Stephane Grévy : [email protected] 8, 2012
Unveiling the intruder deformed 0+2 state in 34Si20
and few words about N=28
IFIN - Bucharest F. Rotaru (PhD) GANIL - Caen IPN - Orsay INR - DebrecenFLNR - Dubna NPI - Rez, IPHC - Strasbourg University of Madrid CEA - Bruyères-le- Châtel
“island of inversion” around 32Mg
0+2 state in 34Si : how the intruder configurations develop at N=20
2ħ32Mg
0ħ
Nħ?
34Si
0ħ
Nħ 3346
36S
32Mg 36S34Si
30Mg
28Mg
Follow the evolution of the "excited" configurations from the stability towards the Island of Inversion Study the evolution of the excited 0+
states
0ħ
2ħ
0ħ
Nħ
28Mg 30Mg
O+2(30Mg) :
W. Schwerdtfeger, PRL2009
1789
5702
0ħ
O+2(32Mg) :
K. Wimmer, PRL2010
1058
34Al
N=20
40Ca
38Ar
36S
30Ne
32Mg
34Si
Search for the 0+2 state in 34Si
hypothesis :
the 0+2 could be directly populated
through the b-decay of a predicted isomeric 1+ state in 34Al.
-All experiments failed in this quest… inelastic scattering, b-decay of 34Al,…
34Al : 4- ground state (p d5/2)5 (n d3/2)+4(f7/2)+1
34Si : 0+2 deformed state p(d5/2)6 (n d3/2)-2(f7/2)+2
34Si : 0+ ground state p(d5/2)6 (n d3/2)+4
34Al : 1+ excited state (E~200 keV) (p d5/2)5 (n d3/2)-1(f7/2)+2
Almost all the calculations predictthe 0+
2 state to be located below the 2+1
decay by : - internal pair creation - internal conversion electron [if E(0+
2) <1022 keV - not expected]
2ħ
1+
0+2
b
Experiment :- production the 34Al in the "predicted" isomeric 1+
projectile fragmentation @ GANIL/LISE
- implantation in a Kp foil
E1D6E2XY
Edeg1&2Erot1
GANIL/LISE3 Experiment, may 2010
e+ e-
0+2 in 34Si : the experiment
F. Rotaru et al., Phys. Rev. Lett.109 (2012)092503
4-
b- measurement of the gamma-rays
2 Ge clovers (EXOGAM)
- trigger on the b-decay from the gs and the isomer and measurement of the energy of both e+ and e- in coincidence
4 Si-SiLi telescopes
44
1+
4-
Ee1+Ee2 = cst = 1697(3) keV
E(0+2) = 1697 keV
0+2 in 34Si : experimental results 1/3
2719(3) 02+
e+ e-
b-
T1/2(0+2) = 19.4(7) ns
Electric monopole strength:
ρ2(E0)=(13 ± 0.9)x10-3
19.4(7) ns
+ 1022 = 2719(3)
F. Rotaru et al., Phys. Rev. Lett.109 (2012)092503
2719(3) 02+
4
1+
4-0+
2 in 34Si : experimental results 2/3 26 (1) msec
Beta decay time from 34Al : e+ e- 19.4(7) ns
54.4 (5) msec
b-
54.4 (5) msec
26 (1) msec
F. Rotaru et al., Phys. Rev. Lett.109 (2012)092503
2719(3) 02+
4
1+ 26 (1) msec4-
0+2 in 34Si : experimental results 3/3
B(E2:2+10+
2) from - B(E2:2+
10+1) = 17(7) e2fm4
Coulex : Ibbotson, PRC80(1998)2081 - Ig(3326 keV)/Ig(606 keV) = 1380(717)
B(E2:2+10+
2) = 61(40) e2fm4
?
17(7
)
F. Rotaru et al., Phys. Rev. Lett.109 (2012)092503
19.4(7) ns
2719(3) 02+
4
1+ 26 (1) msec4-
0+2 in 34Si : mixing and deformation
mixing of the 0+ states : cos² q ~ 0.22
B(E2: 2+10+
1) = 17(7) e²fm4 +
r² = (3Z/4p)²cos² *(1-q cos² )*(q b1²-b2²)²
if spherical-deformed configuration b2 = 0
b2 ~ 0.29
B(E2: 2+10+
2) = 61(40) e²fm4
r²(E0: 0+20+
1) = 13.0(0.9) mu
17(7
)
61(4
0)
F. Rotaru et al., Phys. Rev. Lett.109 (2012)092503
19.4(7) ns
In particular, the major pillars to understand the Island of Inversion are the 0+1,2 states in 30Mg, 32Mg and 34Si
Important to have a interaction capable of describing various situations in a unified manner.
gs
gs
0+sph 0+
sph
0+def
0+def
34Si 32Mg
1058
2713
-4 MeV
- removal of two protons from 34Si 4 MeV shift
gs
gs0+
sph 0+sph
0+def
0+def
30Mg 32Mg
1058
1789
-3 MeV
- addition of two neutrons to 30Mg 3 MeV shift
A good interaction should therefore be able to reproduce :
SDPF-U-SI interaction :
- valence protons : sd shell- valence neutrons : sd or pf shell no (sd pf) neutron excitations
labeled "0ħ"
8 8p n
820
p n
not able to describe nuclei in wich neutronexcitations from sd to pf are importantsuch as, by definition, in the "island of inversion"
To account for (sd pf) neutron excitations :
8 8
off diagonal matrix elements nnpfsdV - Lee-Kahana-Scott G matrix
- scaled as for the description of the SD states in 40Ca (multi p-multi h excitations)
neutron SPE's for sd-pf shells on a 16O core
- sd standard USD- fp no experimental guidance
SDPF-U-SI in case of 0ħ limit 0+
2(30Mg) at the correct energy
SDPF-U-MIX interaction
0+2 in 34Si : Shell Model calculations
Excellent agreement experiment – Shell Model
SDPF-U-MIX
b
1+
4-
0+22713(3)
b
b
61(40)
17(7)
0.550 1+ 92% 2p-1h 4- 78% 0ħ
0+2 86% 2p-2h2570
67
11
3510 2+
~50005-
3-
4-
10%
30%
60%
30 ms
59 ms
26(1)ms
54.4(5)ms
0+1 89% 0ħ
decrease of the 0+def
34Si32Mg33Mg32Mg
Expt. SM
3767 3852
2846 2999
L.Gaudefroy et al, PRL97(2006)
pro
ton
d3/2
-s1/2
an
d d
5/2
48Ca
N=28
48CaCa Z=20
Ar Z=18
S Z=16
Si Z=14
N=20
46Ar
neutron f7/2
0
1
2
3
4
5
6
7
19 20 21 22 23 24 25 26 27 28 29neutron number
En
erg
y (M
eV)
d3/2
s1/2
d5/2
Z=14
Z=16
K isotopes
Study for the 0+2 state in 44S
40Ca
34Si
36S
32Mg
Feeding of the nf7/2
Compression of the ps1/2d3/2 orbitals
Removal of the psd
Reduction of N=28 gap
42Si
44S
2+ 0+ : 770 ± 19 keV
PR
L9
9(2
00
7)0
22
50
3
GANIL 2007
SDPF-U-NR SDPF-U-SI
S. T
ake
uch
i et
al.,
arX
iv:1
20
7.6
19
1a
cce
pte
de
d t
o P
RL
(se
pt.
20
12
, 2
8th)
RIBF 2012
PR
L9
9(2
00
7)0
22
50
3
GANIL 2007
well deformed rotor
Perspectives (from an experimental point of view)
• Better characterize the 1+ isomer in 34Al g factor measurement
mass measurement
• Make the link between N=20 and N=20 : from an island of inversion towards a peninsula
Conclusions• By the study of the 0+
2 states in 34Si we have better characterized the shapecoexistence at N=20
• We used this work to extend the SDFP-U-SI interaction to take into account the neutron excitation above N=20
• We have an interaction SDPF-U-MIX which is now able to describe very well both the N=20 and N=28 regions.
and the GANIL staff for providing beams and support
Large collaboration : many experiments from 1993 to 2012… GANILIPN OrsayCEA BruyèresCEA SaclayIPHCU. of MadridINR DebrecenIFIN BucharestJINR Dubna…
Special thanks to the Madrid-Strasbourg collaboration
N=28
pro
ton
d3/2
-s1/2
an
d d
5/2
48Ca
N=28
48CaCa Z=20
Ar Z=18
S Z=16
Si Z=14
N=20
46Ar
neutron f7/248Ca
HF
B - D
1S
calcu
latio
ns fro
m C
EA
-DA
MStudy for the 0+
2 state in 44S
40Ca
34Si
36S
32Mg
Feeding of the nf7/2
Compression of the ps1/2d3/2 orbitals
Removal of the psd
Reduction of N=28 gap
42Si
44S
2002 :Shell Model predictions : in 44S the ground state could be a mixture of closed shell and np-nh excitations. This mixing will produce a very low lying first excited O+ that might be taken as a signature of spherical-deformed shape coexistence . E. Caurier et al., EPJ A15 (2002)
2004 : Observation of 0+
2 state at low excitation energy (1365 keV) S. Grévy et al., EPJ A25(2005)
GANIL/LISE3: isomer spectroscopy of 44S
Reduced Transition Probability B(E2;0+22+
1) 0+2
2+1
0+1
314
?
?
- Mixing of 0+ states
Monopole strength r2(E0;0+2→0+
1)
- Deformation of 0+ states
0+2
2+1
0+1
E2
E0
Shape Coexistence in 44S
r² = (3Z/4p)²cos² *(1-q cos² )*(q b1²-b2²)²
in agreement with spherical-prolate shape coexistence predicted by Shell Model
b2 = 0.25
0+2
2+1
0+1
E2
E0
Measurement of :- T1/2 (0+
2)- l(E0) / l(E2) B(E2: 0+
22+1) = 42(13) e²fm4
r²(E0: 0+20+
1) = 8.7(7) mu0+
2
2+1
0+1
314
42
8.7
O+2+O+
E(MeV)
mixing of the 0+ states : cos²q=0.88 (5)
+B(E2: 0+
12+1) = 314(88) e²fm4
1365 keV1329 keV
2.6 ms
Perspectives (from an experimental point of view)
N=20- better characterize the 1+ isomer in 34Al
g factor measurement mass measurement
N=28- B(E2) of 40,42Si by Coulomb excitation- E(2+) of 40Mg, 44Si by in-beam g-spectroscopy
Conclusions
by the study of the 0+2 states in 34Si and 44S we characterized the shape
coexistence at N=20 and N=28
colla
bo
ratio
n
and the GANIL staff for providing beams and support
These structures (shape coexistence, deformation…) are not only due to a breakdown of the shell model but also to the enormous correlation energies involvedwhen pair excitations across closed shells are involved
To what degree do the N=20 and N=28 shell closures survives ?
"full (sd)fp" - "(sd)f7/2 "
