1. (Lawrence Berkeley National Laboratory)
Isomer Spectroscopy of the Heaviest Elements
Rod Clark
(Lawrence Berkeley National Laboratory)

2. Outline Motivation for studying structure of heaviest nuclei
K-isomers in Z≥100 region
The Berkeley Gas-Filled Separator (BGS)
Recent results:
50Ti+208Pb→256Rf+2n (σ≈20nb)
48Ca+209Bi→255Lr+2n (σ≈300nb)
Heavy element spectroscopy with GRETINA+BGS
Summary

3. Motivation Single-particle levels → shell structure
Next major spherical gaps
Deformed gaps
Deformation and collectivity
K-isomerism
Rotational structures
Low-lying vibrations
Pairing properties
Multi-quasiparticle states
Effects on rotation
Effects on alpha decay
Effects fission decay

4. K-Isomers in Z≥100 Nuclei RITU at JYFL FMA at ANL
Nature (2006)
FMA at ANL

5. Conversion Electron and Gamma Spectroscopy
S.K.Tandel et al., PRL (2006)

6. Berkeley Gas-filled Separator
 Large acceptance: 45 msr (± 9° vertical, ±4.5° horizontal)
 Highest transmission ( Ni+Pb: 70% Ca+Pb: 60% Mg+U: 18% )
 Large bend angle: 70°
 Lowest background rates ( 40Hz/pmA 20Hz/pmA 100Hz/pmA )

7. Focal Plane Detectors 16×16 strip DSSD 1mm thick, 5cm by 5cm
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
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 (2002).

8. 256Rf: Z=104, N=152 r-e-e-f r-e-e-f
50Ti+208Pb→256Rf+2n at 243 MeV (σ≈20nb), 200pnA, 6 days
Electrons
Gamma Rays
r-e-e-f
r-e-e-f

9. Rf 256 104 152 >2200 t1/2=27(6)ms Kp=(7-,8-) ≈1400 17(2)ms 6-0+ 2+ 4+
Kp=(2-) 3- 4- 5- 6-
≈946
≈46
256 Rf
104
152
Kp=(5-)
≈1120
25(2)ms
≈1400
17(2)ms
Kp=(7-,8-)
t1/2=27(6)ms
>2200
900
H. B. Jeppesen et al.,
Submitted to PRL

10. 255Lr: Z=103, N=152
48Ca+209Bi→255Lr+2n at 222 MeV (σ≈300nb), 300pnA, 4 days
7/2
19/2
~x+800
~x+1400 x

11. 247Es: Z=99, N=148
g-spectroscopy following a-decay of 255Lr→251Md→247Es

12. Eisteinium (Z=99) Systematics Re-examined
251Md
251Md a1 a2 a
g=243
g=294
g=243
g=294
0+x
247Es
247Es
F.P.Hessberger et al., EPJ A (2005)
A. Chatillon et al., EPJ A (2006)

13. ? Eisteinium (Z=99) Systematics Re-examined 251Md 251Md a1 a2 a g=243
247Es
247Es
F.P.Hessberger et al., EPJ A (2005)
A. Chatillon et al., EPJ A (2006)

14. Transfermium Spectroscopy with GRETINA+BGS
The best heavy element separator
with the best g-ray detector system
48Ca+208Pb→254No+2n
σ~2 μb
2000
Counts
Energy (keV)
50Ti+208Pb→256Rf+2n
σ~20 nb 25
Counts
6+→4+
Assumptions for simulation:
sTOT = 1 barn
Target = 0.5 mg/cm2
Beam Current = 50 pnA
eg / crystal =
Mg = 10
→ 30.3 kHz/crystal
Energy (keV)

15. Summary
New generation of spectroscopy experiments on heaviest elements
RITU at JYFL, FMA at ANL, BGS at LBNL,
GABRIELLA at Dubna, SHIP at GSI, VAMOS at GANIL+…
Decay spectroscopy at BGS able to reach Sg (Z=106)
- single-particle states
- K-isomerism
- low-lying rotational and vibrational modes
Prompt spectroscopy with GRETINA at BGS able to reach Rf (Z=104)
- rotation versus fission
- moments of inertia, alignments
- configuration assignments
Can modern microscopic theories reproduce experiment?

16. Thanks!