40Structure of 68Ni :New insights on the low-lying 0+ and 2+ statesfrom two-neutron transfer on 66Ni and b-decay of 68Co
IS467 and IS504 collaborations

Freddy Flavigny
KU Leuven, Instituut voor Kern- en Stralingsfysica, Belgium

freddy.flavigny@fys.kuleuven.beARIS 2014 - June 2014 - Tokyo

Motivation: Shell structure at Z=28 and N=40
3s1/2
2d5/2

501g9/2

28
40

40

2p1/2
1f5/2
2p3/2
1f7/2

ll
llllll
llll

28

28

llllllll

llllllll

p68Nin(See also K. Wimmer’s talk on Friday, session 4A)

Motivation: Shell structure at Z=28 and N=40
Recent experimental work:
•••••
••

•

J. Elseviers et al., to be submitted.
F. Flavigny et al., to be submitted.
S. Suchyta et al., PRC 89, 021301R (2013)
F. Recchia et al., PRC 88, 041302R (2013)
R. Broda et al., PRC 86, 064312 (2012)
C. J. Chiara et al., PRC 86, 041304R (2012)
A. Dijon et al.,
PRC 85, 031301R (2012)

Precise position and firm spin/parity assignment:

Three 0+ states and two 2+ states below 2.8 MeV

Level scheme from F. Recchia et al.
PRC80, 041302R (2013)

Motivation: Shell structure at Z=28 and N=40
Recent experimental work:••••••••

J. Elseviers et al., to be submitted.
F. Flavigny et al., to be submitted.
S. Suchyta et al., PRC 89, 021301R (2013)
F. Recchia et al., PRC 88, 041302R (2013)
R. Broda et al., PRC 86, 064312 (2012)
C. J. Chiara et al., PRC 86, 041304R (2012)
A. Dijon et al.,
PRC 85, 031301R (2012)

Precise position and firm spin/parity assignment:(2p2h)p +(4p4h)nThree 0+ states and two 2+ states below 2.8 MeVState of the art shell model calculations (MCSM [1], SM [2], )(0p0h +2p2h)nSuggests deformed states and shape coexistence• Y.Tsunoda et al., S. Lenzi et al.

Level scheme from F. Recchia et al.
PRC80, 041302R (2013)

 New picture : need to characterize these states[1] Y. Tsunoda et al., PRC89 031301R (2014) [2] S. Lenzi et al., PRC82 054301 (2010)

Experimental approach: 2 complementary data sets

IS504
• Nature of 0+ states in 68Ni
→ 2n-2h• Conf. Mixing of 0+1 and 0+2
PhD thesis, J. Elseviers

66Ni(t,p)68Ni

b-decay oflow-spin
68Co isomer

3s1/22d5/2

501g9/2

28
40

40

2p1/2
1f5/2
2p3/2
1f7/2

llllllll
llll

28

28

llllllll

llllllll

p68Ni

n(2+)
(2+)

4164
4026

2+0+

2743
2511

2+20330+1604

0+068NiExperimental approach: 2 complementary data sets

IS504

IS467 (A=68)• Nature of 0+ states in 68Ni
→ 2n-2h• Revised decay scheme• b-g-E0 coincidences• Conf. Mixing of 0+1 and 0+2
PhD thesis, J. Elseviers

66Ni(t,p)68Ni

b-decay oflow-spin
68Co isomer• 2+ to 0+ connections• Exp. B(E2) ratios

3s1/2
2d5/2

50
1g9/2

28
40

40

2p1/2
1f5/2
2p3/2
1f7/2

llllllll
llll

28

28

llllllll

llllllll

p68Ni

n(2+)
(2+)

4164
4026

2+0+

2743
2511

2+

2033

0+

1604
270(5) ns0+068Ni

b-decay studies in the 68Ni region using resonant laser ionization

Facility:

ISOLDE (p (1.4GeV) → UCx)
thick & hot target

lPure Mn sourcesl Z selection: Laser ionisation (RILIS)l A/Q selection: Spectrometer (HRS)

58Mn
3.0(1)sl A=68l Previous exp. : 2 isomers in 68Co

l (7-)
T1/2= 0,23(3) sl (1+,3+) T1/2 = 1,6(3) sl ISOLDE: Selectivity of 68Fegs (0+) decay

LISOL b-g detection setup at ISOLDE
Top view
Tapesystem

Beamplastic bdetectors

MINIBALLg detectors
DGF system
MINIBALL: 5.8% photo-peak efficiency at 1.332 MeV
3 plastic detectors: 50% beta efficiency
DGF system: digital read-out on event-by-event basis
Polyethylene-borax-lead-brass shielding

8

Feeding of 0+2 state in 68Ni : b-g-E0 coincidencesb1,6(3) sgb

Time difference: tb – tE0

68Co

beam

Top view:

2+2743g (1139 keV)
0+270(5) nse-1604

E00+68Ni(55% conv. e,45% pair cr.)

Feeding of 0+2 state in 68Ni : b-g-E0 coincidencesb1,6(3) sgb

Time difference: tb – tE0

68Co

beam

Top view:

2+2743g (1139 keV)
0+270(5) nse-1604

E00+(55% conv. e,
45% pair cr.)

68Ni

Coincident g rays

b-g-E0 coincidences (590 events) :• Highly selective signal• 1139 and 2421 keV feeding 0+2• E(0+2) = 1603,6(6) keV in agreement
1603,5(3) in [1].
1605(3) in [2]• Irel(0+2→0+1) = 19(8) %[1] F. Recchia et al., PRC88 041302 (2013)[2] S. Suchyta et al., PRC89 021301R (2013)

b-g coincidencesl Clean 68Co low-spin spectrum
llll• Time condition: tb –tPP in [350,2200] ms→ to avoid 68Mn decay (T1/2 =28(3) ms)Low bkg (shielding)Laser ionisation (RILIS)
Mass separation (HRS)
Selectivity of the 68Fegs (0+) decayl Grand daughter decay
l 1/3 statistics previous LISOL studies [1]l Beta-delayed n branches

68Fe decay

68Ga decay

67Fe decay

68Co decay

136I decay

67Co decay

Revised decay scheme(1+,3+)

lNew:
l 710 keV intensity (clean, no high spin)l 1139 and 2421 keV placementl Removed 694 keV (after b-delayed n)
l 814 keV intensity - 5- isomerl Irel(0+2→0+1 = 19(8) %lUpper limits:l Irel(0+3→0+2) < 2(1)%l Irel(0+3→0+2)<4(1)%
Irel(0+3→0+1)[1] W. F. Mueller et al., PRC61 054308 (2000) [2] S. N. Liddick et al., PRC85 014328 (2012)

Revised decay scheme(1+,3+)

lNew:
l 710 keV intensity (clean, no high spin)l 1139 and 2421 keV placementl Removed 694 keV (after b-delayed n)
l 814 keV intensity - 5- isomerl Irel(0+2→0+1 = 19(8) %lUpper limits:l Irel(0+3→0+2) < 2(1)%l Irel(0+3→0+2)<4(1)%
Irel(0+3→0+1)

lInt. balance: test of completeness in the full A=68 chainl Determination of missed feeding:llll

Direct b feeding of gs
Direct b-del.n feeding to gs or isomeric state
Missed E0 decay
Missed g ray feeding to gs or isomeric states

Missed feeding: 42(10)%-> No conclusion on spin assignment from b-feeding[1] W. F. Mueller et al., PRC61 054308 (2000) [2] S. N. Liddick et al., PRC85 014328 (2012)l Exp. VS SM calculations:

B(E2) ratios

1 – Using the LNPS interaction [1]From experiment:

2 – Monte-Carlo shell model calculations [2]B( E 2, 2i  I  )R
B( E 2, 2i  01 )l Main results:
l 2+1 → 0+2Irel < 0.7(2) % → R < 17

MCSM [2]0+1

0+2[1] S. Lenzi et al., PRC82 054301 (2010)[3] d(E2/M1)=-1.5+0.9-1.2 from

2+1[2] Y. Tsunoda et al., PRC89 031301R (2014)

C.J. Chiara et al, PRC86 041304R (2012)

Th: R=12 (MSCM), 4 (LNPS)

l Exp. VS SM calculations:

B(E2) ratios

1 – Using the LNPS interaction [1]From experiment:

2 – Monte-Carlo shell model calculations [2]B( E 2, 2i  I  )RB( E 2, 2i  01 )l Main results:
l 2+1 → 0+2Irel < 0.7(2) % → R < 17Th: R=12 (MSCM), 4 (LNPS)

l 0+3 → 2+1
Th. partial T1/2 of 108 and 1.5 ns (MCSM,LNPS)
Big difference : lifetime measurement needed.

0+3
MCSM [2]0+10+2[1] S. Lenzi et al., PRC82 054301 (2010)[3] d(E2/M1)=-1.5+0.9-1.2 from2+1[2] Y. Tsunoda et al., PRC89 031301R (2014)

C.J. Chiara et al, PRC86 041304R (2012)l Exp. VS SM calculations:

B(E2) ratios

1 – Using the LNPS interaction [1]From experiment:

2 – Monte-Carlo shell model calculations [2]B( E 2, 2i  I  )R
B( E 2, 2i  01 )l Main results:
l 2+1 → 0+2Irel < 0.7(2) % → R < 17

Th: R=12 (MSCM), 4 (LNPS)

l 0+3 → 2+1
Th. partial T1/2 of 108 and 1.5 ns (MCSM,LNPS)
Big difference : lifetime measurement needed.

0+32+

l 2+2 → 2+1
2

MCSM [2]Higher than published values [4]R = 29 and 278 (MCSM,LNPS)

0+10+2[1] S. Lenzi et al., PRC82 054301 (2010)[3] d(E2/M1)=-1.5+0.9

Irel= 11(2)% → R = 448 +185-311 using [3]-1.2 from

2+1[2] Y. Tsunoda et al., PRC89 031301R (2014)

C.J. Chiara et al, PRC86 041304R (2012)l Exp. VS SM calculations:

B(E2) ratios

1 – Using the LNPS interaction [1]From experiment:

2 – Monte-Carlo shell model calculations [2]B( E 2, 2i  I  )RB( E 2, 2i  01 )l Main results:
l 2+1 → 0+2
Irel < 0.7(2) % → R < 17Th: R=12 (MSCM), 4 (LNPS)

l 0+3 → 2+1
Th. partial T1/2 of 108 and 1.5 ns (MCSM,LNPS)
Big difference : lifetime measurement needed.

0+32+24483
keV

2+l 2+2 → 2+14

MCSM [2]Irel= 11(2)% → R = 448 +185-311 using [3]Higher than published values [4]R = 29 and 278 (MCSM,LNPS)

0+1[1] S. Lenzi et al., PRC82 054301 (2010)

0+22+13980
keV[2] Y. Tsunoda et al., PRC89 031301R (2014)

l 2+3 and 2+42+3

Qualitative agreement for (2+4)
Significant discrepancies for (2+3)

Two-neutron transfer reaction: 66Ni(t,p)68Ni

66Ni(t,p)68Ni : Experimental Setup

66Ni(t,p)68Ni• Beam energy: 2.6 MeV/u
Resonant Laser Ion Source- Z-selectivity• Intensity 2.0 x 106 pps

Mass separation- A/Q-selectivity• Target : 500 mg/cm²
3H loaded Ti(40 mg/cm2 3H)

Post-acceleration (REX-ISOLDE)• Measurement time:  100h

• Beam purity >86%

• Proton detection in T-REX:•••

Identification
EnergyAngular distribution• g detection in Miniball:••

EnergyAngular distribution(Doppler correction)

Miniball: Warr EPJ49 (2013)

T-REX: Bildstein EPJ48 (2012)• 8 DE-Erest Barrel det.

• 1 DE-Erest CD detectors• 8 Miniball triple (HPGe) clusters• Crystals: 6-fold segmented• 5% efficiency at 1.33 MeV

3H(66Ni,p)68Ni : Results

66Ni(3H,1H) 68Ni

41+  21+ 1115keV

709

0+22+  01+ 2744keV

0,86 ms

2511
2033

21+  01+ 2033keV

2847
2743
478

Counts / 2keV

52+1139

815

Proton - gamma coincidences2743

Q = 5.12 MeV

2+20330+1604

0+0270(5) ns

68Ni
Proton-gated(t,p) Eex = 0 MeV

21+  01+
background(t,p) Eex = 6 MeV

3H(66Ni,p)68Ni : Backward CD2033

2511

2+

• Population of 02+ and 2+1 states
E = 1621(28) keV - 4.8(16) % of gs
E = 2033(10) keV - 28(4) % of gs• Non-observed direct population of 03+ , 22+ and 2+3 states
0+3 (2512 keV) < 2%2+2 (2744 keV) < 4%2+3 (4026 keV) < 3%based on 478 keV transition
based on 709 keV transition
based on 1515 keV transition

0,86 ms

4780+CD data only

2847
2743

709

1139

815

52+2743

Backward CD (153-173°)

2033

0+

1604

0+068Ni

270(5) ns

Reaction + Structure modelTwo-neutron transfer :Direct + Sequential

502d5/2

28
40

1g9/2

llllllllllll

2p1/2
1f5/2
2p3/2

28llllllll

n40

1f7/267Ni
66Ni
68Ni

Parameters of our calculations:• Finite-range DWBA (code FRESCO[1] )• Glob. Pot. : 3H+66Ni and 1H+68Ni• Two nucleon overlap amplitudes (TNA’s)• Code: NUSHELL (A. Brown, MSU) [2]• Interaction jj44pna from [3]• Model space: f5/2,p3/2,p1/2,g9/2• Calculated 68Ni energies
E(0+2) = 1593 kev, E(2+1) = 2077 keV )[1] www.fresco.org.uk [2] B. A. Brown and W. D. M. Rae, Nushell@MSU 2007 [3] A. F. Lisetskiy et al., PRC 70, 044314 (2004)

28llllllllpReaction + Structure model

2d5/2

50

Two-neutron transfer :Direct + Sequential

28
40

1g9/2

llllllll
llll

2p1/2
1f5/2
2p3/2

28llllllll

n67Ni

40

1f7/2

Neutron occupation numbers

28llllllll

pProton occupation numbers

66Ni
68Ni

jj44pna
A3DA (MCSM)
LNPS

Parameters of our calculations:

68Ni• Finite-range DWBA (code FRESCO[1] )• Glob. Pot. : 3H+66Ni and 1H+68Ni• Two nucleon overlap amplitudes (TNA’s)• Code: NUSHELL (A. Brown, MSU) [2]

Average number of neutrons in a given state:jj44pnaf5/2• Interaction jj44pna from [3]

p3/2

66Ni

gs4,53• Calculated 68Ni energies

68Ni

gs

5,19+0,66

3,59+0,25

1,73+0,66

1,49+0,43

68Ni

0+2

5,01+0,48

3,44+0,10

1,14+0,07

2,41+1,35[1] www.fresco.org.uk [2] B. A. Brown and W. D. M. Rae, Nushell@MSU 2007 [3] A. F. Lisetskiy et al., PRC 70, 044314 (2004)

1,07

g9/2

• Model space: f5/2,p3/2,p1/2,g9/2

E(0+2) = 1593 kev, E(2+1) = 2077 keV )

3,34

p1/2
1,06

66Ni(3H,p)68Ni : Angular distributions

0+ 1
Conclusions:• Reasonable agreement th/exp for 0+1,2 states
Small CMangles

0+ 2

Th:s(0+2) / s(0+1) in [3 ; 7 ] %Exp: s(0+2) / s(0+1) = 4.8(16) % Validation of structure input• No scaling of theory to experiment• Shape very sensitive to intermediate state properties•

First exp. evidence that 0+2 in 68Ni is a neutron excitation above N=40

Outlook•

Future experiments at HIE-ISOLDE in the region of 68Ni:•

80Zn(d,p)81Zn, [R. Orlandi et al., INTC-2012-051 P-352]•70Ni(d,p)71Ni,[J.J Valiente Dobon et al., INTC-2012-050 P-351]•68Ni(d,p)69Ni,••

Coulomb excitation of 68Ni, 70Ni••

[accepted]
d5/2 single particle strength above N=50

Absolute B(E2) values

Decay of 68Mn with the new ISOLDE Decay Station [accepted]•Lifetime of 0+3→2+1 transition (478 keV)