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.     

Light element profiling using nuclear reaction analysis on tapered corrosion sections

A scanned microbeam has been used to profile tapered corrosion sections of thickness up to 500 μm. The method of beam scanning and data collection is described and selected profiles are presented for the reactions D(³He, p)α,¹²C(d, p)¹³C,¹⁴N(p, α)¹²C and¹⁸O(p, α)¹⁵N. Finally the advantages and limitations of the technique are discussed.     

The application of nuclear techniques to high temperature oxidation studies

The¹⁸O(p, α)¹⁵N reaction has been used to determine the¹⁸O distribution in the oxides of a number of alloys which have been oxidised sequentially in natural gas and¹⁸O-labelled gas. A significant feature of all the cases investigated is the penetration of¹⁸O into the oxide formed previously in the natural gas. This penetration may occur in various ways and would be difficult to study by other techniques. The evidence presented here shows that there are subtle differences in oxidation behaviour and confirms that penetration of oxygen is a feature in the oxidation of alloys in which the predominant mechanism is transport of cations. This may have implications in explanations given to account for oxidation kinetics and adhesion and buckling of scales.     

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     

Recent developments in the analytical application of prompt spectrometry

A survey of the possibilities of analysis by alpha-induced prompt gamma-ray spectrometry is reported for 57 elements at a bombarding energy of 5 MeV. Additional data obtained at 11 and 16 MeV are given. Interference-free sensitivities are presented. The use of the position sensitive detector is introduced to overcome problems such as occur in prompt alpha spectrometry from (p, α) reactions. The technique is illustrated by studies on the reaction¹⁹F(p, α)¹⁶O and severely tested for boron analysis using the reaction¹¹B(p, α)⁸Be and measuring the α₀ and α₁ groups.     

Determination of fluorine in organic compounds by epithermal neutron activation analysis

Classical activation analysis of fluorine by thermal neutrons has a limited application because of frequent interference from chlorine, the short half life²⁰F (11.4 s) and too high dead time of detectors. A procedure is described for fluorine determination using¹⁹F (n,p)¹⁹O reaction. Use of a boron carbide shield has no effect on the activity of¹⁹O (boron ratio −1) but considerably reduces background and interference due to¹⁸O (n, γ)¹⁹O reaction. The technique has been successfully applied to the determination of fluorine in organic compounds even in the presence of large amounts of chlorine and oxygen.     

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.      

New method to measure oxygen isotopic concentration ratios18O/16O by gamma-activation analysis,especially in biological media

The photonuclear reactions used for this isotopic analysis are as follows:¹⁶O(γ, n)¹⁵O threshold energy 15.7 MeV;¹⁸O(γ, p)¹⁷N threshold energy 16.3 MeV.¹⁵O is a pure β⁺ emitter of half-life 2.03 minutes, whereas¹⁷N presents a 4.2 second neutron emission. The principle of the method is founded on the simultaneous measurement of the above characteristic radioactivities, the intensities of which are proportional to the respective quantities of¹⁶O and¹⁸O present in the irradiated sample. The potentialities of this new oxygen isotope analysis method, based on the use of an electron accelerator, are described. Detection limit of 0.1 μg¹⁸O is easily attainable. The equipment designed and built to industrialise this technique is described. It allows a hundred samples to be analysed automatically, the accelerator, detection instruments and pneumatic transfer circuits being controlled by a logic system linked to an electronic chronometer.     

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.     

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.      

Environmental isotopes (15N and 18O) in the assessment of groundwater degradation: Aveiro Quaternary aquifer (NW Portugal)

The Aveiro region, situated on the Northwest coast of Portugal is one of the most industrialized areas of Portugal. The shallow Quaternary aquifer system, mainly of detrital sediments of Pleistocene and Holocene ages, is still today an important water resource for this region despite growing evidence of diffuse pollution problems. Isotope techniques have been used to evaluate the aquifer vulnerability to nitrate contamination (δ¹⁸O and δ¹⁵N from NO₃ and δ²H and δ¹⁸O from H₂O). Nitrogen isotopes were used to identify nitrogen sources and assess agriculture, cattle-breeding, urban and industrial contributions to the nitrogen cycle in the Aveiro ecosystem.     

Oxygen and nitrogen in coal by instrumental neutron activation analysis

The feasibility of using fast neutron (14 MeV) activation analysis techniques for the determination of oxygen and nitrogen in coal has been investigated. Conditions that favor instrumental neutron activation analysis (INAA) include the absence of problems associated with sample dissolution and the capability of extremely rapid analyses as compared to older techniques such as the Kjeldahl method for nitrogen. Most previous oxygen determinations have been by difference after major component analyses. In the present study, oxygen was determined in sized coal and its low temperature ash (LTA) with the difference representing the organic oxygen content. Both the oxygen and nitrogen analyses employ a multiscaling technique with the former based on the¹⁶O(n, p)¹⁶N reaction, while the latter utilizes the annihilation radiation produced by the product of the¹⁴N(n, 2n)¹³N reaction. The high-energy gamma-radiation associated with the decay of¹⁶N was essentially free of spectral interferences for coal analysis, although fluorine could cause a primary interference if the F/O ratio exceeds 0.02. In the nitrogen work, experiments were performed to determine correction factors to account for the effects of the¹²C(p, γ)¹³N and¹³C(p, n)¹³N “knock-on” reactions and the³⁹K(n, 2n)³⁸K reaction which produce interfering β⁺ emitting radionuclides. Data are presented for oxygen in Western Kentucky No. 9 and No. 11 coal and coal ash and for nitrogen in eleven different coals.     

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.     

Dose verification by activation in vivo following proton beam eye radiotherapy

This work presents the measurements of proton activation of a group of 15 patients following proton radiotherapy of the eye. Despite the heterogeneity in activation response and reaction cross section compared with the applied uniform dose, it can be shown that induced activity may be related to incident fluence volume and thus provide verification of applied dose. This proton treatment provides in vivo information that is normally unused. Up to 400 kBq was measured at 100-second post-treatment. Significant correlation of the ¹⁵O 511 keV activity with fluence volume is shown. The patient γ-ray spectra are tabulated and discussed. The longer-lived ⁷Be (T _1/2 = 53.1 d) activity, from O and C activation, may provide an additional means of dose verification. The potential of (p,p’γ) reactions was examined by irradiation of phantoms. High energy γ-rays from O and C were measured with a large NaI(Tl) detector, with a yield of 125 γ/cm²/mGy for the ¹⁶O(p,p’γ) reaction.     

Light elements analysis and application to glass industry

Nuclear reactions induced on light elements by low energy deuterons are investigated. Differential cross-sections for¹⁰B(d, β₀)⁸Be,¹⁰B(d, β₁)⁸Be,¹²C(d, p₀)¹³C,¹⁴N(d, β₀)¹²C,¹⁴N(d, β₁)¹²C,¹⁶O(d, p₀)¹⁷O,¹⁶O(d, p₁)¹⁷O and¹⁶O(d, β₀)¹⁴N reactions are measured between 0.5 and 3 MeV at an observation angle of 135° with respect to the incident beam. Possible application of these reactions to the measurement of surface concentration is considered—Special emphasis was given on nitrogen determination in order to study nitrogen concentration in industrial glasses. Surface nitrogen repartition on glass, origin of nitrogen, influence of oxidizing and reducing conditions and glass structure are discussed.     

Determination of boron, fluorine and some medium Z elements in diet samples

As part of the study on “Reference Asian Man” project, dried food from different Asian countries, in powdered form, was analyzed applying different techniques. Boron was determined by measuring prompt alphas in ¹¹B(p,α)⁸Be reaction with 800 keV protons. Coulomb excitation was used for F and Na determination based on ¹⁹F(p,p'γ)¹⁹F (γ -rays: 110 and 197 keV) and ²³Na(p,p'γ)²³Na (γ -ray: 440 keV) reactions with 2.3 MeV protons. The elements Sc, Co, Zn, Rb, Ag and Ce were determined by neutron activation analysis. The elements Ca, Mn, Fe, Ni, Cu, Zn, Sr and Mo were determined by X-ray fluorescence technique. This revised version was published online in August 2006 with corrections to the Cover Date.     

A theoretical investigation of hydrogen bonding effects on oxygen and hydrogen chemical shielding tensors of aspirin

A computational investigation was carried out to characterize the ¹⁷O and ¹H chemical shielding (CS) tensors in crystalline aspirin. It was found that O–H⋯O and C–H⋯O hydrogen bonds around the aspirin molecule in the crystal lattice have a different influence on the calculated ¹⁷O and ¹H CS eigenvalues and their orientations in the molecular frame of axes. The calculations were performed with the BLYP, B3LYP, and M06 functionals employing 6-311++G(d,p) standard basis set. Calculated CS tensors were used to evaluate the ¹⁷O and ¹H chemical shift isotropy (δ_iso) and anisotropy (Δσ) in crystalline aspirin, which are in reasonable agreement with available experimental data. The difference between the calculated NMR parameters of the monomer and molecular clusters shows how much hydrogen-bonding interactions affect the CS tensors of each nucleus.     

Conductance Studies on Complex Formation Between Aza-18-Crown-6 with Ag+, Hg2+ and Pb2+ Cations in DMSO–H2O Binary Solutions

The complexation reactions between Ag⁺, Hg²⁺ and Pb²⁺ metal cations with aza-18-crown-6 (A18C6) were studied in dimethylsulfoxide (DMSO)–water (H₂O) binary mixtures at different temperatures using the conductometric method. The conductance data show that the stoichiometry of the complexes in most cases is 1:1(ML), but in some cases 1:2 (ML₂) complexes are formed in solutions. A non-linear behaviour was observed for the variation of log K _f of the complexes vs. the composition of the binary mixed solvents. Selectivity of A18C6 for Ag⁺, Hg²⁺ and Pb²⁺ cations is sensitive to the solvent composition and in some cases and in certain compositions of the mixed solvent systems, the selectivity order is changed. The values of thermodynamic parameters (ΔH _c^o, ΔS _c^o) for formation of A18C6–Ag⁺, A18C6–Hg²⁺ and A18C6–Pb²⁺ complexes in DMSO–H₂O binary systems were obtained from temperature dependence of stability constants and the results show that the thermodynamics of complexation reactions is affected by the nature and composition of the mixed solvents.     

The use of stable isotopes ratios for authentication of fruit juices

The determination of the content of stable isotopes, ¹⁸O and ²H, respectively, in juice water facilitates the distinction between authentic juices and juices made from concentrates by redilution with tap water. At the same time, the detection of C₄ cane or corn-derived sugar syrups in fruit juices which are produced from C₃ fruit types is thus facilitated by the characteristic differences in ¹³C/¹²C, expressed as δ ¹³C (‰) values due to photosynthetic CO₂ assimilation via the C₃₋, C₄₋, and crassulacean acid metabolism pathways. In this study, the quantitative determination of water added to an authentic juice, on the basis of δ ¹⁸O, and δ ²H values, respectively, was successfully performed. Also, the δ ¹⁸O, and δ ²H of juice water and δ ¹³C of the whole juice in 18 samples were also determined. The results obtained provided us with the possibility of distinguishing between authentic fruit juices and those obtained by redilution of concentrated fruit juices and the detection of C⁴ type added sugar.