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