E. Gerlic

Excitation of inner hole states in heavy nuclei with the (τ, α) reaction at 205 MeV

Abstract Energy spectra have been measured for the (τ, α) reaction at 205 MeV on 90 Zr, 118,124 Sn and 208 Pb. Results on the valence neutron shells and on the inner 1f 7/2 shell in 90 Zr, 1g 9/2 subshell in 118,124 Sn ( T and T > components) and 1h 11/2 subshell in 208 Pb are presented.

New evidence for deep-lying hole strength in 115Sn and 207Pb via the (3He, α) reaction at 283 MeV

Abstract It is found that neutron pick-up cross sections up to 50 MeV excitation energy in 115Sn and 207Pb may account for the total sum rule strength of all inner shells. The 115Sn spectrum exhibits much more pronounced structure than that for 207Pb; in particular the results give first evidence for a concentration of the 1 f 7 2 strength in a bump centered aroudn 15 MeV. No indication for the predicted strong concentration of the 1 g 9 2 strength in 207Pb is found.

Étude du mécanisme de la réaction (3He, α)à217 (205) MeV et de l'excitation d'état de trous dans les couches profondes

Abstract The ( 3 He, α) reaction on 12 C, 16 O, 28 Si, 58 Ni, 90 Zr, 118, 124 Sn and 208 Pb targets has been studied at E 3 He = 217 Me V(or205 MeV) in order to investigate the reaction mechanism at high energy and large momentum transfer. The reaction yields large cross sections at very forward angles and strongly enhances the largest orbital momentum transfers. The main mechanism is direct pick-up although two-step processes are quite important for some transitions. The alpha optical potential choice is of critical importance to reproduce the pick-up angular distributions shapes in the framework of the DWBA-ZR analysis. Very good fits are obtained for the studied nuclei and l -transfers with a unique empirical potential: if V α ( E inc ) = V 3 He(3/4 E inc ) + V n (1/4 E inc ) . The excitation energy spectra have been measured up to 100 MeV in the residual light and medium nuclei, and up to about 16 MeV in heavy nuclei. A survey of the main transitions is given. In addition to the generally well-known low-lying levels, peaks or broad structures are observed for each nucleus at higher excitation energies. They are attributed to pick-up from inner shells: 1s( 11 C and 15 O), 1p( 27 Si), 1d 5/2 + 1p( 57 Ni), 1f 7/2 ( 89 Zr), 1g 9/2 ( 117, 123 Sn)and1h 11/2 ( 207 Pb). The corresponding strengths are evaluated.

Analyzing powers of valence and inner neutron-hole states in 115Sn via the 116Sn(d, t) reaction

Abstract The reaction 116 Sn( d , t) 115 Sn up to 7.5 MeV excitation energy has been studied at 40 MeV incident energy using a vector polarized deuteron beam. The measured analyzing power reveals strong J -dependence effects and has been used to clearly assign the spin of a number of low-lying states in the 115 Sn nucleus. At higher excitation energy, a broad and fragmented bump is observed between 3.7 and 6.0 MeV in 115 Sn. This work reports on one of the first attempts to determine the spin of such structure through polarization measurements. The analyzing power data indicates a mixing of spins J = 9 2 , 1 2 , in agreement with the excitation of the 1 g 9 2 and 2 p 1 2 inner neutron-hole strengths in the 115 Sn nucleus. In addition, some 2 p 3 2 components are observed around ~ 4.6 MeV excitation energy.

High-lying valence and inner-proton-hole states in 207Tl via the (d, 3He) reaction at 108 MeV

The excitation energy spectra of the residual nucleus 207Tl have been investigated up to 14 MeV using the (d, 3He) reaction at 108 MeV. New high-lying states are observed for the first time up to 8.3 MeV, in addition to the five known low-lying levels. Beyond 7.13 MeV excitation energy, weaker structures are observed riding over a wide asymmetric bump. DWBA analysis of the angular distributions has allowed l attributions and the determination of valence and inner-hole spectroscopic factors. It is found that the valence levels at 1.33, 1.67 and 3.47 MeV exhaust respectively about 65%, 60% and 45% of the 1h11/2, 2d5/2 and 1g7/2 sum rules. The main part of the missing strengths is found below 7.13 MeV. The 2d5/2 and 1g7/2 holes contribute mainly to some well concentrated groups, whereas the 1h11/2 strength is distributed more smoothly. Small contributions of 1g9/2 and 2p strengths are tentatively identified below 7.13 MeV. The upper energy region may approximately account for the 1g9/2 and (1f5/2) total sum rules and about 60% of the 2p strength. The deduced experimental strength functions are compared with theoretical calculations.

Spin of deep-hole states in 111Sn via the 112Sn(d, t) reaction

Abstract Analyzing powers measured in the study of 112 Sn ( d , t ) at 40 MeV bombarding energy show strong J-dependence and have been used to clearly assign the spin of a number of low-lying states in the residual nucleus. At high excitation energy (3.5–6 MeV). the inner-hole strength is shared between clearly isolated peaks on one hand and a fragmented structure on the other. This work reports on the determination of the spin of the inner-hole states and consequently on a more precise measurement of the overlapping regions between 1 g 9 2 , 2 p 1 2 , 2 p 3 2 Subshell components. The analyzing power data shows that the group of peaks located between 3.4 and 4.5 MeV consist of spins J = 9 2 + 1 2 , in agreement with the excitation of the 1 g 1 2 and 2 p 1 2 inner- hole strengths in 111Sn. In addition a substantial amount of the 2 p 3 2 component is observed between 4.5 and 6.0 MeV. The results of the data analysis allow us to clearly eastablish the spreading of the 1 g 9 2 innerhole strength and to a lesser extent the strong fragmentation of the 2 p 1 2 and 2 p 3 2 inner-hole subshells.

Inner-hole excitations in 89Zr and 91Mo via the (3He,α) reaction at 97 MeV

The nuclei 89Zr and 91Mo have been investigated up to an excitation energy of about 25 MeV using the (3He, alpha ) reaction at 97.3 MeV incident energy. In addition to the well known low-lying levels and analogue states strongly excited groups of levels centered around 4.4 MeV are confirmed to belong to the 1f7/2 neutron inner shell in 89Zr, with a maximum of about 50% of the sum rule strength. A corresponding group, with comparable strength, is found for the first time in 91Mo at nearly the same excitation energy. In addition, and for both nuclei, two much smoother structures are observed lying under and beyond the analogue states. The authors discuss their possible attribution to the 1f7/2 T components respectively. Contributions from 1d inner shells are also considered. In both nuclei, new IAS fragments have been identified.

High lying two-neutron hole states in 206Pb and 114Sn observed via the (α, 6He) reaction at 218 MeV

Abstract Strong enhancements of two-neutron hole states are observed in a (α, 6 He) reaction study at 218 MeV on 208 Pb and 114 Sn target nuclei. Selective population of high-spin states, characteristic patterns of the angular distributions and successful direct one-step analysis of the data are the main attractive features of the (α, 6 He) process at high incident energy. As illustrative examples, spin and configurations of levels or structures in 206 Pb and 114 Sn are reported.

First observation of T> = 452 inner hole states in 207Pb

Abstract The first four isobaric analog states in 207 Pb, T > = 45 2 , were found around E x = 20 MeV with the reaction 208 Pb(τ, α) 207 Pb at 102 MeV incident energy. The excitation energies, widths and angular distributions were measured. Spectroscopic factors were deduced by DWBA analysis.

The (τ, α) reaction at 216 MeV

Abstract The (τ, α) reaction on 12C and 16O targets has been studied at Eτ = 216 MeV in order to investigate the reaction mechanism at high energy and large momentum transfer.