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  • Author or Editor: J. Debrun x
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Résumé  

Nous montrons que l'activation par les protons de 11 MeV permet le dosage non destructif de traces d'impuretés dans des échantillons d'Argent, d'Aluminium et de Cobalt. Nous avons pour le moment étudié le dosage de 30 éléments dans Al et Co et de 24 dans Ag. Nous avons choisi les protons car ces particules sont les seules qui permettent d'effectuer un dosage non destructif dans Ag et Co, au niveau des traces sans interférence, et ceci pour de nombreux éléments. Le cas de l'aluminium a été étudié, bien que les neutrons puissent ici être utilisés pour l'analyse non destructive car l'activation dans les protons permet de doser facilement des éléments autres que ceux dosés en irradiant dans les neutrons. Ces premiers résultats nous conduisent à penser que l'activation dans les protons sera très employée dans les cas où l'activation neutronique est en difficulté (exemple de Ag, Co, Ir, HgTe, AsGa, terres rares, etc.).

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Abstract  

Tritons accelerated up to 3.5 MeV by a Van de Graaff, were used to study the16O(T, n)18F reaction, which was then applied to the analysis of oxygen in metals and semiconductors. The calculated sensitivity for the determination of oxygen is 0.5 ppb at 3.5 MeV. Si, Ti and Mo were analyzed non-destructively at 3.5 MeV and the results agreed with results obtained by other methods. Pure Ge and AsGa were analyzed non-destructively at 3 MeV and the detection limits were respectively 25 and 6 ppb.

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Abstract  

We have irradiated 30 elements with 11 MeV protons and we present here: (1) The specific activities for the main radioisotopes produced by (p, n) or (p, α) reactions (on main γ rays except the 511 keV). (2) The main γ energies of these radioisotopes (at ±0.3 keV) when they have not been accurately measured previously. (3) The limits of detection or the lowest amounts measured in samples of Al, Ag or Co. From these preliminary results it can be deduced that 11 MeV protons offer new possibilities in the field of activation analysis.

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Abstract  

The sensitivities for the determination of 25 elements from Z=4 to Z=33, using 3.5 MeV triton activation, were calculated from experimentally measured yields for 50 radioisotopes obtained via (t, n), (t, d), (t, 2n) or (t, α) reactions. For an irradiation of 1 hour at 1 μA, the calculated detection limits are better than 100 ppb for B, N, O, F, Na, Mg, Al, Si an S. Because of the Coulomb barrier, triton activation is of considerable interest for non destructive analysis of low Z elements in medium and high Z matrices. Finally integrated activation curves of high sensitivity elements were determined.

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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  

The oxygen and carbon concentrations on metal surfaces were determined by two methods. The first method was based on the detection of the emitted particles in the12C(d,p)13C and16O(d, p)17O reactions, the second one on the measurement of the induced radioactivities in the12C(d,n)13N and16O(t,n)18F reactions, respectively. The results, obtained by the two different methods for high purity metals, were in agreement. A type of error which exists in the determination of trace amounts of carbon and oxygen in pure metals by combustion and reductive fusion was quantitatively demonstrated. This error exists also in the determination of oxygen by 14 MeV neutron bombardment.

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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  

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  

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  

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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