Radiation Measurements 43 (2008) 1354 – 1356 www.elsevier.com/locate/radmeas CO 2 treatment and vacuum effects in proton beam micromachining of PADC E. Baradács a , ∗ , I. Csige b , I. Rajta b a Department of Environmental Physics, University of Debrecen, H-4026 Debrecen, Poroszlay u. 6, Hungary b Institute of Nuclear Research of the Hungarian Academy of Sciences, H-4001 Debrecen, P.O. Box 51, Hungary Received 23 October 2007; accepted 11 February 2008 Abstract Polyallyl diglycol carbonate (PADC) has been shown to be a suitable material as a thick resist for proton beam writing [Rajta, I., Baradács, E., Bettiol, A.A., et al., 2005. Optimisation of particle fluence in micromachining of CR-39. Nucl. Instrum. Methods B 231, 384.]. This material is commonly used as an etched track type particle detector. In most cases it is used to detect alpha particles in normal air conditions. However, to use this material as proton or alpha micromachinable resist, one needs to irradiate the material in vacuum. In this work, we investigated the effects of vacuum on the micromachinable properties of PADC. Our investigations proved that there were no drawbacks of the vacuum storage of the samples; so we concluded that PADC is a suitable material as a PBM resist in this respect, too. Another part of the current work concentrated on the effect of post-irradiation CO 2 treatment of the samples. Such a treatment increased the radiation sensitivity of PADC, i.e. reduced the required irradiation fluence. We have found that approximately 60% of fluence that of not-treated samples was sufficient to develop fully the radiation damaged structures. © 2008 Elsevier Ltd. All rights reserved. Keywords: CR-39; Polyallyl diglycol carbonate (PADC); Vacuum effects; Fluence sensitivity; CO 2 treatment; Proton beam writing 1. Introduction Polyallyl diglycol carbonate (PADC) has been shown to be a suitable material as a thick resist for proton beam writing (Rajta et al., 2005). This material (also known by its commercial name: CR-39), is commonly used as an etched track type particle detector. In most cases it is used in environmental radon detec- tors, where it detects alpha particles in normal air conditions. However, to use this material as proton or alpha micromachin- able resist, we need to irradiate the material in vacuum. It has been found that if the irradiation of PADC material is made in vacuum, then the storage of it in vacuum for a few hours be- fore and least for a few minutes after the irradiation reduces its sensitivity for the development of tracks of nuclear parti- cles by chemical etching (Csige et al., 1988). We have sus- pected that this phenomenon may play an important role in the process of proton beam micromachining of this material; ∗ Corresponding author. Tel.: +36 52 509 200; fax: +36 52 416 181. E-mail address: baradacs@dragon.unideb.hu (E. Baradács). 1350-4487/$ - see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2008.02.007 therefore in this work, we have investigated the effects of vac- uum on the micromachinable properties of PADC. On the other hand it has also been found that treatment of PADC after irradiation and before etching in CO 2 significantly enhances its sensitivity for etching single (proton and alpha-) particle tracks (Csige, 1997). Therefore the other part of the current work concentrated on the effect of post-irradiation CO 2 treatment of the samples on the micromachinable properties of PADC. 2. Experimental Tastrak type etched track detector, a PADC material, man- ufactured by Track Analysis System Limited (Bristol, UK) was used in the experiments as a target material. Samples of PADC were cut from large sheets of Tastrak with nominal di- mensions of 275 mm × 300 mm × 1 mm. The sample size was 12 mm × 16 mm × 1 mm. Proton irradiation of PADC samples was performed at the nuclear microprobe facility at Institute of Nuclear Research, Debrecen, Hungary (Rajta et al., 1996; Kertész et al., 2005;