View
215
Download
1
Category
Tags:
Preview:
Citation preview
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
Recommended