1. Natalia Cieplicka-Oryńczak
Angular correlations of g rays from 206Tl produced in thermal neutron capture
Natalia Cieplicka-Oryńczak
Institute of Nuclear Physics, Polish Academy of Sciences, Kraków, Poland
Shapes and Symmetries in Nuclei: from Experiment to Theory , 6-10 November 2017, Gif-sur-Yvette, France

2. Physics motivation Why the 206Tl nucleus?
The ideal nucleus for testing the shell-model calculations: couplings between valence proton hole and valence neutron hole
Very good system for studying phonon (3– of 208Pb)-valence holes coupling
Z=82
N=126
208Pb
206Tl

3. Experiment – ILL Grenoble (28/01 – 06/02/2017)
205Tl(n,g)206Tl reactions
neutron flux 108n/(s  cm2)
1.9-g target of 205Tl (99.9% enriched)
221 hours of measurements
Capture state at neutron binding energy
1/2+
(0+,1+)
6.5 MeV
205Tl
We expect to populate the states with spins values from 0 to 3 0–
8 HPGe clovers of FIPPS array (32 crystals) – coincidence measurements of gamma rays
206Tl

4. g-coincidences – first results
gate 305
305

5. g-coincidences – first results
gate 4660
4660
266
305
1844
649
1195
1578
1209
1042
1844
649
305
266

6. g-coincidences – first results
gate
5017
330
852
1182
1486
852
1182
635
330
305
305

7. Angular correlations of g rays1 2 
The angular correlation function for a pair of coincident g rays connecting the nuclear states with spins Ji  J  Jf is usually expressed as:
W(Θ) = 1 + A2 P2(cos Θ) + A4P4(cos Θ)
Θ – the angle between the direction of emission of two g rays
Pn(cos Θ) – Legendre polynomials
An=qnA(1)A(2) – the coefficients which depend on the attenuation factor qn as well as on the multipolarities of 1 and 2 g rays and the spins of involved nuclear states
8 detectors of FIPPS were arranged into ring around the target at every 45° so the analysis of angular correlations of gamma rays could be performed
Angles between the cristals => 20 experimental points

8. Angular correlations of g rays
0+,1+
649
5854 E1 ?
Multipolarity of the 5854-keV g ray (theoretical values for different spin hipothesis):
E  1–  A2 = 0.5, A4 = 0.0
E  1–  A2 = -0.25, A4 = 0.0
1 –
649 M1
0 –

9. Angular correlations of g rays
0+,1+
5143
0 –
(0,1,2)–
1360
1055
1 –
305

10. Angular correlations of g rays
0 –
1360 M1
711
1 –
649 M1
649
0 –

11. Angular correlations of g rays
0+,1+ E1
5505 2–
(2,3)–
998
(3) –
3 –
801
(M1) M1
535
2 –
266

12. Angular correlations of g rays
(1 –)
1486
(M1+E2)
837
1 –
649 M1
649
0 –

13. Theoretical calculations?
132Sn
208Pb
3s 1/2
2d 3/2
1h 11/2
2d 5/2
1g 7/2
3p 1/2
2f 5/2
3p 3/2
1i 13/2
2f 7/2
1h 9/2 p n
206Tl: one proton-hole one neutron-hole nucleus
The 206Tl nucleus, having just one proton-hole and one neutron-hole with respect to the best known doubly magic core 208Pb, is an ideal system for testing old and developing new shell model interactions in the south-west quadrant of the nuclear chart with respect to 208Pb.
Rydstrom, 206Pb, 206Tl, and 206Hg (Nucl. Phys A512,217(1990)): adjusting some diagonal matrix elements to reproduce more accurately the energies in 206Pb: neutron-hole, neutron-hole (also for 206Tl: proton-hole, neutron-hole, and 206Hg: proton-hole proton-hole).
Shell-Model calculations with Kuo-Herling interactions

14. Theoretical calculations
132Sn
208Pb
3s 1/2
2d 3/2
1h 11/2
2d 5/2
1g 7/2
3p 1/2
2f 5/2
3p 3/2
1i 13/2
2f 7/2
1h 9/2
0 –
2 –
1 –
3 –
(2,3) –
(1,2) –
(0) –
(2) –
(1,2,3) –
(1) – p n
206Tl: one proton-hole one neutron-hole nucleus
The 206Tl nucleus, having just one proton-hole and one neutron-hole with respect to the best known doubly magic core 208Pb, is an ideal system for testing old and developing new shell model interactions in the south-west quadrant of the nuclear chart with respect to 208Pb.
Rydstrom, 206Pb, 206Tl, and 206Hg (Nucl. Phys A512,217(1990)): adjusting some diagonal matrix elements to reproduce more accurately the energies in 206Pb: neutron-hole, neutron-hole (also for 206Tl: proton-hole, neutron-hole, and 206Hg: proton-hole proton-hole).
Shell-Model calculations with Kuo-Herling interactions

15. Thank you for your attention!
Summary
The new data from 205Tl(n,g)206Tl experiment at FIPPS will allow to extend the level scheme of 206Tl.
Angular correlations of gamma rays will help with spin assignments to the excited states.
The level structure of 206Tl investigated in neutron-capture reactions is very good testing ground for the future theoretical calculations around the 208Pb core.
Thank you for your attention!