Pergamon Radiation Measurements, Vol. 26, No. 5, pp. 739-741, 1996 Copyright © 1996 ElsevierScienceLtd Printed in Great Britain.All rights reserved PII: 81350-4487(96)00076-5 1350-4487/96$15.00+ 0.00 SHORT COMMUNICATION ENHANCEMENT OF TRACK CONTRAST IN CN 85 BY METHYLENE BLUE S. MAYAKI and A. TIDJANI* Laboratoire des DSTN, Facult6 des Sciences, Universit6 CAD de Dakar, Dakar-Fann, S6n6gal (Received 23 January 1996; revised 18 July 1996) 1. INTRODUCTION One of the fundamental problems involved in the evaluation of SSNTD is the determination of the track integral density value. This may he achieved by several methods: (a) direct count by an optical microscope; (b) an image analyzer system involving an optical microscope coupled with a computer con- trolling the process; or (c) a spark counter that is appropriate to LR-115 type II. The two last methods are very convenient but their cost is relatively high. They also suffer from inefficiency due to the recovery of tracks in the case of the spark counter and to the phase contrast optic in the image analyzer. On the other hand, optical microscopy is often used with a degree of efficiency very close to 100%. The main disadvantage of this method is that it is tedious and time consuming; however, it is still the method of choice in our laboratory. Often it is desirable to make easier the recognition of tracks. Methods of improving contrasts, enlarging the track, or marking its location clearly, have been investigated by several groups. Contrast enhance- ment can be achieved by filling etched tracks with metals (Possin, 1970), dye (Cross and Tommasino, 1967) or ink (Lal et al., 1968). Other more or less sophisticated procedures exist. The present report deals with enhancing track contrast to improve the count with optical microscopy of CN 85. For this, a staining procedure recently used to make trees permanently visible in irradiated polymers is tested herein (Ashcraft and Eichhorn, 1978; Tidjani and Arnaud, 1995). 2. EXPERIMENTAL Cellulose nitrate, named CN 85, manufactured by Kodak Path6 (France) is used in this study. It has a thickness of about 100 ~tm of cellulose nitrate (C6HsOsN2)n. The thickness of each detector was measured using a "Millitron 12.00 IC" comparator (Mahr Ltd) before and after any chemical process. CN 85 samples were irradiated in a vacuum chamber with an 24'Am source and protected from alpha particles with oblique incidence by using a collimator. This one also serves to confine the area of interest. To obtain a best efficiency of registration the energy of ~t-particles that was emitted by the 24'Am source was reduced from 5.4 to 3.4 MeV by interposing a polycarbonate absorber between the alpha source and the detector. Use of appropriate irradiation conditions ensures that a convenient number of latent tracks will be obtained. After the or-irradiation operation, CN 85 samples were pro- cessed at a temperature of(60 _+ 1)°C in 2.5 N NaOH solution. Etching time is set at 2 h. After etching, the detectors were cleaned with water and dried at room temperature. Tracks counting and measurements of track diameters were performed with a microscope coupled with a TV monitor. The ratio W/VB that describes the shape and size of the track and known as the track sensitivity was assessed (but not discussed). We used traditional methods for calculating the bulk etch rate v.: • the change in the detector thickness (Fleischer et al., 1975); or • the mass change of the detector (Henke etal., 1986). *To whom all correspondence should be addressed. 739