New technique to determine beta half-lives in complex background conditions - PowerPoint PPT Presentation

1 / 12
About This Presentation
Title:

New technique to determine beta half-lives in complex background conditions

Description:

New technique to determine beta half-lives in complex background. conditions ... active stopper. 4 double-side strip detectors: surface: 5x5 cm2. thickness 1 mm ... – PowerPoint PPT presentation

Number of Views:20
Avg rating:3.0/5.0
Slides: 13
Provided by: teresakurt
Category:

less

Transcript and Presenter's Notes

Title: New technique to determine beta half-lives in complex background conditions


1
New technique to determine beta half-lives in
complex background conditions
  • T. Kurtukian-Nieto1, J. Benlliure1, K.-H.
    Schmidt2, L. Audouin3, F. Becker2, B.
    Blank4, E. Casarejos1, M. Fernandez-Ordoñez1, J.
    Giovinazzo4, D. Henzlova2, B. Jurado4, J.
    Pereira1, F. Rejmund5, and O. Yordanov2
  • 1 Universidad de Santiago de Compostela, E-15782
    Santiago de Compostela, Spain
  • 2 Gesellschaft für Schwerionenforschung mbH
    (GSI), D-64291 Darmstadt, Germany
  • 3 Institut de Physique Nucléaire, F-91406 Orsay
    Cedex, France
  • 4 CENBG, F-33175 Gradignan, France
  • 5 GANIL, Bd Henri Becquerel, BP 55027, 14076 Caen
    Cedex 5, France

2
Layout
  • Introduction
  • Experiment
  • Numerical analysis method
  • Results
  • Conclusion

3
Experiment
208Pb(1 A GeV)Be (107 ions/s)
4
Implantation-decay correlations
Spill length 2 s Cycle 10 s
5
Numerical analysis method
  • conventional analysis tools, based on analytical
    time-distribution functions could not be applied
  • A new analysis procedure has been developed to
    extract the ß-decay half-lives by using a
    numerical function

Background evaluation (uncorrelated events)
backward-time correlations
6
Monte-Carlo simulation
  • The time sequence of fragment implantation and ß
    detection are simulated according to the
    experimental conditions observed in the FRS
  • spill sequence
  • fragment implantation rate
  • background rate during spill and pause
  • leaving two free parameters the lifetimes and
    the efficiency
  • The code produces time-correlation spectra in
    forward- and backward-time direction.

7
Fitting procedure example
spillpause
only pause
8
Fitting procedure example
spillpause
  • The ratios typical behaviour
  • Starts with a value larger than one.
  • It decreases and crosses the value of one at
    about 2?.
  • At still larger times, the ratio decreases
    further due to the 'shielding' of background
    correlations in forward time direction
  • We learn that it is necessary to make
  • time correlations covering several spills in
    order to distinguish between different lifetimes.

only pause
9
Fitting procedure example
  • Results for 195Re

only pause
spillpause
T1/2 s
T1/2 s
10
Applicability of the method
NF be the total number of implanted fragments
nb the background rate of beta-like signals
e the beta detection efficiency
Nº. of 'true' beta decays detected during a time
T1/2 after the implantation
The N. of beta-like background detected in the
same time is
From the experience we gained during the analysis
we found that we can expect to obtain reliable
results with our analysis method if
11
Results
Nuclide T1/2 / s(experiment) Gross Theory1 FRDM RPA Gross Theory2
202Ir125 113 8.5 68.4
199Ir122 6 (3 -5) 96.6 370.6
198Ir121 82 377.1
200Os124 6 (4 -3) 16 187.1
199Os123 5 (4 -2) 17.2 106.8
196Re121 3 (1 -2) 5.1 3.6
195Re120 61 10.3 3.3
194Re119 10.5 16.1 70.8
1 T.Tachibana, et al. Proc. ENAM95, Arles, 1995,
p.7632 P. Möller, et al. Phys. Rev. C 67, 055802
(2003) (incl. deformation and 1. forbidden)
12
Conclusions
  • We have developed a new numerical method for
    extracting the half-life information from
    delayed-coincidence experiments in the case of
    complex background conditions.
  • The method is also applicable for any other kind
    of complex time-dependent background.
  • With this method, we have provided a tool which
    considerably extends the possibilities for
    exploiting the manifold advantages of the
    in-flight technique in determining half-lives of
    exotic nuclei.
  • Beta half lives have been measured for 8 new
    neutron-rich isotopes.
  • Many measured values deviate strongly from the
    Gross Theory and from the FRDM RPA Gross
    Theory. (T1/2 values are smaller than expected.
    r-process is faster.)
Write a Comment
User Comments (0)
About PowerShow.com