Radiation Measurements 43 (2008) S106 – S110 www.elsevier.com/locate/radmeas Loss of carbonate ester bonds along Fe ion tracks in thin CR-39 films T. Yamauchi a , ∗ , S. Watanabe a , A. Seto a , K. Oda a , N. Yasuda b , R. Barillon c a Graduate School of Maritime Sciences, Kobe University, 5-1-1 Fukaeminami-machi, Higashinada-ku, Kobe 658-0022, Japan b National Institute of Radiological Sciences, 4-9-1 Anagawa, Chiba 263-8555, Japan c Institut Plurisdisciplinaire Hubert Curien (UMR 7178), 67037 Strasbourg Cedex 2, France Abstract In order to identify the chemical modification along nuclear tracks in CR-39 detectors, we have made a series of FT-IR measurements for thin CR-39 plastic films irradiated by Fe ions. The films were reduced in the thickness by long time chemical etchings down to 5 m from as-received CR-39 sheets of 100 m thick. It enabled us to obtain unsaturated IR spectra. The samples were exposed to 147 MeV Fe ions at HIMAC in air. Amount of loss of carbonated ester bonds due to the exposure was assessed from the changes in the absorbance of C&O and C–O–C bonds with Fe fluence. The assessed G-value for destroying carbonate ester bonds was found to be about 10 (scission/100 eV). © 2008 Elsevier Ltd. All rights reserved. PACS: 61.80.Ed; 61.62.Pv Keywords: Latent track; Track chemistry; G-value; CR-39; FT-IR 1. Introduction In our last study on 130 MeV carbon ion tracks in CR-39, we had found that the parts between two carbonate ester bonds in each repeat unit of the polymer networks were segmented into small molecules, including two CO 2 for each, along ion trajectory (Yamauchi et al., 2005a). We think such relatively long part segmentation promises CR-39 to be a prominent track detector. This finding was based on in situ FT-IR mea- surements for the film of 15 m thick at the medium energy line facility of the GANIL, Caen, France. We had confirmed the decrease of ether bonds, 1099 and 1141 cm -1 , and at- tained successfully two important parameters of the G-value of 5.5 (scissions/100 eV) and the corresponding track core ra- dius of 1.1nm. We observed an obvious formation of CO 2 , 2338 cm -1 , and assessed the G-value of 3.6 and track core size of 0.63 nm. Unfortunately we had failed to take into account the escape of CO 2 during the irradiation and the measurements. In addition, we had simply applied a specific mole absorption co- efficient of gaseous CO 2 to this case where the revolution of the ∗ Corresponding author. Tel.: +81 78 431 6307; fax: +81 78 431 6369. E-mail address: yamauchi@maritime.kobe-u.ac.jp (T. Yamauchi). 1350-4487/$ - see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2008.04.044 molecule was suppressed. It was easy to observe the absorption band of CO 2 , but quantitative treatments for this gas were still difficult. FT-IR measurements for thin CR-39 films have been tried by several authors, which were prepared by chemical etchings. For examples, Lounis-Mokrani et al. (2003) studied the chemical and optical modifications of CR-39 films induced by 22.5 MeV proton beams as well as giving a well-summarized assign- ments for the peaks on IR spectra. Tse et al. (2006) examined photo-degradation process in CR-39 films by UV radiation at various wavelengths. Recently, UV-cured CR-39 films on PET were developed for the purpose of radiobiological experiments (Gaillard et al., 2005). These are, however, too thick to obtain an un-saturated IR spectrum for the carbonate ester bonds, from which CO 2 gases are produced by the radiological scission. In the present study, we obtained the thin CR-39 films below 5 m by chemical etchings. We found the G-values of the loss of carbonate ester bonds and assessed the cor- responding track core radius. The obtained result supports our previously proposed view that the part between two carbonate ester bonds are segmented along ion tracks in CR-39.