K-Isomers in the transfermium region
Barbara Sulignano
Ultimate goal:
Where is the next shell gap in the superheavy region ?
Probe :
K isomers in very heavy nuclei (Z~100 and N ~152)
Experimental technique
Prompt and delayed spectroscopy of
Perspectives
Instruments of the future
CEA DSM Dapnia SPhN
254,252No
Chart of nuclei
Production of SHE
s ~ 1pb
Nuclear structure investigation
s~ 0.3-3 mb
CEA DSM Dapnia SphN
Nilsson single particle energies / MeV
• Protons, Z = 110
• Neutrons, N = 162
•
•
• 1i11/2
• 1j13/2
• 3p1/2
• 1k17/2
• 2h11/2
• 3p3/2
• 2f5/2
• 3d3/2
• 4s1/2
• 2g7/2
• 3d5/2
• 2f7/2
• 1h9/2
• 1i13/2
ž
ž
[N n z  ]
1/2
9/2
[404]
7/2
[413]
5/2
5/2
[422]
7/2
3/2
[431]
9/2
1/2
[440]
3/2
g9/2
• 1j15/2
• 2g9/2
• 1i11/2
• P. Möller et al, 1997
CEA DSM Dapnia SphN
Spherical
Prolate
Single particle energies at Z = 100, N = 152
Mean field with SLy4,
M. Bender et al.
CEA DSM Dapnia SphN
Macroscopic-microscopic model,
A. Sobiczewski et al.
Problem : Position of shell gaps are model dependant
Experimental investigations are necessary
•Beta decay
•In-beam spectroscopy of odd nuclei
•Isomeric decay
K-isomer
CEA DSM Dapnia SphN
What we can learn from K-isomers
• Information about Nilsson level energy gaps
– E.g. Is the energy gap at Z=102 or Z=100?
For the gap at Z=102 the low lying p-p states should be observed.
• Influence on stability of super heavy elements
– Isomeric state may be a key factor in enhanced stability of these
nuclei when isomeric lifetime exceeds the g.s. lifetime.
Experimental information see e.g. 270Ds or 250No.
Supported also by theory.
F.R. Xu et al. Phys. Rev. Lett. 92, 252501 (2004)
• Pair gap
– The pairing interaction is one of the most important residual and is
still not described satisfactory
• Rotational states
– Study of populated rotational states built on g.s. or isomeric
states
CEA DSM Dapnia SphN
What is a K isomer?
Why K isomers occur?
• Deformed nucleus
• Breaking of particle pairs at Fermi
Surface
• Excitation energy of quasi-particle:
Collective rotation
Single particle
K is the Projection
of Total Intrinsic
angular momentum
on the symmetry
axis
E  (   ) 2  2
K = Ω1+ Ω2
π = π1π2
Ω2π2
Isomers decay by:
Fermi surface
electron conversion,
Ω1π1
Ωπ[NnzΛ]
gamma emission,
particle emission (p, a, +, -)
SF
CEA DSM Dapnia SphN
ground state
2-qp state
Isomer
Identification
Spontaneous fission –
250No
D. Peterson et al. Phys. Rev. C74 014316 (2006)
only tentative assignment is possible T1/2=43 ms
T1/2=3.7 ms
?
g
Direct measurements of the electromagnetic transitions in the nucleus are
necessary
- Lifetimes
-Decay mode
-Energies of transitions
- Branching ratios

With high enough statistic one can obtain all possible information!!!
- Energy of excited levels
- Spin & parity
- Deformations
CEA DSM Dapnia SphN
Techniques
Prompt spectroscopy At target position
beam
g
Filter
recoil
TOF
faisceau
g det
Isomer t
Si -det
1) Recoil implanted in pixel of DSSD
2) Gamma-rays at target position in coincidence
with recoil
 Rotational bands built on gs or K-isomer
g.s.
CEA DSM Dapnia SphN
Delayed spectroscopy At focal plane
Isomer t
g /e-
Filter
beam
Target
recoil
TOF
1) Recoil implanted in pixel of DSSD
2) Burst of conversion electrons in same pixel
from isomer decay
3) Gamma-rays in coincidence with electron burst
4) Recoil decays in same pixel by alpha/fission
 Isomeric decay.
Key idea was to tag on isomer by searching for burst of conversion
electrons and using a single pixel as a calorimeter.
G.D. Jones (Liverpool), NIM A 488 471 (2002)8
CEA DSM Dapnia SphN
g
g.s.
a
t
Evidence for K-Isomers in
48Ca
+
206Pb
252No
252No
at SHIP (GSI)
+ 2n
s (252No) = (426 ± 2) nb
Kp= 8-
Kp= 2-
a) Re- g(e-)
b) Re – g (e-)- a
c) Re – g (e-) Sf
CEA DSM Dapnia SphN
Kp= 0+
B.Sulignano et al. EPJ (2007)
Evidence for K-Isomers in 252No
Two-quasi-particle neutron states:
(5/2+[622] 9/2-[734]) 2- - 929 keV
(7/2+[624] 9/2-[734]) 8- - 1254 keV
W-S calculation of levels in 252No
11/2- [725]
-5.50
7/2+ [613]
-5.72
3/2+ [622]
-5.78
-5.93
1/2+ [620]
Kp= 8-
Kp= 2-
152
9/2- [734]
-7.00
Fermi level
-7.31
-7.57
-8.07
150
7/2+ [624]
5/2+ [622]
1/2+ [613]
B.Sulignano et al. EPJ (2007)
CEA DSM Dapnia SphN
K-Isomers of
48Ca
+208Pb 
254No
254No
at RITU
s (254No) = (2050 ± 460) nb
Delayed Re-gamma-electron coincidence for the short lived isomer.
Kp= 16+
T1/2 = 275 (7) ms
Delayed Re-gamma-electron coincidence for the short lived isomer.
Kp= 8T1/2 = 198 (13) ms
Kp= 3+
254
102
CEA DSM Dapnia SphN
No152
Herzberg et al. Nature 442, 896 (2006)
C.Gray-Jones et B.Sulignano, PRL to be published
K-Isomers of
254No
Two-quasi-particle proton states:
(1/2-[521] 7/2-[514]) 3+ - 988 keV
Kp= 16+
(9/2+[624] 7/2-[514]) 8- - 1293 keV
W-S calculation of levels in
254No
5/2- [512]
-1.87
106
-2.54
-2.81
Fermi level
-3.28
104
102
9/2+ [624]
7/2- [514]
1/2- [521]
100
-4.11
-4.49
CEA DSM Dapnia SphN
98
7/2+ [633]
3/2- [521]
Kp= 8Kp= 3+
254
102
No152
R.-D. Herzberg et al., Nature 442 (2006) 896-899
Systematics for N=150, N=152 known isotones
CEA DSM Dapnia SphN
7/2+
11/2–
9/2+
7/2–
1/2–
100
152
Z
100
Fermi level
N
100
Z
7/2+
11/2–
9/2+
7/2–
1/2–
250Fm
7/2+
3/2–
1/2+
CEA DSM Dapnia SphN
7/2+
11/2–
3/2+
1/2+
152
7/2+
9/2–
3/2–
1/2+
7/2+
5/2+
N
7/2+
5/2+
N
100
9/2–
Z
Fermi level
9/2–
9/2+
7/2–
1/2–
3/2+
1/2+
152
Fermi level
152
3/2–
1/2+
7/2+
5/2+
254No
3/2+
1/2+
7/2+
9/2–
3/2–
1/2+
7/2+
11/2–
9/2+
7/2–
1/2–
3/2+
1/2+
7/2+
Z
252No
7/2+
5/2+
N
252Fm
Can modern theories reproduce experiments ?
n
p
X data
CEA DSM Dapnia SphN
J.P. Delaroche et al., NPA 771 (06) 103
Summary
The study of deformed nuclei in the region of Nobelium through the
use of in beam and focal plane decay spectroscopy
isomeric states have been observed in 250,252, 254No and 250Fm
 Investigation of deformed shell gaps
Determination of the single particle orbitals
Long term goal Location of the next closed proton and neutron
closed spherical shells above 208Pb.
Excitation energies and configurations of two quasi particle states
= stringent test for current nuclear structure models.
Planned investigation:
Z=102 isotopes 252No (RITU 2008)
 Structure the K-isomer (neutron or proton?)
N=150, 152 isotones like
CEA DSM Dapnia SphN
254.256Rf
OUTLOOK
• S3 (Super Separator Spectrometer): very high intensity stable beams
of SPIRAL2 ranging from 1pµA up to 1pmA .
 Synthesis (Z>118) and delayed Spectroscopy (Z>106) of SHE
Examples :
58Fe + 208Pb  264Hs + 2n (σ=60pb)
32S + 238U  266Hs +4n (σ= ? pb)
CEA DSM Dapnia SphN
OUTLOOK
• SAGE (Silicon And Germanium): electron detection coupled with
JUROGAM gamma detector
 spectroscopy of odd nuclei dominated by highly converted M1
transition
CEA DSM Dapnia SphN