Rapid evolution of collectivity at N=Z- recent results from level lifetime measurementswith GRETINA

Hiro IWASAKI(NSCL/MSU)

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Collective modes in atomic nuclei- characterized by the ground-state shape as a single basis
6+

6+

0+ 2+ 4+4+2+4+

2+0+

2+0+0+

collectivity
spherical

vibration

deformedE(4+)/E(2+) =

≈ 1.2

2

3.3

B(E2;4+→2+)=
B(E2;2+→0+)

1-10

2

1.43

What will happen if two different shapes coexist ?
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Shape transition in the Kr ground states
M. Bender et al., PRC 74, 024312 (2006)

0+272Kr 74Kr 76Kr 78Kroblate

Aprolate

OblateProlateUnperturbed
EnergyNilsson orbitals
for 74Kr (Z=36, N=38)
How about excited states (2+ and 4+) in 72Kr ? → B(E2) measurement
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Challenges with GRETINA

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GRETINA at NSCL

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TRIPLEX(TRIple PLUNGER for EXOTIC BEAMS)

New approaches in lifetime studies
with TRIPLEX and GRETINA
N(decay)

Target Degrader

TargetDegrader

Degraderreduced(differential)

GammaSpectrum

Beamslow

2nd Degrader

fastEg6/6/2014 ARIS2014

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Simulated
spectra4+ , 5.2(2)ps558keV
455keV2+ , 33.7(2)ps
A.Gorgen et al.

74Kr

EPJA26(05)153

TargetBe0.75mm

Degrader Degrader
TaTa
0.125mm 0.1mm

90 deg2+4+

ForwardEdop (keV) vs Theta (deg)
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Edop (keV)

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Measuredspectra4+ , 5.2(2)ps558keV
455keV2+ , 33.7(2)ps
A.Gorgen et al.

74Kr

EPJA26(05)153

TargetBe0.75mm

Degrader Degrader
TaTa
0.125mm 0.1mm

90 deg2+4+

ForwardEdop (keV) vs Theta (deg)
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Edop (keV)8

independent
Results for 74Kr and 72Kr Model
B(E2) determination[1][1][2]

H.Iwasaki et al., PRL112 (2014) 142502

6/6/2014 ARIS2014[1] A.Gorgen et al., EPJ A 26 (2005) 153[2] A.Gade et al., PRL95 (2005) 022502
9E(2+), E(4+) and B(E2) systematics
Shape evolution between
Rapid evolution of collectivity in 72Krandoblate

prolatewith E(4+)/E(2+) =1.86 and B(E2;4+→2+)/B(E2;2+→0+) = 3.4

72Kr 74Kr 76Kr 78Kroblate

Aprolate

72Kr 74Kr 76Kr 78KrA

72Kr : H.Dejbakhsh et al., PLB249(1987)463, 74,76Kr : E.Clement et al., PRC 75 (07) 054313*) e.g.
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Comparison with (beyond) mean-field theory

[1]

[1]

[2]

[2]

A.Petrovici et al., NPA665 (00) 333, M.Bender et al., PRC74 (06) 024312
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M.Girodet al., PLB676(09) 39, J.-P.Delaroche et al., PRC 81 (10) 014303[1] K.Sato et al., NPA 849 (2011) 53[2] Y.Fu et al., PRC87 (2013) 054305 11

Summary∙ Lifetime measurement of the yrast 2+ and 4+ states in 72Kr atN=Z has been performed at NSCL using the advanced gammaray array GRETINA.
∙ A new plunger system (TRIPLEX) was developed, which
extends the sensitive range of lifetime that can be covered witha single setup and thus enables us to study several states
simultaneously.
∙ System and methodology have been established for future
GRETINA campaigns with fast rare isotope beams.
∙ A rapid shape transition in low-spin yrast states in the selfconjugate nucleus 72Kr have been discussed based on themeasured rapid evolution of collectivity.
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12Collaborators
LBNL: I-Yang Lee, C.Campbell

Cologne
York: A.Dewald, T.Braunroth: R.Wadsworth

CMU: K.Wimmer, A.Westerberg, C.Bancroft, D.Barofsky, J.LloydGANIL: A.Lemasson

NSCL: C.Morse, K.Whitmore, C.Loelius, D.Smalley,A.Gade, D.Weisshaar, D.Bazin, J.Berryman, T.Baugher,
S.R.Strogerg, V.M.Bader, E.Lunderberg, C.Langer, F.Recchia

TU Darmstaft: C.Walz

GRETINA was funded by the US DOE – Office of Science.
Operation of this array at NSCL is supportedby NSF under cooperative agreement PHY-1102511 (NSCL)
and DOE under Grant No. DE-AC02-05CH11232 (LBNL).
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Thank you

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