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. EdinburghChalmers 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 LaboratoryLBNL Berkeley – GANIL – JAEA

CERN-INTC-2009-037, INTC-P-272 

November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 2

Island of inversion

normalsd

configurations

30Mg

29Na

33Al32Al31Al

31Mg 32Mg

30Na 31Na

34Al

33Mg

intruderfp

configurations

Na

28Na

MCSM, SDPF-MY. Utsuno et al., PRC 70, 044307 (2004)

gs properties

November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 3

28Na – level scheme

V. Tripathi et al., PRL 94, 162501 (2005)

• No intruder component in gs wave function (from g factor)• Excited states: correspondence exp theory not obvious?!?• Low-lying negative parity states predicted by MCSM Measure for size of the N=20 gap

Y. Utsuno et al., PRC 70, 044307 (2004)

November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 4

Experimental programme

Q00 = 1.32 MeV … optimal matching for population of states in the region of interest

Competing reactions (PID needed):(d,t) Q00 = -0.47 MeV(p,d) Q00 = -4.07 MeV

29Na 30Na28Na27NaPossible future experiments:

2H(28Na, 29Na)1H Q00 = 2.19 MeV3H(27Na, 29Na)1H Q00 = -0.5 MeV3H(28Na, 30Na)1H Q00 = -1.69 MeV

… to map transition into the „island“

2H(27Na, 28Na)1H

November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 5

27Na (5/2+): no intruder component in gs, odd proton in d5/2 orbital

Transfer to an odd-even nucleus … coupling of odd proton and odd neutron

Odd neutron in positive parity orbital d3/2

… positive parity states formed

Odd neutron in negative parity orbitals f7/2 or p3/2

… negative parity states formed

28Na> = 27Na> n>

What happens to 27Na „core“ in 28Na?? Relative spectroscopic factors

• No intruder component in |27Na> core SFs large (e.g. for transfer to gs of 28Na)

• Intruder component in |27Na> core SFs smaller

November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 6

2H(27Na,28Na)1H @ 3 MeV/u

L=1,2,3

• FRESCO• optical potentials scaled from reactions with stable nuclei• all spectroscopic factors set to unity

NEWS: MCSM can now calculate also SFs!!! (Y. Utsuno, priv. communication)

November 16, 2009 | 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, andUK groups … (now also) TU Darmstadt

November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 8

2H(27Na,28Na)1H @ 3 MeV/u

• d/d: a few mb/sr • pronounced angular distributions L=1,2,3 well distinguishable

„Blind“ zone

November 16, 2009 | 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 needed to find optimum!

or

November 16, 2009 | 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 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

November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 11

Beam intensity

T1/2

[ms]PSB Yield [/C]

IntensityIS482 [/s]

Estimate [/s]

27Na 301 8.5·106 2·105

28Na 30.5 9.6·105 < 2·104

29Na 44.9 1.5·105 3-4·103

30Na 48 5.1·104 0.6-1·103

ISAC-2 @ TRIUMF: 27Na, expected intensity 104/s

• standard UCx target, surface ionisation

November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 12

Beam composition

• Contaminations: Al and small amount Mg (from Na decay) … as seen in experiment IS482 (29,30Na)

• Na/Al ratio much more favourable for lighter masses because of larger Na and smaller Al yields

• Monitored by E-E telescope or Bragg chamber in beam dump

• (d,p) reaction on 27Al: Q00 = 5.5 MeV - stable nucleus (suppressed by time gate on proton impact) - high-lying states populated - level scheme and -rays of 28Al well known (NNDC)

• RILIS to improve Na/Al ratio??? - ionisation scheme exists and has been tested U. Köster et al., Spec. Acta Part B 58, 1047 (2003) - … high demand for RILIS NOT necessary for 27Na (maybe for 28Na in a future Addendum)

November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 13

Rate estimate and beam time request2H(27Na, 28Na)1H @ 3 MeV/u … as first reaction of the programme

- First transfer experiment with an odd-even nucleus @ REX-ISOLDE- Main physics aim: low-lying negative parity states size of N=20 gap in 28Na … explore the „shallow water around island of inversion“

• Cross sections > 20 mb, target 5 m CD2, T-REX ≈ 62% and MINIBALL ≈ 8%

400 protons/h (rate per populated state) 30 proton--coincidences/h (≈ 50 counts/peak in -gated -spectrum, V. Tripathi et al.)

3000 counts (-gated protons) in 4 days T-REX divided in 10 angular bins >100 counts/bin, <10% statistical error

+ 1 day for beam preparation

We request 15 shifts (5 days) of beam time