Atar, L.

Aumann, T.

Caesar, C.

Enders, J.

Heine, M.

Panin, V.

Paschalis, S.

Scheit, H.

Wamers, F.

GSI Repository

Direct Reactions with Light Neutron-Rich Nuclei∗L. Atar1,2, T. Aumann1,2, J. Enders1, H. Scheit1,2, S. Paschalis1, F. Wamers1,2, V. Panin1,2, C.Caesar1,2, M. Heine1,2, and the R3B Collaboration1TU Darmstadt, Germany; 2GSI Darmstadt,GermanyQuasi free (p,2p) and (p,pn) knockout reactions withradioactive beams in inverse kinematics allow us to ob-tain spectroscopic information about valence and deeplybound single-particle states and to study their evolutionover a large variation in isospin. Recent studies have shownthat the occupancies of loosely bound valence nucleons inneutron- or proton-rich nuclei have a spectroscopic factorclose to unity, whereas single-particle strength for deeplybound nucleons is suppressed in isospin asymmetric sys-tems compared to the predictions of the many-body shellmodel [1]. Further experimental and theoretical studies areneeded for a qualitative and quantitative understanding.For this aim a series of measurements have been per-formed on the complete oxygen isotopic chain using theexisting experimental setup LAND/R3B at GSI (Cave C).In the experiment S393 the primary beam 40Ar with an en-ergy of 600 AMeV is fragmented into the exotic ions on aberyllium target using the Fragment Separator FRS.A/Z2.65 2.7 2.75 2.8 2.85 2.9 2.95 3 3.05 3.1Z45678910010203040506023OFigure 1: Identification plot of the incoming ions with thegraphical cut around the 23O.The charge Z and mass A of the projectiles hitting thetarget in Cave C are determined from energy-loss and time-of-flight measurements using silicon PIN diodes and plasticscintillators before the target. Figure 1 depicts charge ofions versus A/Z ratio for a run optimized for transportationof ions with ∼ A/Z=3. One can identify here the isotopesfrom helium up to fluorine.In order to reconstruct the reaction channel of interestthe outgoing fragments are detected and tracked by usingsilicon strip detectors (SSD), the dipole magnet ALADIN,fibre detectors and Time of Flight Wall detector (TFW),which are located downstream of the target. Two SSDs arelocated after the target and offer a good charge resolution.Figure 2 shows the reconstructed fragment-mass distri-bution for the incoming beam 23O on the target CH2 by∗Supported by GSI F&E and HIC for FAIR. Work is part of HGS-HIRe.applying a cut on outgoing Oxygen ions (Z=8). Addition-ally it is required that the cyrstal ball detector (XB), whichsurrounds the target area and consists of 162 NaI(Tl) crys-tals, detects at least one high energetic nucleon (neutron).tracked mass [u]16 17 18 19 20 21 22 23051015202530354045Figure 2: Tracked mass of the outgoing Oxygen fragmentsafter one neutron removing from the projectile 23O.An indication of the quasi free knockout reactions is theangular correlation between the knocked-out nucleon fromthe projectile and the protons from the CH2 target. Fig-ure 3 presents the polar (left) and the azimuthal (right) cor-relation of proton and neutron of the investigated reactionchannel 23O(p,pn)22O. Due to the momentum conservationproton and neutron show opposite azimuthal angels, whilethey are scattered within a polar angle 0◦ < θ < 90◦ bysharing the beam energie of ∼ 500 MeV. Background, in-cluding reactions induced by the carbon in the target, havebeen subtracted using measurements with empty and car-bon target. [deg]1θ0 10 20 30 40 50 60 70 80 90 [deg]2θ0102030405060708090-210-1101 [deg]1φ0 50 100 150 200 250 300 350 [deg]2φ050100150200250300350-210-1101Figure 3: Angular correlations of protons from the CH 2target and neutrons from the projectile 23O. Left: polar-angle correlations; right: azimuthal-angle correlations.References[1] A. Gade et al., Phys. Rev. C77 (2008) 044306.GSI SCIENTIFIC REPORT 2012 PHN-ENNA-EXP-25155

Direct Reactions with Light Neutron-Rich Nuclei

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Direct Reactions with Light Neutron-Rich Nuclei

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