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Exploring Shape Coexistence in the Island of Inversion in 32Mg

Proposal for searching the 02+ state in 32Mg using a two-neutron transfer reaction. Experiment details, detector setup, beam conditions, and potential outcomes are outlined. Requesting beam time for study continuation.

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Exploring Shape Coexistence in the Island of Inversion in 32Mg

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  1. Shape coexistence in the “island of inversion”:Search for the 02+ state in 32Mgapplying a two-neutron transfer reaction Proposal INTC-2008-008 / P-239 Thorsten Kröll Physik-Department E12, TU München, Germany Maier-Leibnitz-Laboratorium für Kern- und Teilchenphysik, Garching, Germany

  2. ... north-west coast • Coulex results 30,32Mg • g-factors of g.s.´s • (compiled by G. Neyens) Coexistence of spherical and deformed states normal sd configurations Migration of 0+ states ... 2p-2h 0+ ??? 31Al 33Al 34Al 32Al 2+ inversion 30Mg 33Mg 32Mg 31Mg 0p-0h 0+ 30Mg 32Mg 31Na 29Na 30Na intruder fp configurations ... second 0+ in 32Mg has not been observed so far !!! Exploring the “island of inversion” … Experiments at ISOLDE in 2007: IS409/410: “safe” Coulex of 31Mg IS454: one-neutron transfer to 31Mg IS414: 0+→0+ E0 transition in 30Mg … more than 30 years after its discovery there is still a vital interest in the “island of inversion” !!!

  3. … by a two-neutron transfer reaction Similar particle-hole configurations n large overlap of wave functions èlarge spectroscopic factors for transfer ... selective population! normal sd configurations intruder fp configurations 2n-transfer 1/2+ 0+ 30Mg 31Mg

  4. DWBA calculation • optical model parameters • extrapolated from exp´s • with stable Mg/Si beams • all spectroscopic factors • are set to 1 • SFs to g.s. and 21+ state • should be smaller because • of different p-h-structure • dominant contribution for • 02+ state is one-step • transfer of neutron pair • cross section rather • insensitive on structure • of intermediate states • in 31Mg 3H (30Mg, 32Mg) 1H @ 2 MeV/u Calculation by K. Wimmer (TUM)

  5. V. Bildstein et al. (TUM) Si detector array Set-up MINIBALL epart = 62% • Major upgrade of instrumentation at REX-ISOLDE • (... funded by TUM, KU Leuven, Univ. of Edinburgh, CSNSM Orsay) • Includes improved beam diagnostics • active collimator (4 PIN diodes) in front of chamber • segmented diamond detector at target position • ... successfully used in Oct/Nov 2007 (IS454) Upgrade planned for 2008 DE detectors to identify electrons in backward direction e- : b, E0, ...

  6. Tritium target • Tritium loaded Titanium foil • 48 mg/cm2 3H / 450 mg/cm2 Ti • activity: 10 GBq ... conform with CERN Specification No. 4229RP20070405-GD-001 Test experiments Two-neutron transfer reaction • 3H (40Ar, 42Ar) 1H @ 90 MeV (2.25 MeV/u) performed at HMI (Berlin) • 48 mg/cm2 3H / 450 mg/cm2 Ti ó26 GBq (at date of production) • 0.6 enA è100 part-pA = 6 ·108 part/s • è monitoring of elastic scattering èno loss of Tritium! • èno outgasing of Tritium! • è loss of H is observed only at intensities > 5 part-nA RBS study at MLL (with deuterated Ti foil) Conclusion • stable under beam conditions • mechanically stable (Ti carrier) è non-problematic mounting èThe use of such a target is feasible at REX-ISOLDE

  7. Simulation of experiment I 3H (30Mg, 32Mg) 1H @ 2 MeV/u States included in simulation Forward Backward 2+ CD Barrel Barrel CD 0+ 2+ 0+ 32Mg Simulation by V. Bildstein and K. Wimmer (TUM)

  8. Identification of 0+ state (I) ... by the following observables: Energies of the protons and/or the de-exciting g-rays èexcitation energy Nicest case: protons p can be separated from other proton lines If not ... decay to 2+ state ? g-ray observed in coincidence (reduced statistics !) BUT: works for only t < 20 ns If decay not observable: prompt protons in coincidence with 885 keV g-ray subtracted (BUT: MINIBALL is not a good veto) JJJ p JJ p 0+ E2 (g, e-) J p 2+ 885 keV E0 0+

  9. Dℓ = 0 Dℓ = 2 ... already „jump“ in counting rate passing the „gap“ at 90° is sensitive to Dℓ !!! Identification of 0+ state (II) ... by the following observables: Angular distribution of the protons / orbital momentum transfer Dℓ èspin assignment Cross section / relative spectroscopic factor èconfiguration • Simulation • 9 days of beam time • 105 part/s • 50-300 counts/18° < 15% statistical error not covered by detector Simulation by V. Bildstein and K. Wimmer (TUM)

  10. Summary and beam time request Shape coexistence in the “island of inversion”: Search for the 02+ state in 32Mg applying a two-neutron transfer reaction • Reaction : 3H (30Mg, 32Mg) 1H @ ≈ 2 MeV/u • dTarget = ≈ 48 mg/cm2 tritium in Ti (low beam energy to avoid fusion with Ti) • UCx target + RILIS Þ beam intensity: 105 s-1 (obtained for IS409/410 in 2007) Experimental set-up: - New array of Si detectors (particle detection) & MINIBALL (g detection) - beam composition: “LASER ON/OFF”, Bragg detector, release curves From calculated cross section Þ≈4 protons h-1 9 days of beam time Þ ≈ 700 counts (18° binning Þ ≈ 100 counts per bin) + 1 day for beam preparation We request 30 shifts (10 days) of beam time ... if succesfully demonstrated, two-neutron transfer reactions will open a new field for studies of shape coexistence, pairing etc., in particular at HIE-ISOLDE energies!!

  11. … the collaboration Proposal INTC-2008-008 / P-239 Th. Kröll1, K. Wimmer1, R. Krücken1, V. Bildstein1, T. Behrens1, T. Faestermann1, R. Gernhäuser1, M. Mahgoub1, P. Maierbeck1, D. Habs2, P. Thirolf2, T. Morgan2, W. Schwerdtfeger2, R. Lutter2, P. Van Duppen3, R. Raabe19, N. Patronis3, N. Bree3, M. Huyse3, O. Ivanov3, J. Diriken3, I. Stefanescu18, J. Van de Walle4, E. Clement19, J. Cederkäll4, D. Voulot4, F. Wenander4, L. M. Fraile5, T. Davinson6, P. J. Woods6, T. Nilsson7, E. Tengborn7, R. Chapman8, J. F. Smith8, L. Angus8, M. Labiche17, P. Wady7, D. Jenkins9, J. Butterworth9, B. S. Nara Singh9, S. Freeman10, C. Fitzpatrick10, A. Deacon10, P. Butler11, M. Scheck11, A. Blazhev12, N. Warr12, P. Reiter12, M. Seidlitz12, G. Georgiev13, E.Fiori13, R. Lozeva13, N. Pietralla14, G. Schrieder14, D. Balabanski15, G. Lo Bianco16, S. Nardelli16, and the REX-ISOLDE and MINIBALL collaborations 1 TU München – 2 LMU München – 3 KU Leuven – 4 CERN Genève 5 UC Madrid – 6 University of Edinburgh – 7 Chalmers TH Göteborg 8 University of the West of Scotland, Paisley – 9 University of York 10 University of Manchester– 11 University of Liverpool – 12 Universität zu Köln 13 CSNSM Orsay – 14 TU Darmstadt – 15 INRNE Sofia – 16 Università di Camerino 17Daresbury Laboratory–18Argonne National Laboratory–19GANIL Caen

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