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  • Author or Editor: G. Blondiaux x
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Abstract  

During ion bombardment, thermal diffusion and radiation enhanced diffusion of atoms occur. These phenomena may be a source of error in ion beam analysis, particularly in radioactivation analysis if contaminant surface atoms are present. It is shown here that penetration of18F (derived from surface oxygen by nuclear reaction) in germanium single crystals, does not extend appreciably farther than the maximum range of the recoiling18F nuclei. Since the analyzed depth is over an order of magnitude larger than the recoil, the validity of charged particle activation analysis at the ppb level in the present case (oxygen→18F in germanium), is clearly demonstrated.

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Abstract  

The 12C(d,n)13N reaction, at 2 MeV, was used for the stoichiometric determination of carbon in reference materials and sintered pellets of SiC ceramics. The preliminary results show higher percentage of carbon on the surface in comparison to the core of the sintered ceramics, indicating the existence of carbon contamination on the surface, possibly caused by the sintering process itself.

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Abstract  

Ubiquitous elements like carbon and oxygen always contaminate surfaces and, therefore, are the soucre of important analytical errors at trace level. Even in the case of radioactivation (with charged particles), where the sample can be etched after irradiation, analytical problems exist. In this work, we show that laser desorption/ablation can efficiently clean surfacaes, in the case of GaAs samples, resulting in better analytical conditions. Under ultra high vacuum, these surfaces remain clean long enough, so that the analysis of carbon and oxygen can be carried out using various nuclear methods, according to the needs of the analyst.

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Abstract  

Some studies show that a coral implanted on bone tissue is gradually transformed to become a neoformed bone. In our work, we have, for the first time, determined quantitatively by NAA the transformation of a coral used as a biomaterial implanted in vivo in some ovine jaw-bones. Each month and during 9 months, biopsies were extracted. For neutron production, the nuclear reaction9Be(d,n)10B was used with 17.5 MeV energy deuterons. The neutrons had a mean energy of 7 MeV and a flux of 1012n cm–2s–1. The radioactivation generated permitted concentration measurements of Ca, P, Mg, Sr and F in each part of the biopsies and a study of mineral transformations versus time in the coral implanted. Three months after implantation, Ca belonging to CaCO3 represented 11% and Ca provided by the apatite formed represented 20% of the total mass. These quantitative evaluations clearly showed that five months after implantation, the coral had become a neo-formed bone.

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Abstract  

A method for boron determination based on 11B(p, a)8Be reaction is described. The irradiations were performed with 800 keV protons and the alphas were counted with 2 PIPS detectors at an angle of 150° to the beam direction. The method is simple and permits the determination of boron at g/g level in biological materials and sub-g/g level in metals, alloys etc.

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Abstract  

It is shown that the instrumental analysis of carbon and oxygen in GaAs, at trace level, can be achieved by irradiation with low energy deuterons and tritons (3 MeV). The experimental sensitivities are 6 ppb/weight for the16O( 1 3 H,n)18F reaction and 25 ppb/weight for the12C( 1 2 H,n)13N reaction. Applications related to the metallurgy of GaAs are described.

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Abstract  

In orthopaedic surgery, synthetic biomaterials encountered a great success. In this work, the “in-vivo” behaviour of aragonite synthesized in our laboratory was studied. The in vivo experiments have been carried out on femurs sites of nine ovine. Neutron activation analysis was applied to evaluate the ossification kinetics of synthetic aragonite. The content of several elements (Ca, P, Sr and Mg and phosphorous to calcium ratio) were determined versus time after implantation. Results showed that the biomaterial undergoes a lot of transformations during time. The chemical composition of the aragonite was modified and progress to become close to that of an ovine bone. Biological studies assess its biocompatibility.

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Abstract  

Two important problems are discussed: equations and data used for quantitation on one hand, diffusion under irradiation on another hand. It is suggested that recent semiempirical stopping power data for hydrogen and helium are sufficiently accurate to be used in any good calibration method, while for heavier ions it is preferable to use the “double reaction method”, which avoids the use of stopping power data. The problem of the additivity of the stopping powers in the case of compounds is also discussed and it is shown in a specific case that BRAGG-KLEEMAN's rule is valid. Deep diffusion under irradiation has sometimes been mentioned (e.g. F in Ge, Cu in Si): it can be an important source of errors in trace analysis. The possible deep diffusion of F in Ge has been studied: it is shown that such a diffusion does not occur, while surface contamination problems can lead to erroneous observations.

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Abstract  

Gamma-ray self-absorption in stainless steel samples has been studied with an experimental method based on fast neutron activation and a Monte Carlo calculation technique adapted to the experimental conditions. A relation between self-absorption and absorption of -photons inside stainless steel samples was found. The influence of the -ray energy and sample depth have been investigated. Agreement between the two methods has been found.

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Abstract  

InP samples were analyzed by charged particle activation analysis. Proton activation at 12 MeV permits the nondestructive survey of 30 elements. The main impurities are Ti, Fe, Ga and Zn (1015 to 2·1016 at/cm3). Oxygen was analyzed separately by triton activation at 3 MeV; the oxygen concentration is normally less than 1016 at/cm3.

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