93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of...

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Isomers and intermediate-spin states of 93,95,96 Rb Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray spectroscopy at neutron guides •Prompt-fission studies with large arrays •Summary of Recent Results Excited states in 93,95,96 Rb •Future projects at JYFL

Transcript of 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of...

Page 1: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Isomers and intermediate-spin states of 93,95,96Rb

Gary Simpson LPSC Grenoble

•Experimental techniques•Delayed γ-ray spectroscopy at neutron guides•Prompt-fission studies with large arrays

•Summary of Recent ResultsExcited states in 93,95,96Rb

•Future projects at JYFL

Page 2: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

• Lack of data on single-particle orbits outside 78Ni – νh11/2

• Can extract this information from multi-quasiparticle isomers but expected T1/2<500 ns

• Rb nuclei good candidates to search for such isomers

• Can 78Ni be used as a closed core?

• Can the shell-model reproduce the onset of defomation?

Page 3: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

• ToF gives v• Chamber gives K.E.→can get m→Observe isomer decays from the mass-identified complementary fragment

Use different instrumentsFIFI (FIssion Fragment Indentifier) Spectrometer (Manchester) at PF1B neutron guide

Page 4: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Lots of shielding

Compact array of 15 Ge crystals, each ~60 % rel. eff.(UK-France loan pool + Cologne Cluster)

Page 5: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Use known isomers to calibrate mass of complementary fragment measured by FIFI

Mean neutron evaporation 2.4 n/fission

Page 6: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Can see and mass-identify several new isomers

Aisomer=93.2(4)

Aisomer=94.8(4)

Page 7: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Isomeric half lives obtained

G. Simpson et al. Phys. Rev. C 82 (2010) 024302

Page 8: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Gate on strong, delayed lines in 248Cm data-see same lines as in FIFI data set + new ones

X rays give Z of complementary (Pr) and hence Z of isomeric fragment (Rb)So isomer belongs to 93Rb

Page 9: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Further gating gives the following level scheme

Can get spins using ang. corr.

Page 10: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Results in agreement with

Page 11: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Gate on 191 and 619-keV lines in 252Cf data set

A=95 isomer

New decay scheme

Isomer originates from πg9/2 orbit

Page 12: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray
Page 13: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Shell-Model Interpretationby K. Sieja (GSI/Strasbourg)

CD-Bonn potential, G-matrix renormalizationAntoine code (m-scheme)78Ni core π 1f5/2, 2p1/2, 1p3/2, 1g9/2ν 2d5/2, 3s1/2, 2d3/2, 1g7/2, 1h11/2Up to 7 p-h excitations from Z=38, N=56

Page 14: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Shell-model Interpretation

27/2- isomer has πg9/2 ν(g7/2 h11/2) configuration

Page 15: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Why does the isomeric lifetime go from 100 ns to 100 ms when going from 95Y to 97Y?

d5/2 is full, now filling s1/2 → 27/2- isomer ~1 MeV lower in energy and cannot decay to 23/2-

Is there an equivalent 27/2- ms isomer in 95Rb?

Page 16: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray
Page 17: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Problems with the interaction-recently shown that 78Ni is not a good inert core for Cu isotopes

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J. A. Pinston et al. Phys. Rev. C 71 (2005) 064327

Spherical

Deformed

Challenge for the shell model-shape coexistence

Page 19: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

The Lohengrin Fission-Product Spectrometer

Separates according to A/q and E/q

No ion source - no chemical selectivity

Neutron flux 5×1014 n/s/cm2

~2×1012 fissions/s(3.5 mg of 239Pu 742 b)

Flight time 1-2 µs -can use isomers

A/δA~250

Rates at focal point ~ 3000 ions of 132Sn /s

Solid angle < 2 x 10-5

Page 20: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

A=100 Q=20 E=100 MeV

Q ,A

1680

1785

1890

1995

20100

21105

22110

∆E

ET

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Page 22: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

A = 100 region

N=59

Previous studies in this area used beta-decay which could only populate spherical s1/2, d3/2 and g7/2

Page 23: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Kr nuclei

S. Naimi et al. Phys. Rev. Lett. 105 (2010) 032502

M. Keim et al. Nucl. Phys. A586 (1995) 219

Page 24: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Combination of Eurogam II and Lohengrin data Observation of 3 different shapes in 99,101Zr and 97Sr

Intermediatedeformationβ2=0.32

Spherical

Strongly deformed β2= 0.41

W. Urban, J.A. Pinston et al. Eur. Phys. J. A 16, 11 (2003)

Page 25: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

ν9/2[404] was assigned to these states from

Partial half-lives of decays to known states -gives spin 9/2

Angular correlations between states of known spin.

An assignment of 7/2 was rejected from branching ratios of transitions decaying out of isomeric states (Alaga rules)

ν9/2[404] orbital should show little alignment (spin is along symmetry axis)

Ix=√(I+1/2)2-K2 where Ix is spin proj. on symmetry axis

Page 26: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Schematic representations of deformed configurations of odd-mass Sr and Zr isotones

h11/2

g9/2

56

58

60

E/hω0

β2

Kleinheinz et al.P.R.L. 32, 68 (1974)Similarity to lanthanides11/2[505] n-hole states

9/2+

3/2-

1/2-

3/2- band 9/2+ band

N=59

core

Page 27: 93,95,96 Gary Simpson LPSC Grenoble •Experimental ... · Isomers and intermediate-spin states of 93,95,96Rb. Gary Simpson LPSC Grenoble •Experimental techniques •Delayed γ-ray

Conclusions• First delayed spectroscopy of fission products at a

neutron-guide• New isomers found and identified with T1/2~100 ns

in Rb isotopes• Shell-model interpretation works reasonably well –

but can be improved• 27/2- isomer of 93Rb has πg9/2 ν(g7/2 h11/2)

configuration• 9/2+ isomer of 95Rb has a πg9/2 configuration• If 96Kr is not strongly deformed, a new or improved

explanation must be found for shape changes in the A=100 region