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

Motivation:Motivation:

Elastic scattering is a peripheral process, Elastic scattering is a peripheral process, it probes the tail of the it probes the tail of the wave function. One can learn about surface properties, such as size wave function. One can learn about surface properties, such as size of nuclei and surface diffuseness → useful to to investigate halo of nuclei and surface diffuseness → useful to to investigate halo structure.structure.

Reactions of halo and weakly bound nuclei helps to better Reactions of halo and weakly bound nuclei helps to better understand the continuum.understand the continuum.

Many papers have appeared in the last few years where these Many papers have appeared in the last few years where these topics have been studied theoretically.topics have been studied theoretically.

Experimental requirements:

Experimentally detailed elastic scattering angular distributions as well as other open reaction channels must be measured.

6He+197Au

6He+208Pb

Ecm=12.4 MeV

RR44He≈0.65bHe≈0.65b

RR66He≈1.45bHe≈1.45b

A.Di Pietro et al. Phys. Rev . C 69 (2004) 044613

Observations: Observations:

Reduction of elastic cross-section → large reaction cross-sectionReduction of elastic cross-section → large reaction cross-section

Direct processes dominate the total reaction cross section Direct processes dominate the total reaction cross section

Neutron transfer processes play an important roleNeutron transfer processes play an important role

O.R. Kakuee eta al. NPA 728(2003) 339

Fragmentation beam => large beam Fragmentation beam => large beam energy spread => results suffer from the energy spread => results suffer from the beam quality.beam quality.

Mazzocco et al. Eur. Phys. J. Special Topics 150, 37 (2007)Mazzocco et al. Eur. Phys. J. Special Topics 150, 37 (2007)

E(MeV)E(MeV)

Cou

nts

Cou

nts

1111BeBe beam energy profilebeam energy profile

Elastic scatteringElastic scattering

Transfer/break-up

Angular distributionAngular distribution6464Zn(Zn(1111Be,Be,1010Be)Be)

99Be+Be+6464Zn Zn RR=1080 mb=1080 mb1010Be+Be+6464Zn Zn RR=1230 mb=1230 mb1111Be+Be+6464Zn Zn RR=2250 mb=2250 mb

≈1 b

8B+58Ni E.Aguilera et al. Phys. Rev. C 79, 021601(R) 2009

Elastic scattering angular distributionsElastic scattering angular distributions

8B+58Ni @ Elab=23.4 MeV

Some details of this experiment:Some details of this experiment:

In-flight produced In-flight produced 88B beamB beamBeam divergence ±3°Beam divergence ±3°Angular detector opening Angular detector opening ± 6° ± 6°Telescope was used to measure at most two anglesTelescope was used to measure at most two anglesTotal energy detector thickness 500 Total energy detector thickness 500 mm

Large reaction cross-Large reaction cross-section extracted from section extracted from

elastic scatteringelastic scattering

Proposed experiment:Proposed experiment:88B+B+6464Zn elastic scattering angular distribution at EZn elastic scattering angular distribution at E8B8B=3.1 MeV/u=3.1 MeV/u

Transfer and break-up cross-sectionsTransfer and break-up cross-sections

Improvements:Improvements:88B post-accelerated ISOL beamB post-accelerated ISOL beamLarge solid angle + high granularity → good angular resolutionLarge solid angle + high granularity → good angular resolution Complete and detailed angular distributionComplete and detailed angular distributionCoincidence measurementCoincidence measurement

We aim at measuring also elastic scattering with We aim at measuring also elastic scattering with 10,1110,11B and possibly B and possibly 77Be on Be on 6464ZnZn

Angular distribution steps:Angular distribution steps:for for 110° at steps of110° at steps of3° (3° ( ±1.5°) ±1.5°) forfor >110° at steps of >110° at steps of5° (5° ( ±2.5°)±2.5°)

Questions:7Be coming from break-up or transfer?

Is it possible to discriminate? 7Be-proton coincidences needed.

88B+B+5858Ni Ni 77Be inclusive spectra measured → large cross-section foundBe inclusive spectra measured → large cross-section found

From comparison with calculations the p-halo structure of From comparison with calculations the p-halo structure of 88B is claimedB is claimed V.Guimares et al. Phys. Rev. Lett. 84,1862(2000V.Guimares et al. Phys. Rev. Lett. 84,1862(2000))

8B

7Be

1H

64Zn

64Zn(8B,7Be 1H)Break-up

7Be

64Zn

1H

64Zn(8B,7Be)65Ga*Transfer

TransferTransferQgg=7.32 MeVQgg=7.32 MeV

Qopt=-3.67 MeVQopt=-3.67 MeVE*(65Ga)= 10.99 MeVE*(65Ga)= 10.99 MeV

65Ga

Experimental 7Be energy spectrum88B+B+5858NiNi

88B+B+5858Ni Ni Monte Carlo simulation7Be energy spectrum from break-up

E (MeV)

How to estimate coincidence efficiency?How to estimate coincidence efficiency?

J.J.Kolata PHYS. REV.C 63, 024616(2002)

Experimental angular distributionExperimental angular distribution88B+B+5858NiNi

7 B

e

1H

Monte Carlo simulationsMonte Carlo simulations88B+B+6464ZnZn

J.J.Kolata PHYS. REV.C 63, 024616(2002)

7Be 1H

E (MeV) E (MeV)

Simulated Simulated 77Be and p energy spectraBe and p energy spectra

Background Background spectrum from spectrum from 88Be(2Be(2++) decay) decay

~~1.5 MeV1.5 MeV ~~5 MeV5 MeV

The branching to high energy level could generate background

at backward angles where no telescope is used

To dramatically reduce the background To dramatically reduce the background a selection on Ta selection on Tebisebis time spectrum can time spectrum can

be made (reduction factor 0.5%)be made (reduction factor 0.5%)

Beam time request: Beam time request: 21 shift21 shift to perform elastic scattering angular distribution to perform elastic scattering angular distribution and and 77Be+p coincidence measurement.Be+p coincidence measurement.

Some example of the counting statisticsSome example of the counting statisticsii 8 8B=5x10B=5x1033andandsrsr

≈≈300 counts in 7day 300 counts in 7day (( ±1.5°)±1.5°)

≈≈90 counts in 7day (90 counts in 7day ( ±1.5°) ±1.5°) ≈≈30 counts in 7day (30 counts in 7day ( ±2.5°) ±2.5°)

These counts can be doubled at the angles were left and right detectors can be These counts can be doubled at the angles were left and right detectors can be summed up.summed up.

Transfer/break-upTransfer/break-up

77Be singles ≈700 in the angular region 10°Be singles ≈700 in the angular region 10° 77Be-p coincidences ≈500Be-p coincidences ≈500

Additional Additional 5 shifts 5 shifts of stable beam are requested for setting-up the electronics and of stable beam are requested for setting-up the electronics and most important for angle and solidangle determination via Rutherford scattering.most important for angle and solidangle determination via Rutherford scattering.

4 shifts 4 shifts are requested for testing the beam are requested for testing the beam

Total number of shifts 30Total number of shifts 30