R. Dayras

Mesures de corrélations angulaires et de vies moyennes dans 57Co

Abstract The reaction 54Fe(α, p)57Co at 9.86, 10.02 and 10.40 MeV incident energies was used to measure the proton-gamma angular correlations in the Litherland-Ferguson geometry and to measure the mean lifetimes by the Doppler-shift attenuation method. The mixing ratios have been obtained for levels at 1.897, 2.134, 2.311 and 2.879 MeV. The mean lifetimes have been determined for 14 levels up to 2.9 MeV. The spins have been unambiguously assigned to all levels up to 2.311 MeV and to the 2.879 ( 3 2 − ) and 2.981 ( 1 2 + ) MeV levels. The partial radiative widths have been determined for all levels, except 1.505 MeV, up to 2.311 MeV.

Level structure of 55Co, 51V and 49V from γ-decay

Abstract Gamma-rays following 54 Fe( 3 He, d) 55 Co, 50 Ti( 3 He, d) 51 V, 48 Ti(α,p) 51 V and 46 Ti(α,p) 49 V reactions have been measured. Branching ratios have been deduced for levels in 55 Co up to 4.185 MeV, in 51 V up to 2.699 MeV and in 49 V up to 2.409 MeV. On the basis of the decay schemes and previously established l -values, the following J π assignments have been made: 55 Co 2.162 MeV, 3 2 − ; 2.559 MeV, 3 2 − ; 2.938 MeV, 1 2 − ; 51 V 2.410 MeV, 3 2 − ; 49 V 1.141 MeV, 5 2 − ; 2.234 MeV, 3 2 or case5 2 . The 1 2 + states in 51 V (at 2.547 MeV) and in 49 V (at 1.646 MeV) were observed to decay predominantly to the lowest 3 2 − state. This indicates some admixture to the main component of the 1 2 + state, which gives rise to the E1 transition.

Étude de 53Mn suivant la réaction (α, pγ)

Abstract The 53Mn levels are investigated up to 2.4 MeV excitation following the 50Cr(α, pγ)53Mn reaction. The (αp, γ) angular correlations are measured in the Litherland-Ferguson geometry II. The measured excitation function between 8 and 11 MeV permitted to choose for each level a suitable incident energy. For the levels at 1.438, 1.617, 2.271 and 2.404 MeV the following Jπ values are proposed: 11 2 − , 9 2 − , 5 2 and 3 2 − . Gamma-ray branching and mixing ratios were also obtained. In 53Mn, the M1 transitions are inhibited so that they are in the shell-model equivalent nucleus 51V. Also the level ordering is the same for both nuclei. The results are compared with previous experiments and theoretical predictions.

Étude du noyau 61Cu par la réaction 58Ni(α, pγ)61Cu

Abstract Gamma-ray spectroscopy of 61 Cu nucleus was undertaken up to 2.5 MeV excitation by the 58 Ni(α, pγ) reaction at E α = 10.0 MeV. Using a Ge(Li) detector, accurate values for energy levels and branching ratios have been obtained. For most of the levels, up to 2.1 MeV excitation, spin assignments and γ-ray mixing ratios have been obtained by using the Litherland- Ferguson angular correlation measurements method. The experimental results are compared to a recent shell-model calculation, based on intermediate coupling of a proton to the 60 Ni core.

Etude du noyau 63Cu par la reaction 60Ni(α, pγ)63Cu

Abstract The level structure and the decay properties of low-lying levels in 63 Cu have been investigated via the 60 Ni(α, pγ) 63 Cu reaction at E α = 11.7MeV. Using a Ge(Li) detector, the correlations of twenty-five primary γ-rays in coincidence with protons, stopped in an annular detector at approximatively 180° with respect to the beam direction, were measured. From these measurements, branching ratios, γ-ray mixing ratios and spin assignments have been obtained for most of the levels up to 2.4 MeV excitation.

Etude des niveaux de 57Co jusqu'à 1.90 MeV

Abstract The 57 Co levels are excited through the reaction 54 Fe(α, p) 57 Co at 10.23 MeV and 10.30 MeV incident energies. The coincidence gamma-ray spectra are observed with a Ge(Li) detector and the angular correlations (αp, γ) are measured in the Litherland-Ferguson geometry for the 1.22, 1.68 and 1.75 MeV levels. The following results are obtained: 1.22 MeV level J π = 9 2 − , 1.68 MeV level J π = 11 2 − ( 9 2 − ) . The corresponding E2/M1 amplitude mixing ratio for the transition 1.22 MeV → 0 is −0.22, and for the transition 1.68 MeV → 1.22 MeV it is 0.00 (0.9). A transition 1.90 MeV → 1.22 MeV is obtained in addition to the transition 1.90 MeV → 0. It is concluded that the levels at 1.75 MeV and 1.90 MeV are doublets.

Mesures de vies moyennes dans le noyau 61Cu

Abstract Lifetimes for the first ten excited states of 61 Cu have been measured by the Doppler-shift attenuation method. Gamma rays from the 58 Ni(α, pγ) 61 Cu reaction were observed, in coincidence with protons, in a Ge(Li) detector at θ / gg = 130°, 90°, 60° and 0° at incident energy of 10.01 MeV. The radiative partial widths are obtained.

Interprétation des niveaux de 57Co par l'interaction cȩur-particule

Abstract The experimental data for 57 Co are interpreted on the basis of the particle-core coupling model. The core is assumed to be 56 Fe (in the ground and the excited states), and the particle (proton) states taken into account are: 1 f 7 2 , 2 p 3 2 , 2 p 1 2 and 5 2 . Th factors, and γ-ray transition probabilities and mixing ratios for the first nine levels are fitted quite well with the model.