Gamma transition intensity determination using multidetector coincidence data Guilherme Soares Zahn a,Ã , Frederico Antonio Genezini a , Cibele Bugno Zamboni a , Manoel Tiago Freitas da Cruz b a Instituto de Pesquisas Energe´ticas e Nucleares, P.O. Box 11049, 05422-970 Sa ˜o Paulo, SP, Brazil b Instituto de Fı ´sica da Universidade de Sa ˜o Paulo, P.O. Box 66318, 05315-970 Sa ˜o Paulo, SP, Brazil article info Article history: Received 14 January 2009 Received in revised form 27 March 2009 Accepted 2 April 2009 Available online 10 April 2009 Keywords: Multiparametric measurements Gamma–gamma coincidence Data analysis Transition intensities Angular measurements abstract This work describes two similar methods for calculating gamma transition intensities from multidetector coincidence measurements. In the first one, applicable to experiments where the angular correlation function is explicitly fitted, the normalization parameter from this fit is used to determine the gamma transition intensities. In the second, that can be used both in angular correlation or DCO measurements, the spectra obtained for all the detector pairs are summed up, in order to get the best detection statistics possible, and the analysis of the resulting bidimensional spectrum is used to calculate the transition intensities; in this method, the summation of data corresponding to different angles minimizes the influence of the angular correlation coefficient. Both methods are then tested in the calculation of intensities for well-known transitions from a 152 Eu standard source, as well as in the calculation of intensities obtained in beta-decay experiments with 193 Os and 155 Sm sources, yielding excellent results in all these cases. & 2009 Elsevier B.V. All rights reserved. 1. Introduction The intensity of gamma transitions is an essential parameter for many applied nuclear physics techniques (like NAA or radiometric measurements); also, in b-decay experiments, the b feeding of the excited levels of the daughter nuclide and the logðftÞ of the corresponding decays are usually deduced from the intensity imbalance in these excited levels. Nevertheless, the precise determination of these transition intensities is usually highly overlooked; a large amount of the decay data found in the most recent compilations come from singles spectroscopy [1], which is a technique that shows serious shortcomings when there is more than one transition with very similar energies, for instance. The way to overcome these limitations is to use gamma–gamma coincidence measurements, where one can easily distinguish between two transitions close in energy by analyzing the coincidence relations with other transitions; these coinci- dence measurements have been used to determine transition intensities for many years (e.g., Ref. [2]), but with the introduction of multiparametric, multidetector arrays, the techniques devel- oped in the early days have become either obsolete, as they use only a single detector pair to do the intensity determination—thus resulting in much lower statistics—or only approximate, explicitly leaving aside the influence of the angular correlation term [3], and frequently deprived of precise experimental uncertainties, quoting only rough estimates [5–11]. On the other hand, experiments aimed at the determination of gamma transition multipolarities or multipolar mixing ratios (d) and spin and parity of excited levels are often performed using angular measurements, either in-beam—like in heavy ion induced reactions—or out-of-beam, in delayed decay or spontaneous fission experiments. In most of these experiments, all the data analysis focuses only on the angular information, leaving aside the relevant gamma intensity information that could be derived from the non-angular coefficients and could lead to the precise determination of some gamma transition intensities. Therefore, in this paper two methods for the determination of gamma transition intensities using angular coincidence measure- ments are presented. The first one uses the normalization parameters of the angular correlation fit to determine the intensities without any approximation; the second one uses a variation of a quite usual procedure, but with a full mathematical treatment that, instead of neglecting the angular correlation effects, makes use of their angular symmetries to, on average, eliminate their influence on the intensity results. 2. Theoretical basis Assume that there are two photons, g a and g b , emitted by a nucleus in rapid succession (it is said that they belong to ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/nima Nuclear Instruments and Methods in Physics Research A 0168-9002/$ - see front matter & 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2009.04.001 Ã Corresponding author. Tel.: +551131339974; fax: +551131339960. E-mail address: gzahn@ipen.br (G.S. Zahn). Nuclear Instruments and Methods in Physics Research A 605 (2009) 339–343