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Latest SEASTAR Results with MINOS+DALI2 in the 110Zr region

Nancy PaulCEA Saclay—Université Paris-Saclay

NUSTAR Annual Meeting, March 2017

Overview

2

Motivation and Setup

• E2+ as a probe of structure evolution

• The SEASTAR Campaign• MINOS+DALI2 @ RIKEN

Physics Cases—What happens beyond N=60?

• 88-94Se—shape coexistence?• 98-100Kr—quantum phase transition?• 110Zr—tetrahedral? harmonic oscillator?

Summary

• The emerging picture of 60<N<70 structure evolution

Motivation: Understanding Structure Evolution

3

126

82

8 2028

50

2

new magicnot magic

Evolution of nuclear structure with N/Z not fully understood• Disappearance of known magic numbers• Appearance of new magic numbers

stable nuclei

known nucleiunknown nuclei (prediction)

Probes of structure evolution• First 2+ excited states

(this work)• Masses, radii, transition

probabilities,…….

magic

not magic28

Clear signature for (non-)magic nuclei

Taken from B. Bastin et al, PRL 99 (2007)

Experiment: The SEASTAR Campaign

4

o Goal: First E2+, E4

+ measurements of selected most exotic nuclei through (p,2p) reaction

o Innovation: MINOS+DALI2 detectorso Spokespersons: P. Doornenbal and

A. Obertellio Multiyear campaign:

o 2014 ~78Nio 2015 ~110Zr and south o 2017 ~52Ar, 62Ti

2.6 2.7 2.8

Prot

on n

umbe

r Z

28

29

30

31

32

33b

79Cu

80Zn

2.6 2.7 2.8

28

29

30

31

32

Mass-to-charge ratio

1

10

102

103

104

c

78Ni

RRC

IRC

SRC

BigRIPS

RILAC2

fRC

ZeroDegree

Primary target

Secondary target (10 cmt LH2)MINOS (proton tracker)DALI2 (γ-ray detector)

0 50 m

a

Primary beam: 238UEnergy: 345 MeV/U, Intensity: 30 pnAβ @ MINOS: 0.6c

RIBF@ RIKEN

DALI2+MINOS detectors

5

DALI2o 182 NaI(Tl) scintillatorso 35% efficiency @ 500kevo 9% resolution (FWHM) @ 662 kevo ~15-160° angular coverage

Takeuchi et al, NIM A 763 (2014)

MINOSo LH2 target +TPCo Thick target → high luminosityo Reaction vertex → Doppler correctiono >95% 1p detection efficiency

Obertelli et al, EPJA 50 (2014)

à (p,2p) knockout reactions

MINOS

6

proton

proton

gamma

!"#$$%&')#''&)*&" =!,(1 − 01234,)

1 − 06�

Beam

!, = gamma energy in lab0=nucleus velocity at vertex

4,=photon emission angle relative to beam

Motivation: What Happens Beyond N=60?

7

N=60o Rapid onset of deformation @ N=60 in Zr chain—competing prolate

configuration, interacting p-n orbitals (Federman-Pittel mechanism, type II shell evolution

of Otsuka)o Same effect when removing protons?o Complicated shape coexistence—rich testing ground for structure modelso New effects at N=70?

Results: Se Isotopes And SCCM Calculations

8

o Measurement consistent with D1S+PCM calculations from Tomas Rodriguez

o Calculations show oblate-prolatetransition at N=56, then sharp prolate-oblate transition at N=58.

o No indication of N=56 subshell closure (90Se)

PCM

86Se 88Se 90Se 92Se 94Se

Figures from S. Chen and T.R. Rodriguez

Figure from S. Chen

Results: 98,100Kr (courtesy of F. Flavigny)

9

0

50

100

0

200

400

600

800

Co

un

ts /

10

ke

V

200 400 600 800

E(keV)

0

20

40

60

Co

un

ts /

20

ke

V

0 300 600 900-10

0

10

20

30

Co

un

ts /

20

ke

V

(a) 99

Rb(p,2p)98

Kr 190-220 keV

470-500 keV

(b) 101

Rb(p,2p)100

Kr

Gate

Gate

56 60 64Number of neutrons

0

0.5

1

1.5

E(2

1

+)

(Me

V)

(this work)

Kr (Z=36)

Sr (Z=38)

Zr (Z=40)

98Kr

100Kr

309(10)

0

329(7)

545(17)

21

+21

+

(02

+,2

2

+)

(41

+)

01

+0

1

+0

309

329

498

216

638(25)

638

(a) (b)827(20)

E(21+) evolution:

o Overall progressive decrease for Kro Not as brutal as Zr and Sr, but presento Stabilization at N=64Intruder configuration:o First evidence in neutron rich Kr isotopes

Results: 98,100Kr (courtesy of F. Flavigny)

10

o Coexistence of prolate and oblate shapes

o Prolate intruder state competing at low energy

o Origin of drop at N=62? Unclear from theory

96Kr

98Kr

100Kr

Motivation: 110Zr (Z=40, N=70)

11

o Conflicting theoretical predictionsoWeakening of spin-orbit splitting,

shell gap at N=70?

oTetrahedral symmetry?o40,70, both tetrahedral magic

numberso Dudek et al, PRL 88 (2002); Dudek et al, PRC 69

(2004);

oDeformed, shape coexistent?o Delaroche et al, PRC 81 (2010); Geng et al, PTP

110 (2003); Kortelainen et al, PRC 82 (2010); Skalski et al, NPA 808 (2008); Xu et al, PRC 65 (2002); Petrovici et al, J. Phys. Conf. Ser., Sorgunlu and Van Isacker; Bender et al. PRC 2009.

o Important benchmark for theory

Plot from Lorusso et al, PRL 114 (2015)

Astrophysical interest:o Shell-stabilized 110Zr potential

explanation for r-process model discrepancies before A=130 peak?

No existing evidence of stabilized 110Zr (published spectroscopy of 108Zr, beta decay lifetime of 110-112Zr)

Still missing direct structure measurement!

Results: 112Mo and 110Zr

12

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(�+) ���(�)

(�+) ���(��)

(�+) ��(��)

���

���

���

!!"!"!+

("+) #$%(##)

(&+) %'%("#)("+) &$%(##)

!"#

$"%

!"#

Energy (keV)0 100 200 300 400 500 600 700

Cou

nts

/ 10

keV

50

100

150

200

250

300 Zr110

Cou

nts

/ 5 k

ev

200400600800

100012001400160018002000

Mo112

100 200 300 400 5000

20

40

60

80 Gate 150-210 keV

100 200 300 400 500

0

20

40

60

80 Gate 190-250 keV

Results: 110Zr Theory Comparison

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��+ ��+

��-��+

��+��-

13

Tetrahedral predictions Tagami et al, PRC 87 (2013)

o Best agreement with MCSM calculationsà prolate deformation in ground stateTogashi et al, PRL 117 (2016)

o Qualitative agreement with Gogny and Skyrme calculationso Exclude tetrahedral symmetry in ground state of 110Zro 110Zrà Well deformed, rotational nucleus

Figure from Togashi et al, 2016

Z30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64

42R

2

3

(keV

)1+

Ener

gy 2

200

400

600

800

1000

1200

Results: N=70 Theory Comparison

Z30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64

42R

2

3

(keV

)1+

Ener

gy 2

200

400

600

800

1000

1200

Z30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64

42R

2

3

(keV

)1+

Ener

gy 2

200

400

600

800

1000

1200

14

NNDC-evaluated dataThis work

D1S+5DCH Delaroche, Girod, Libert(CEA)

D1S+PCMRodriguez (Madrid)

SLyMR0+PCMBally (CEA), Bender (IPNL), Heenen(Bruxelles)

Z30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64

42R

2

3

(keV

)1+

Ener

gy 2

200

400

600

800

1000

1200 N=70

R42

=E(

4 1+ )

E(2 1+ )

vibrator

rigid-rotor

The New Picture Beyond N=60

15

N54 56 58 60 62 64 66 68 70 72

(keV

)1+

Ener

gy 2

0

200

400

600

800

1000

1200

1400

1600

Zr (Z=40)Sr (Z=38)Kr (Z=36)Se (Z=34)

ü Smooth behavior in Se consistent with shape coexistenceü Evidence for shape coexistence and rise in deformation at @ N=62ü 110Zr—well deformed, no magicity nor tetrahedral symmetry, shape coexistence

16

Thank you!A. Corsi, A. Obertelli, G. Authelet, F. Chateau, A. Delbart, J.-M. Gheller, A. Giganon, A. Gillibert, V. Lapoux, J-Y. Roussé, C. Santamaria, J.-P. Delaroche, J. Libert, M. Girod, B. Bally

T. Ando, S. Momiyama, R. Taniuchi, M. Niikura, H. Sakurai, T. Saito, K. Wimmer, S. Nagamine, T. Otsuka

A. Jungclaus, V. Vaquero

L. Cortes, V. Werner

A. Blazhev, M. Dewald,K. Moschner,

T. Arici, M. Górska, C. Lizarazo

R. Caroll, Z. Patel, Z. Podolyak, M. Rudigier, C. Shand

F. Browne, A. Bruce, C. Nobs

P. Doornenbal, H. Baba, S. Chen, T. Motobayashi, D. Steppenbeck, T. Uesaka

F. Flavigny, L. Olivier, S. Franchoo, A. Gottardo

J. Liu, Z. Xu

N. Nakatsuka

L.X. Chung, B. Linh

R. Orlandi

M. BenderP.-H. Heenen

T.R. Rodriguez

17

Backup Slides

Energy (keV)0 100 200 300 400 500 600 700 800

Cou

nts

/ 5 k

ev

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Backup: 112Mo—high stats case

18

Energy (keV)0 100 200 300 400 500 600 700 800

Cou

nts

/ 5 k

ev

0

200

400

600

800

1000

1200

1400

1600

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2000

Energy (keV)0 100 200 300 400 500 600 700 800

Cou

nts

/ 5 k

ev

0

200

400

600

800

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1400

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2000

Energy (keV)0 100 200 300 400 500 600 700 800

Cou

nts

/ 5 k

ev

0

200

400

600

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1000

1200

1400

1600

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Energy (keV)0 100 200 300 400 500 600 700 800

Cou

nts

/ 5 k

ev

0

200

400

600

800

1000

1200

1400

1600

1800

2000 112Mo Experimental spectrum

Normalized bremsstrahlung background

Subtracted spectrum+fit

0

100

200

300

225 230 235 240Energy (keV)

Life

time

(ps)

Hal

f-life

(ps)

Backup: Experimental setup @ RIKEN

192.6 2.7 2.8

Prot

on n

umbe

r Z

28

29

30

31

32

33b

79Cu

80Zn

2.6 2.7 2.8

28

29

30

31

32

Mass-to-charge ratio

1

10

102

103

104

c

78Ni

RRC

IRC

SRC

BigRIPS

RILAC2

fRC

ZeroDegree

Primary target

Secondary target (10 cmt LH2)MINOS (proton tracker)DALI2 (γ-ray detector)

0 50 m

a

A/q2.55 2.6 2.65 2.7 2.75 2.8

Z

38

39

40

41

42

43

44

45

1

10

210

110Zr

112Mo

A/q2.55 2.6 2.65 2.7 2.75

Z

39

40

41

42

43

44

45

1

10

210

111Nb

113Tc

BigRIPS—entering LH2 target ZeroDegree—reaction products

A/q

Primary beam: 238UEnergy: 345 MeV/U, Intensity: 30 pnAβ @ MINOS: 0.6c

Energy (keV)0 100 200 300 400 500 600 700 800

coun

ts

0

50

100

150

200

250

300 subtracted spectrumsimu+bkg170 kev, 200 ps355 kev, 100ps

Proof of principle: 108Zr—two peak fit

20

0

100

200

300

400

500

600

700

800

900

140 150 160 170 180Energy (kev)

Hal

f−lif

e (p

s)

0

100

200

300

400

500

600

700

800

900

140 150 160 170 180Energy (kev)

Hal

f−lif

e (p

s)

From Kameda et al 2012

21+→ 01

+

chi221

+→ 01+

probability

110Zr—Forward Angles

21

Energy (keV)0 200 400 600 800 1000

Cou

nts

/ 5 k

eV

0

10

20

30

40

50

60

h_SpectrumDALI_forward

Proof of principle: Background subtraction-86Ge

22

Lifetime effects

23

keV0 50 100 150 200 250 3000

1000

2000

3000

4000

5000

6000

7000 180 kev, 0ps180 kev, 100ps180 kev, 200ps180 kev, 350ps

Half-life (ps) Centroid (keV)

0 180

100 173

200 167

350 159