A.Di Pietro, P.Figuera, M.Fisichella, M.Lattuada, M.Milin, A.Musumarra, M.G.Pellegriti,

1. A.Di Pietro, P.Figuera, M.Fisichella, M.Lattuada, M.Milin, A.Musumarra, M.G.Pellegriti, V.Scuderi, D.Torresi, E.Strano, N.Soic, M.Zadro Elastic scattering and reaction mechanisms in the collision 8B+64Zn around the Coulomb barrier.

2. Motivation: Elastic scattering is a peripheral process, it probes the tail of the wave function. One can learn about surface properties, such as size of nuclei and surface diffuseness → useful to to investigate halo structure. Reactions of halo and weakly bound nuclei helps to better understand the continuum. Many papers have appeared in the last few years where these topics have been studied theoretically. Experimental requirements: Experimentally detailed elastic scattering angular distributions as well as other open reaction channels must be measured.

3. Results with 6He Ecm=12.4 MeV sR4He≈0.65b sR6He≈1.45b O.R. Kakuee eta al. NPA 728(2003) 339 A.Di Pietro et al. Phys. Rev . C 69 (2004) 044613 6He+197Au Observations: Reduction of elastic cross-section → large reaction cross-section Direct processes dominate the total reaction cross section Neutron transfer processes play an important role 6He+208Pb

4. 11Be Counts E(MeV)‏ Experiments with11Be beam beam energy profile Fragmentation beam => large beam energy spread => results suffer from the beam quality. 11Be + 209Bi No effect on the total reaction cross-section in 11Be case, comparison with 9Be. Mazzocco et al. Eur. Phys. J. Special Topics 150, 37 (2007)

5. 10,11Be+64Zn experiment @ Rex- ISOLDE Elastic scattering 9Be+64Zn sR=1080 mb 10Be+64Zn sR=1230 mb 11Be+64Zn sR=2250 mb Transfer/break-up Angular distribution 64Zn(11Be,10Be) s≈1 b

6. 8B+58Ni E.Aguilera et al. Phys. Rev. C 79, 021601(R) 2009 Elastic scattering angular distributions 8B+58Ni @ Elab=23.4 MeV • Some details of this experiment: • In-flight produced 8B beam • Beam divergence ±3° • Angular detector opening Dq ± 6° • Telescope was used to measure at most two angles • Total energy detector thickness 500 mm Large reaction cross-section extracted from elastic scattering

7. Proposed experiment: 8B+64Zn elastic scattering angular distribution at E8B=3.1 MeV/u Transfer and break-up cross-sections Detection system: 4 DE-E Si telescopes at forward angles q<110° DE: 20 mm SSSD detector (16 strips) E: 500-1000 mm DSSSD (16+16strips) 2 detectors at backward angles q>110° 40 mm DSSSD (16+16strips) Angular distribution steps: for q 110° at steps ofq3° (Dq ±1.5°) for q >110° at steps of q=5° (Dq ±2.5°) We aim at measuring also elastic scattering with 10,11B and possibly 7Be on 64Zn • Improvements: • 8B post-accelerated ISOL beam • Large solid angle + high granularity → good angular resolution • Complete and detailed angular distribution • Coincidence measurement

8. 8B+58Ni 7Be inclusive spectra measured → large cross-section found From comparison with calculations the p-halo structure of 8B is claimed V.Guimares et al. Phys. Rev. Lett. 84,1862(2000) 64Zn(8B,7Be 1H) Break-up 64Zn(8B,7Be)65Ga* Transfer Questions: 7Be coming from break-up or transfer? Is it possible to discriminate? 7Be-proton coincidences needed. 1H 7Be 8B 7Be 1H 64Zn 64Zn 65Ga Transfer Qgg=7.32 MeV Qopt=-3.67 MeV E*(65Ga)= 10.99 MeV

9. How to estimate coincidence efficiency? Experimental 7Be energy spectrum 8B+58Ni 8B+58Ni Monte Carlo simulation 7Be energy spectrum from break-up J.J.Kolata PHYS. REV.C 63, 024616(2002) E (MeV)

10. Experimental angular distribution 8B+58Ni Monte Carlo simulations 8B+64Zn q 7Be J.J.Kolata PHYS. REV.C 63, 024616(2002) The efficiency to detect 7Be-protons coincidences larger than 70% q 1H

11. Simulated 7Be and p energy spectra 7Be 1H E (MeV) E (MeV) By considering the 7Be angular distribution measured by Kolata et al. we expect to detect 500 coincidences in the front detectors assuming i8B 5x103pps in 21 shifts

12. Backgroundproblems with 8B beam Background aspectrumfrom8Be(2+) decay The branching to high energy level could generate background at backward angles where no telescope is used ~1.5 MeV ~5 MeV To dramatically reduce the background a selection on Tebis time spectrum can be made (reduction factor 0.5%)

13. Beam time request: 21 shift to perform elastic scattering angular distribution and 7Be+p coincidence measurement. Some example of the counting statistics i8B=5x103andDW=0.03 sr q=80° ≈300 counts in 7day (Dq ±1.5°) q=100° ≈90 counts in 7day (Dq±1.5°) q=130° ≈30 counts in 7day (Dq ±2.5°) These counts can be doubled at the angles were left and right detectors can be summed up. Transfer/break-up 7Be singles ≈700 in the angular region 10° q  40° 7Be-p coincidences ≈500 Additional 5 shifts of stable beam are requested for setting-up the electronics and most important for angle and solidangle determination via Rutherford scattering. 4 shifts are requested for testing the beam Total number of shifts 30