Mesures de vies moyennes par effet Doppler

A. Gallmann, F. Haas, B. Heusch, M. Toulemonde
1969 Revue de Physique Appliquée  
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more » ... français ouétrangers, des laboratoires publics ou privés. 216 For each level the unshifted y-ray energy at 900 with respect to the incoming beam and the shifted y-ray energy at 00 were measured. For the measurements with gaseous stopping media, the energy of the y-rays emitted in the recoil direction was measured at different pressures up to 30 kgjcm2. Measurements with recoils into vacuum or low pressure were performed in order to obtain the fully shifted y-ray energies. These were always found to be in good agreement with the calculated energies. An illustrative example of the results obtained for two gamma-rays in the 4OAr(oc, n)43Ca experiment is given in the figure 1. III. Analysis of the data. -The measured Doppler shift F, as a fraction of the full shift, was used to derive the nuclear lifetimes. The centroids of the peaks define the energies of the gamma-rays. The F(T~ curves were obtained from the theoretical formalism given by Blaugrund [1]. It takes into account the electronic and nuclear contributions to the slowing down and the nuclear scattering of the recoil ions. The electronic contribution is corrected by including the periodic variations of the experimental electronic stopping cross-sections with the atomic number of the recoil ion. Also an adjustable parameter fn for the nuclear contribution is introduced. For the ions considered here, no experimental range-energy data are available from which one could deduce the correct value of fn. However, this latter can also be found when states with well known lifetimes are present, and has been tentatively taken to be about 0.3 of the Fermi-Thomas value [2]. ~. REFERENCES [1] BLAUGRUND (A. Résumé. 2014 Des vies moyennes de niveaux nucléaires ont été déterminées par la méthode de l'effet Doppler. Les rayonnements gamma de désexcitation ont été détectés dans des compteurs Ge(Li). Des vies moyennes ont été obtenues pour les niveaux 0,953 MeV de 12B et 6,44 MeV de 14N. Abstract. -Lifetimes of nuclear states have been obtained by the Doppler shift attenuation method. The 03B3-rays were detected in lithium-drifted germanium counters. Lifetimes of the 12B 0.953 MeV and the 14N 6.44 MeV levels are reported. REVUE DE PHYSIQUE APPLIQUÉE
doi:10.1051/rphysap:0196900402021601 fatcat:v3cl75dza5hirjodyw7nr5t6yq