1. Michael Dworschak, GSI for the SHIPTRAP collaboration
First direct Penning trap
mass measurements on
transuranium elements
with SHIPTRAP
Michael Dworschak, GSI
for the SHIPTRAP collaboration

2. Outline Introduction SHIPTRAP setup
Direct mass measurements for Z > 100
Conclusions

3. Regions of interest at SHIPTRAP82
Heavy
Elements
126
proton emitters 50
N=Z, rp-process
- Strong repulsive force due to large number of protons
- Stability of SHE only due to shell effects
- For nobelium:
T(SF) > T(alpha) 82 28 20 50 8 28 20 8

4. Spontaneous Fission → ↑ a a E / MeV 2 E / MeV 2 (LD) B Coulomb energy
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
1,1
-150
-125
-100
-75
-50
-25 25 50 75
100
125
150
175
F.P.Heßberger
Spalt1 B f
net effect
Coulomb energy
Surface energy
E / MeV a 2
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1,0
-20
-15
-10 -5 5 10 15 20 25 d U s
= shell effect at saddle point gs
= shell effect at ground state B f
(LD) = liquid drop fission barrier
= B
(LD) + (+ )
liquid drop
+ shell effects
F.P.Heßberger
spalt2
(LD) →
‚disrupting‘ force ←
‚backdriving‘ force
E / MeV ↑
scission point a 2

5. Shell corrections in the region of heavy elements
100
120
114
162
184
108
152 N Z

6. Deformation in the region of heavy elements
P.Möller et al. At. Data and Nucl. Data Tab. 59, 185 (1995)

7. The Recoil Separator SHIP
velocity filter
≈ 5 MeV/u
0.1-1 MeV/u
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8. The SHIPTRAP set-up
to buncher
SHIP beam

9. Principle of Penning Traps
Cyclotron frequency:
q/m
PENNING trap
Strong homogeneous
magnetic field
Weak electric 3D
quadrupole field
end cap
ring
electrode

10. Ion Motion in a Penning Trap
Motion of an ion is the superposition of three characteristic
harmonic motions:
axial motion (frequency fz)
magnetron motion (frequency f–)
modified cyclotron motion (frequency f+)
In an ideal Penning trap the frequencies of the radial motions obey the relation
Typical frequencies
q = e, m = 100 u,
B = 7 T
 f- ≈ 1 kHz
f+ ≈ 1 MHz

11. TOF Resonance Mass Spectrometry
Time-of-flight resonance technique
Scan of excitation frequency
trap
drift-
tube
detector B
Injection of ions into the trap
and excitation of radius r-
Excitation near fc
 coupling of radial motions, conv.
1 m
Ejection along the magnetic field lines
 radial energy converted to axial energy
Time-of-flight (TOF) measurement

12. TOF Resonance Mass Spectrometry
Time-of-flight resonance technique
trap
drift-
tube
detector B
1 m

13. TOF Resonance Mass Spectrometry
Time-of-flight resonance technique
trap
drift-
tube
detector B
1 m
Resolving power:

14. Mass determination
Relation between cyclotron frequency and mass due to
Fluctuations of magnetic field due to temperature and pressure changes
-> Calibration needed
Determine atomic mass from frequency ratio
with a well-known “reference mass”
Normally 85Rb or 133Cs are chosen as reference masses

15. SHIPTRAP Performance Mass resolving power of m/dm ≈ 100,000
in purification trap:
 separation of isobars
ground
state 1/2+
isomeric
state 11/2-
Mass resolving power of
m/dm ≈ 1,000,000
in measurement trap:
 separation of isomers

16. Direct Mass Measurements above Z = 100
Requirements:
energy matching of reaction products to trap's energy scale
high efficiency to deal with very low production rates
1 Z=102 (s  mb)
1 Z=112 (s  pb)
high cleanliness for low background
stable and reliable operation over extended time

17. Production of nobelium isotopes
Fusion-evaporation
4.5MeV/u
about 1013 particles / s
200 keV/u
about 1 particle / s

18. Production of nobelium isotopes
Fusion probability increasing with beam energy
Survival probability of compound nucleus decreasing with beam energy
208Pb(48Ca,1-3n) No

19. Direct Mass Measurements of 252-254No
100
120
114
162
184
108
152 N Z

20. Direct Mass Measurements of 252-254No
August 2008:
Pb(48Ca,2n) No
doubly-charged nobelium ions extracted
low production rates:
-> about 4 h for each resonance
133Cs used as reference mass (same q/m ratio)
Production rate
Half-life
Half-life of isomer
resonances
252No
0.4 atoms / s
2.44(4) s
110(10) ms 3
253No
1 atom / s
1.62(15) min
< 1 ms 5
254No
2 atoms / s
51(10) s
266(2) ms 4

21. Direct Mass Measurements of 252-254No
Results in agreement with previous AME values
ME uncertainties in the order of keV
First direct mass measurements in the region Z > 100

22. Principle of mass determination with a decay energies

23. Definitions in the Atomic Mass Evaluation
Primary data: determined by at least two independent measurements
Secondary data: determined by only one measurement

24. Combining the results from a decays and Penning trap
Difficulties:
decays not between ground states
"broken" a-chains
energy summing with conversion electrons

25. Combining the results from a decays and Penning trap
Difficulties:
decays not between ground states
"broken" a-chains
energy summing with conversion electrons

26. Combining the results from a decays and Penning trap

27. Link to island of stability
Combine new, directly measured masses and a-decay spectroscopy
Determine the masses of short-lived higher-Z nuclides
To be determined:
a-decay of 262Sg (15%)

28. Direct Mass Measurements of 255Lr
Extend direct mass measurements to higher Z
252No
253No
254No
Rf, Sg,...
255Lr
103
255Lr+
April 2009:
209Bi(48Ca,2n)255Lr
rate of incoming particles for 255Lr only 0.3 ions/s
singly and doubly-charged ions extracted
255Lr nuclide with lowest rate ever measured in a Penning trap

29. The Route to SHE increase sensitivity and efficiency
(non-destructive) detection system with single-ion sensitivity
new cryogenic gas cell
improve primary beam
access to more neutron-rich nuclides
hot-fusion reactions with actinide targets
connection to gas-filled separator TASCA

30. Summary and Outlook
First direct mass measurements of nobelium isotopes have been performed with SHIPTRAP
Using results from direct mass measurements more primary nuclides could be obtained
Nobelium isotopes linked to superheavy elements by a-decay chains
Next step: go to higher-Z nuclides
In the long-term future: Penning traps can contribute to identify long-lived SHE

31. SHIPTRAP Collaborators
M. Dworschak, D. Ackermann, K. Blaum, M. Block, C. Droese,
S. Eliseev, E. Haettner, F. Herfurth, F. P. Heßberger, S. Hofmann,
J. Ketter, J. Ketelaer, H.-J. Kluge, G. Marx, M. Mazzocco, Yu. Novikov,
W. R. Plaß, A. Popeko, D. Rodríguez, C. Scheidenberger, L. Schweikhard,
P. Thirolf, G. Vorobjev, C. Weber
Thank you for your attention !

33. Penning trap basics B Axial motion: oscillation in E-field
z 0 Ф0 B
Magnetron motion:
E x B drift
Axial motion:
oscillation in E-field
Reduced cyclotron motion:
Relevant for mass measurements:

34. Cyclotron frequency measurement
off res.
m ~ r w
on res.
trap
drift-
tube
detector B
Michael Block
DPG-Frühjahrstagung, München 2006

35. Super Heavy Elements Z N GSI elements Z = 107-112
100
120
114
162
184
108
152 N Z
GSI elements Z =
112 Rg Ds Mt Hs Bh
how heavy can the elements be?
location of the island of stability?
structure of SHE?
stability due to shell effects
 accurate binding energies needed No

36. TOF Cyclotron Resonance Curve
TOF as a function of the excitation frequency
off res.
on res.
Resolving power:
Determine atomic mass from frequency ratio
with a well-known “reference mass”.