Probing Shell Structure in Neutron-Rich Nuclei above 48 Ca: Using the Tools at Hand Day 2

A U.S. Department of EnergyOffice of Science LaboratoryOperated by The University of Chicago

Argonne National Laboratory

Office of ScienceU.S. Department of Energy

Probing Shell Structure in Neutron-Rich Nuclei above 48Ca:Using the Tools at Hand

Day 2

Michael P. Carpenter

RIA Summer School SeminarJuly 2006

Pioneering Science andTechnology

Office of Science U.S. Department

of Energy

Outline of Lectures

Day 1• Nuclear Structure – a brief perspective • Changing Shell Structure in the Neutron Rich world.• -decay studies and deep inelastic reactions to

study excited states in 54Ti and 56Ti – looking for evidence of shell gaps at N=32 and N=34.

Day 2• Coulomb Excitation of 52,54,56Ti• 2-proton knockout and -decay into 52Ca• 56,58,60Cr using Gammasphere and the FMA• Future plans.



of Energy

N = 32 Gap: YES N = 34 Gap: NO

00+

15542+

1554

26754+

1121

31996+

524

61357+

2936

65398+

3340

404

6769(9+ )

230

7570(10 + )

8790(11+

)

50Ti

00+

17562+

27044+

33886+

58977+

64008+ 66299+

751610 +

879011+

GXPF1

00 +

10502+

1050

23184 +

1268

30296 +

711

4288(8 + )

1259

6693(10 + )

2405

8857

2164

9088

2395

231

52Ti

00 +

12132 +

24184 +

31036 +

45398+ 4750

7 +

61818 +

679010+

75109 +

953811+

1067212+

GXPF1

00 +

1495(2 +)

1495

2497(4 +)

1002

2936(6 +)

439

5111

2175

(7 + )

5459(8 + )

2523

348

5904(8 + )

2967

6187(9 + )

728284

6432(10+ )

245

54Ti

00 +

15092 +

26334+

31526 +

53847+

57708+

62088+

65639 + 679310

+

907511+

1048712+

GXPF1

00 +

1128(2 + )

1128

2289(4 + )

1161

2979(6 + )

690

((8 + ))

1230

56Ti

00+

15162+

25294+

30446+

8 + 53529

+ 5387

693710 +

GXPF1

3228 34

R.V.F. Janssens et al., PLB 546, 22 (2002) B. Fornal et al., PRC 70, 064304 (2004)

1129



of Energy

Beyond 2+ Energies

E(2+) values are a strong indicator of shell structure, but..

Additional evidence for the presence or absence of shell effects is most welcome and very desirable!

Measure B(E2; 0+ 2+) values

At present, this can only be done with Ti nuclei from fragmentation

Intermediate Energy Coulomb Excitation!



of Energy

Coulex of 132,134Sn at HRIBF

• rays measured with BaF array for 132,134Sn

• Surprise B(E2) increases for 132Sn.

R. Varner et al., Eur. Phys. J. A25, s01 (2005) 391.



of Energy

Beyond 2+ Energies: B(E2; 0+ 2+) valuesAu

bmin

Smaxbmin = a0 cot (max/2) /

a0 =ZS ZAu e2

m0c2 2

Zero degree detector

Ti

ETi ≈ 80 MeV/nucl.

≈ 0.4, ≈ 1.1bmin ≈ 20 fm

“touching spheres”1.2(ATi

1/3+AAu1/3) ≈ 11 fm

TOF +

SeGA array

Primary Beam: 130 MeV/u 76Ge Yields: 24000 s-1 52Ti; 2400 s-1 54Ti; 75 s-1 56Ti



of Energy

SEGA Array @ NSCL

The 75% Ge Crystal has its outer electrode divided into 8 segments along the crystal axis and 4 segments perpendicular to the axis, resulting in 32 fold segmentation

SEGA with 16 Ge

W. Mueller et al., NIMA 466, 492 (2001)

beam



of Energy

GRETINA (Segmented Ge-Shell)

• Tapered hexagon shape.• Highly segmented 6x6=36• 7 modules with 4 crystals each –

cover ≈ 1π solid angle (cover 4π will take 30 modules).



of Energy

SEGA and GRETINA

Gamma-ray energy (2keV/channel)

30Na from 32Al Beam

30Na from 30Mg Beam

340

370410250

175

190

150

140

340

370410

250

175

770430 (3+--2+)

Simulation SeGA Simulation GRETINA

30Mg (pn) → 30Na (100 MeV/u) v/c=0.43charge exchange reactionGamma-gamma coincidence

NSCL data SeGA (E. Rodriguez-Vieitez et al.)



of Energy

Particle Identification at the S800



of Energy

76Ge and 197Au: the Test CasesLab Frame

Projectile Frame

Primary beam: 76Ge @ 140 MeV/nucl.Secondary beam: 76Ge @ 81 MeV/nucl.

= 0.392197Au target thickness: 257.67 mg/cm2

max = 3.06° (CM)Number of 76Ge particles detected: 26.1E6

76Ge•E= 562.6(6)keV(<max) = 394(47) mb•B(E2, ) = 2923(346) e2fm4

•Adopted values:•E= 562.93(3)keV•B(E2, ) = 2780(30) e2fm4

197Au•E= 547.03(24) keV(<max) = 94(20) mb•B(E2, ) = 4223(898) e2fm4

•Adopted values:•E= 547.5(3) keV•B(E2, ) = 4494(409) e2fm4



of Energy

197Au check: Do we know what we are doing?

D.-C. Dinca et al., PRC 71, 041302(R) (2005)



of Energy

An accurate technique that allows for absolute B(E2) measurements

-50

-25

0

25

50

75

100

125

150

175

200

225

250

40Ar 36Ar 24Mg 30S 78 Kr 58Ni 76Ge 26Mg

Intermediate-energyCoulomb excitationAdopted value

Adopted and measured B(E2) values for stable nuclei

Adopted valueCoulomb excitationResonance fluorescenceDoppler shift attenuationRecoil distributionElectron scatteringIntermediate-energyCoulomb excitation

Mg26

B(E2) values fromdifferent methods for 26Mg

J. Cook et al., (NSCL/MSU)



of Energy

B(E2; 0+ 2+) values

52Ti, 2+ 0+ (g.s.) 54Ti, 2+ 0+ (g.s.) 56Ti, 2+ 0+ (g.s.)

56TiE= 1129(7) keV(<max) = 155(51) mbB(E2, ) = 599(197) e2fm4






of Energy

Shell Effects in Ti isotopes: What do we know?

48Ti 50Ti 52Ti 54Ti 56Ti200

400

600

800

B(E

2, )

(e2 f

m4 )

26 28 30 32 34 N

48Ti 50Ti 52Ti 54Ti 56Ti

600

800

1000

1200

1400

1600

1800

2000 26

E(2

+) E

nerg

y (k

eV)

28 30 32 34

From an experimentalist’s point of view: N = 28 and N=32 gaps are quite visiblein BOTH the E(2+) energies and in the B(E2;0+ 2+) values

and there is no experimental evidence for a N=34 gap




of Energy

Comparison with GXPF1

48Ti 50Ti 52Ti 54Ti 56Ti200

400

600

800

B(E

2, )

(e2 f

m4 )

26 28 30 32 34 N

GXPF1

The Shell Model with the GXPF1 interaction has problems with(a)N=34 and with (b) the B(E2) values for ALL Ti

48Ti 50Ti 52Ti 54Ti 56Ti0

500

1000

1500

2000

E(2+) GXPF1

26

E(2

+ ) Ene

rgy

(keV

)

28 30 32 34N

ep = 1.5, en = 0.5




of Energy

Possible Interpretation



of Energy

FPD6 and GXPF1

The data may be telling us that the gap between p3/2 and p1/2 is at least as large as GXPF1 says, but that p1/2 and f5/2 are at leastas close together as FPD6 indicates

FPD6



of Energy

32 34

(6+)

(4+)

Recent Theory Development: GXPF1AGXPF1A vs GXPF1:T=1 matrix elementsinvolving p1/2 and f5/2

modified p1/2 - f5/2) gap

reduced by ~0.5 MeV

M. Honma et al., Proc. ENAM (2004)



of Energy

31 33

exp

Recent Theory Development: GXPF1A

B. Fornal et al., PRC in press



of Energy

Comparison with GXPF1A

48Ti 50Ti 52Ti 54Ti 56Ti200

400

600

800

B(E

2, )

(e2 f

m4 )

26 28 30 32 34 N

GXPF1

48Ti 50Ti 52Ti 54Ti 56Ti0

500

1000

1500

2000

E(2+) GXPF1

26

E(2

+ ) Ene

rgy

(keV

)

28 30 32 34N

GXPF1AGXPF1A

M. Honma et al., Proc. ENAM (2004)



of Energy

Value of effective charges?

B(E2) = (Apep + Anen)2

A Ap An 48 8.8 15.450 10.7 9.552 9.0 14.454 10.7 10.656 10.3 11.4



of Energy

Value of effective charges?

B(E2) = (Apep + Anen)2

A Ap An

48 8.8 15.450 10.7 9.552 9.0 14.454 10.7 10.656 10.3 11.4

With ep= 1.15 en= 0.8 according to R. du Rietz et al., PRL 93, 222501 (2004)



of Energy

Experimental Evidence for N=32 Gap: 52Ca

J.I. Prisciandaro et al., PLB 501, 17 (2001)

E(2+) in 52Ca comes from a1983 ISOLDE -decay study (A.Huck et al., PRC 31, 2226 (1985))where the separation between decay and n-delayed decay wasa problem

At NSCL 52Ca intensity is too small for aCoulex experiment 2p knockout!!

(?)— Exp.

○ FPD6

GXPF1

28 34

32



of Energy

2p knockout into 52Ca

Direct processKnock-out of 2 f7/2 protons from 54Ti

Cross section is small (~ 0.32 mb) 52Ca is magic

No direct feeding of 2+ state: Consistent with a Neutron excitation

A. Gade et al., PRC in press.



of Energy

2p knockout into 52Ca

2p knockout provides a way to study proton cross-shell excitations in n-rich nuclei

3- is (d3/2 or s1/2)-1 (f7/2)) excitation

A. Gade et al., PRC in press.



of Energy

2p-knockout “by-products”

First Transitions in 55Ti from 2p-knockout with 57Cr



of Energy

Pushing towards n-rich Cr: 59,60Cr

•59Cr from 48Ca(13C,2p)59Cr at 130 MeV•60Cr from 48Ca(14C,2p)60Cr at 130 MeV

s(2p) < 1 mb s(3n/4n) ~ 100 mb

S.J. Freeman et al., PR C 69, 064301 (2004)



of Energy

14C(48Ca,2p)60Cr @ 130 MeVE

E

ET2

M/Q

Pushing towards n-rich Cr: 60Cr

Ni

FeMnC

r

Ca scattered beam

Ti

60/17

57/16

56/16

60/17

57/16

56/16

Ni

FeMnC

r

Ca scattered beam

Ti



of Energy

Fe

Mn

Cr

824438339

1291

569250129

1007 1070643

ray energy (keV)

643

810815

986 1033607

60Cr

M=60 dataM=60 data

M=60 Z=24 M=60 Z=24 datadatawith subtractionswith subtractions

Pushing towards n-rich Cr: 60Cr

S. Zhu et al., to be published



of Energy

Gate on 644 keV

Gate on 810-815 keV

Gate on 985 keV 815

815 985

985643

643

ray energy (keV)

Cou

nts

per c

hann

el

M=60M=60Z=24 Z=24 datadata

0+

2+

643 keV

Cr60

985 keV

815 keV

1033 keV

Pushing towards n-rich Cr: 60Cr (N=36)

S. Zhu et al., to be published



of Energy

Pushing towards n-rich Cr: 57Cr (N=33)

A. N. Deacon et al., PLB 622, 151 (2005) .

A=57

A=57Z=24

14C(48Ca,n)57Cr @ 130 MeV



of Energy

57Cr: signs of collectivity

A. N. Deacon et al., PLB 622, 151 (2005) .

g9/2 prolate structure also seen in 55Cr

Good agreement with GXPF1



of Energy

Fed in 59V β decay, most likely in νf5/2 → πf7/2, expect at least 5/2− to have νf5/2 parentage

9/2+ @ only 503 keVOblate deformation?Weak coupling?

Honma, Otsuka, Brown and Mizusaki: full fp basis, GXPF1

interaction

Interpretation: 59Cr (N=35) and the Shell Model

0+

2+880

Cr58

S.J. Freeman et al., PR C 69, 064301 (2004)

13C(48Ca,2p)59Cr @ 130 MeV



of Energy

Deformation Forms Shell Gaps Too!

N=341/23/2 [301]9/2 [404]

5/2 [303]

1/2



of Energy

1.6 MeV

Prolate band,terminating

503 keV & isomer

Oblate structure

57,59Cr: Shape Driving by the g9/2 orbital

S. Freeman et al. PRC 69, 064301 (2004)A. Deacon et al. PLB 622, 151 (2005)



of Energy

More from the Deep Inelastic

56Cr32

58Cr34

60Cr36

•E(2+0+) decreases with A• Level sequence not regular just yet!? Small oblate deformation ?

48Ca + 238U and 48Ca + 208Pb

Zhu et al., to be published



of Energy

Conclusions & Outlook

• Neutron-rich nuclei continue to surprise us! - there is a N=32 shell gap just above 48Ca in Ti (and Cr) confirmed by level structure and B(E2; ) - first indications for the onset of oblate(?) deformation (and the shape driving influence of the g9/2 orbital) seen

in 59,60Cr - 54Ca is an important measurement (N=34 gap)

• Theory needs work - the GXPF1 interaction is not the complete answer - the location of the p1/2 and f5/2 orbitals in n-rich nuclei

above 48Ca needs further study - the g9/2 intruder needs to be included



of Energy

Approach: -decay spectroscopy of fragments with (A,Z) selections NSCL, ISAC prompt -ray spectroscopy following deep inelastic reactions (thick & thin targets) ATLAS Coulomb excitation NSCL, (HRIBF) fusion-evap. reactions @ radioactive targets ATLAS knockout reactions from fast fragments NSCL

Data obtained with each of these techniques and facilities complement each other!

Where did we go and what did we do



of Energy

Don’t Forget your Collaborators!

• ANL: R.V.F. Janssens, S Zhu, M.P. Carpenter F.G. Kondev et al.,

• NSCL: P. Mantica, S. Liddick, et al., A. Gade, D.-C. Dinca, D. Bazin, et al.,

• Cracow: B. Fornal, R. Broda et al.• Manchester: S. Freeman, A. Deacon, et al.• Lowell: P. Chowdury• FSU: S. Tabor et al.• TRIUMF: G. Hackman, C. Morton et al.

• Theory: M. Honma, T. Otsuka, B.A. Brown, T. Mizusaki

Probing Shell Structure in Neutron-Rich Nuclei above 48 Ca: Using the Tools at Hand Day 2

Documents

Transcript of Probing Shell Structure in Neutron-Rich Nuclei above 48 Ca: Using the Tools at Hand Day 2