H. Langevin-Joliot

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.

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.

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.

Separation energy dependence of hole form factors

Abstract Form factors of fragmented hole states are studied within the quasiparticle-phonon model, using the inhomogeneous equation method. The validity of this method is successfully checked by comparison with coupled equation solutions in schematic vibrational model cases. A systematic investigation of form factors is performed for neutron and proton hole states in the valence and first inner shells of 208 Pb. Large fluctuations of form factor radii are observed for individual levels superimposed on a general increase with separation energy. Average characteristics are introduced for groups of levels, namely the mean form factors, summed source terms and correction potentials, and their behaviour is presented. The role of the relative values of the interaction radius parameter and binding well radius is discussed in detail.

Recent results on the isoscalar spin response in 40Ca and 12C

Abstract A signature S d y of isoscalar spin-transfer strength has been tested in the inelastic scattering of 400 MeV deuterons from 12 C. It was applied to search for ΔS =1 ΔT =0 strength in 40 Ca and 12 C. In 40 Ca, spin excitations were found in the 9 MeV region and over a broad range in the continuum with a cluster of strength around 15 MeV. In 12 C, ΔS=1 ΔT =0 levels were observed at 12.7 MeV (well known T =0 1 + level), 18.3 MeV (2 − T =0 level) and 20.4 MeV. Resonances were found at 20 MeV and at 30 MeV. Beyond 35 MeV the ΔS =1 ΔT =0 response is similar to the one observed in 40 Ca. Microscopic DWIA calculations agree nicely with the 12 C data.