Effects of high neutron doses and duration of the chemical etching on the optical properties of CR-39 G.S. Sahoo a , S.P. Tripathy a,n , S. Paul a , S.C. Sharma b , D.S. Joshi a , A.K. Gupta b , T. Bandyopadhyay a a Health Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India b Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India HIGHLIGHTS  The variation of optical properties of CR-39 at very high neutron dose is analyzed. Etching process is found to play a crucial role for change in optical properties of neutron-irradiated CR-39.  The optical absorbance varies linearly at lower dose, at very high dose absorbance saturation occurs. The dose at which saturation absorbance is observed shifts towards lower neutron dose with increase in etching time.  The rate of decrease in optical band gap with respect to neutron dose is found to be more at higher etching durations. article info Article history: Received 7 January 2015 Received in revised form 13 February 2015 Accepted 28 February 2015 Available online 9 April 2015 Keywords: CR-39 Neutron dosimetry Etching Optical band gap abstract Effects of the duration of chemical etching on the transmittance, absorbance and optical band gap width of the CR-39 (Polyallyl diglycol carbonate) detectors irradiated to high neutron doses (12.7, 22.1, 36.0 and 43.5 Sv) were studied. The neutrons were produced by bombardment of a thick Be target with 12 MeV protons of different fluences. The unirradiated and neutron-irradiated CR-39 detectors were subjected to a stepwise chemical etching at 1 h intervals. After each step, the transmission spectra of the detectors were recorded in the range from 200 to 900 nm, and the absorbances and optical band gap widths were determined. The effect of the etching on the light transmittance of unirradiated detectors was insignif- icant, whereas it was very significant in the case of the irradiated detectors. The dependence of the optical absorbance on the neutron dose is linear at short etching periods, but exponential at longer ones. The optical band gap narrows with increasing etching time. It is more significant for the irradiated do- simeters than for the unirradiated ones. The rate of the narrowing of the optical band gap with increasing neutron dose increases with increasing duration of the etching. & 2015 Elsevier Ltd. All rights reserved. 1. Introduction CR-39 is one of the solid polymeric track detectors (SPTDs) widely used at accelerator and reactor facilities for neutron spec- trometry and dosimetry (Phillips et al., 2006; Castillo et al., 2013). The chemical composition of the detector, C 12 H 18 O 7 , is close to that of human soft tissue (Zhou et al., 2007), which makes the material suitable for neutron dosimetry. The nuclear tracks produced in this polymer as a result of neutron-induced damage are almost per- manent and widely used for radiation detection. The track for- mation in CR-39 is accompanied by changes in structural, optical, mechanical, electrical and chemical properties of the polymer (Calcagno et al., 1992; Tidjani and Watanabe, 1995; Steckenreiter et al., 1997; Fink et al., 1995; Mishra et al., 2000). These changes are caused by cross-linking, free radical formation, chain scission, irreversible bond cleavages, and other processes (Bouffard et al., 1997; Klaumünzer et al., 1996; Marletta, 1990; Lee, 1999). The changes in various properties of CR-39 induced by electrons, protons, alpha particles and swift heavy ions have been in- vestigated by many authors (Lounis-Mokrani et al., 2003; Singh and Prasher, 2004; Sharma et al., 2007; Nouh and Abutalib, 2010; Kumar et al., 2012; Ghazaly and Hassan, 2014; Saad et al., 2014; Abdul-Kader et al., 2014; Butt et al., 2014). Characteristics of this polymer irradiated with neutrons have also been studied by some authors (Kumar et al., 2010, 2011; Kalsi and Agarwal, 2008). It is well-known that the number of tracks increases with the neutron fluence and their quantification becomes difficult when Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/apradiso Applied Radiation and Isotopes http://dx.doi.org/10.1016/j.apradiso.2015.04.002 0969-8043/& 2015 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail addresses: sam.tripathy@gmail.com, tripathy@barc.gov.in (S.P. Tripathy). Applied Radiation and Isotopes 101 (2015) 114–121