In-beam -ray spectroscopy of neutron-rich nuclei in the uranium region

through the heavy-ion transfer reaction

ISHII Tetsuro

Japan Atomic Energy Agency

JAEA H. Makii, M. Asai, H. Koura, K. Tsukada, A. Toyoshima, M. Matsuda, T. Shizuma, S. IchikawaTokyo Institute of Technology S. Shigematsu, T. KohnoNational Defense Medical Colledge A. MakishimaKomazawa Univ. J. Kaneko, M. OgawaOsaka Univ. I. Hossain, Ibaraki Univ. H. Toume

JAEA-Tokai Tandem Accelerator

Where are deformed / spherical shell gaps ? high-L (k17/2) orbitals ?

► In-beam -ray spectroscopy using heavy-ion transfer reactions - 238U,244Pu,248Cm targets; (18O,16O), (18O, 20Ne) selection of reaction channels using Si E-E ► First -ray measurements of 236Th, 240,242U, 246Pu, 250Cm

- establishment of ground-state bands up to 12+ states ► Systematics of E(21

+) in the neutron-rich U region - disappearance of N=152 deformed shell gap at 94Pu - possibility of the spherical shell gap at N=164 for 256U164

Nuclear structure at the largest neutron number

-stabilit

y

More Neutron-rich than the -stability

(18O,16O) 2n stripping

(18O,20Ne) 2p pickup

294110Ds184T1/2 ~300y

Ge

Ge

Si E-E

Target

Si E-E

18Obeam

16O,17O,

40o

248Cm

18O beam 162 MeV(18MV) @Tokai-Tandem248Cm target (0.8mg/cm2) 3mm, 45kBq

4 Si E-E telescopesE: 75m thickness

6 Ge detectors eff = 12% @ 0.2 MeV 3% @ 1.3 MeV

Experimental setup

0 100 200 300 400

0

20

40

60

-ray Energy (keV)

Cou

nts

/0.6

67ke

V

110+

K

1

170

226

279

326

250Cm-

O

N

C

B

Be

F

Si E-E PLOT

248Cm(18O,16O)250Cm; 2neutron-stripping

0 100 200 300 4000

1000

2000

Energy (keV)

Cou

nts

/0.6

67ke

V

170

K

1 +

110

226

279

326

250Cm-4 →2

6 →4

8 →6

10 →

8

12 →

10E∝AZ2/E

E-E Plots & -ray spectra of 250Cm154

~0.5mb

0 100 200 300 400

0

20

40

60

-ray Energy (keV)

Cou

nts

/0.6

67ke

V

110+

K

1

170

226

279

326

250Cm-

248Cm(18O,16O)250Cm; 2neutron-stripping

　 Complete selection of -rays in residual nuclei by measuring outgoing particles - Z, A, and kinetic energies -

0 100 200 300 4000

1000

2000

Energy (keV)

Cou

nts

/0.6

67ke

V

170

K

1 +

110

226

279

326

250Cm-4 →2

6 →4

8 →6

10 →

8

12 →

10

Si E-E PLOT

gate

Ex of 250Cm < Sn

E-E Plots & -ray spectra of 250Cm154

250Cm15496

48

158

327

553

832

1158

2

4

6

8

10

12

0

110

170

226

279

326

0 keV

240U14892

45

151

313

529

793

1100

847

945

1088

1276

2

4

6

8

10

12

35

7

9

0

106

163

216

264

308

0 keV

Level schemes of 240U, 246Pu and 250Cm by (18O,16O)

246Pu15294

47

155

321

544

818

1141

2

4

6

8

10

12

0

108

167

222

275

323

0 keV

Level Schemes of 236Th and 242U by (18O,20Ne)

236Th14690

48

160

329

553

826

2

4

6

8

10

0

112

170

224

273

0 keV

242U15092

48

158

328

552

2

4

6

8

011

016

922

50 keV

if deformed shell gap exists,

pairing energy gap ()

moment of inertia (E2+ )

138 140 142 144 146 148 150 152 154 15635

40

45

50

55

60

Neutron Number

E(2

+)

(keV

)

90Th

92U

94Pu

96Cm

98Cf

100Fm

102No

N=152

Five new data

cranking model

138 140 142 144 146 148 150 152 154 15635

40

45

50

55

60

90Th 92U 94Pu96Cm 100Fm98Cf

102No

N=152

Neutron Number

E(2

+)

(keV

)

Experiment

Calculation

Sobiczewski et al., PRC 63(2001)034306

Moments of inertia and N=152 deformed shell

Narrower energy gap at N=152 for 94Pu

0

200

400

600

800

1000

94247Cm

249Cf 251Fm

9/2

1/2

7/2

5/2

N=151 Energy Levels

7/2

Ex

(keV

)

245Pu 96 98 100253No 255Rf102 104

9/2 5/27/21/2

1/27/2

152

Experiment

9/2[734]

7/2[613]

7/2[624]

3/2[622]

1/2[620]

5/2[622]

1/2[750]

9/2

15/2

0

2227/2

9/2

269

331

7/2 194

5/2265

3/25/27/2

9/2

580619665

728

1/25/2

7/29/2

311360

428464

3/27/2

11/2

643681

765

194.1

70.475.1

269.1331.2

315.3354.7

(47)

282.9

320.8

217.6

301.5

T1/2=340(20) ns

245Pu15194

2519/2+

245Pu151

1/2[620]

9/2[734]present in-beam -ray data

combined with the (d,p) data at ANL in ’70s

138 140 142 144 146 148 150 152 154 15635

40

45

50

55

60

Neutron Number

E(2

+)

(keV

)

90Th

92U

94Pu

96Cm

98Cf

100Fm

102No

N=152

Possibility of spherical shell closure of N=164 in the U region

pairing energy gap ()

moment of inertia (E2+ )

138 140 142 144 146 148 150 152 154 15635

40

45

50

55

60

Neutron Number

E(2

+)

(keV

)

90Th

92U

94Pu

96Cm

98Cf

100Fm

102No

N=152

25692U164 is spherical ？

Minimum

Deformed shell gap

N=126

S.P.E. calculated by Koura-Yamada potential (modified Woods-Saxon)

Summary

• First measurements of deexcitaion -rays in 5 neutron-rich nuclei in the U region

(18O, 16O) 2n-strippping; 240U, 246Pu and 250Cm up to 12+ ~0.5mb (18O, 20Ne) 2p-pickup ; 236Th and 242U up to 10+ and 8+ ~b

- complete selection of -rays by Z and M by measuring the outgoing particles with Si E-E 250Cm154 : first in-beam -ray study beyond N=152

• Disappearance of N=152 deformed shell gap for 94Pu - from the systematics of the E(21

+) energies

and from the single particle levels in 245Pu151

• Possibility of the spherical shell closure of N=164 - supported by the calculation using the Koura-Yamada potential

240U: T. Ishii et al., Phys. Rev. C 72 (2005) 021301(R)250Cm: T. Ishii et al., J. Phys. Soc. Jpn. 75 (2006) 043201