Fission-Fragment Spectroscopy @ the I.L.L.

Gary Simpson LPSC, Grenoble

Recent Studies

Stopped-Beams pool

A large Ge array on a
thermal neutron guide?
 The ILL
• Operates the world's most intense neutron
source (1.5 x 10 15 n/s/cm2)
• International lab (12 member countries)

• Houses ~45 instruments

• 430 staff members

• Budget ~90 M Euro

• ~225 days of beam per year

800 experiments
per year

1500 visiting
scientists per year
 The Lohengrin Fission-Product Spectrometer
(Radioactive beam Facility)
Flight time 1-2 μs
-can use isomers

Separates according to
A/q and v/q

No ion source - no
chemical selectivity
Rates at focal point
~ 1500 ions of 132Sn /s A/δA~250 ~2'1012 fissions per
second at target
(3.5 mg of 239Pu 742 b)
 Experimental Setup

129
Sn

Conversion-electron
detection efficiency ~25%.
Detect conversion electrons
> 15 keV
Big improvements in Gamma-ray detection efficiency

Pool for stopped beams? (β-decay, Isomers)

Would give big improvements at GANIL, ALTO,
ISOLDE, ILL ....
 Stopped-Beams Pool

Factor of ~3 improvement for isomer experiments at

Lohengrin (~order of magnitude for γ−γ coincidences)

Factor of ~2 improvement for fast-timing

experiments at ISOLDE
Easier improvement than increased beam intensity

Optimal use of resources?

Swap 4-6 Clovers from and array of ~25 Clovers with phase-1 s
4-6 Clovers factor of 2-3 gain for stopped beam experiments

Only 16 channels -easy to integrate into existing DAQs

Already made bids for funding

:French ANR: G. Simpson, G. Georgiev, F. Ibrahim
:Belgium: G. Neyens
 Deformation and Shape Coexistence in the A~100 region
(LPSC, ILL, Warsaw, Manchester)

Only observation of any gammas in this nucleus

π(g9/2)
ν(h11/2)

Spherical Deformed
π[3/2 431] ν[3/2 541]

Quadrupole moment of 2-
ground state measured
J. Genevey et al. Phys. Rev. C 71, 064327 (2005)
First observation of any gamma rays in 95Kr

Structure does not seem to change far

from stability!

J. Genevey et al. Phys. Rev. C 73, 037308 (2006)

 region 132Sn

(LPSC, ILL, Napoli, Warsaw)

-These nuclei
µs isomers in the vicinity of the are very difficult
to measure
magic 132Sn
-symmetric
134 136
fission region
Xe Xe

136I 138I 13
6
128Te 130Te 132
Te 135Te X
e
127Sb 129Sb 130Sb 131Sb 133Sb 136Sb

124
Sn 125Sn 126Sn 127Sn 128Sn 129Sn 130 132Sn
Sn
1
123
In 125In 126In 127In 128In 129 130In
In

125
Cd
J. Genevey et al. Phys. Rev. C 67, 054312 (2003)
First substantial spectroscopic information in 129In
A. Scherillo et al. Phys. Rev. C 70, 054318 (2004)

Complements previous beta-decay studies

Calculation by Napoli Group
effective n-n interaction
deduced from CD-Bonn
potential. Correctly reproduces
the observed level scheme.

Simplistically yrast states

in 129In are from νh11/2-2
coupled to πg9/2-1

E(I)
unique parity
states +
effective
I interaction

n-n or p-p
j2

States are lower in energy due

to attractive ν−π interaction
 Cd and In nuclei close to 132Sn
A. Scherillo et al, Phys. Rev. C 70 (2004) 054318.

 Collectivity in Cd nuclei?
(shell quenching?)

 Why are 2+ states systematically

higher in calculations?

Need lifetime measurements (or

Coulex)

Similar phenomena observed

208
in
equivalent nuclei near Pb.
 Isomer Collaboration

LPSC Grenoble -J. Genevey, J.A. Pinston, G. Simpson

ILL -R. Orlandi, A. Scherillo, I.
Tsekhanovich
Napoli -A. Covello, A. Gargano
Cologne -N. Warr, J. Jolie
 Spontaneous Fission

Nuclei produced in mass range ~70-160

~4 neutrons per fission -secondary fragments remain very

neutron rich!

6-8 h mean spin (observed spins up to ~20 h) -reaction

multiplicity ~10

~100 nuclei available for prompt fission study per fissioning

system -with current technology e.g. Euroball/Gammasphere
(Normally use γ−γ−γ coincidences. To build level schemes).

One experiment published ~60 articles including several

PRLs (248Cm + EurogamII) -optimal use of resources?

Can also measure

lifetimes (ps DPM, ps-ns plunger) -A.G. Smith
g-factors -A.G. Smith
 Example of Physics
Combination of Eurogam II and Lohengrin data
Observation of 3 different shapes in 99,101Zr and 97Sr

Very deformed β2=0.41

Intermediate
deformation
β2=0.32

Spherical

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

 Schematic representations of deformed
configurations in Sr and Zr isotones
E/hω0

Kleinheinz et al. N=59

h11/2 P.R.L. 32, 68 (1974)
Lanthanide
3/2-

5/ 2 core
[53
3/ 2] 9/2+
2[
54 1/2-
1]
3/2- band 9/2+ band
1/

60
2[
55

58
0]

56

4 ]
0
[4
2
9/

β2
g9/2
Disadvantage of s.f. -limited to two sources (252Cf, 248Cm)
Solution -use thermal-neutron-induced fission
(tried early 1990's W.R. Philips, J.L. Durell & co TESSA
Brookhaven)
Change mass distribution by changing target
 Compare with Spontaneous fission

~30 new nuclei available for study !

Propose to use two

different targets 241Pu
(1010 b) and 235U (560 b)

-(233U)
 Thermal neutrons on 241Pu

132
Mass 85 region Sn region
See properties of nuclei close to Nuclei have a simple structure -good for testing
78Ni (r-process nuclei). the shell model far from stability.
Few orbits play important roles in Shell model calculations work quite well for In
deformation nuclei close to 132Sn -but less well away from it.
 Neutron Guides
Reflect neutrons!
No fast neutrons
No gamma-ray background
Flux up to 1.3 x 1010 n/s/cm2
(PF1B)
Thermal neutrons have meV energy

Beam profile on target

 Key Measurements and Nuclei

Spectroscopy (γ−γ−γ) In and Cd nuclei close to 132Sn

Neutron-rich mass 80-95 region

Yield measurements for reactors (heavy region not well measured -current
reactors are operating at 40 % of their current theoretical efficiency!)

Lifetimes (DPM, plunger)

g-factors (Missing gR values in several regions!)

 What kind of array do we need?

Need γ−γ or γ−γ−γ coincidences to build level schemes -strong function of array efficiency.

~10 % efficiency(at 1.3 MeV) needed, but must be able to handle multiplicity 10.

What is available?

Winter shutdown for most accelerators -

but ILL still runs

ILL direction are willing to

write a letter of support

Welcome collaborators

Far future AGATA 201?

even s.f. (γ−γ−γ)
 Facts and figures about fast neutrons in proposed experiment

2 x105 fissions/s
2.5 neutrons/fission (241Pu)
detectors at 15 cm
x2 weeks = 2.1 x 108 n/cm2 on detectors

detectors at 20 cm
x2 weeks = 4.7 x 107 n/cm2 on detector

Limit Euroball 1.5 x108 per detector

Limit ORTEC = 1 x109 /cm2

Compare with spontaneous fission experiments at Gammasphere

e.g. J. K. Hwang, Phys. Rev C 73, 044316 (2006)
252
Cf ~28 μCi (3% fission)
3.1 x105 fissions/s
3.76 neutrons/fission (252Cf)
detectors at 25.4 cm
x 2 weeks = 1.7 x 107 n/cm2 on detectors
=8.5 x 108 per detector
 Experiments using Neutron Guides

-Search for isomers 30 ns> t1/2>1 μs

FiFi -ILL, LPSC, Manchester,
Cologne, Warsaw
 Collaboration

LPSC Grenoble -J. Genevey, J.A. Pinston, G. Simpson

Univ. Warsaw -W. Urban, A. Zlomaniac
ILL -R. Orlandi, A. Scherillo, I. Tsekhanovich
Manchester Uni -J.L. Durell, A.G. Smith, A. Thallon, B.J. Varley
Uni. of Cologne -J. Jolie, N. Warr
Napoli -A. Covello, A. Gargano

Other members of Lohengrin Community

ILL -Ulli Koster

University of Uppsala -H. Mach
Unversity of Camerino -D. Balabanski
IPN Orsay -G. Georgiev
Bruyeres-Le-Chatel -J.M. Daugas