Nele Kesteloot

Coulomb excitation of 196,198,200,202Po studied at REX-ISOLDE with the Miniball γ spectrometer

Nele Kesteloot

B. Bastin, Y. Blumenfeld, N. Bree, P. Butler, E. Clement, J. Diriken, A. Dorsival, V. Fedosseev, L. Gaffney, T. Giles, T. Grahn, A. Herlert, M. Huyse, J. Iwanicki, J. Konki,T. Kröll, R. Krucken, B. Laurent, N. Lecesne, B. Marsh, P. Molkanov, E. Piselli, E. Rapisarda, P. Reiter, M. Scheck, M.

Seidlitz, M. Seliverstov, M. Sferrazza, B. Siebeck, M. Sjodin, T. Stora, J. Taprogge, H. Tornqvist, E. Traykov, J. Van de Walle, P. Van Duppen, D. Voulot, N. Warr, F. Wenander, K. Wrzosek and M.

Zielinska

2

● The polonium isotopes

● The Miniball detection setup

● Experimental campaign● Preliminary results on 196Po● X rays

● Results on 200Po

● Hg coulex results

● Future perspectives

Outline

18th of December 2012 Isolde Workshop 2012

Isolde Workshop 2012 3

The polonium isotopes

(π1h9/2)2

Generalized seniority

Shape coexistence

T.E. Cocolios et al. PRL 106:052503 (2011)

N =

116

M.D. Seliverstov et al., in preparation

Change in nuclear structure

Transition expected around 200Po

R. Julin et al JPG 27:R109 (2001)A.M. Oros et al NPA 645:107 (1999)

18th of December 2012

The polonium isotopes Experimental campaign Results on 200Po Future perspectivesThe Miniball detection setup Hg coulex results


Why Coulomb excitation?


Laser spectroscopy

β decayIn beam

α decay

Coulomb excitation

AtZ = 85

PoZ = 84

RnZ = 86

N. Bijnens et al, PRL 75 (1995) 4571

R. Julin et al, JPG 27 (2001) R109K. Helariutta et al, EPJA 6 (1999) 289A. Maj et al, NPA 509 (1990) 413W. Younes et al, PRC 52 (1995) R1723

N. Bijnens et al, PRL 75 (1995) 4571J. Wauters et al, PRL 72 (1994) 1329

T. Grahn et al, PRL 97 (2006) 062501T. Grahn et al, PRC 80 (2009) 014323

T.E. Cocolios et al PRL 106,052503 (2011)

Lifetime measurements



The Miniball detection setup


θP

200Po 570 MeV

target 104Pd2 mg/cm2

EP

ET

196Po 198Po 200Po 202PoBeam energy

[MeV/u]2.85 2.85 2.85 2.85

Target 104Pd 94Mo104Pd

104Pd 94Mo104Pd

Beam purity ~50% ~97.5% 99.9% ~98%

Contaminant 196Tl 198Tl 200Tl 202Tl

Beam time ~63h ~26h ~46h ~6h

Year 2012 2012 2009 2012



Kinematics

Particle gamma events for 196Po on 104Pd


104Pd

Counts /M

eV/strip


196Po


Typical gamma spectra



196Po on 104Pd

202Po on 94Mo200Po on 104Pd

198Po on 94Mo

Particle gamma events, Doppler corrected for projectile

463 keV2+0+ 196Po 605 keV

2+0+ 198Po

666 keV2+0+ 200Po

677 keV2+0+ 202Po

556 keV2+0+ 104Pd

556 keV2+0+ 104Pd

871 keV2+0+ 94Mo

871 keV2+0+ 94Mo


Preliminary results on 196Po: Gamma spectra


Laser ONLaser OFF

Particle gamma eventsDoppler corrected for projectile

Xrays

104Pd196Po

196Po

196Po

0+

2+

2+4+

0+

0

463.1

891 859.1

558

196Po

196Tl


196Po

104Pd196Po

196Po

196Tl 2- ground state7+ isomer


Preliminary results on 196Po: X rays

Conversion of observed 196Po gamma rays

X rays

Conversion of observed 196Tl gamma rays

Atomic production of K vacancy in ion-atom collision


0+

2+

2+4+

0+

0

463.1

891 859.1

558

196Po

E0 transition 0+2 0+

1

Theoretical formula for cross section

Discrepancy between theory and experimentEmpirical correction using 202Po


Use laser ON/OFF data


Results on 200Po

● Analysis in final stage● BUT: on hold● Preliminary result for atomic X rays used

● <0+1||E2||2+

1> is stable● B(E2;0+2+) = 35(5) W.u.

● <2+1||E2||2+

1> is negative ● Large uncertainty● Consistent with zero




B(E2) values in 182,184Hg



182Hg

N. Bree, K. Wrzosek-Lipska private communication

184Hg


● Oblate deformation of ground state● Excited 0+

2 is more deformed than ground state● 0+

2 state can be triaxially deformed in 184Hg

Quadrupole sum rules method



AHg AHg

D. Cline, Ann Rev Nucl Part Sci 36 (1986) 683

Overall deformation Triaxiality

N. Bree, K. Wrzosek-Lipska private communication


Future perspectives

● Experimental campaigns (2009 and 2012) very succesful

● Analysis will yield a lot of information● B(E2;0+2+) values of 196,198,200,202Po● Quadrupole moments of first 2+ state in 196,198,200,202Po● Comparison of our B(E2;0+2+) value for 196Po with result from

lifetime experiment T. Grahn et al, PRC 80 (2009) 014323

● Parasitic information on 196Tl

● Results will be compared to theoretical models● Beyond mean field calculations● Symmetry guided models



Thank you for your attention!


Parasitic data on 196Tl

18th of December 2012Energy (keV)

Cou

nts/

keV

Single gamma spectrum

426 keV

611 keV

505 keV 635 keV

695 keV

7+

2-

394.2

0

196Tl

196Hg

2+

0+

426.3

0

1036.2 1+,2+1061.6 4+

5-17577-1841

426

635611

695

5-,6,7-2346505

Isolde Workshop 2012 1618th of December 2012

Extracted matrix elements in 182-186Hg

Isolde Workshop 2012 1718th of December 2012

Extracted matrix elements in 182-186Hg


196Tl level scheme



196Tl decay


Isolde Workshop 2012 20Obtain sensitivity on the diagonal matrix element of the first

excited state by scanning the center of mass range!

Particle detector

Ranges in Gosia



Coincidence spectrum



Summary of information



Unobserved transitions: upper limits

● Upper limit = number of counts that would give rise to a peak above the background

● Same integration window as in main peak (30 keV)● UPL = N + 3σ● Correct for detection efficiency

611keV transition:UPL = 587 cts

666 keV transition:N = 8.31(10).103 cts



● Disregard X rays and higher lying states● Normalize projectile to target excitation

● <0+||E2||2+> = 1.03(8) eb● <2+||E2||2+> = 0.55 eb

● = starting point for Gosia 1

First order solution in Gosia 2

0+

2+ 666

200Po

8.79(10).104

1.762(15).105

556

104Pd0+

2+


<0+||E2||2+> [eb]

<2+ ||

E2||2

+ > [e

b]


Gosia 1

● Gosia input• 6 experiments

o 5 experiments for 5 angular ranges (no X rays)o 6th experiment with total yield for 2+0+ and X rays

• 6 stateso Virtual 1+ state to simulate E0 transitiono 2 buffer states

● 9 data points• 7 yields• 1 known branching ratio• 1 known matrix element (<0+||E2||2+> = 1.03(8) eb)

● 7 free matrix elements• Couple <0+

1||E2||2+1> and <2+

1||E2||4+1>

• Treat virtual M1 matrix elements as one matrix element18th of December 2012


Gosia 1: solutions

χ² 1,02 1,09 1,12 1,30 1,40 1,44 1,45 1,53

<0+1||E2||2+

1> 1,04 1,00 1,04 1,05 1,04 1,06 1,03 1,01

<0+1||E2||2+

2> 0,55 0,33 0,24 0,29 0,35 0,19 0,49 0,26

<2+1||E2||2+

1> -2,00 -2,71 -1,30 -2,92 -0,75 -0,34 -3,14 -0,78

<2+1||E2||0+

2> 1,42 2,86 2,33 2,76 1,41 1,89 2,20 2,21

<2+1||E2||2+

2> 2,97 -1,65 1,28 1,59 1,89 1,03 2,68 -1,30

<0+2||E2||2+

2> 3,09 3,80 3,63 3,29 4,75 5,62 2,48 4,72



Atomic production of K-vacancy in ion-atom collision

Method: N.Bree 2010

● Theoretical formula

● Empirical correction● Based on experimental data in Po region● Comparison with 188Hg coulex data

● Geometrical correction● Range of particle detector

● Estimate: 5.6(21).103

Range particle detector

J.D. Garcia et al, RMP 45 No 2 (1973) 111


The polonium isotopes Preliminary results on 196Po X rays Results on 200Po Future perspectivesThe Miniball detection setup


Gosia analysis

8.8(

1).1

04

1.3(

2).1

04

α=0.0126

α=0.01479

α=0.11

BR=1.16(42)E0UnobservedUpper limitConversion coefficient

59440.11

5944

1811

210

86

1715


● Normalisation to target excitation

● Virtual 1+ state● Buffer states

Gosia: T. Czosnkyka, D. Cline, C.Y. Wu Bull. Amer. Phys. Soc. 28, 745 (1983)



Preliminary results of the Gosia analysis

● Gosia 1 & 2 analysis in progress

● <0+1||E2||2+

1> is stable● B(E2;0+2+) = 35(5) W.u.

● <2+1||E2||2+

1> is negative ● Large uncertainty● Consistent with zero




X rays


Particle particle gamma eventsDoppler corrected for projectile = 202Po

0+

2+

2+

4+

0

677.2

1248.61302.5

202Po

94Mo

202Po

Xrays


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Nele Kesteloot