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The polar experience: IGISOL proposal I77, study of the beta decay of 102,104,105Tc by means of the total absorption
techniqueA. Algora
IFIC-Univ. Valencia
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Contents
• Motivations, original plans
• Experimental setup, preparation
• Experimental problems
• Techniques of analysis
• Monte Carlo simulations of the setup
• Some spectra, first steps
• Future
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Some definitions
)()(
i
i
i
i iii
N
E
tNEtf
Decay energy of the nucleus i
Number of nuclei i at the cooling time t
Decay constant of the nucleus i
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Motivations, original plans
The main motivation
of this work was the
study of Yoshida and
coworkers (Journ. of
Nucl. Sc. and Tech.
36 (1999) 135)
See 239Pu example,
similar situation for
235,238U
239Pu example
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Motivations, original plans
Solution: underestimation of the E energy of some nuclides with half lives in the range of 1000s
Assuming some decay chains with appropriate characteristics, the discrepancy is solved
X chain (released E=1.5 MeV)
X1(T1/2=200 s)→X2(T1/2=800 s)
Our motivation was to measure the beta decay of the proposed nuclei using the total absorption technique.
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In their work (detective work) Yoshida et al. identified some nuclei that may be responsible for the under-estimation of the E component.Possible nuclei that may be blamed for the anomaly were 102,104,105TcExplanation: not correctly measured, certainly suffer from the Pandemonium effect, their half lives are in the range, and their fission yields are also the required to solve the discrepancy
Motivations, original plans
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Experimental setup, preparation
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Experimental setup, preparation
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Experimental setup, preparation
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Experimental setup, preparation
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Experimental setup
Ge det.
TAS det
(Det 1 & det 2).
Tape station
Rad. beam .
Si det.
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Experimental problems, solutions
ZAN Z+1AN-1 + e- + for
ZAN Z-1AN+1 + e+ + for +
ZAN + e- Z-1AN+1 + + xray EC
ZAN
Z+1AN-1
-
The problem of the contaminations:
• T1/2, laser ionization scheme, trap
• In this case the β delayed neutron emission is not a problem
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Experiment preparation
Nucleus T1/2 Cross Sec.
104Zr 1.2s 0.360611
104Nb 4.8s 8.846785
104Mo 60s 28.197895
104Tc 18.3m 11.677034
104Ru stable 0.628251
104Rh 42s 0.004392
104Pd stable 0.000004
Nucleus T1/2 Cross Sec.
105Nb 2.95s 3.113171
105Mo 35.6s 20.985006
105Tc 7.6m 18.378065
105Ru 4.44h 2.091102
105Rh 35.36h 0.030913
105Pd stable 0.000059
G. Lhersonneau et al., Eur. Phys. J A 9 (2000) 385
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The ion guide technique
Generic ion guide: the nuclear reaction products are stopped in a gas and are transported through a differential pumping system into the accelerator stage of the mass separator. The process is fast enough for the ions to survive as single charged ions. The system is chemically insensitive and very fast (sub-ms).
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The IGISOL technique
Details of our experiment:
Beam: 30 MeV proton (5microA)
Target: natural U
Target thickness: 15 mg/cm2
Target dimensions: 10x50 mm, tilted 7 degrees
Yield of 112Rh: 3500 atoms/microC
Tight collimation scheme to avoid contamination of neighbour mases (losses of 25%)
Fission ion guide: 2700 ions/s per mb, eff. of 1.6x10-4 relative to the production in the target
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Cycles for 104Tc (T1/2= 18.3m)
Beam gate
Measuring time
Tape movement
1 h
30 m
T1/2 of possible contaminants: 104Mo (60 s), 104Rh(42 s), 105Tc(7.6m)
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Cycles for 105Tc (T1/2= 7.6m)
Beam gate
Measuring time
Tape movement
12 m
8 m
T1/2 of possible contaminants: 105Mo (35.6 s), 105Rh(4.44 h), 104Mo(60 s), 104Tc(18.3 m),
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104Tc TAS spectrum
Qβ=
560
0 k
eV
Las
t kn
own
leve
l: 42
68
ke
V
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105Tc TAS spectrum
Qβ=
364
0 k
eV
Las
t kn
own
leve
l: 24
04
ke
V
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Techniques of analysis
• We use the methods of analysis developed by the Valencia group. In particular the Expectation Maximization (EM) method
• First step: the implementation of the geometry of the setup for the Monte Carlo simulations and to test it with sources
• Calculation of the response function, and then the analysis itself
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Monte Carlo simulations of the setup: geometry
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Monte Carlo simulations of the setup
The Monte Carlo simulations require the implementation of the geometry in full detail
Example: details of the Si holder and the rollers
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Monte Carlo simulations of the setup
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Monte Carlo simulations of the setup
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Monte Carlo simulations of the setup
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Analysis of 104Tc
Expectation Maximization (EM) method:• modify knowledge on causes from effects
jjji
jjiij fPfdP
fPfdPdfP
|
||
Algorithm:
ik
skik
is
jij
iij
sj fR
dfR
Rf
)(
)()1( 1
Some details:
Known levels up to: 1515 keV excitation
From that level up to the Qβ value we use an statistical model
(Back Shifted Fermi formula for the level density with parameters taken from the RIPL database (102Ru,106Pd)
Branching ratios
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Results of the analysis for 104Tc
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Future
• 102Tc case, 100Tc case
• We need to develop a better tape station system
• There are new possibilities using laser ionization schemes
• ???
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The people involved in the “polar” project
J.L. Tain, B. Rubio, E. Nácher, L. Caballero, J. Agramunt, A. B. Perez, W. Gelletly, L. Batist, A. Garcia, J. Äystö, H. Penttilä, I. Moore, P. Karvonen, A. Jokinen, S. Rinta-Antila, A. Kankainen, T. Eronen, U. Hager, T. Sonoda, J. Hakala, I. N. Izosimov, T. Yoshida, F. Storrer, A. L. Nichols, G. Lhersonneau, K. Burkard, W. Huller, A. Krasznahorkay, A. Vitéz, J. Gulyás, M. D. Hunyadi, A. Algora