A. Gallmann

Niveaux excités de 19O étudiés par la réaction 18O(d, p)19O

Abstract A Buechner-type magnetic spectrograph has been used to study the 18 O(d, p) 19 O reaction between 20° and 130° with respect to the incident deuteron beam at E d = 5 MeV. Proton groups corresponding to previously reported levels, up to 4.118 MeV excitation energy in 19 O, have been observed and the energies of nine excited states are determined. No evidence is found for the previously reported levels at 0.348, 1.257 and 3.791 MeV. Comparison of the proton angular distributions with PWBA predicted shapes indicates l n = 2 for the levels at 0.097, 2.370, 3.160 and 3.237 MeV. Gamma radiation was observed with Ge(Li) detectors. Particle-γ and γ−γ coincidence measurements were performed at E d = 3 MeV. The gamma branching ratio of the 1.468 MeV state to the ground state has been found to be (3.1±1.7)%. The present results are compared with previous work and discussed in the frame of the shell model.

Étude du noyau 28Mg par la réaction 26Mg(t, pγ)28Mg

Resume Angular correlation and Doppler shift attenuation methods were used to measure γ-ray branching ratios, spins, mixing ratios and lifetimes of 28 Mg excited states between 4.9 and 5.8 MeV, produced in the 26 Mg(t, pγ) reaction at E t = 2.54, 2.90 and 3.20 MeV. Gamma rays were detected in coincidence with proton groups, observed at 0° and 180° for the angular correlation measurements, and at 180° for the DSA measurements. The results for the excitation energies (keV), J π and τ m (ps) are: 5171.9 ± 0.5, 3 − , 0.18 ± 0.02; 5192.7 ± 0.7, 1 − , − , + , 0.30 ± 0.05. Two previously unreported levels were identified at 4560.8 ± 0.8 keV ( J = 1) and 5184.6 ± 0.7 keV. Other levels have been observed at 5469.1 ± 0.8 and 5672.8 ± 0.8 keV ( J π = 2 + ). The 28 Mg spectrum is compared with other experimental results and with recent theoretical predictions.

Résonances dans la réaction 10B+α par L'étude des rayonnements γ détectés avec un semi-conducteur Ge(Li)

Abstract A Ge(Li) detector has been used to study gamma rays from the 10 B(α, pγ) 13 C and 10 B(α, αγ) 10 B reactions. Relative cross sections for the 3.088, 3.682 3.852 and 0.717 MeV gamma rays have been obtained, and excitation curves at 90° for α-particles with energies from 1 to 3.5 MeV are given corresponding to excited levels between 12.3 and 14.1 MeV in 14 N.

Étude des premiers niveaux excités de 19O par des mesures de corrélations angulaires et de vdzs moyennes

Abstract To study the lowest levels of 19 O, pγ angular correlations (method II) and lifetime measurements (DSAM), have been performed in the 18 O(d, pγ) 19 O and 17 O(t, pγ) 19 O reactions. The mean lives are the following: 1472 keV level: τ = 0.90 ± 0.23 ps, 2372 keV level: τ > 3.5 ps, 2779 keV level: τ = 117 ± 26 fs. Mixing ratios have also been obtained. Some probable values and some upper limits for the spins of 5 levels are given. The level scheme is compared with results of shell-model calculations.

Étude de transitions γ dans le noyau 19O

Abstract The 18 O(d, pγ) 19 O reaction has been investigated at E d = 5 MeV . A Ge(Li) detector and a NaI(Tl) crystal were used to detect γ-rays in coincidence with reaction particles detected near 180°. Excitation energies have been obtained for the 19 levels at 1470±3, 2369±4, 2777±3, 3157±3 and 3944±3 keV and gamma-ray branching ratios have been determined for these levels.

Transitions électromagnétiques dans le noyau 32Si atteint par la réaction 30Si(t, pγ)32Si

The γ-decay of 32Si levels was studied in the 30Si(t, p)32Si reaction at Et = 2.5, 2.9 and 3.3 MeV. Coincident DSA measurements and p-γ angular correlations (method II) yield excitation energies, branching and mixing ratios, spins and mean lifetimes. The levels at 1.94 and 5.29 MeV have Jπ = 2+ and 3(−) and τm = 0.48 ± 0.07 and 0.17 ± 0.04 ps, respectively; for six other levels lifetime limits are given. The 5.41, 5.95, 6.19, 6.39 and 6.71 MeV levels have J = 1, 2, 1, 2 and 1, respectively; the latter level has not been observed before. Most of the results are in good agreement with previous data.

Etude de 17N par la reaction 18O(t, αγ)17N

Abstract The first six excited states of 17 N have been studied by using the 18 Ot, αγ) 17 N reaction at a bombarding energy of E t = 3.5 MeV. Alpha-gamma angular correlation measurements (method II) were used to determine spins, mixing ratios and branching ratios. The 1.37, 1.85, 1.91, 2.53, 3.13 and 3.20 MeV levels have been assigned the spins 3 2 , 1 2 , 5 2 − , 5 2 + , 7 2 and 3 2 respectively. Excitation energies are also given. Most of the results are in good agreement with previous data or suggested values. Mixing ratios have been obtained for the first time. The level scheme of 17 N is compared with some T = 3 2 analogue states in 17 O and 17 F and with results of recent shell-model calculations.