arXiv:nucl-ex/0612017v2 5 Jul 2007 Linear polarization sensitivity of SeGA detectors D. Miller a,b,* , A. Chester a,b , V. Moeller a,b , K. Starosta a,b , C. Vaman a , D. Weisshaar a a National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824, USA b Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA Abstract Parity is a key observable in nuclear spectroscopy. Linear polarization measurements of γ-rays are a probe to access the parities of energy levels. Utilizing the segmentation of detectors in the Segmented Germanium Array (SeGA) at the NSCL and analyzing the positions of interaction therein allows the detectors to be used as Compton po- larimeters. Unlike other segmented detectors, SeGA detectors are irradiated from the side to utilize the transversal segmentation for better Doppler corrections. Sensitivity in such an orientation has previously been untested. A linear polarization sensitivity Q ≈ 0.14 has been measured in the 350-keV energy range for SeGA detectors using α-γ correlations from a 249 Cf source. Key words: segmented germanium detectors, polarization sensitivity, gamma-ray Compton polarimeters PACS: 29.30Kv 1. Introduction 1.1. Overview Identifying parity of energy levels in nuclei is vi- tal in understanding phenomena far from the val- ley of beta-stability such as the emergence of new shell gaps and the migration of single-particle lev- els with unique parities [1]. When a nucleus decays from an excited state, the information about the parity of the state can be extracted from the linear polarization and angular distribution of the radia- tion. With knowledge of the angular distribution, * Corresponding Author: Tel.: +1-517-333-6416; fax: +1- 517-333-5967. Email address: damiller@nscl.msu.edu (D. Miller). determination of the parity change requires only the knowledge of the sign of the polarization. 1.2. Compton Polarimeters Polarimeters based on the sensitivity of Comp- ton scattering to polarization have been built and used for fifty years [2] by the nuclear structure com- munity. The first and simplest setup consisted of two γ -ray detectors where one functioned as the scatterer and the second served as the analyzer. This setup has been optimized for maximum po- larization sensitivity [3] at the expense of photo- peak efficiency using a small scatterer and four an- alyzing crystals. Composite detectors such as the Clover [4] are natural Compton polarimeters when analyzing scattering between neighboring crystals. The sensitivity is reduced due to the proximity of Preprint submitted to Elsevier Science 8 February 2008