Study of single particle properties of
neutron-rich Na istopes on the
„shore of the island of inversion“
by means of neutron-transfer reactions
CERN-INTC-2009-037, INTC-P-272
Thorsten Kröll*
*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
Island of inversion
normal
sd
configurations
28Na
gs properties
31Al
32Al
33Al
34Al
30Mg
31Mg
32Mg
33Mg
29Na
30Na
31Na
Na
intruder
fp
configurations
November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 2
MCSM, SDPF-M
Y. Utsuno et al.,
PRC 70, 044307 (2004)
28Na
– level scheme
• 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
V. Tripathi et al., PRL 94, 162501 (2005)
Y. Utsuno et al., PRC 70, 044307 (2004)
November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 3
Experimental programme
2H(27Na, 28Na)1H
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
Possible future experiments:
27Na
28Na
2H(28Na, 29Na)1H
Q00 = 2.19 MeV
3H(27Na, 29Na)1H Q
00 = -0.5 MeV
3H(28Na, 30Na)1H Q
00 = -1.69 MeV
… to map transition into the „island“
November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 4
29Na
30Na
|28Na> = |27Na> |n>
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
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 | 5
2H(27Na,28Na)1H
@ 3 MeV/u
• FRESCO
• optical potentials scaled from reactions with stable nuclei
• all spectroscopic factors set to unity
DL=1,2,3
NEWS: MCSM can now calculate also SFs!!! (Y. Utsuno, priv. communication)
November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 6
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
November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 7
2H(27Na,28Na)1H
@ 3 MeV/u
• ds/dW: a few mb/sr J
• pronounced angular distributions
 DL=1,2,3 well distinguishable J
„Blind“
zone
November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 8
T-REX … proposed improvement
Detector arrangement now:
„blind“ zone around 90°
Target
New arrangements under consideration
or
… simulations needed to find optimum!
November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 9
Observables and results
Data set rich of spectroscopic information
• Angular distribution of protons
 orbital angular momentum transfer
 parity of states
• Energies of protons and coincident g-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 g-rays
 … allows to determine (or, at least, to restrict) spin of states
November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 10
Beam intensity
• standard UCx target, surface ionisation
T1/2
[ms]
PSB Yield
[/mC]
Intensity
IS482 [/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
November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 11
Estimate
[/s]
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 DE-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 g-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 | 12
Rate estimate and beam time request
2H(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 mm CD2, eT-REX ≈ 62% and eMINIBALL ≈ 8%
 400 protons/h (rate per populated state)
 30 proton-g-coincidences/h
(≈ 50 counts/peak in b-gated g-spectrum, V. Tripathi et al.)
 3000 counts (g-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
November 16, 2009 | INTC Meeting | TUD - Institut für Kernphysik | Thorsten Kröll | 13

INTC-P-272-ThKroell - Indico