A. Giovagnoli

Etude des possibilites d'utilisation analytique des isomeres nucleaires produits par reactions (γ, γ′) entre 6 et 8 MeV

en The production of metastable isomers by irradiation of Ge, Se, Br, Sr, Y, Zr, Rh, Ag, Cd, In, Sn, Te, Ba, Er, Yb, Hf, W, Os, Ir, Pt, Au, Hg and Pb in the bremsstrahlung of 6 to 8 MeV electrons was studied. An analytical methodology was developed and accurate analysis of noble metals in their metallurgical residues was achieved.

Study of the incorporation and repartition of boron and carbon in Czochralski grown GaAs using charged particles activation

Charged particles activation methods were developed to study the incorporation and the repartition of B and C at trace level in GaAs ingots grown by the Czochralski method with liquid B2O3 encapsulation. The 10B(d, n)11C and 12C(d, n)13N reactions were used for the analysis of boron and of carbon. Radiochemical separations of 11C and of 13N after irradiation were necessary. For the separation of 11C the samples were oxidized in a mixture of B2O3 and Pb3O4, and CO2 was trapped in KOH. For the separation of 13N, the samples were fused under argon in a graphite crucible, and N2 trapped on titanium at 900°C. Detection limits were ∼1014 at./cm3 for carbon and 3×1014 at./cm3 for boron. Important (factors ⋍ 50) concentration variations could be correlated to the growth conditions, particularly the percentage of water in B2O3. A segregation of B and C in the ingots was also observed. B concentrates at the tail end, and C concentrates at the seed end.

Studies on Polycrystalline Silicon for Solar Applications, including Characterization of Trace Elements B, C and Al by Charged Particles Activation Analysis

Nuclear methods of analysis were used to study the behaviour of trace elements during the metallurgy of polycrystalline silicon for solar applications: these impurities may have an influence on the efficiency of the solar photocells made out of this silicon. The ingots were prepared in a graphite boat by the Bridgman method without seed, using electronic grade silicon as a starting material. Most impurities were determined by neutron activation, the global level being low: ¿ 3.1015 at/cm3. Charged particles were used to determine B, C and Al. For boron, the 10B (d,n)11C reaction with subsequent chemical separation of 11C was used; for carbon, we used non-destructive analysis and the 12C(d,n)13N reaction. For low levels of aluminum in silicon no suitable method existed; we could solve this problem using fast neutrons from the 9Be (d,n)10B reaction and the reaction 27A1 (n,¿)24 Na. Interferences from Mg (undetected) and from Si itself were negligible, the detection limit being 5.1014 at/cm3 in ultra pure silicon. High Carbon levels were found close to the solubility limit (2.1018 at/cm3); there is a significant segregation at the top, at the edges and at the bottom of the ingots. Activation results were used to calibrate infrared absorption at low temperature for the determination of carbon in silicon. Residual B and Al concentrations are low. Ingots doped with B or Al were analyzed, the doping with Al being inefficient. Boron was homogeneously distributed, while Al segregated at the top and at the grain boundaries.

Characterization of Semiconductor Materials by Charged Particle Activation

Results obtained during the past few years by research groups working on joint projects, mainly in view of a better knowledge of GaAs, are summarized here. The procedures of radioactivation analysis with charged particles (deuterons and tritons) are described to some extent. Finally, some important aspects of charged particle activation analysis, namely : calibration, etching after irradiation and diffusion during irradiation, are discussed.

Charged-particle activation methods for the analysis of carbon and oxygen in high-purity gallium

Methods for the instrumental analysis of C and O at trace level in high-purity gallium were developed. The 12C (d, n)13N and 16O(t, n)18F reactions were used between 2.5 and 3.5 MeV, allowing analyses down to tens of ppb/weight. The 16O(p, α)13N reaction at 15 MeV was also used; in this case 13N has to be separated radiochemically.

Measurement of etching after irradiation with charged particles by using the matrix activation

Abstract In the proposed method, activation of the sample matrix itself is used to measure the extent of etching after activation with charged particles. In a given energy region, a small variation of the incident beam energy, which corresponds to a small thickness of sample, will lead to a large variation of the activation yield. The method is applied to the determination of oxygen by the 16O(31H, n)18F reaction, and of carbon by the 12C(21H, n)13N reaction, in gallium arsenide and a titanium alloy. The results are in good agreement with those obtained by mechanical systems.

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

Abstract Study of the 14N(d,n)15O reaction at low energy and application to the determination of nitrogen in zirconium The 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%.

Fast analysis of oxygen in fluoride glasses (ZBLAN) by charged-particle activation [16O(d, n)17F]

Abstract Oxygen was analyzed in fluoride glasses of the ZBLAN type (ZrF4BaF2LaF3AlF3NaF). The method is charged-particle activation with deuterons at 2.8 MeV; the nuclear reaction is 16O(d, n)17F. Direct gamma-ray spectrometry is performed on the activated samples, after etching to eliminate surface oxygen. The analysis takes ∼ 15 minutes; the sensitivity is ∼ 25 ppm/weight which is sufficient considering that the lowest oxygen content in the glass is ∼ 200 ppm/weight, with the present technology of fabrication.

Proton activation analysis for the determination of trace elements in high purity ZrF4 used for the fabrication of low-loss optical fibres

Abstract Fluoride glasses may be used in the future for the making of ultralow-loss optical fibres at 2.5 μm. Low absorption can only be achieved if the glasses contain ppb levels of some transition elements and of lanthanides. So the starting materials (ZrF4, A1F3, NaF, LaF3 …) must be purified and controlled. At the present time, there is a lack of suitable standard analytical methods; we have therefore developed a method based on proton activation at 23 MeV. In this work we present analytical results for the determination of Fe and Ni in ZrF4, at trace level. ZrF4, as a powder, is irradiated for 2 h at 0.5 μA. After dissolution in HF, the matrix activity is eliminated by combining different radiochemical separations. The activity of the radioisotopes of interest, 56Co for Fe, 57Ni for Ni, is then determined by gamma-ray spectrometry.