1. on behalf of ‘Astatine and Gold’ Collaboration
Shape coexistence and charge radii in thallium, gold and astatine isotopes studied by in-source laser spectroscopy at RILIS-ISOLDE
A. Barzakh
Petersburg Nuclear Physics Institute, Gatchina, Russia
on behalf of ‘Astatine and Gold’ Collaboration

2. Astatine-Gold collaboration (IS534)
University of York, United Kingdom
A. N. Andreyev, V. Truesdale
RILIS and ISOLDE, Geneva, Switzerland
S. Rothe, B. A. Marsh, A. M. Sjodin, T. C. Cocolios, V. N. Fedosseev M. D. Seliverstov
Institut für Physik, Johannes Gutenberg-Universität Mainz, Mainz, Germany
S. Raeder, K. D. A. Wendt
University of the West of Scotland, United Kingdom
X. Derkx, V. Liberati, J. Lane, K. Sandhu
Instituut voor Kern- en Stralingsfysica, K.U. Leuven, Leuven, Belgium
L. Ghys, C. Van Beveren, E. Rapisarda, D. Pauwels, D. Radulov, Yu. Kudryavtsev,
M. Huyse, P. Van Duppen
Comenius University, Bratislava, Slovakia
S. Antalic, Z. Kalaninova
PNPI, Gatchina, Russian Federation
A. Barzakh, D. V. Fedorov, P. Molkanov
University of Manchester, UK
K. Lynch, I. Straschnov...
team
K.Blaum, C. Borgmann, F. Herfurth, M.Kowalska, S.Kreim, D.Lunney, V.Manea, D.Neidherr, M.Rosenbusch, L. Schweikhard, F. Wienholtz, R. Wolf, K. Zuber.

3. Outlook Resonance Ionization Laser Ion Source (RILIS) at ISOLDE
IS and hfs measurements for the long chain of At isotopes
“Back to sphericity” in the lightest Au isotopes
Conclusions
all results are preliminary!

4. Laser Ion Source at ISOLDE
Laser beams
Experiments
Mass separation
Target Hot Cavity Extractor
Ion Source
Reaction products
(neutral)
Ions
Protons
Target material
60 kV
Isotope/isomer shift
A-1,Z
A,Z
Isotope shift (IS), hyperfine structure (HFS) measurements: The wavelength of the narrow-band laser is scanned across the chosen transition. The photoion current at the collector of the mass separator increases at the resonance.
Detection of photoion current by measuring FC current, a//g or ToF spectra while scanning the frequency

5. RILIS upgrade CVL to Nd:Yag Green Beams 90 W @ 532 nm UV beam
10kHz rep rate
6 - 8 ns pulses

6. RILIS upgrade Laser ion source at ISOLDE Nd:YAG lasers Dye lasers
Dye+Ti:Sa system
3 Ti:Sa lasers:
5 GHz linewidth
Up to 5 W output power
680 – 1030 nm (fund.)
35 ns pulse length
Laser ion source at ISOLDE
Nd:YAG lasers
Dye lasers
Ti:Sa lasers
Since the two systems can be used either independently or in combination, there exists far greater flexibility for switching from one ionization scheme to another or rapidly changing the scanning step.

7. Detection: Windmill System at ISOLDE
A. Andreyev et al., PRL 105, (2010)
Annular Si Si
MINIBALL Ge cluster
Annular Si
pure 50 keV beam
from RILIS+ISOLDE Si ff a
50 keV beam
from ISOLDE ff
C-foil
C-foils
20 mg/cm2
Si detectors
The WM technique requires waiting for the decay of the isotope (usually, α-decay). Not practical for long-lived or stable isotopes (or for β-decaying).
Setup: Si detectors from both sides of the C-foil
Large geometrical efficiency (up to 80%)
2 fold fission fragment coincidences
ff-γ, γ-α, γ-γ, etc coincidences

8. Detection: MR-TOF MS at ISOLDE
Multi-reflection time-of-flight mass separator (MR-TOF MS)
~1000 revolutions, ~35 ms, m/Δm ~ 105
MR-TOF MS is not limited by decay scheme or long half-lives
MR-TOF MS offers a way to separate background for direct single-ion detection using MCP (time scale: tens of ms).
R. N. Wolf et al., Nucl. Instr. and Meth. A 686, (2012), S. Kreim et al., INTC-P-299, IS 518 (2011)

9. Shape coexistence and charge radii in Pb region
Tl: IS511 ISOLDE
and IRIS (Gatchina)
Pb: ISOLDE, PRL98, (2007) H. De Witte et al.
Po: ISOLDE,
PRL106, (2011)
T. Cocolios et al.
85At? ?

10. Photoionization scheme for the radioactive element At
216 nm
795 nm
532 nm IP
Optimal photoionization scheme.
Narrow band lasers can be used
for the 1st and 2nd transitions
6p48p(?), J=3/2
6p47s, J=3/2
6p5, J=3/2
ISOLDE + TRIUMF, Canada:
Many new atomic levels were found
Transition strengths were measured
For the first time the ionization potential was measured

11. Astatine HFS spectra
216 nm
795 nm
532 nm IP
1st step scanning is better for δ<r2> extraction
2nd step scanning is better for hfs analysis
(Q and μ determination)

12. IS534 October 2012: Charge radii of At isotopesWM FC WM
MR-TOF MS

13. October 2012: IS534 experiment at ISOLDE – Au isotopes
267.7 nm
306.6 nm
674.1 nm IP
autoionizing state
Au ionization scheme

14. IS534: Charge Radii of Au isotopes, ISOLDE 2012
level ordering for Au isomers at A=178 was determined
in dedicated ISOLTRAP measurements
Deformation jump toward less deformed shapes in the light Au isotopes
Shape coexistence in 178Au (large deformation difference between 2 states)
Shape staggering near 181Au and 178Au

15. Confirmed prediction: “return to sphericity” in Au
J.L. Wood, E.E. Zganjar, C. De Coster, K. Heyde, Nucl. Phys. A 651 (1999) 323
new results

16. Summary: Charge Radii in Pb region? ?
Astatine seems to follow Po δ<r2> trend (“early onset of deformation”)
Intruder isomer shift in 197At (shape coexistence, similar to Tl nuclei)
“Back to sphericity” in the lightest Au isotopes
Pronounced odd-even staggering (A=181,178) and shape coexistence (A=178) in Au
isotopic chain

17. Conclusions
IS’s and hfs’s for 10 At isotopes (isomers) were measured for two transitions, 216 nm and 795 nm, The fast switching between these modes of scanning provides much more flexibility to experiment and gives more reliable and complementary data for analysis (especially for atoms without known spectroscopic information).
MR-TOF mass separator was used for photo-ions detection for the first time. This method seems to be indispensable for measurements with great surface ionized background and for long lived isotopes with great yield and/or absence of alpha decay mode.
Using WM installation for photo-ions detection gives the possibility to obtain wealth of additional nuclear spectroscopic information (decay schemes, spin and parity assignment etc.) without supplementary time requirement.
Coordinated (ISOLDE&IRIS) program for Tl isotopes investigation enabled us to use both installation more efficiently.
Very interesting results for At and Au isotopes by IS/hfs measurements were obtained: “inverse jump of deformation”, unexpected spin assignments, shape isomers etc. The study of shape coexistence in the lead region will be continued: to go further for Au’s, to fill the gaps and go further for At’s (ISOLDE), to investigate Bi isotopes (IRIS), etc.

18. For p-s transition (as 216 nm transition
in At) the assumption MSMS=(0±1)·MNMS
is commonly used
F(At) is calculated with the assumption of MSMS=0 from the condition
that δ<r2>124, 122 is equal to the “parabola” value at Z=85

19. King plot for 216 nm and 795 nm lines in At
207
198g
198m
217
F216/F795(At)=-2.26(8)
compare with F256/F843(Po)=-2.241(7)
for similar transitions in Po
Isotope shift δ A,A’:
Δσ for different transitions should lie on a straight line with a slope Fλ1/ Fλ2

20. Isomer selectivity for 197,198At
Isomer selectivity enables to measure masses of 197g,198gAt at ISOLTRAP and receive nuclear spectroscopic information for pure g.s.

21. Isomer selectivity for 178Au
Isomer selectivity enables to measure masses of 178g,178mAt at ISOLTRAP and therefore to establish level ordering

22. 0—>0 transition is forbidden!
Jf=1/2
F’2
F’1
F’1=0
I=1/2
0—>0 transition is forbidden! F2
F2=1
Ji=1/2 F1
F1=0
Only 3 rather than usual 4 lines will be seen in the hfs spectra of isotopes with I=1/2

23. IS534: Hyperfine Structure Scans for 177,179Au
179Au (WM)
177Au (WM)
Number of peaks and their intensities ratio
fix ground state spins of 177,179Au: I=1/2
179Au 3/2+ calculated
179Au 1/2+ calculated

24. Why is 1/2+1/2+ 181Tl177Au a decay hindered?
m~1.6mN , pure sph. 3s1/2,
(as in the heavier Tl’s)
1/2+
HF>3
I=3/2
m~1.1mN , (preliminary)
mixed/def/triaxial 3s1/2,/d3/2
1/2+
Plot from A.Andreyev et al., PRC 80, (2009)

25. Additional atomic spectroscopic information for Astatine
216 nm
795 nm
532 nm IP
58805 cm-1,
J=3/2 or 5/2
J=3/2
J=3/2
I=1/2
F1=1
Jf=3/2
F2=2
F’1=1
F’2=2
Ji=3/2
F1=1
Jf=5/2
F2=2
F’1=2
F’2=3
Ji=3/2
The number of peaks (4 rather than 3) unambiguously
point to J=3/2 for cm-1 atomic state in At

26. Hyperfine structure anomaly for Au isotopes

27. King plot for 276 nm and 535 nm lines in Tl

28. Charge Radii of Tl isotopes, ISOLDE & IRIS (Gatchina)
Long chain (N from 102 to 116) of the (intruder) isomeric states with the deformation markedly greater than the deformation of g.s. (shape coexistence). Previously known isomeric chain is extended for both sides (N>112, N<106). For the first time the great isomer shift was found for odd-odd nuclei also (A=186, 184).

29. Comparison of relative δ<r2> for Pb and Tl nuclei
For the sake of clarity, only the results for the even-neutron nuclei are presented. The corresponding picture for odd-neutron nuclei is quite similar. The Tl radii perfectly follow the pattern of the Pb radii even below the midshell at N = 104 where the well known pronounced deviation from this behavior, connected with the onset of permanent prolate deformation, was found for the adjacent Hg (Z = 80) and Au (Z = 79) nuclei.

30. Magnetic moments for Tl nuclei
Newly measured magnetic moments for Tl isotopes at and below the midshell
(N≤104) perfectly follow the trends for heavier Tl isotopes with the same spin.

31. Isomer shift for intruder states in Tl nuclei
The most striking finding is the unexpected growth of the isomer shift between
ground (1/2+) and isomeric (intruder) states (9/2-) in odd Tl nuclei. All calculations predicted that the difference in deformation (i.e., isomer shift) between g.s. and m.s. is nearly constant or even decreases after A=187.