Nuclear Instruments and Methods in Physics Research A 558 (2006) 497–503 CdZnTe Frisch collar detectors for g-ray spectroscopy Alireza Kargar, Andrew M. Jones, Walter J. McNeil, Mark J. Harrison, Douglas S. McGregor Ã S.M.A.R.T. Laboratory, Department of Mechanical and Nuclear Engineering, Kansas State University, Manhattan, KS 66506, USA Received 28 September 2005; accepted 29 November 2005 Available online 21 December 2005 Abstract Low-energy g-ray spectra were collected from 241 Am, 57 Co, 133 Ba, 198 Au, 137 Cs and 235 U using a 3.4  3.4  5.7 mm 3 CdZnTe detector utilizing an insulated Frisch ring. The CdZnTe detector was fabricated from a single crystal and a copper shim was used as the Frisch collar. Room-temperature energy resolution of 1.45% full-width half-maximum (FWHM) was obtained for 137 Cs at 661.7 keV without electronic correction. The detector fabrication process is described and the resulting energy spectra are discussed. The detector fabrication process is described and the resulting energy spectra are discussed. The detector full-energy-peak intrinsic efﬁciency is reported for different g-ray energies, speciﬁcally from 241 Am, 57 Co, 133 Ba and 137 Cs. r 2005 Elsevier B.V. All rights reserved. PACS: 29.30.Kv; 29.40.n Keywords: Gamma ray detector; Gamma ray spectrometer; CdZnTe detector 1. Introduction CdZnTe has been studied for many years as a material for room-temperature, high-energy resolution g-ray detec- tors. Commercial and prototypical detectors are now available for medical imaging, industrial tomography and astrophysics. However, a simple device for accurately identifying radionuclides has not been available until recently with the advent of the semiconductor Frisch collar spectrometer [1–3]. Previous ‘‘single carrier’’ CdZnTe devices either lacked sufﬁcient energy resolution, were complex to operate, or expensive to manufacture. Energy resolution of planar CdZnTe devices is degraded by poor charge-carrier collection. The problem arises from electron and hole trapping, in which the hole trapping is much more deleterious than the electron trapping. Hole transport properties, such as mobility (m) and lifetime (t), within CdZnTe are generally poor compared to many other semiconductor materials. Various methods have been presented to improve the energy resolution of CdZnTe devices, with most methods concentrating on reducing the degrading effects of hole trapping, including variations using the small pixel effect [4], co-planar grids [5], and geometric weighting [6,7]. The virtual Frisch grid effect in solid-state radiation detectors has been studied in various forms to overcome the problem of severe hole trapping [1–3,7–12]. A brief explanation of the Frisch grid effect [13] and its application for a semiconductor device has been previously presented in literature [7,8]. Devices using contacts applied directly to a semiconductor surface have voltage limitations imposed by leakage currents ﬂowing between the virtual grid region and the collecting anodes. Frisch collar planar devices show spectroscopic improvement with minimal leakage current between the grid and anode [1–3,10–12]. The Frisch collar device also shows enhancement in charge collection efﬁciency without substantially increasing leakage current [3]. Excellent results have been achieved using this technique with the Frisch collar extending the entire length of the detector [12]. It has been shown elsewhere that applying the Frisch collar to a planar detector restructures the weighting potential such that the electrons contribute signiﬁcantly ARTICLE IN PRESS www.elsevier.com/locate/nima 0168-9002/$ - see front matter r 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2005.11.211 Ã Corresponding author. Tel.: 01 785 532 5284; fax: 01 785 532 7057. E-mail address: mcgregor@ksu.edu (D.S. McGregor).