Post on 16-Oct-2021
Alpha-decay Spectroscopy of Transfermium Nuclei
at JAEA
Advanced Science Research Center, Japan Atomic Energy Agency
Masato Asai
JAEA Tandem accelerator
Tandem
accelerator Superconducting
Linac booster
Recoil mass
separator (RMS)
JAEA Tandem
accelerator
• Beam line to irradiate actinide target
• Gas-jet transport system
• On-line isotope separator (ISOL)
R5
R3
New actinide
target beam line
for fission studies
(Under construction)
Beam
Target
Target chamber
Beam Gas-jet transport
Actinide target beam line
232Th 231Pa 232U, 233U, 235U, 238U 237Np 239Pu, 244Pu
Hood
241,243Am 248Cm 249,251Cf
Actinide targets available at JAEA tandem
Spin-parity and configuration assignments are very scarce !
especially in the region of Z > 101 and N > 153
Pb,Bi + 48Ca,50Ti,…
Current status of spectroscopic studies for superheavy nuclei
Spin-parity and configuration assignments are very scarce !
especially in the region of Z > 101 and N > 153
Pb,Bi + 48Ca,50Ti,…
Current status of spectroscopic studies for superheavy nuclei
Spin-parity and configuration assignments are very scarce !
especially in the region of Z > 101 and N > 153
Pb,Bi + 48Ca,50Ti,… 248Cm,251Cf + 12,13C,18O,…
Current status of spectroscopic studies for superheavy nuclei
Si PIN photodiodes
18 x 18 mm2
GeGe
Pb shield
Stepping motor
Gas-jet transport
Rotating wheel
120 g/cm2 PET
Catcher foils (
x
40)
Vacuumchamber
261Rf,
257No
from JAEA
Tandem accelerator
Gas-jet transport + Rotating wheel system
257No 13C beam
He/KCl Target chamber Rotating wheel a-g detection system
248Cm target
257No
Gas-jet transport
25 m
Detection efficiency
Si (a) : 80%
Ge (g) : 30%
Experimental setup:
Experimental setup (2):
Gas-jet coupled on-line isotope separator (ISOL)
Conversion electron measurement
4000 5000 6000 7000 8000 9000
0
100
200
a-particle Energy (keV)
Counts
/ 9
.6 k
eV
257No
254Fm
a-singles spectrum of 257
No and a decay curve of 257
No a particles
0 50 100
102
103
T1/2 = 24.5(5) s
Time (s)
Co
un
ts / 7
.0 s
257No a
a-singles spectrum of 257No measured by using gas-jet transport
0
10
20
Counts
/ 0
.4 k
eV
Fm
L x
77
102
124
g-ray spectrum
136
a-g (e) coincidence results for 257
No
0 50 100 150
0
10
20
Energy (keV)
Counts
/ 0
.8 k
eV
77 L
77 M 124 L
124 M
102 L
Electron spectrum
257No155
1/2+
(3/2+)
(5/2+)
3/2+
253Fm153
12
4.1
(7
8)
M1
77
.0 (
10
0)
M1
3/2+ 24.5 s
0
22.3
47.1
124.1 83%
17%
HF=1.3
a
1/2+[620]
3/2+[622]
3/2+[622]
10
1.8
(5
7)
13
6.4
(1
8)
(5/2+) 158.7 < 4%
HF=15
The ground-state configuration
of 257
No was identified.
3/2+[622]
M. Asai et al., PRL 95, 102502 (2005).
a-g(e) coincidence result for 257No
0 100 200 300
0
10
20
Energy (keV)
Counts
/ 0
.8 k
eV
231.4
169.6
61.7
Fm
Ka X
Fm
K X
Fm
L X 259
Noa-g coincidence 259
No
255Fm
0
61.7
231.4
61.7
169.6
231.4
7/2+
9/2+
9/2+
7/2+[613]
9/2+[615]
9/2+[615]
a
9/2+
M1/E
2
M1/E
2
a-g coincidence measurement for 259No
The 169 and 231 keV g rays were
also observed in the EC decay of 255Md (g.s. 7/2-[514]).
Ahmad et al., PRC 61 (2000) 044301.
248Cm(18O,a3n)259No: 13 nb
~900 a counts for 9 days
Production of 259Rf
• 249Cf(13C,3n)259Rf ~ 6 nb
• 248Cm(16O,5n)259Rf ~ 5 nb
• 251Cf(12C,4n)259Rf ~ 100 nb (HIVAP calc.)
It is almost impossible to obtain a large amount of isotopically enriched 251Cf
material !
Mixed Cf target
• 249Cf(62%), 250Cf(14%), 251Cf(24%)
• Residue of 40-year-old 252Cf neutron source
• Small-size target : φ1.4 mm x 420 g/cm2 = 6.5 g
• Total radioactivity : 4.1 MBq
• 600 pnA 12C beam is focused on this small target
3 cm
φ1.4-mm Cf target
Cf
0 50 100 150 200 250 3000
10
20
30
Counts
/ 0
.8 k
eV
Gamma-ray Energy (keV)
1/2+[620]
14
6.7
12
5.6
97
.3
3/2+
5/2+
3/2+[622]
3/2+[622]
a259Rf155
255No153
146.7
0
49.421.1
3.0 s
No
L X
Su
m 97
.3
12
5.6
+ N
o K
aX
14
6.7
259Rf155 a-g coin.
Gate: 8510-8810 keV
8000 8500 9000
0
50
100
a-particle Energy (keV)
Counts
/ 1
0 k
eV
x 1/20
254N
o +
255N
o
257N
o
256N
o
258L
r 8
62
0 259R
f 8
78
0+
257R
f
257R
f 9
02
0
211mP
o 8
88
0
259Rf
a singles255N
o06 s612 s
+259R
f +
257L
r
a-g coincidence spectrum
a-singles spectrum
0
20
40
Counts
/ 0
.4 k
eV
257No
77
.0 2
57N
o
10
1.8
257N
o
12
4.1
257N
o a 4540 countsL X
ra
ys
257N
o
0 50 100 150 200 250
0
20
40
Energy (keV)
Counts
/ 0
.4 k
eV
261Rf +257No7
7.0
10
1.8
12
4.1
261Rf 2370 aL X
ra
ys
261 R
f +
257 N
o
75.7
82.7
Sum
L X
+ L
X
257No 2630 a
Gamma-ray spectra in coincidence with a particles of 261Rf and 257No
• Intense No L X rays
• 75.7 keV 4 counts
• 82.7 keV 5 counts
consistent with E2
261Rf !
7/2[613]
9/2[615]
253Cf155
255Fm155
257No155
257Fm157
259No157
261Rf157
9/2[615] (9/2[615])
9/2[615]
9/2[615]
7/2[613] 3/2[622]0
241
0
231
0
~110
94%
~100%
N = 155
N = 157
~100%
9/2[615]
62
7/2+
9/2+
9/2+
9/2+
9/2+
7/2+
62
9/2+
3/2+
(7/2+)
5/2+
3.5%
75
.78
2.7
Discussion
• Neutron configurations in N = 155 and 157
isotones
• Neutron configurations in N > 157 nuclei
1/2[620]
7/2[613]
3/2[622]
249Cm153251Cf153
253Fm153
253Cf155
255Fm155
257No155
7/2[613] 7/2[613] 3/2[622]
3/2[622]
3/2[622]7/2[613]
1/2[620]3/2+
1/2[620]0
49
208
0
106
178
022
124
99% 98% 83%
17%
N = 153
N = 155
255No153
1/2[620]
3/2[622]
0
147
259Rf155
3/2[622]
Ground-state configuration of N = 155 isotones
and levels in N = 153 daughters
Inverted !
1/2+[620]
7/2+[613]
3/2+[622]
152 152
3/2+[622]
Z = 98, 100 Z = 102, 104, 106
7/2+[613]
Neutron
configuration
Resulting from
deformation change
Inversion of 7/2+[613] and 3/2+[622] orbitals
Macroscopic-microscopic model calculation by T. Ichikawa
7/2+[613] and 3/2+[622] energies
are inverted at Z > 102
Higher-order deformation
parameters contribute to
the change of these
single-particle eneriges
• Z = 98,100 --- 7/2+[613]
• Z = 102,104 --- 3/2+[622]
Reproduced well !
92 96 100 104 108-0.5
0
0.5
S
.P.E
. (M
eV
)
7/2+[613]
1/2+[620]11/2-[725]3/2+[622]9/2+[615]
152
162N = 155
92 96 100 104 108
0
0.1
0.2
Atomic Number
2
4
6
8
n
N = 155
FRLDM + Folded-Yukawa
single-particle potential
Ground states of N=155 isotones
7/2[613]
9/2[615]
253Cf155
255Fm155
257No155
257Fm157
259No157
261Rf157
9/2[615] (9/2[615])
9/2[615]
9/2[615]
7/2[613] 3/2[622]0
241
0
231
0
~110
94%
~100%
N = 155
N = 157
~100%
9/2[615]
62
7/2+
9/2+
9/2+
9/2+
9/2+
7/2+
62
9/2+
3/2+
(7/2+)
5/2+
3.5%
75
.78
2.7
Ground-state configuration of N=157 isotones
152
3/2+[622]
7/2+[613]
1/2+[620]
11/2-[725]
9/2+[615]
152
9/2+[615]
N=153 N=157
Discussions Neutron orbitals
in N > 157 nuclei
257No155
253Fm153
1/2+[620]
3/2+[622]
3/2+[622]
12
41
02
77
a
261Rf1578.28 MeV
68 s
8.22 MeV8.32 MeV
9/2+[615]
83
76
9/2+[615]
0 keV
~110 keV
261Rf (68 s) High-
spin ground state
Discussions Neutron orbitals
in N > 157 nuclei
257No155
253Fm153
1/2+[620]
3/2+[622]
3/2+[622]
12
41
02
77
a
261Rf1578.28 MeV
68 s
8.22 MeV8.32 MeV
2.6 s
8.52 MeV
9/2+[615]
>110 keV
83
76
9/2+[615]
0 keV
1/2+[620] or
3/2+[622]
~110 keV
261Rf (68 s) High-
spin ground state
261mRf (2.6 s)
Low-spin Isomer
257No155
253Fm153
1/2+[620]
3/2+[622]
3/2+[622]
12
41
02
77
a
261Rf1578.28 MeV
68 s
8.22 MeV8.32 MeV
2.6 s
8.52 MeV
265Sg159
269Hs161
9/2+[615]
>110 keV
83
76
9/2+[615]
0 keV
1/2+[620] or
3/2+[622]
1/2+[620] or 3/2
+[622]
1/2+[620] or 3/2
+[622]
8.84 MeV
8.69 MeV
~110 keV
Discussions
261Rf (68 s) High-
spin ground state
261mRf (2.6 s)
Low-spin Isomer
269Hs Low-spin
ground state
1/2+[620] or 3/2+[622]
1/2+[620]
3/2+[622]
Neutron orbitals
in N > 157 nuclei
257No155
253Fm153
1/2+[620]
3/2+[622]
3/2+[622]
12
41
02
77
a
261Rf1578.28 MeV
68 s
8.22 MeV8.32 MeV
2.6 s
8.52 MeV
265Sg159
269Hs161
9/2+[615]
>110 keV
83
76
9/2+[615]
0 keV
1/2+[620] or
3/2+[622]
1/2+[620] or 3/2
+[622]
1/2+[620] or 3/2
+[622]
8.84 MeV
8.69 MeV
~110 keV
Discussions
261Rf (68 s) High-
spin ground state
261mRf (2.6 s)
Low-spin Isomer
269Hs Low-spin
ground state
1/2+[620] or 3/2+[622]
1/2+[620]
3/2+[622]
Neutron orbitals
in N > 157 nuclei
152
3/2+[622]
7/2+[613]
1/2+[620]
11/2-[725]
9/2+[615]
152
9/2+[615]
N=153 N=157
152
9/2+[615]
N=161
1/2+[620]
Calculated neutron orbitals
S. Cwiok et al., NPA 573 (1994) 356.
261Rf
269Hs
2
6
4
Nilsson-Strutinsky approach with an
average Woods-Saxon potential
1/2+[620]
3/2+[622]
11/2-[725]
7/2+[613]
9/2+[615]
1/2+[620]
3/2+[622]
11/2-[725]
7/2+[613]
9/2+[615]
152
162
261Rf157
269Hs161
2
6
Small
Large
4Small
Summary
• Alpha-decay spectroscopy of 255,257,259No and 259,261Rf
was performed at JAEA tandem accelerator using 248Cm
and 251Cf targets and gas-jet transport technique
• Order of neutron orbitals was found to be inverted
between N=153 and N=161 nuclei, indicating the higher-
order deformation change
Ideas of future plan
• Mass-separated Lr isotopes are available (T.K. Sato)
Spectroscopy of Lr
Fission studies of Lr
E(2+) measurement of 260No158 through EC decay of 260Lr
Rotating-wheel a-
detection system
Tape transport system
a-energy spectrum of
mass-separated 256Lr
Lr ionization
efficiency is 40%
Detector station at ISOL beam line
(Presentation by T.K. Sato)
He/CdI2
Analyzing
Magnet Differential
pumping Extractor
Gas-jet
transport
256Lr Beam
Target
Surface ionization
ion source
Rotaing-wheel a-
detection system
Si detectors Lr Lu
Successful ionization and mass separation of Lr isotope
JAEA Tandem accelerator
256Lr (T1/2=30 s)
ProductsBeam
Target
He/KCl
Rotating-wheel a-detection system
Gas-jet transport (~20 m)
Source
Gas-jet • Small Si detector (8 mmf)
• Source-to-detector
distance ~5 mm
• Detection efficiency
~10%
+
Experimental setup
Si
Good a-energy resolution ! FWHM ~ 10 keV
wheel
• Thin source +
JAEA Tandem accelerator
High-resolution a fine-structure spectroscopy
0
20
40
60
Counts
/ 7
.2 k
eV
8222 keV
Sum8323 keVFWHM
= 30 keV
8000 8100 8200 8300
100
101
102
Counts
/ 4
keV 3/2+[622]
3/2+
5/2+
7/2+
3/2+
5/2+ 1/2+
1/2+[620]
Alpha Energy (keV)
Sum
1/2+3/2+5/2
+
3/2+5/2+
7/2+
3/2+[622]
1/2+[620]
3/2+[622] 3/2+
257No
253Fm
02247
124159
205a
8222 keV
8323 keV
FWHM= 12 keV
a-particle spectra of 257No
30 keV
11 keV
Spin-parities and single-particle
configurations can be identified
0
20
40
60
Counts
/ 7
.2 k
eV
8222 keV
Sum8323 keVFWHM
= 30 keV
8000 8100 8200 8300
100
101
102
Counts
/ 4
keV 3/2+[622]
3/2+
5/2+
7/2+
3/2+
5/2+ 1/2+
1/2+[620]
Alpha Energy (keV)
Sum
1/2+3/2+5/2
+
3/2+5/2+
7/2+
3/2+[622]
1/2+[620]
3/2+[622] 3/2+
257No
253Fm
02247
124159
205a
8222 keV
8323 keV
FWHM= 12 keV
FWHM Only through a-energy spectrum
• Rotational-band energies
• Hindrance factors
3350 3360 3370 3380 3390 3400
0
20
40
60
80
100
Channel Number
Counts
/ C
hannel
8446 keV
8405 keV
256No a spectrum
High-resolution a-energy measurements
E(2+) = 42.1 ± 1.3 keV
→ 2+
→ 0+
2+
0+
90%
10%
256No
252Fm
0+
a
g
248Cm(12C,4n)256No → 252Fm
238U(16O,6n)248Fm → 244Cf
238U(12C,6n)244Cf → 240Cm
235U(12C,5n)242Cf → 238Cm
233U(12C,5n)240Cf → 236Cm → 232Pu
7500 7600 7700 7800 7900 8000
0
100
200
300
Energy (keV)
Counts
/ 2
.5 k
eV
7874 2
48 F
m
7831 2
48 F
m
7539 2
49 F
m
248Fm a spectrum
2+
0+
248Fm
244Cf
0+
a
g