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The γ-γ angular correlations have been performed in 123Te isotope, from the γ-ray spectrum in coincidence with the 158.7 keV, 3 2 + → 1 2 + transition. The A2(1) factor is measured for 5 transitio between 5 levels and the first excited state 3 2 + . The spin of the levels at 439.2, 505.2, 687.7, 697.1 and 783.4 keV (respectively 3 2 , 5 2 , 3 2 , 7 2 and 3 2 or 5 2 and the mixing parameter of the 280.6 and 346.3 keV transitions are deduced.

L'etude des γ associes a la desexcitation de 123I a l'aide d'une jonction au Ge (resolution 4,5 keV) nous a permis de preciser les energies des rayonnements deja connus et de mettre en evidence de nouvelles transitions aux energies de 183, 192, 248, 538, 574, 624, 736 et 784 keV. Ces resultats, ainsi que des spectres de coincidence γ-γ obtenus avec un circuit semi-rapide (2τ = 35 ns) associe a deux detecteurs NaI, nous conduisent a proposer un schema de niveaux de 123Te comportant 3 nouveaux etats aux energies de 697, 784 et 895 keV.

The low-lying excited levels of 198, 200, 202Pb have been studied by observing γ- and β-rays and γ−γ coincidences in bismuth decay. Decay schemes have been proposed for these nuclei. Half-lives were determined for the 9−, 7−, 5− and 4+ levels in 200Pb, and for the 5− level in 198Pb. Microscopic calculations have been made with Gaussian and surface delta interactions to account for level schemes. The results are discussed.

Life-time measurements were carried out by using time to amplitude conversion methods, the information being classified in a two- or three-dimensional spectrum by means of an on-line IBM 360-50 computer. In the first case, the zero time corresponds to the compound nucleus formation and is defined by a fast coincidence between a prompt γ-ray and the beam pulse detected by a thin plastic foil. In this way, the time distributions of all the γ-rays associated with a given reaction are simultaneously measured and can be extracted from the resulting 1024 (Eγ) × 256 (time) channels spectrum. The random coincidence peaks shown by all the curves with the same repetition rate as that of the cyclotron frequency (150–200 ns) can be eliminated by computing the difference between the contributions of a γ-ray and of the continuous background. However, as it is rather difficult to resolve the components of a complex decay curve, when several half-lives of intermediate levels interfere, we turned to a three-dimensional analysis in order to estimate these components. The pulse starting the TAC is due to the same type of coincidence as before but the γ-rays taken into account are now delayed relative to the compound nucleus formation. The size of this delayed γ spectrum is limited by the computer memory and only eight energy regions can be selected (four peaks and the backgrounds nearby, for example). By treatinf the 8 (Eγ2) × 1024 (Eγ2) × 256 (time) channels spectrum obtained, we can derive the decay curves of all the γ-rays with respect to each of the delayed γ transitions.

The low-lying excited states of 194, 196, 198, 200 Pb have been studied through the de-excitation γ-rays following the reactions Os( 12 C, 4n), W( 16 O, 4n) and Re( 14 N, 5n). Prompt and delayed spectra, γ-γ coincidences, γ-ray angular distributions and γ-ray time distributions have been obtained. Half-lives were measured for the 12 + level in the four isotopes, for the 9 − level in 194, 196, 200 Pb, for the 7− level in 200 Pb and for the 5− level in 196, 198 Pb. The results of microscopic calculations, performed with either a Gaussian interaction or a surface delta interaction, are compared to the experimental level schemes and transition probabilities, and discussed.

Coulomb excitation experiments have been performed on the two stable odd-mass tellurium isotopes using a N 3+ beam from the Orsay cyclotron. The reduced excitation probabilities of the following levels: 439.2 keV (3/2 + ) and 505.2 keV (5/2 or 3/2 + ) in 123 Te, 443.5 keV(3/2 + ), 463.4 keV (5/2 + ) and 671.3 keV (5/2 + ) in 125 Te were measured by this method. Some B (E2) and B (M1) transition probabilities are deduced from experiments. The results are discussed in terms of de Shalit's model and Kisslinger and Sorensen's calculations.

L'etude par spectroscopie γ des isotopes pairs du tellure de masse 118 a 126 permet d'etendre la systematique des niveaux ayant une energie de 0 a 3 MeV. Les tellures-122 a 130 ont ete egalement etudies par excitation coulombienne ainsi que 124Sn avec des ions 14N3+ ayant une energie de 44 et 48 MeV.

The even lead isotopes with mass number A = 200 to A = 194 were produced by (heavy ions, x n) reactions and the de-excitation ? cascades studied. Evidence was found for new experimental levels. Among these, the low-lying 12+, 10+ and 9- states provide information which can be directly compared with the theoretical results.

L'etude de la desintegration de UX1 (234Th) vers les niveaux de UX2 (234mPa) nous a permis de mettre en evidence de nouvelles transitions γ dans ce dernier corps, entre 115 et 185 keV.

Excitation functions are given for the following proton reactions on O/ sup 16/ at proton energies of 20 to 150 Mev: (p,pn)O/sup 16/. ((p 2p2n) and (p alpha ) N/sup 13/. STA(p 3p3n) and (p n alpha )!C/sup 1 and STA(p,5p5n) and (p,3p3n alpha ) and (p,pn alpha )!Be/sup 7/. The shapes and amplitudes of these excitation functions are compared with those of C/sup 12/ and F/sup 19/. (T.F.H.)

Les raies γ de desexcitation du noyau 192Pb forme par la reaction 156Gd(40Ar, 4 n) ont ete etudiees a l'aide d'un dispositif d'analyse quadridimensionnelle, les informations recueillies etant du type : Eγ1 ⊗ Eγ2 ⊗ T12 ⊗ TH.F.. Un schema de niveaux comprenant deux sequences distinctes, l'une a parite positive, l'autre a parite negative est propose.