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.     

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 profiles in Antarctic meteorites by nuclear reaction analysis (NRA)

Terrestrial fluorine enrichment on Antarctic meteorites can be measured by detection of γ-rays from the nuclear reaction ¹⁹F(p,αγ)¹⁶O, which is induced by a scanning proton beam. The technique (Nuclear Reaction Analysis by Proton Induced Gamma Emission: PIGME-NRA) allows simultaneous measurement of distribution and concentration without any chemical sample treatment and is not destructive. By using two detectors (HPGe and NaI) and taking into account the background contribution of the main interfering elements, the detection limit is below 10 μg/g. The information obtained allows to estimate the maximum exposure duration of meteorites on the Antarctic ice surface. Received: 15 July 1997 / Accepted: 11 December 1997     

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 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 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.      

Trace analysis of fluorine by the Coulomb excitation method

The reaction¹⁹F(p, p′ γ)¹⁹F was used for the determination of fluorine concentration in biological materials such as lichen tissues and human bones. By means of this method, fluorine air contamination in the vicinity of aluminium works and the level of fluorine intoxication of exposed persons were investigated.     

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.      

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.     

Utilization of cyclotron produced fast neutrons in the activation analysis for oxygen

The possible application of cyclotron-produced fast neutrons to activation analysis for oxygen based on the¹⁶O(n, p)¹⁶N reaction has been investigated. Neutrons were produced by bombarding a thick beryllium target with 22 to 45 MeV deuterons. It was found that the sensitivity increases rapidly with the energy of the deuterons. Using 45 MeV deuterons and a 10 μA beam current a sensitivity of about 20 counts per 1 μg oxigen could be achieved, enabling the determination of less than 1 μg oxigen. In a direct comparison it was experimentally established that the sensitivity for cyclotron-produced neutrons assuming a deuteron beam of about 10 μA, is up to two orders of magnitude higher than that achievable for 14 MeV neutrons with a flux of about 10¹⁰ n/s. The interference of fluorine is at about the same level for both the cyclotron-produced and 14 MeV neutrons. Using cyclotron-produced fast neutrons in the investigated energy range, sodium and magnesium can also interfere, but only to a very much lower extent.     

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.     

A study of thermally oxidized SiO2 surface layers by means of nuclear reactions

Conclusions The nuclear reaction from low-energy deuteron-bombardment has proved to be a valuable tool for surface oxide layer examination. Using the¹⁶O(d, p)¹⁷O and¹⁶O(d, α)¹⁴N reactions, some important properties of Si−SiO₂ structures, such as total number of oxygen nuclei and oxygen concentration profile, can be determined in one measurement with an accuracy of several percent, within one hour. Some effects of oxygen deficiency in SiO₂ layers of thicknesses exceeding 6000 ? have been found. A more detailed study of this effect will be the subject of forth-coming experiments.     

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.     

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%.     

Epithermal/Fast Neutron Cyclic Activation Analysis for the Determination of Fluorine in Environmental and Industrial Materials

Pseudocyclic activation analysis (12-second irradiation, 12-second count, 5 cycles, 25 minutes between cycles) is used to determine fluorine in plastic and rubber with detection limits in the range 15–40 mg/kg. The detection of fluorine in materials containing high concentrations of aluminum is improved using the ¹⁹F(n,p)¹⁹O reaction, induced by fast neutrons, (30-second irradiation, 30-second count, 25-minute decay between cycles). The method was applied to a biomonitoring survey in the vicinity of an aluminum smelter in the Årdal region, Norway. The fluorine concentration in the moss and soil samples could be determined in all samples above the detection limits of 50 and 100 mg/kg, respectively.     

Application of prompt activation analysis in the determination of fluorine in tea,in international geochemical standards,bones and teeth of experimental animals

By making use of the ¹⁹F(p,αγ)¹⁶O reaction the F-concentrations of different varieties of tea leaves, of some international geochemical reference materials, and of the bones and teeth of some experimental animals have been determined. The tea leaves from Ceylon (ordinary), Orange Pekoe (special Ceylon), China (ordinary black), Lapsang Souchong (special smoked Chinese) and Darjeeling (India) were found to contain 170 ppm, 170 ppm, 120 ppm, 160 ppm and 100 ppm of fluorine, respectively, The F-concentrations of established geochemical reference materials, NIM-D, NIM-N, NIM-P and NIM-S, from the National Institute of Metallurgy, South Africa were determined to be 60 ppm, 120 ppm, 130 ppm and 190 ppm, respectively. The bones of rabbits, who were given fluoridated water, were found to contain much higher amount of fluorine than the bones of the control rabbit. Furthermore, the rabbits who were kept on fluoridated water for 45 days, had almost double the amount of F in their bones than the rabbits who were given fluoridated water for only 15 days. Similarly, the teeth of grown-up monkeys who were given fluoridated water since birth had double the amount of fluorine than those of the control monkey.     

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.     

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.     

Determination of lithium and halogens and the significance of lithium to the understanding of cosmochemical processes

With a newly developed method fluorine and the other halogens have been measured in terrestrial, meteoritic and lunar samples. As a valuable byproduct lithium was determined also via teh reactions⁶Li (n,α)t→¹⁶O (t, n)¹⁸F. From our measurements the following new values for the “cosmic” abundance are derived (in atoms per 10⁶ Si atoms) F 750, Cl 4350, Br 8.83, and I 1.14. We could show that the Li/Be or Li/Zr ratios can be used to estimate the ratio of the Mg-silicates to the group of refractory elements and in course to calculate the bulk composition of the Moon and other planetary objects.