thorsten kröll*

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-2010-007, INTC-P-276

February 4, 2010 | 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

29Na


29Na – 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


Experimental programme

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

29Na 30Na28Na27NaPossible future experiments:

2H(27Na, 28Na)1H Q00 = 1.32 MeV3H(27Na, 29Na)1H Q00 = -0.5 MeV3H(28Na, 30Na)1H Q00 = -1.69 MeV

… to map transition into the „island“

2H(28Na, 29Na)1H


7/2-, 9/2-3/2-, 5/2-

1/2-

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

29Na> = 28Na> n>

What happens to 28Na „core“ in 29Na?? Relative spectroscopic factors

• No intruder component in |28Na> core SFs large (e.g. 1/2+, 9/2+, negative parity states)• Intruder component in |28Na> core SFs smaller (gs, second 3/2+, first and second 5/2+, 7/2+)


2H(28Na,29Na)1H @ 3 MeV/u

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

L=1,2,3


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


2H(28Na,29Na)1H @ 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 partlyto cover region around 90°


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


Beam intensity

T1/2

[ms]

PSB Yield

[/C]

Intensity

IS482 [/s]

Estimate

[/s]

27Na 301 8.5·106 2·105**

28Na 30.5 9.6·105 2·104

29Na 44.9 1.5·105 6.6·103*

30Na 48 5.1·104 1.3·103*

* M. Seidlitz et al., ISOLDE Workshop 2009** ISAC-2 @ TRIUMF: 27Na, expected intensity 104/s

• standard UCx target, surface ionisation


Beam composition

• Contaminations: Al (estimate: Na/Al ≈ 1.5) and Mg (from Na decay) … extrapolated from experiment IS482 (29,30Na)

• Monitored by E-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 -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(?) We do NOT request the use of the RILIS for this experiment … but would like to encourage further developments for Na beams


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 size of N=20 gap in 29Na• composition of wave functions for excited states • Cross sections > 20 mb• Target 10 m CD2 (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 CD2 target and neutron-rich beams at REX-ISOLDE


Rate estimate and beam time request (II)

Rate estimate (based on beam intensity of 2·104/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

thorsten kröll*

Documents

neutrons neutron transfer

neutron wave function

population of states

na n28na

na core sfs smaller

na core sfs large

negative parity orbitals

gs wave function