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

Contents

• Motivations, original plans

• Experimental setup, preparation

• Experimental problems

• Techniques of analysis

• Monte Carlo simulations of the setup

• Some spectra, first steps

• Future

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

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

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.

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

Experimental setup, preparation

Experimental setup, preparation

Experimental setup, preparation

Experimental setup, preparation

Experimental setup

Ge det.

TAS det

(Det 1 & det 2).

Tape station

Rad. beam .

Si det.

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

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

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).

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

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)

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),

104Tc TAS spectrum

Qβ=

560

0 k

eV

Las

t kn

own

leve

l: 42

68

ke

V

105Tc TAS spectrum

Qβ=

364

0 k

eV

Las

t kn

own

leve

l: 24

04

ke

V

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

Monte Carlo simulations of the setup: geometry

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

Monte Carlo simulations of the setup

Monte Carlo simulations of the setup

Monte Carlo simulations of the setup

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

Results of the analysis for 104Tc

Future

• 102Tc case, 100Tc case

• We need to develop a better tape station system

• There are new possibilities using laser ionization schemes

• ???

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