First observation of the competitive double-gamma (“γγ/γ”) decay process

¹ Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany
² Department of Physics, University of Saskatchewan, Saskatoon S7N5E2, Canada

^a e-mail: pietralla@ikp.tu-darmstadt.de
^b present addres: Bosch AG, Reutlingen
^c e-mail: hscheit@ikp.tu-darmstadt.de

Published online: 19 January 2016

Abstract

First observation of the competitive double-γ decay process is presented. It is a second-order electromagnetic decay mode. The 662-keV decay transition from the 11/2⁻ isomer of ¹³⁷Ba to its ground state proceeds at a fraction of 2 × 10⁻⁶ by simultaneous emission of two γ quanta instead of one. The observed angular correlation and energy distribution of coincident γ quanta are well described by a dominant M2 – E2 and a minor E3 – M1 contribution to the double-γ decay branch. The data were well accounted for by a calculation using the Quasiparticle Phonon Model.