Transcript Document

LOI for the AGATA-PRESPEC campaign, GSI
Relativistic Coulomb excitation for probing special effects
of neutron-proton correlations around 100Sn
B. Cederwall, R. Wadsworth, G. De France et al.
N=Z line coincides with doubly-magic core
Single-particle states wrt
100Sn
core
Neutron-proton correlations in identical
orbitals
Neutron-proton (isoscalar) pairing
Emergence of collectivity
...
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
Main physics aims
• Verify Isoscalar spin-aligned neutron-proton coupling scheme in 92Pd (96Cd)
• Investigate Collective strength in
106,108Te, 112Xe
by measuring B(E2; 0+→ 2+)
Builds on our spectroscopic work at GANIL and JYFL
and theoretical calculations by J. Blomqvist, R. Liotta, C. Qi, D. Delion et al.
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
The nature of nuclear pair correlations
and their effect on nuclei near N=Z
When approaching N=Z, ”normal” pair correlations may remain or even
be extended:
Near N=Z we can have T=1, I=0 (”isovector”) nn, pp Cooper pairs
as well as np Cooper pairs (neutrons and protons occupy identical orbits)
and/or: T=0, I=1... (”isoscalar”) np pairing
Does T=0 pairing exist and, if so, how should it best be revealed?
So far, the search for T=0 np pairing has focused on special features:
- g.s. binding energies of odd-odd nuclei
- high-spin properties of N=Z nuclei (delayed alignments?)
- deuteron transfer reactions
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
The isoscalar (np) pair gap is predicted to
increase sharply as NZ
Calculation by W. Satula, R. Wyss
Phys. Rev. Lett. Vol. 86, 4488 (2001)
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
“New” effects of neutron-proton correlations
around 100Sn
•
Shell model calculations by J. Blomqvist et al. predict strong T=0 neutronproton (np) correlations leading to an isoscalar spin-aligned np coupling
scheme for N=Z nuclei close to 100Sn.
An ”unexpected effect” of the NSM appearing in this exotic region of the
nuclear chart
•
Evidence for onset of collectivity, possibly induced by np pairing*) in
neutron deficient Te and Xe nuclei
•
The proposed experiments aim to confirm these theoretical predictions by
measuring B(E2;0+ 2+) values.
*) M. Sandzelius, B. Hadinia, B. Cederwall, et al., Phys. Rev. Lett. 99, 022501 (2007).
QRPA + np pairing calculations by D.S. Delion, R. Liotta et al. , PRC in press
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
What is the g.s. structure of N=Z nuclei below 100Sn?
For 92Pd and 96Cd neutrons and protons
mainly occupy the g 9/2 subshell
92Pd
96Cd
100Sn
100Sn
The conventional picture :
Ψ=({νg 9/2-2}0+)n x ({πg 9/2-2}0+)n
This would lead to a normal seniority type spectrum of
low-lying excited states
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
Shell Model calculations predict strong np interactions
 Transition to new spin-aligned T=0 np coupling scheme
for N=Z nuclei below 100Sn (J. Blomqvist et al.)
92Pd
Model space: g9/2 (and f5/2 , p3/2 ,p½ )
96Cd
100Sn
100Sn
Aligned np coupling:
Ψ=[({νg 9/2-1 x πg 9/2-1}9+)2]0+
x [({νg 9/2-1 x πg 9/2-1}7+)2]0+
Bo Cederwall
Ψ=[({νg 9/2-1 x πg 9/2-1}9+)2]0+
AGATA Physics WS, Istanbul May 2010
Pd level systematics near N=Z
92Pd,
theory
92Pd,
exp
94Pd,
theory
94Pd,
exp
96Pd,
theory
96Pd,
exp
Shell model calculations by J. Blomqvist, R. Liotta, C. Qi
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
Pd level systematics near N=Z
- effects of np interactions
Shell model calculations by J. Blomqvist, R. Liotta, C. Qi
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
New manifestation of T=0 np ”pairing”?
92Pd
l=8
l=6
96Cd
100Sn
l=8
l=8
100Sn
l=8
l=6
”Nuclear belly dancers”
Special deuteron-hole cluster like ground states imply significant deformation
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
B(E2; 0+  2+) – sensitive probe of neutron-proton interactions
Shell model calculations by J. Blomqvist, R. Liotta, C. Qi
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
Enhanced collective strength at N=Z
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
Evidence for enhanced collective
strength in Te and Xe nuclei approaching N=Z
Te experimental E(2+) and B(E2; 2+→ 0+)
TZ=1 nucleus 106Te : B. Hadinia, B. Cederwall et al., Phys. Rev. C 72, 041303 (2005)
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
Xe experimental E(2+) and B(E2; 2+→ 0+)
TZ=1 nucleus 110Xe; M. Sandzelius, B. Hadinia,, B. Cederwall et al., Phys. Rev. Lett. 99, 022501 (2007)
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
Quadrupole collectivity
The traditional view of the mechanism behind deformation and
collectivity: long range np QQ interactions
Taken from R.F. Casten, 2003
Taken from R.F. Casten, 2003
These trends can change with np pairing as N→Z !
Enhancement of collectivity due to np (short-range) pairing
correlations predicted in new calculations by D.S Delion, R. Liotta et al.
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
New QRPA + np pairing calculations predict enhanced
collectivity near the N=Z=50 double shell closure induced by
np pairing correlations (D.S. Delion, R. Liotta et al.)
p-h excitations
induced by
np pairing
Bo Cederwall
Strong decrease in E(2+)
with increasing Δpn
Much smaller effect
from long-range QQ np int.
AGATA Physics WS, Istanbul May 2010
Shell model calculations for light Te isotopes indicate that
configuration mixing due to the monopole tensor force
between primarily the proton 0g7/2 and neutron 1d5/2 orbitals
can induce enhanced collectivity (C. Qi, R. Liotta et al.)
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
Octupole deformation and correlations near N=Z
202
134
88
56
34
Strong octupole correlations are expected
in nuclei where normal-parity single-particle
states and intruder states differing by
Δl = Δj = 3 are near the Fermi surface.
“Doubly-magic octupole-deformed”
nucleus predicted by theory
112
56
Ba 56
Next to 112Ba (accessible with current
technology?) 110Xe56 and 109I56 might have
the largest octupole stability.
Coherent octupole correlations for
neutrons and protons should occur
near N=Z.
Can we observe additional enhancement
due to dynamic np correlations ?
Enhanced octupole correlations in light Te-Xe nuclei
J.F. Smith et al.
Phys. Lett B523, 13 (2001)
(Gammasphere)
Bo Cederwall
G. de Angelis et al.
Phys. Lett B535, 153 (2002)
(Euroball)
G.F. Lane et al.
Phys. Rev. C57, R1022 (1998)
(Gammasphere)
AGATA Physics WS, Istanbul May 2010
Proposed Experiments
• Measure B(E2; 0+2+) for isotopic chain 92,94,96Pd
(from N=Z to N=50 closed shell)
• Measure E(2+) for 96Cd and B(E2; 0+2+) for 96,98Cd
(from N=Z to N=50 closed shell)
• Search for decay of 16+ spin trap isomer for 96Cd
Confirm spin-aligned neutron-proton coupling scheme and
characterize np interactions (T=0/T=1)
• Measure E(2+) for 106Te and B(E2; 0+2+) for 106,108Te, 112Xe
Measure and characterize collective strength
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
Experimental details
Projectile fragmentation FRS – AGATA – LYCCA
92-96Pd: LISE++ calc for primary beam 106Cd
Ebeam = 650 MeV/u Ibeam = 1 pnA
S4 ion and γγ-ion rates
Setting 1: optimizing for 92Pd
Setting 2: optimizing for 94Pd
Assume 15% AGATA pp efficiency, σ(Coulex) from DWEIKO
92Pd
Setting
94Pd
96Pd
S4
(s-1)
γ-ion
(per day)
S4
(s-1)
γ-ion
(per day)
S4
(s-1)
γ-ion
(per day)
1
1.6
200
8.0
1000
-
-
2
-
-
1000
1.2·105
300
3.8·104
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
Experimental details, ct’d
Projectile fragmentation FRS – AGATA – LYCCA
96-98Cd: LISE++ calc for primary beam 112Sn
Ebeam = 650 MeV/u Ibeam = 1 pnA
S4 ion and γγ-ion rates
Setting optimized for 96Cd
Assume 15% AGATA pp efficiency, σ(Coulex) from DWEIKO
96Cd
98Cd
S4
(s-1)
γ-ion
(per day)
S4
(s-1)
γ-ion
(per day)
0.1
13
4.0
500
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
Experimental details, ctd’
Projectile fragmentation FRS – AGATA – LYCCA
106,108Te, 112,114Xe : LISE++ calc for primary beam 144Sm
Ebeam = 950 MeV/u Ibeam = 1 pnA
S4 ion and γγ-ion rates
Setting 1: optimizing for 106Te
Setting 2: optimizing for 112Xe
Assume 15% AGATA pp efficiency, σ(Coulex) from DWEIKO
106Te
Setting
108Te
112Xe
114Xe
S4
(s-1)
γ-ion
(per day)
S4
(s-1)
γ-ion
(per day)
S4
(s-1)
γ-ion
(per day)
S4
(s-1)
1
0.2
25
20
2.4·103
-
-
-
2
-
-
-
-
30
3.6·103
1.0·103
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
γ-ion
(per
day)
1.2·105
Backup slides
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
92Pd
analysis (prel) γγ2n
Three γ rays firmly identified, mutually concident
γ -gated on
6 +-
4+
γ -gated on 2+- 0+
Bo Cederwall
4 +- 2 +
4 +- 2 +
2 +- 0 +
6 +- 4 +
AGATA Physics WS, Istanbul May 2010
92.94,96Pd
levels and the role of T=0 np interactions at N=Z
92Pd
theo
full np
92Pd
96Pd
T=0
92Pd
92Pd
Bo Cederwall
theo
no np
T=1
theo
96Pd
exp
AGATA Physics WS, Istanbul May 2010
96,98Cd
Shell model calculations by
. Blomqvist, R. Liotta, C. Qi et al.
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
Pd level systematics near N=Z
Shell model calculations by J. Blomqvist, R. Liotta, C. Qi
Bo Cederwall
AGATA Physics WS, Istanbul May 2010
96,98Cd
level and the role of T=0 np interactions at N=Z
96Cd
theo
full np
Bo Cederwall
96Cd
theo 96Cd
no np
T=0
96Cd
98Cd
theo
98Cd
T=1
AGATA Physics WS, Istanbul May 2010