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Thorsten Kröll*

Thorsten Kröll*

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Thorsten Kröll*

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  1. Study of single particle properties of neutron-rich Na istopes on the „shore of the island of inversion“ by means of neutron-transfer reactions Thorsten Kröll* CERN-INTC-2010-007, INTC-P-276  *TU Darmstadt – TU München – CERN – KU Leuven – Univ. Edinburgh Chalmers TH Göteborg – Univ. West of Scotland, Paisley – IPN Orsay LMU München – Univ. York – Univ. Manchester – Univ. Liverpool Univ. Köln – CSNSM Orsay – Univ. Ioannina – IRNRE Sofia Univ. Camerino – Århus Univ. – UC Madrid – Daresbury Laboratory LBNL Berkeley –GANIL – JAEA Work supported by BMBF (Nr. 06DA9036I), LOEWE / HIC for FAIR, and the MINIBALL/REX-ISOLDE collaborations

  2. 29Na Island of inversion normal sd configurations gs properties Na 31Al 33Al 34Al 32Al 30Mg 33Mg 32Mg 31Mg 31Na 28Na 29Na 30Na intruder fp configurations MCSM, SDPF-M Y. Utsuno et al., PRC 70, 044307 (2004) February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 2

  3. Negative parity states predicted by MCSM è … Size of the N=20 gap 29Na – level scheme • 50%/50% mixture normal/intruder in • gs wave function (from g factor) • Excited states: correspondence • exp ó theory not obvious?!? • No spin assigments, no configurations 1/2- 3/2-, 5/2- 7/2-, 9/2- Y. Utsuno et al., PRC 70, 044307 (2004) V. Tripathi et al., PRL 94, 162501 (2005) February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 3

  4. Possible future experiments: 2H(27Na, 28Na)1H Q00 = 1.32 MeV 3H(27Na, 29Na)1H Q00 = -0.5 MeV 3H(28Na, 30Na)1H Q00 = -1.69 MeV … to map transition into the „island“ Experimental programme 2H(28Na, 29Na)1H Q00 = 2.19 MeV … optimal matching for population of states in the region of interest Competing reactions (PID needed): (d,t) Q00 = 2.71 MeV … leading to 27Na (p,d) Q00 = -1.32 MeV 28Na 27Na 29Na 30Na February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 4

  5. 1/2- 3/2-, 5/2- 7/2-, 9/2- |29Na> =|28Na> Ä |n> 28Na (1+): no intruder component in gs; odd d5/2 proton + odd d3/2 neutron Transfer of one neutron … coupling of odd proton and two neutrons Neutron transfer to positive parity orbital d3/2 … positive parity states formed … pairing has to be considered Neutron in negative parity orbitals f7/2 or p3/2 … negative parity states formed • What happens to 28Na „core“ in 29Na?? • èRelative spectroscopic factors • No intruder component in |28Na> core • è SFs large (e.g. 1/2+, 9/2+, negative parity states) • Intruder component in |28Na> core • è SFs smaller (gs, second 3/2+, first and second 5/2+, 7/2+) February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 5

  6. 2H(28Na,29Na)1H @ 3 MeV/u • FRESCO • optical potentials scaled from reactions with stable nuclei • all spectroscopic factors set to unity DL=1,2,3 February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 6

  7. Experimental set-up (2008) - T-REX and MINIBALL CD beam barrel T-REX was funded and built by TU München, KU Leuven, CSNSM Orsay, CERN, and UK groups … (now also) TU Darmstadt February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 7

  8. Try to re-arrange barrel detectors partly to cover region around 90° 2H(28Na,29Na)1H @ 3 MeV/u • ds/dW: a few mb/sr J • pronounced angular distributions • èDL=1,2,3 well distinguishable J „Blind“ zone February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 8

  9. Observables and results Data set rich of spectroscopic information • Angular distribution of protons • è orbital angular momentum transfer • è parity of states • Energies of protons and coincident g-rays (essential!!!) • è level energies • Relative SFs • è identify possible intruder configuration (excitation of a neutron-pair • across N=20) in neutron wave function … at least qualitatively • Orbital angular momentum transfer • Relative SFs • Decay pattern of excited states • Angular distribution of g-rays • è … allows to determine (or, at least, to restrict) spin of states February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 10

  10. Beam intensity • standard UCx target, surface ionisation * M. Seidlitz et al., ISOLDE Workshop 2009 ** ISAC-2 @ TRIUMF: 27Na, expected intensity 104/s February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 11

  11. Beam composition • Contaminations: Al (estimate: Na/Al ≈ 1.5)and Mg (from Na decay) • … extrapolated from experiment IS482 (29,30Na) • Monitored by DE-E telescope or Bragg chamber in beam dump • (d,p) reaction on 28Al (T1/2 = 2.2 m): Q00 = 7.21 MeV • - long-lived nucleus (suppressed by time gate on proton impact) • - high-lying states populated • level scheme and g-rays of 29Al well known • RILIS to improve Na/Al ratio??? • - ionisation scheme exists and has been tested • … but improvement will be small • - LIST development • … not tested online, very low yield, slow(?) • è We do NOT request the use of the RILIS for this experiment • … but would like to encourage further developments for Na beams February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 12

  12. Rate estimate and beam time request (I) • 2H(28Na, 29Na)1H @ 3 MeV/u … as first reaction of the programme • First transfer experiment with an odd-odd nucleus @ REX-ISOLDE • Main physics aims … explore the „shallow water around island of inversion“ • identification of negative parity states è size of N=20 gap in 29Na • composition of wave functions for excited states • Cross sections > 20 mb • Target 10 mm CD2 (standard thickness at REX-ISOLDE) • eT-REX ≈ 62% and eMINIBALL ≈ 8% • Cross section for fusion-evaporation with d (no protons, few a‘s) • and C (4-20 mb/sr for protons, up to 100 mb/sr for a‘s) • BUT: forward peaked, no discrete lines, no g-coincidences, a‘s stopped • in DE detector … • … hence, has never been a problem in any transfer experiment • performed with CD2 target and neutron-rich beams at REX-ISOLDE February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 13

  13. Rate estimate and beam time request (II) Rate estimate (based on beam intensity of 2·104/s) è 80 protons/h (rate per populated state) è6 proton-g-coincidences/h (compared to ≈ 50 counts/peak in b-gated g-spectrum, V. Tripathi et al.) è1500 counts (g-gated protons) in 10 days T-REX divided in 10 angular bins è >50 counts/bin, <15% statistical error + 1 day for beam preparation We request 33 shifts (11 days) of beam time February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 14