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* Work supported by BMBF (Nr. 06DA9036I), LOEWE / HIC for FAIR, and the MINIBALL/REX-ISOLDE collaborations *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 CERN-INTC-2010-007, INTC-P-276

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

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

4. February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 4 Experimental programme Q 00 = 2.19 MeV … optimal matching for population of states in the region of interest Competing reactions (PID needed): (d,t) Q 00 = 2.71 MeV … leading to 27 Na (p,d) Q 00 = -1.32 MeV 29 Na 30 Na 28 Na 27 Na Possible future experiments: 2 H( 27 Na, 28 Na) 1 H Q 00 = 1.32 MeV 3 H( 27 Na, 29 Na) 1 H Q 00 = -0.5 MeV 3 H( 28 Na, 30 Na) 1 H Q 00 = -1.69 MeV … to map transition into the „island“ 2 H( 28 Na, 29 Na) 1 H

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

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

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

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

9. February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 9 T-REX … proposed improvement Detector arrangement now: „blind“ zone around 90° New arrangements under consideration Target Simulations started to find optimum Mechanical constraints or

10. February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 10 Observables and results Angular distribution of protons  orbital angular momentum transfer  parity of states Energies of protons and coincident  -rays (essential!!!)  level energies Relative SFs  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  -rays  … allows to determine (or, at least, to restrict) spin of states Data set rich of spectroscopic information

11. February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 11 Beam intensity T 1/2 [ms] PSB Yield [/  C] Intensity IS482 [/s] Estimate [/s] 27 Na3018.5·10 6 2·10 5** 28 Na30.59.6·10 5 2·10 4 29 Na44.91.5·10 5 6.6·10 3* 30 Na485.1·10 4 1.3·10 3* * M. Seidlitz et al., ISOLDE Workshop 2009 ** ISAC-2 @ TRIUMF: 27 Na, expected intensity 10 4 /s standard UC x target, surface ionisation

12. February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 12 Beam composition Contaminations: Al (estimate: Na/Al ≈ 1.5) and Mg (from Na decay) … extrapolated from experiment IS482 ( 29,30 Na) Monitored by  E-E telescope or Bragg chamber in beam dump (d,p) reaction on 28 Al (T 1/2 = 2.2 m): Q 00 = 7.21 MeV - long-lived nucleus (suppressed by time gate on proton impact) - high-lying states populated level scheme and  -rays of 29 Al 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(?)  We do NOT request the use of the RILIS for this experiment … but would like to encourage further developments for Na beams

13. February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 13 Rate estimate and beam time request (I) 2 H( 28 Na, 29 Na) 1 H @ 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  size of N=20 gap in 29 Na composition of wave functions for excited states Cross sections > 20 mb Target 10  m CD 2 (standard thickness at REX-ISOLDE)  T-REX ≈ 62% and  MINIBALL ≈ 8% Cross section for fusion-evaporation with d (no protons, few  ‘s) and C (4-20 mb/sr for protons, up to 100 mb/sr for  ‘s) BUT: forward peaked, no discrete lines, no  -coincidences,  ‘s stopped in  E detector … … hence, has never been a problem in any transfer experiment performed with CD 2 target and neutron-rich beams at REX-ISOLDE

14. February 4, 2010 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 14 Rate estimate and beam time request (II) Rate estimate (based on beam intensity of 2·10 4 /s)  80 protons/h (rate per populated state)  6 proton-  -coincidences/h (compared to ≈ 50 counts/peak in  -gated  -spectrum, V. Tripathi et al.)  1500 counts (  -gated protons) in 10 days T-REX divided in 10 angular bins  >50 counts/bin, <15% statistical error + 1 day for beam preparation We request 33 shifts (11 days) of beam time