Upload
others
View
4
Download
0
Embed Size (px)
Citation preview
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)
2 of 22
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)
2 of 22
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)
2 of 22
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)
3 of 22
What we know about this region
176 180 184 188 192190182 1861784 of 22
What we know about this region
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
What we know about this region
176 180 184 188 192190182 186178
Increase in2+ energyMore spherical structure
176Hg
R. Julin et al., J. Phys. G 27(7):R109 (2001).
Strong E0 component22+ → 21+Strong Mixing
184,186Hg
M. Scheck et al., PRC 83 037303 (2011).
4 of 22
What we know about this region
176 180 184 188 192190182 186178
Increase in2+ energyMore spherical structure
176Hg
R. Julin et al., J. Phys. G 27(7):R109 (2001).
Strong E0 component22+ → 21+Strong Mixing
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)
4 of 22
What we know about this region
176 180 184 188 192190182 186178
Increase in2+ energyMore spherical structure
176Hg
R. Julin et al., J. Phys. G 27(7):R109 (2001).
Strong E0 component22+ → 21+Strong Mixing
184,186Hg
M. Scheck et al., PRC 83 037303 (2011).
182-188Hg COULEXN. Bree et al., PRL 162701 (2014)
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)
4 of 22
What we know about this region
176 180 184 188 192190182 186178
Increase in2+ energyMore spherical structure
176Hg
R. Julin et al., J. Phys. G 27(7):R109 (2001).
Strong E0 component22+ → 21+Strong Mixing
184,186Hg
M. Scheck et al., PRC 83 037303 (2011).
182-188Hg COULEXN. Bree et al., PRL 162701 (2014)
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)
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)
5 of 22
Experiment using Galileo (+NeutronWall)
6 of 22
Experiment using Galileo (+NeutronWall)
6 of 22
Experiment using Galileo (+NeutronWall)
6 of 22
Experiment using Galileo (+NeutronWall)
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
Experiment using Galileo (+NeutronWall)
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
Experiment using Galileo (+NeutronWall)
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
� Background from Fission (e.g. Fusion-Fission)
� Background from Coulex⇒ Reduced by condition 1n > 1
8 of 22
Experiment using Galileo (+NeutronWall)
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
� Background from Fission (e.g. Fusion-Fission)
� Background from Coulex⇒ Reduced by condition 1n > 1
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
(Ab)Using for suppressing Coulex
� First timecompletely digitalNeutronWall
� Very “dirty”selection ofneutrons
� Fast onlineselection of ZCOin order to reducedata rate
� Nearly dead-timefree
Used neutron condition
9 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
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
9 of 22
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
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◦
−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
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 @ 119◦
−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
Very preliminary results
� Accelerator problems duringexperiment ⇒only 2.5 days of beam time
� 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).
12 of 22
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
13 of 22
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)
14 of 22
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