~ Pergamon Radiation Measurements, Vol. 24, No. 4, pp. 407-410, 1995 Copyright © 1995 ElsevierScienceLtd Printed in Great Britain. All rights reserved 1350-4487/95 $9.50 + .00 1350-4487(95)00021-6 CHARACTERISTICS OF TL AND PTTL GLOW CURVES OF GAMMA IRRADIATED PURE Li2B407 SINGLE CRYSTALS Y. KUTOMI,* M. H. KHARITAt and S. A. DURRANI School of Physics and Space Research, University of Birmingham, Birmingham BI5 2TT, U.K. (Received 27 September 1994; revised 18 January" 1995; in final form 15 February 1995) Abstract--The TL glow curve of X-ray irradiated pure and Cu-doped Li2 B 4 07 shows that the most intense TL peak is at 160°C. In the present work the characteristics of the TL and PTTL glow curves from gamma irradiated pure Li2B407 single crystal samples (prepared by Mitui Kinzoku Kougyo, Japan) have been studied. The samples were irradiated with different gamma doses (from 0.5 up to 500 Gy) using a 6°Co gamma ray source at a dose rate of 78 Gy h -~. The TL glow curve shows three intense peaks (at ~ 160, 260 and 305°C) and three weak ones (at ~ 110, 140 and 220°C). The most intense TL peak is at 160°C, which agrees with the TL glow curve from X-ray irradiated samples [Kutomi Y. and Tomita A. (1990) TSEE and TL of Li2 B407 : Cu single crystals. Radiat. Prot. Dosim. 33, 34%350]. The 305°C peak in gamma irradiated samples also appears to be very intense, which indicates its possible use in high-dose high-temperature dosimetry. Further, the characteristics of the PTTL glow curve have been studied as a function of ultraviolet exposure and number of repeated PTTL cycles. INTRODUCTION It is well known that lithium borate (Li2B4OT) pow- der is a nearly tissue-equivalent material (Jayachan- dran et al., 1968) used as a converter screen for thermal neutrons, and also in albedo dosimetry. Li2B407 has very low photon energy dependence (Aitken, 1985), and its single crystals (used in this work) are transparent to visible light, which makes them very effective for the collection of emitted light from the inner parts of the sample. The aforemen- tioned properties, together with the resistance to humidity (due to its stoichiometric matrix compo- sition) and easy handling compared with powder samples, make the Li2B407 single crystal ideal for thermoluminescence dosimetry. In this work the properties of TL and PTTL glow curves of gamma irradiated pure Li2B407 single crystals have been investigated. prior to irradiation. The TL and PTTL signals were obtained by heating the sample up to 410°C in an oxygen-free, dry nitrogen atmosphere at a heating rate of 2°C s ~ (unless otherwise stated). A filter to cut off the infrared radiation was used between the sample and the quartz-window photomultiplier tube (EMI 9804QA, with high sensitivity and good spec- tral response, peaking at 400 nm). The samples were irradiated at room temperature, while placed in a 3 mm thick aluminium holder and using an 11.6 TBq (~313 Ci) 6°Co gamma ray source at a dose rate of 78Gy h ~. The phototransferred thermolumines- cence (PTTL) measurements were carried out using a low-pressure mercury lamp emitting chiefly at a wavelength of 254 nm (which produced a power density of 300 #W cm -2 at 152 mm below the source position), with a high efficiency filter to minimize the visible portion of the emitted light. EXPERIMENTAL METHODS AND SAMPLE PREPARATION Pure Li2B407 single crystals were obtained from the Mitui Kinzoku Kougyo Co., Japan, as chips of ~0.7ram thickness which were cut from a large single crystal and polished with no. 500 emery cloth. Twenty samples (each ~4 × 4mm and 37.8mg in weight) were used repeatedly. The samples were annealed at 750"C for 60 min in a platinum crucible RESULTS AND DISCUSSION The TL glow curve consists of three intense peaks, designated I~, II~ and III~, at ~ 160, 260 and 305°C, respectively, and three weak peaks, designated Iw, IIw and III w, at ~ 110, 140 and 220'~C, respectively. (The focus in this work will be on the three intense peaks.) In order to investigate the heating-rate effects, the samples were annealed at 750°C for 60 min and then given a gamma dose of 50 Gy. Three samples were * Permanent address: Faculty of Engineering, Kansai University, Suita, Osaka 564, Japan. t Permanent address: Atomic Energy Commission, Damascus PO Box 6091, Syria. 407