International Conference on Nuclear Data for Science and Technology 2007
DOI: 10.1051/ndata:07685

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, D. Cortina-Gil¹, M. Fernandez-Ordoñez¹, J. Giovinazzo⁴, D. Henzlova², B. Jurado⁴, J. Pereira¹, F. Rejmund⁵ and O. Yordanov<sup>2, 6

1</sup>  Universidad de Santiago de Compostela, 15782 Santiago de Compostela, Spain
²  Gesellschaft für Schwerionenforschung mbH (GSI), 64291 Darmstadt, Germany
³  Institut de Physique Nucléaire, 91406 Orsay Cedex, France
⁴  CENBG, 33175 Gradignan, France
⁵  GANIL, Bd Henri Becquerel, BP. 55027, 14076 Caen Cedex 5, France
⁶  INRNE, 1784 Sofia, Bulgaria

teresa.kurtukian@usc.es

Published online: 21 May 2008

Abstract
Very neutron-rich nuclei near the A = 195 r-process waiting point were produced as projectile fragments from a ²⁰⁸Pb primary beam at GSI, Darmstadt, by cold fragmentation. After in-flight separation, the fragments were implanted in an active catcher, and time correlations to the subsequent beta-decay were established. Due to the periodic operation cycles of the synchrotron, providing the primary beam, the background shows a complex time structure, which prevents applying well established analytical methods to extract the half-life information. A new mathematical analysis method has been developed, which is based on a Monte Carlo code, simulating the time sequence of implantation and beta detection according to the experimental conditions, leaving the beta lifetimes and the beta detection efficiency as free parameters. In addition, both the analysis of the experimental data and the simulation were performed in time-reversed sequence. The ratio of forward/backward time spectra contains the information of the "true" fragment-beta correlations. Half-lives were obtained from two-dimensional fits of the measured and simulated ratios of time correlations in forward- and backward-time direction by the least-squares method, being the lifetime and the beta-detection efficiency the two fitting parameters. Half-lives of 8 heavy neutron-rich nuclei approaching the r-process waiting point A = 195 have been determined.

© CEA 2008