E. Hourani

GRAAL: a polarized γ-ray beam at ESRF☆

The GRAAL facility produces a highly polarized gamma-ray beam by Compton scattering of laser photons on the electrons of the European Synchrotron Radiation Facility (ESRF) at Grenoble. Preliminary results have been obtained with the LAGRANGE detector showing its excellent performances.

One-nucleon pickup reactions on 32S: Experimental results and shell-model calculations

Abstract The 32S(d,3He)31P and 32 S ( 3 He ,α) 31 S reactions have been investigated at incident energies of Ed = 27 MeV and E3He = 25 MeV. The experimental values of excitation energies (0 ⩽ Ex(MeV) ⩽ 8) have been compared with the predictions of a complete sd-shell space, shell-model calculation. Spectroscopic factors obtained for 22 levels of 31S through the DWBA analysis of the experimental angular distributions have also been compared with the shell-model predictions. In order to reconcile the experimental and shell-model predicted values of the spectroscopic factors, the geometrical parameters of the spin-orbit part of the transferred nucleon potential are required to be smaller than those of the central part as it was previously observed in studies of the one-proton (3He,d) stripping reaction. The experimental fragmentation of the 1d 5 2 and 2s 1 2 strengths is correctly reproduced by the shell-model calculations. Twenty pairs of levels were identified as mirror states in the 31S and 31P nuclei and the ambiguities concerning the Jπ-values of eleven 31S levels could be removed.

The γ-decay of the 1g92 and 2p inner-hole states in 111Sn via the 112Sn(3He, αγ) reaction at 32 MeV

Abstract The γ-decay of the deeply-bound hole states in 111Sn has been investigated at 32 MeV incident energy by means of the 112Sn(3He, αγ) reaction. The α-particles emitted near 0° were detected in a Si counter located at the image plan of the superconducting solenoidal spectrometer SOLENO. The γ-rays in coincidence with the α-particles were detected by two Ge(Li) detectors located at 90° and 142° with respect to the beam direction, respectively. Energies, spins and decay schemes have been established for the low-lying states up to 2.5 MeV excitation energy in 111Sn. The γ-decay of the broad bump, located around 4.2 MeV and previously attributed to neutron pick-up from the inner 1 g 9 2 , 2 p 1 2 , and 2 p 3 2 neutron. Subshells, reveals the importance of quasiparticle-phonon m the spreading mechanism of the inner-hole strengths. The 1 g 9 2 and 2p strength functions have been deduced from the α-decay of the enhanced structures (3 ≦ Ex≦ 8 MeV). They are compared to the ones measured in previous inclusive neutron pick-up experiments and to those calculated in the framework of the quasiparticle-phonon nuclear model.

Single-particle and core-excited states in 49Sc: (I). The 48Ca(3He, d)49Sc reaction

Abstract The 48 Ca( 3 He, d) 49 Sc reaction has been studied at 25 MeV incident energy. Angular distributions have been measured from 5° to 40° using a split-pole spectrometer, for about 160 levels located up to 18 MeV excitation energy. A local zero-range DWBA analysis has been carried out, using Gamow functions as form factors in the case of unbound states; l -assignments and spectroscopic factors are obtained for a large number of levels, most of them previously unknown. The summed experimental spectroscopic strengths for the T , l = 1 and l = 3 levels are in good agreement with the shell-model sum-rule limits for 1f-2p proton states, and their energy centroids have been determined. The lg 9 2 strength in 49 Sc is strongly fragmented: about 27% of the T strength is carried by twenty-three levels located between 6.5 and 13.5 MeV. Spectroscopic factors for analog states are compared with those from previous (p, p), ( 3 He, dp) and (d, p) experiments.

Evidence for the strength in 41Sc and proton decay mode

Abstract The centroid of the widely spread 1 g 9 2 proton particlestrength in 41 Sc has been located at E x =8.8 MeV. Relatively large decay branching ratios to the ground state and the first 3 − level of 40 Ca have been observed in the 40 Ca( 3 He, dp) reaction at E 3He =240 MeV.

Two-step processes in the 40Ca(α, 3He)41Ca reaction

Abstract The 40 Ca(α, 3 He) reaction has been studied at 36 MeV incident energy. About fifty levels have been observed up to 7.1 MeV excitation energy and angular distributions were measured from 6–60° using a split-pole spectrometer. A local zero-range DWBA analysis has been carried out, and the deduced l -assignments and spectroscopic factors are compared with those obtained from previous neutron stripping experiments. Core-excited states in 41 Ca with a [3 − ⊗ f 7,2 ], [2 + ⊗ f 7,2 ] and [5 − ⊗ f 7,2 ] component previously observed in inelastic scattering experiments, are selectively excited by the (α, 3 He) reaction. Their angular distributions are compared with coupled-reaction-channel calculations, assuming a pure two-step reaction mechanism. The agreement between theory and experiment may be considered as rather satisfactory for a number of levels. In particular the 1 2 + and 3 2 + levels and the high-spin states with J π = 9 2 − , 11 2 + , 15 2 + and 17 2 + are successfully described within the framework of the weak-coupling model.

Direct transfer and two-step processes in the 42Ca(α, 3He)43Ca reaction

Abstract The 42 Ca(α, 3 He) 43 Ca reaction has been studied at 36 MeV incident energy. Angular distributions have been measured from 4° to 42° using a split-pole spectrometer and position sensitive Si detectors, for about 40 levels located up to 6 MeV excitation energy. A local zero-range DWBA analysis has been carried out; l = 3 and 4 assignments are tentatively proposed for levels located above 4 MeV excitation energy, indicating a strong fragmentation of the 1 f 5 2 strength between 4 and 6 MeV and the location of the main component of the 1 g 9 2 strength above 6 MeV. A number of weakly excited levels cannot be reproduced by DWBA analysis. Their angular distributions have been compared with the results of coupled-reaction-channel calculations assuming two-step excitation of weak coupling states with a [ 42 Ca ∗ ⊗ f 7 2 structure. A reasonable agreement has been obtained, confirming that the two-step process cannot be neglected in the analysis of the (α, 3 he) reaction.

Large anisotropy difference in the NNπ system for π° and π± channels

Cross sections and beam asymmetries for the reaction p(pπ0)pp have been measured for incident polarized proton energies from the threshold to 1 GeV, and compared with those for the charged pion channels in p(n,π±)NN reactions. The observed anisotropy difference around 540 MeV has been ascribed to the 3D1 partial wave contribution to the np initial state. (AIP)