- shape coexistence in the neutron-deficient hg isotopes ...€¦ · 92intruder bands observed for...

Shape coexistence in the neutron-deficient Hg isotopes studied via lifetimemeasurements

P.R. John, D. Mengoni, D. Bazzacco, A. Boso, S. Lenzi, R. Menegazzo, F. Recchia, G. ColucciDipartimento di Fisica and Astronomia, Università di Padova and INFN, Sezione di Padova, Italy.

M. Siciliano, A. Goasduff, J.J. Valiente-Dobón, G. de Angelis, G. Jaworski, D. Testov, D.R. Napoli, F. Galtarossa, M. CicerchiaINFN, Laboratori Nazionali di Legnaro, Italy.

Th. Braunroth, A. Vogt, B. BirkenbachInstitut für Kernphysik der Universitat zu Köln, Germany.

J. PakarineDepartment of Physics, University of Jyväskylä, University of Jyväskylä, Finland

B. Melon, A. Nannini, M. RocchiniDipartimento di Fisica, Universita degli Studi di Firenze, INFN Sezione di Firenze, Firenze, Italy

G. Benzoni, N. CieplickaDipartimento di Fisica and INFN, Sezione di Milano, Italy.

B. de Canditiis, F. Davide, D. Quero, D. Ashad, P. RathDipartimento di Fisica and INFN, Sezione di Napoli, Italy.

W. Witt, P. Koseoglu, J. WiederholdInstitut für Kernphysik der Technischen Universität Darmstadt, Germany

June 29, 2016

The neutron-deficient isotopes around N ≈ 104

� Intruder bandsobserved for176−190Hg

� Differentdeformation:� ground state

band oblatedeformed

� Intruder bandprolatedeformed

K. Heyde and J.L. Wood, Rev.Mod. Phys. 83 (2011)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

172 176 180 184 188 192 196 200 204

92 96 100 104 108 112 116 120 124

Exci

tatio

n En

ergy

[MeV

]

Mass Number, A

Neutron Number, N

0+

2+4+

6+

8+

10+

12+

4+

6+

6+

8+

0+2+

4+6+

8+10+

12+

˜ Adapted from L.P. Gaffney et al., Phys. Rev. C 89, 024307 (2014)

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The neutron-deficient isotopes around N ≈ 104

� Intruder bandsobserved for176−190Hg

� Differentdeformation:� ground state

band oblatedeformed

� Intruder bandprolatedeformed

K. Heyde and J.L. Wood, Rev.Mod. Phys. 83 (2011)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

172 176 180 184 188 192 196 200 204

92 96 100 104 108 112 116 120 124

Exci

tatio

n En

ergy

[MeV

]

Mass Number, A

Neutron Number, N

0+

2+4+

6+

8+

10+

12+

4+

6+

6+

8+

0+2+

4+6+

8+10+

12+

This Presentation

˜ Adapted from L.P. Gaffney et al., Phys. Rev. C 89, 024307 (2014)

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Two state configuration mixing

� Two state configuration mixing model: observed states are amixture between these two unperturbed intrinsic states |Jo〉 , |Jp〉:

|Ja〉 = α1 |Jp〉+ α2 |Jo〉|Jb〉 = −α2 |Jp〉+ α1 |Jo〉

� Changing contribution as a function of neutron number

� Transition prolate deformed → mixing → oblate deformation� Maximum mixing in the 2+1 state for

184HgK. Heyde and J.L. Wood, Rev. Mod. Phys. 83 (2011)

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What we know about this region

176 180 184 188 192190182 1861784 of 22


176 180 184 188 192190182 186178

Increase in2+ energyMore spherical structure

176Hg

R. Julin et al., J. Phys. G 27(7):R109 (2001).

4 of 22


176 180 184 188 192190182 186178


176Hg


Strong E0 component22+ → 21+Strong Mixing

184,186Hg

M. Scheck et al., PRC 83 037303 (2011).

4 of 22


176 180 184 188 192190182 186178


176Hg



184,186Hg

M. Scheck et al., PRC 83 037303 (2011).

180-186Hg PlungerT. Grahn et al., PRC 80 014324 (2009)M. Scheck et al., PRC 81 014310 (2010)L.P. Gaffney et al., PRC 89 024307 (2014)

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176 180 184 188 192190182 186178


176Hg



184,186Hg

M. Scheck et al., PRC 83 037303 (2011).

182-188Hg COULEXN. Bree et al., PRL 162701 (2014)


4 of 22


176 180 184 188 192190182 186178


176Hg



184,186Hg

M. Scheck et al., PRC 83 037303 (2011).

182-188Hg COULEXN. Bree et al., PRL 162701 (2014)


Galileo

4 of 22

188Hg – at the edge of shape coexistence

� At the heavy edge of the shapecoexistence

� Ground state band supposed oblatedeformed

N. Bree et al., Phys. Rev. Let. 112:162701 (2014).

� Degree of mixing not yet firmlyconfined

˜Adapted from F. Hannachi et al., Nucl. Phys.A 481, 135-160 (1988)

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Experiment using Galileo (+NeutronWall)

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d2.5 mg/cm2 natTa

600 µg/cm2 160Gd

11 mg/cm2 197Au

34S @ 185MeV 188Hgβ=0.0179

+6n

� 34S + 160Gd ⇒ 188Hg + 6 n� We arrived up-to 7 pnA using Tandem and Alpi� Main evaporation residual 188Hg > 50% of total ER� Probability of detecting at least 1n > 17 of 22


0

2e+06

4e+06

6e+06

8e+06

1e+07

1.2e+07

1.4e+07

1.6e+07

0 100 200 300 400 500 600 700

Counts

/0.5

keV

Energy (keV)

Ta

Au

Au Ta

Ta

Au

Au

Ta

Au

� Background from Fission (e.g. Fusion-Fission)

� Background from Coulex⇒ Reduced by condition 1n > 1

8 of 22


0

2e+06

4e+06

6e+06

8e+06

1e+07

1.2e+07

1.4e+07

1.6e+07

0 100 200 300 400 500 600 700

Counts

/0.5

keV

Energy (keV)

Ta

Au

Au Ta

Ta

Au

Au

Ta

188H

g

Au



8 of 22


0

2e+06

4e+06

6e+06

8e+06

1e+07

1.2e+07

1.4e+07

1.6e+07

0 100 200 300 400 500 600 700

Counts

/0.5

keV

Energy (keV)

Ta

Au

Au Ta

Ta

Gd

Au

Au

Ta

188H

g

Au



8 of 22

(Ab)Using for suppressing Coulex

� First timecompletely digitalNeutronWall

� Very “dirty”selection ofneutrons

� Fast onlineselection of ZCOin order to reducedata rate

� Nearly dead-timefree

Clean neutrons

9 of 22






Used neutron condition

9 of 22






0

500000

1e+06

1.5e+06

2e+06

2.5e+06

0 100 200 300 400 500 600 700

Counts

/keV

Energy (keV)

neutron gated spectra

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Very preliminary results

� Accelerator problems duringexperiment ⇒only 2.5 days of beam time

� Analysis is still in its early phase

Gate in flightSpectra

2+1 ⇒ 0+gs transition @ 152◦

10 of 22






−100 0

100 200 300 400 500 600

s u

20mu

−100 0

100 200 300 400 500 600

60mu

−100 0

100 200 300 400 500 600

100mu

−100 0

100 200 300 400 500 600

200mu

−100 0

100 200 300 400 500 600

300mu

−100 0

100 200 300 400 500 600

400mu

−100 0

100 200 300 400 500 600

390 400 410 420 430 440

Energy (keV)

600mu

10 of 22






−100 0

100 200 300 400 500 600

s u

20mu

−100 0

100 200 300 400 500 600

60mu

−100 0

100 200 300 400 500 600

100mu

−100 0

100 200 300 400 500 600

200mu

−100 0

100 200 300 400 500 600

300mu

−100 0

100 200 300 400 500 600

400mu

−100 0

100 200 300 400 500 600

390 400 410 420 430 440

Energy (keV)

600mu

11 of 22



� Focused on the 2+1 state

� only 2-3 distances with in-flightcomponent for higher-spin states

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

50 100 150 200 250 300 350 400 450 500

R

Distance (mu)

R(S/Tot)

R(U/Tot)

� T1/2 = 26 (3) ps

� not corrected for ≈ 30% feeding of 135 (15) ns isomeric state� Very preliminary result, analysis still ongoing

� From Coulex: T1/2 = 13.1+23−18 ps N. Bree et al., Phys. Rev. Let. 112:162701 (2014).

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Outlook and future perspective

� Promising data and great performance of the system, Plungerstable up-to 7 pnA

� Finish to analyse the data

� Investigate the option to use NeutronWall as a multiplicity filter

� Accelerator problems during the experiment ⇒ Recovery beamtime in July

� Study of 190Hg

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190Hg – a γ-soft nucleus?

� Transition between shape coexistenceand single minimum

� Change in configuration� Signs of γ-softness

J.P. Delaroche et al., Phys. Rev. C 50:2332, (1994).

� Dipole bands with π(2p4h)configuration observed

A.N. Wilson et al., Phys. Let. B 81, B 505(1):614, (2001).

� Super deformed band observedA.N. Wilson et al., PRL 104, 162501 (2010).

3

2

4 5 68

1012

16

18 20

24

28

35

45

6 50o

15o

30o

45o

60o

10

0.0 0.2 0.4 0.6 0.8

˜Adapted from J.-P Delaroche et al., Phys.Rev. C 81, 014303 (2010)

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Thank you for your attention

Thank you for your attentionAlso special Thanks to M. Loriggiola and A. Goasduff, G. Jaworski

15 of 22

Shape coexistence and lifetime measurements

� Transition strengths very sensitive to the wave functions� Huge change in nuclear structure, but B(E2; 2+1 → 0+gs) ≈ 50 W.U.� Change in major contribution with higher spins

L.P. Gaffney et al., Phys. Rev. C 89, 024307 (2014)

Adapted from L.P. Gaffney et al., Phys. Rev. C 89, 024307 (2014).16 of 22

Cross section estimate 190Hg

� Gemini

17 of 22

Cross section estimate 188Hg

� Gemini

18 of 22

Fission 190Hg

� Gemini

19 of 22

Fission 188Hg

� Gemini

20 of 22

Proposed experiment (alternative)

� Setup Galileo + Cologne Plunger (+ Euclides as veto)

� Reaction 40Ar + 154Sm and 152Sm (500µg/cm2 evaporated on1.2 mg/cm2 181Ta) 1 pnA

� Reaction channel −4n for 188Hg and 190Hg� 12 target-stopper distances between 10µm and 1200µm each 4 h

� Energy lower ⇒ less contribution of fission

Energy Channel σ-xn Fraction γ − γ-coinc./h 2+/4+172 MeV −4n 190Hg 13 mbarn 55.4% 900178 MeV −4n 188Hg 19 mbarn 72% 1200

+ 1 day for change of energy + calibration⇒ 5 days of beam time

21 of 22

190Hg a γ-soft nucleus

Adapted from J. P. Delaroche et al., Phys. Rev. C 50, 02332 (1994).22 of 22

Motivation – Shape coexistence in the neutron-deficient Hg isotopesExperimentAppendixAppendix

- shape coexistence in the neutron-deficient hg isotopes ...€¦ · 92intruder bands observed for...

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