Characteristics of the solid state nuclear detector CR-39 for neutron radiography purposes Reynaldo Pugliesi *, Marco A. Stanojev Pereira, Marco A.P.V. de Moraes, MaÂrio O. de Menezes Divisa Äo de FõÂsica Nuclear, TFF, Instituto de Pesquisas Energe Âticas e Nucleares, IPEN/CNEN-SP, Caixa Postal 11.049, Pinheiros, CEP 05422-970 Sao Paulo, SP, Brazil Received 2 December 1997; received in revised form 13 April 1998; accepted 14 April 1998 Abstract The solid state nuclear track detector CR-39, together with a natural boron converter screen have been used as an image-detector system for neutron radiography purposes. In order to determine its radiographic characteristics, the image-detector system was irradiated up to neutron exposures around 6  10 10 n/cm 2 in a radiography facility installed at the IEA-R1 Nuclear Research Reactor. The detectors were chemically etched in a KOH (30%) aqueous solution at 708C. The best radiography conditions were obtained for neutron exposures ranging from 1  10 9 to 2  10 10 n/cm 2 and for 25 min etching time. The present results were compared with those determined for other track detectors and discussed according to the theory of the image formation in solid state nuclear track detectors. This theory is based on the optical properties of a single track. # 1999 Elsevier Science Ltd. All rights reserved. 1. Introduction The ability of solid state nuclear track detectors (SSNTD) to register local damages of individual radi- ation events and their insensitivity to visible light, b and g radiations are some of the characteristics that makes these detectors attractive for neutron radiogra- phy (NR) purposes (Fleischer et al., 1975; Lferde et al., 1984). In the NR technique, the sample is irradiated in an uniform neutron beam and a screen converts the trans- mitted thermal neutrons to ionizing radiation which is able to induce damages into the SSNTD. Damages can also be induced by direct collision between fast neu- trons and the bonded hydrogen of the detector. This contribution should be evaluated for the characteriz- ation of SSNTD for NR studies. By means of an ade- quate chemical etching the damages are enhanced, giving rise to tracks which will form a visible image (Lferde et al., 1984). Ilic has proposed a theory, based on the optical properties of a single track, which explains the image formation process in SSNTD (Ilic and Najzer, 1990a,b,c,d). The objectives of the present work were to investi- gate the main characteristics of the SSNTD CR-39 with a natural boron converter screen, for neutron radiography purposes. The optimum etching times and neutron exposures for the best image contrast and res- olution have been determined. The present results are compared with those previously determined for CN-85 (Assunc ° aÄo et al., 1992) and Makrofol-E (Assunc ° aÄo et al., 1994), employing the same methodology used in this work and are discussed according to Ilic's theory. 2. Experimental The NR facility is installed at the radial beam-hole #08 of the 2MW pool type IEA-R1 Nuclear Research Reactor (de Menezes, 1994). The main characteristics of the neutron beam are listed in Table 1. The ex- Applied Radiation and Isotopes 50 (1999) 375±380 0969-8043/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0969-8043(98)00092-X Applied Radiation and Isotopes PERGAMON * Corresponding author. E-mail: pugliesi@curiango.ipen.br.