A novel Al 2 O 3 fluorescent nuclear track detector for heavy charged particles and neutrons G.M. Akselrod a , M.S. Akselrod a, * , E.R. Benton b , N. Yasuda c a Landauer, Inc., Stillwater Crystal Growth Division, 723 1 2 Eastgate Rd., Stillwater, OK 74074, USA b Eril Research, Inc., 1110 S. Innovation Way, Ste. 100, Stillwater, OK 74074, USA c National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan Received 18 August 2005; received in revised form 22 December 2005 Available online 10 March 2006 Abstract A novel Al 2 O 3 fluorescent nuclear track detector (FNTD), recently developed by Landauer, Inc., has demonstrated sensitivity and functionality superior to that of existing nuclear track detectors. The FNTD is based on single crystals of aluminum oxide doped with carbon and magnesium, and having aggregate oxygen vacancy defects (Al 2 O 3 :C,Mg). Radiation-induced color centers in the new material have an absorption band at 620 nm and produce fluorescence at 750 nm with a high quantum yield and a short, 75 ± 5 ns, fluorescence lifetime. Non-destructive readout of the detector is performed using a confocal fluorescence microscope. Scanning of the three-dimensional spatial distribution of fluorescence intensity along the track of a heavy charged particle (HCP) permits reconstruction of particle trajectories through the crystal and the LET can be determined as a function of distance along the trajectory based on the fluorescence intensity. Major advantages of Al 2 O 3 :C,Mg FNTD over conventionally processed CR-39 plastic nuclear track detector include superior spatial resolution, a wider range of LET sensitivity, no need for post-irradiation chemical processing of the detector and the capability to anneal and reuse the detector. Preliminary experiments have demonstrated that the material possesses a low- LET threshold of <1 keV/lm, does not saturate at LET in water as high as 1800 keV/lm, and is capable of irradiation to fluences in excess of 10 6 cm 2 without saturation (track overlap). Ó 2006 Elsevier B.V. All rights reserved. PACS: 29.40.Wk; 61.80.Hg; 61.80.Jh; 61.82.Ms; 61.72.Ji; 78.70.g; 78.55.m Keywords: Radiation measurements; Nuclear track detectors; Heavy charged particles; Linear energy transfer; Confocal fluorescence microscopy; Aluminum oxide crystals; Three-dimensional imaging 1. Introduction The radiation dosimetry community has long sought a dosimeter that overcomes the numerous limitations of cur- rent passive detector technology. Such a passive integrating detector would be sensitive to charged particles over a broad range of LET, require little or no post-exposure chemical processing, be capable of non-destructive (i.e. multiple) readouts using fully automated equipment, and possess the capability of being erased and reused. Thermo- luminescent detectors (TLD) [1] and optically stimulated luminescence detectors (OSLD) [2], while fully reusable and highly sensitive to low-LET radiation, can only mea- sure high-LET radiation of heavy charged particles (HCP) with reduced efficiency and possess little or no sensitivity to neutrons. In addition, TLD can only be read out a single time. Solid state detectors such as CR-39 plastic nuclear track detector (PNTD) [3] possess a sensitivity to radiation with LET in water (LET 1 H 2 O) above 5 keV/lm and to neutrons (via neutron-induced proton recoil tracks) [4], but lack sensitivity to lower LET radiation. CR-39 PNTD can only be used once and must be chemically etched prior 0168-583X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2006.01.056 * Corresponding author. Tel.: +1 405 3775161; fax: +1 405 7432966. E-mail address: makselrod@landauerinc.com (M.S. Akselrod). www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B 247 (2006) 295–306 NIM B Beam Interactions with Materials & Atoms