Conversion electrons from high-statistics β-decay measurements with the 8π spectrometer at TRIUMF-ISAC

¹ Department of Physics, University of Guelph, Guelph, ON N1G2W1 Canada
² Department of Chemistry, Simon Fraser University, Burnaby, BC V5A1S6 Canada
³ TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T2A3 Canada
⁴ Department of Physics, University of the Western Cape, P/B X17, Bellville, ZA-7535 South Africa
⁵ iThemba LABS, P.O. Box 722, Somerset West 7129, South Africa
⁶ School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
⁷ Departments of Chemistry and Physics & Astronomy, University of Kentucky, Lexington, Kentucky 40506, USA
⁸ Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70808, USA

^a e-mail: pgarrett@physics.uoguelph.ca
^b present address: DESY Photon Science, Notkestrasse 85 D-22607 Hamburg, Germany
^c Present address: Department of Physics, University of Ottawa, 150 Louis-Pasteur, Ottawa, ON K1N 6N5, Canada
^d Present address: Instituut voor Kern-en Stralingsfysica, K.U. Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
^e Present address: Department of Physics, Colorado School of Mines, Golden, Colorado 80401, USA
^f Present address: Department of Physics, Tennessee Technological University, Cookeville, Tennessee 38505, USA
^g Present address: National Superconducting Cyclotron Laboratory, Michigan State University, 640 South Shaw Lane, East Lansing, Michigan 48824, USA
^h Present address: Diamond Light Source Ltd., Diamond House, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0DE, United Kingdom

Published online: 5 September 2016

Abstract

The 8π spectrometer, located at TRIUMF-ISAC, was the world’s most powerful spectrometer dedicated to β-decay studies until its decommissioning in early 2014 for replacement with the GRIFFIN array. An integral part of the 8π spectrometer was the Pentagonal Array for Conversion Electron Spectroscopy (PACES) consisting of 5 Si(Li) detectors used for charged-particle detection. PACES enabled both γ − e⁻ and e⁻ − e⁻ coincidence measurements, which were crucial for increasing the sensitivity for discrete e⁻ lines in the presence of large backgrounds. Examples from a ¹²⁴Cs decay experiment, where the data were vital for the expansion of the ¹²⁴Cs decay scheme, are shown. With suffcient statistics, measurements of conversion coeffcients can be used to extract the E0 components of J^π → J^π transitions for J ≠ 0, which is demonstrated for data obtained in ¹¹⁰In→¹¹⁰Cd decay. With knowledge of the shapes of the states involved, as obtained, for example, from the use of Kumar-Cline shape invariants, the mixing of the states can be extracted.