine concentrations are considered. The detection limits for these two elements are shown to be 5·10⁻³ μg·cm⁻² with protons of energy between 1,350 and 1,500 keV. The method is compared with that based on the detection of prompt γ-rays from the reactions⁷Li(p, γ)⁸Be and¹⁹F(p, α γ)¹⁶O.      

Determination of carbon impurities in epitaxial layers from semiconductor silicon by means of charged particles

The energy-dependent range of charged particles in activation analysis according to the reaction¹²C(d,n)¹³N permits the method to be applied to carbon determination in model epitaxial layers of sufficient thickness. We investigated 100 μm epitaxial layers of the n-type and undoped 50 μ layers as to p⁻ Czochralski substrates. Deuterons were slowed down with Cu and Ta foils having a limiting energy of 13.5 MeV, to 4.2 MeV and 2.9 MeV, respectively. In the resulting activation depths of 52 and 102 μm, the sensitivity of the method, which is 3·10¹⁴ at ·cm⁻³C at E_d=10 MeV in silicon, is reduced to 25% and 10%, respectively. An optimal flux of 0.9 μA·cm⁻² was maintained. After irradiation, 20 or 10 μm were etched off. The sample was inductively fused at 1500 K in a Pb₃O₄/B₂O₃ mixture.¹³N was passed with He as carrier gas into an absorption vessel kept at 77 K, and its activity was measured in γ, γ-coincidence.     

Investigation of water diffusion into quartz using ion beam analysis techniques

Diffusion of water into quartz was studied by measuring H and ¹⁸O concentration profiles in surface layers of quartz samples treated hydrothermally in the range of 125° C to 200° C. Sample surfaces were orientated normal to the c-axis. The measurements were performed using the nuclear reactions ¹H(¹⁵N,αγ)¹²C and ¹⁸O(p,α)¹⁵N. The diffusion profiles have widths of up to 500 nm. Diffusion rate constants derived from the profiles are in the range of 10^–15 cm²/s to 10^–18 cm²/s and show a distinct temperature dependence, yielding a rough estimate of about 60 kJ/mole for the activation energy. Received: 24 June 1996 / Revised: 20 January 1997 / Accepted: 22 January 1997     

Comparison of the3He/16O and1H/18O prompt nuclear reactions for lattice location measurements of oxygen in niobium

Experimental data are presented for comparison of the determination of oxygen by the¹⁶O(³He, p)¹⁸F,¹⁶O(³He, α)¹⁵O and¹⁸O(p, α)¹⁵N prompt nuclear reactions, and of their use in the lattice location, by the ion-channelling technique, of oxygen atoms in single crystal targets of elements such as niobium, where oxygen contents of ≈0.1 atomic % or more can be obtained. Both reaction cross-sections and lattice-defect production rates are considered in the comparison. Details are given of an arrangement for automatic crystallographic angular scanning of nuclear reaction and backscattering yields in channelling/lattice location measurements.     

The determination of carbon,nitrogen and oxygen in gases by neutron time-of-flight spectrometry

Carbon, nitrogen and oxygen were determined in gases by time-of-flight spectrometry of prompt neutrons from the respective reactions¹²C(d, n)¹³N,¹⁴N(d, n)¹⁵O and¹⁶O(d, n)¹⁷F, produced by a pulsed beam of deuterons of 2 MeV (for nitrogen) or 3 MeV. The analysis is non-destructive and requires about 15 min. per sample. The relative standard deviation for all three elements was about ±3%. Detection limits, using a total irradiation current of 20 millicoulombs, for carbon, nitrogen and oxygen, respectively, were 6·10⁻⁸ g, 2·10⁻⁷ g and 1.7·10⁻⁷ g per cm² cross-sectional area of irradiating beam.