Radioactivity decay studies of heavy fission products at TRISTAN and ISOLDE�

from Coryell to CARIBU�

William B. Walters�

Department of Chemistry and Biochemistry�University of Maryland�

College Park MD 20742 USA�

This work has been supported by the US Department of Energy under grant DE-FG02-94-ER40834.�

This is a photograph of Charles Coryell taken in about 1954. Charles was in Inorganic Chemist recruited from UCLA in 1942 to head the effort at ORNL to study the fission-produce yields. �

At Cal Tech, he had become and remains famous for a paper… “Pauling and Coryell” that opened Pauling’s life-long study of hemoglobin and blood chemistry. �

Charles’ group discovered element 61 during the war, and named it Promethium, Pm, for the god of fire. The work was published in a 3 volume series with Sugarman.�

And, in 1956, he was the first to identify the solar abundance peaks at N = 50, 82, and 126 with closed neutron shells to provide a basis for r- and s-process nucleosynthesis.�

1912 - 1971�

My plan is to follow the study of fission-product decay from:�

MIT via chemical methods�

TRISTAN on-line mass separation with limited ion-source selectivity�

ISOLDE on-line mass separation with laser ionization, �

�ion-source selectivity and suppression of some elements,�

�and molecular-ion selectivity�

Two theses were prepared in the 1970 time frame at MIT, one by my student, Ken Apt, and one by Coryell’s student, Hasan Erten.�

Sb chemistry: 130,131,132,133Sb decay fast gas chemistry SbH3�

Halogen chemistry, 134,136I 86,87Br�

This is a “big picture chart” showing the location of the MIT work.�

Ce

La

Ba

Cs

Xe

Eu

Sm

Pm

Nd

Pr

Te

Sb

Sn82 83 84 85 86 87 88 89 90 91 92 93 94 95

63

62

61

60

59

58

57

56

55

54

52

51

50

I 53

126 127 128 129 130 131 132 133 134 135 136 137 138 139 140

127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144

130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145

145 146 147 148 149 150 151 152 153 154 155 156 157 158

144 145 146 147 148 149 150 151 152 153 154 155 156 157

143 144 145 146 147 148 149 150 151 152 153 154 155 156

142 143 144 145 146 147 148 149 150 151 152 153 154 155

141 142 143 144 145 146 147 148 149 150 151 152 153 154

140 141 142 143 144 145 146 147 148 149 150 151 152 153

139 140 141 142 143 144 145 146 147 148 149 150 151 152

138 139 140 141 142 143 144 145 146 147 148 149 150 151

77 78 79 80 81

137 138 139 140 141 142 143 144 145 146 147 148 149 150

136 137 138 139 140 141 142 143 144 145 146 147 148 149

135 136 137 138 139 140 141 142 143 144 145 146 147 148

76

At Maryland during the 1970’s, we had been working with 3-detector angular correlations and proposed an extension to 4 detectors for the work at TRISTAN.�

The isotopes that could be studied were the thermal-neutron fission products of 235U.�

This is a summary of work out group performed at TRISTAN. Craig Stone studied the Sn isotopes, Scott Faller worked on the Xe decay, and Dave Robertson� worked on the Ba decay. Ion source development started with Re ionizer for Ba nuclei, then plasma for the Sn isotopes and LaBr6 for Iodine. Finally, we could do the short-lived 127Sn decay. Overall, decays from 27 nuclei were studied.�

Ce

La

Ba

Cs

Xe

Eu

Sm

Pm

Nd

Pr

Te

Sb

Sn82 83 84 85 86 87 88 89 90 91 92 93 94 95

63

62

61

60

59

58

57

56

55

54

52

51

50

I 53

126 127 128 129 130 131 132 133 134 135 136 137 138 139 140

127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144

130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145

145 146 147 148 149 150 151 152 153 154 155 156 157 158

144 145 146 147 148 149 150 151 152 153 154 155 156 157

143 144 145 146 147 148 149 150 151 152 153 154 155 156

142 143 144 145 146 147 148 149 150 151 152 153 154 155

141 142 143 144 145 146 147 148 149 150 151 152 153 154

140 141 142 143 144 145 146 147 148 149 150 151 152 153

139 140 141 142 143 144 145 146 147 148 149 150 151 152

138 139 140 141 142 143 144 145 146 147 148 149 150 151

77 78 79 80 81

137 138 139 140 141 142 143 144 145 146 147 148 149 150

136 137 138 139 140 141 142 143 144 145 146 147 148 149

135 136 137 138 139 140 141 142 143 144 145 146 147 148

76

decaystructure

4+ 644�

2+ 252�

6+ 1132�

6+ 1417�

Our initial interest was in the 144Ba decay to odd-odd 144La, which has been published, and opened our interest in Vladimir Paar’s parabolas. In the process, we also studied 144Ce.�

Chien Chung had worked out this decay scheme containing 400 gamma rays and 80 levels. We had no idea how to publish it, so the data were sent to the Nuclear Data Center. PC’s and Lotus 1-2-3 came along just in time to make it possible to organize the data in a useful way.�

When high-energy beta’s are placed, more neutrino energy is lost compared to the real “lower-energy” beta for which less neutrino energy is lost.�

In the mid 90’s Reg Greenwood asked for the spreadsheet with the gamma list in order to make a comparison with their Total Absorption Spectrum�

2+�4+�3-�

144La 3-�

Literature�

Chung et al.�

Four ~25% Ge detectors�

1979RI09 Z.Phys. A290, 311 (1979)�

C.Ristori, J.Crancon, K.D.Wunsch, G.Jung, R.Decker, K.-L.Kratz�

Half-Lives and Delayed Neutron Emission Probabilities of Short-Lived Rb and Cs Precursors�

RADIOACTIVITY 94,95,96,97,98Rb, 143,144,145,146,147Cs [from on-line separator]; measured T1/2, delayed-neutron emission probabilities.�

1979EP01 Phys.Rev. C19, 1504 (1979)�

M.Epherre, G.Audi, C.Thibault, R.Klapisch, G.Huber, F.Touchard, H.Wollnik�

Direct Measurements of the Masses of Rubidium and Cesium Isotopes Far From Stability�

NUCLEAR STRUCTURE 74,75,76,77,78,79,90,91,92,93,94,95,96,97,98,99Rb; 117,118,119,120,121,122,123,124,126,138,140,141,142,143,144,145,146,147Cs; measured masses; deduced two-neutron separation energies, evidence for deformation around N=60.�

doi: 10.1103/PhysRevC.19.1504 �

1980SC16 J.Phys.(London) G6, 1291 (1980)�

S.M.Scott, W.D.Hamilton, P.Hungerford, D.D.Warner, G.Jung, K.D.Wunsch�

The Neutron-Rich Barium Isotopes�

RADIOACTIVITY 142,144,146Cs [from 235U(n, F), mass separation]; measured Eγ, Iγ, γγ(θ). 142,144,146Ba levels deduced J, π, δ. Interacting boson model.�

1983RE10 Phys.Rev. C28, 1740 (1983)�

P.L.Reeder, R.A.Warner�

Delayed Neutron Precursors at Masses 97-99 and 146-148�

RADIOACTIVITY 97,98,99Rb, 97,98,99Sr, 97,98,99Y, 146,147Cs, 147,148Ba, 147,148La(β-n) [from 235U(n, F), E=thermal]; measured T1/2, β-delayed neutron emission probabilities. On-line mass separation, multiscaling technique.�

doi: 10.1103/PhysRevC.28.1740 �

1976LU02 Phys.Rev. C13, 1544 (1976)�

E.Lund, G.Rudstam�

Delayed-Neutron Activities Produced in Fission: Mass Range 122-146�

RADIOACTIVITY 123,122Ag, 127,128,129,130,131,132In, 128Cd, 133,134Sn, 134,135,136Sb, 136Te, 137,138,139,140,141I, 141,142,143,144,145,146Cs; measured delayed neutrons, T1/2.�

doi: 10.1103/PhysRevC.13.1544 �

OSTIS at Grenoble�

ISOLDE at CERN�

OSTIS at Grenoble�

OSIRIS at Studsvik�

TRISTAN at BNL�

The TRISTAN operation ground to a halt in the late 1980’s owing to safety concerns at the HFBR. OSTIS also was closed.�

Meantime…..�

The data flowing in from Supernova 1987a fueled a new interest in r-process nucleosynthesis that provided motivation for added measurements of the decay and structure properties of nuclei that lie in the path of the r-process. �

Since the Seuss and Urey paper in 1956, there had been much interest in the astrophysical production of heavy elements.�

This report by Coryell came almost immediately after a Seuss and Urey paper reporting good solar abundances..�

129Ag was deemed important on DAY ONE. �

In other words, there were two waiting points, one for capture of neutrons on a slow time scale on elements near stability, and one for nuclei much farther from stability that must be on a faster time scale�

The major BBFH paper appeared in 1957, but was preceded in October, 1956, by an article in Science.�

Stated another way, BBFH were aware of the �Coryell work prior to this article and their seminal article in 1957.�

It was THIRTY years after Coryell, and BBFH before the first successful measurement for the 130Cd half life emerged at ISOLDE. This was a very hard measurement, and did not bode well for further work with the plasma ion source.�

Along came this report from GSI that chemical selectivity could be achieved by the user of laser ionization.�

60 kV�

1996�

A = 127�

A = 128�

Figure by P. Moller�

August 1997�

Setup in 1996 had been done with stable 107Ag which has a ½- ground-state spin. The question was raised about hyperfine interactions and whether some adjustment would help yields for the expected 9/2+ spin for 129Ag. The answer was yes. In other words, hyperfine tuning could provide “isomer-specific” ionization.�

0

500

1000

1500

2000

2500

3000

0

2 104

4 104

6 104

8 104

1 105

10.00 20.00 30.00 40.00 50.00 60.00 70.00

Data 3

Ag-123 Ag-125A

g-12

3 Ag-125

A

0

500

1000

1500

2000

2500

3000

6

8

10

12

14

16

18

20

20.00 30.00 40.00 50.00 60.00 70.00

Hyperfine splitting for 123,127Ag

Ag-123 Ag-127

Ag-

123 A

g-127

Laser frequency

November 1997�

9/2+

7/2+ 343

1/2- 506

Ag47 52

999/2+ 0

7/2+ 98

1/2- 274

Ag47 54

1019/2+ 0

9/2+ 28

1/2- 134

Ag47 56

1037/2+ 0

1/2-

9/2+

Ag47 761237/2+

1/2-

7/2+

Ag47 78125

1/2-

9/2+Ag47 80

127

7/2+

0 0 0

Well established data Speculative351/384 = 0.37 center351/384 = 0.08 edge

These β-delayed neutron data support the presence of β-decaying ½- isomers in 125,127Ag, but not necessarily 123Ag, but Pn could be a factor.�

The search for 129Ag was performed at the “green” setting.�

The astrophysical impact was large as the short half life “lowered the impact of” 129Ag as a major waiting-point nucleus, and also strongly suggested that the lower N = 82 isotones would also have shorter half-lives and also not be major waiting points. Although it was a “theoretical surprise”, any look at the half-lives for the lighter Ag nuclei measured in 1996 could see…… 150…. 100….. 80….. 60….40.�

The successful development and utilization of the Resonance Ionization Laser Ion Source (RILIS) then paved the way to develop ionization schemes for Cd, In, Sn, and Sb.�

The study of the decay of the Cd isotopes was improved significantly by the development of means to suppress ionization of daughter In isotopes. This was done by using a quartz transfer tube onto which the In stuck.�

Jading, Moller, Walters, Mishin, Kratz…. For the CERN Courier�

This drawing exhibits the difference between the measured mass of 130Cd and the value calculated by the FRDM, showing that 130Cd is 1.6 MeV less bound than expected.�

Also shown is the measured position of the 1+ level in 130In that is 740 keV higher in energy than the value calculated prior to the measurement. The measured value can be fitted by a 30% reduction in the proton-neutron interaction strength.�

Hence, there is now evidence that some reduction in both “neutron-neutron” and “proton-neutron” interactions may be needed.�

131Cd: 68(3) ms 132Cd 97 (10) ms 133Cd 57(10)�

The 68 (3) ms half-life and 3.5% Pn values for 131Cd remain somewhat anomalous and deserve more attention.�

The green dot is the 1986 point whereas the red dots are from the 1999 measurements performed with RILIS. One observation is that, at that time, nearly all calculated half-lives were HIGHER the values eventually observed.�

Cd�

unpublished�

0.1

132

STABBa

Cs

Xe

I

Te

Sb

Sn

In

Cd

Ag

56

55

54

53

52

51

50

49

48

47

133 134 135 136 137 138 139 140

133 134 135 136 137 138 139 140 141

131

142134 135 136 137 138 139 140 141

135 136 137 138 139 140 141

136 137 138 139 140 141

137 138 139 140 141

138 139 140 141 142 143 144 145 146

142 143 144 145

142 143 144

142 143

132 133 134 135 136 137 138 139

STAB

83 m 13 d 18 m 11 m 14 s 11 s 4 s 2.2 s

32 m 9 m 1.1 m 25 s 1.8 s 1.8 s 1.0 s 0.6 s30 y

3.8 m 14 m 40 s 14 s 1.7 s 1.25 s 0.5 s 0.4 s

6.6 h 83 s 25 s 6.5 s 2.3 s 0.9 s 0.5 s 0.2 s

42 m 19 s 18 s 2.5 s 1.4 s

2.5 m 0.8 s 1.7 s 0.9 s

40 s 1.4 s 1.0 s

0.3 s 0.20s 0.17 s

1431.60.1

3.01.00.2.04

15211010

63

.03

67

1

2416

172.9

0.1 850.53 s 0.25 s 0.27 s 0.1 s 0.1 s

22 30 58 75 500.5 s

40

0.35 s

50

0.1 s

90

92 ms

95

0.14 s

90

0.4 s

12

49 s

10 s

STAB2.5 m

13 d2 y

9 h

2.3 h 20 h 52 m

25 m 3 d 15 m

6 m 23 m 3 m

2. m 1.7 m 56 s

0.8 s 0.60s 0.5 s

132

133

131

135

136

137

132

133

131

135

136

134

134

132

131

135

134

133

130

129

128

130

129 130

STAB

STAB

STAB

19 s

15 m

53 mSTAB

28 h

4 m

300 ms

55 m

9 s

4 m

58 s

30 h

3.7 m

39 m

1.2 s

7 m

129 130 131 132128127

129 130 131128127126

3 h

2 d5 d

1.5 h

0.3 s0.3 s

68 ms 97 ms

46 ms79 ms 58 ms98 ms

0.4 s 0.3 s

30.8 s

3 m

35 ms

133

57 ms125

155

162104242

During the past 15 years, the half-lives have been measured from 129Ag to 139Sb. The work at N = 82 has improved the ability to extrapolate “down the N = 82 chain” to make better estimates for the other N = 82 “likely waiting-point isotopes”. The IMPACT is that it is now possible to provide a “reasonable” model fit for the r-process yields!!!! These data make it possible to account for the “steep” left slope of the peak owing to the shorter-than-expected half-lives up the N = 82 chain, and, perhaps, somewhat longer-than-expected half-lives for the Sn and Sb nuclei.�

123 to 139�

One major impact of these measurements has been the ability to identify model calculations that do not provide good fits to the data. For 128Pd, the range is from 30 to 50 ms. For 126Ru, the maximum is only about 20 ms…..not much waiting with that half-life.�

135

51 84Sb

135

50 85Sn

7/2-

7/2+(5/2+) 282

Qβest 9000 keV

νf7/2νh9/2πh11/2 Sn7/2-

πd5/2

πg7/2

4000-5000

Pn = 21(5)%

Sn = 3100 keV

1015

1207

707

1118

282

733

1015

925

1207

134

50 84Sn

15/2+

19/2+1343

11/2+725

1072

1246

2+

4+

6+

0+

24018+

23/2+1972νf7/2νh9/2

νf7/2νf7/2

t1/2 = 530(25) ms

5/2- 9/2-

134

51 83Sb

0-1-

031731

7

n

n

135

51 84Sb

7/2+

6463/2+ 7185/2+ 73411/2+ 9179/2+ 9411/2+10037/2+

12177/2+110715/2+

125719/2+

207223/2+

OXBASH CALCULATION: B. A. BROWN, 2000

10995/2+

12365/2+

Korgul et al.

Bhattaccharyya et al.

13871105

1387 145611

7414

56

20891807

The 718-keV level is ~ 70 % single-particle d5/2.

133

51 82Sb

7/2+

5/2+ 963

This is the first level scheme from Jason Shergur’s study of 135Sn decay to 135Sb.�

Sn50 83

1337/2- 0

3/2- 854

νh9/2 15619/2-

νp3/2

νf7/2

1/2- 1390νp1/2

5/2- 2004νf5/2

13/2+ 2694(200)

νi13/2

Sn = 2455 (45)

133

51 82Sb

7/2+

5/2+ 962

2793πh11/2

πd5/2

πg7/2

11/2-

3/2+ 2440πd3/2

1/2+ 2xxxπs1/2

001

23

45

6

7

2

3 45

12

3 4 5

6

1

1

1

010

1

134

51 83Sb

01- 80-

3582-

8041-

9812-

12872-

16731-

21391-

23341-

28850-

30171-

KH208

3- 351

00- 131-

3832- 3303-

8851-9352-

19001-

21701-

24301-

10+ 9+

8

2797-

4425- 5554- 6176-

13518-

24079+

271410+

3057-

4225-5654-6456-

16568-

28619+282910+

Experiment high-spin

beta decaySn-134 Sn-135-n

23

10756-

12834-13285-

15165-

1385(5-)13073-14513- 14754-

19102-

2

2- 1330

10+1+

~38501+38541+

νf7/2

νf7/2

νf7/2

νp3/2

νp3/2

νp3/2

νf5/2

νf5/2

νi13/2

νh9/2

νh9/2

πh11/2

πh11/2

πg7/2

πg7/2

πg7/2

πg7/2

πg7/2

πd3/2

πd5/2

πd5/2

πd5/2

26 ps2.3 ns

This result was obtained with an ISOLDE ion source using Sulfur gas, enriched in 34S in the ion source, creating SnS+ ions that are 34 mass units heavier than the isobaric Cs that is strongly ionized. The ½+ level shown below was populated in beta-delayed neutron decay from 136Sn decay. The calculation had been previously published indication the level should be at 527 keV…… ..it was found at 523 keV.�

110�The good news is that the most exotic nuclei will be at the highest mass and well separated from the the daughter, slower-decaying nucleus.�

Thank you for your attention.�