## 1 Introduction  
Radiochromic films undergo a visible color change directly after exposure to radiation without chemical processing for the development of the image by a dye creation through a radiation-triggered polymerization process. This feature has made radiochromic films a preferable tool for two-dimensional dose verification and quality assurance (QA) of external beams such as photons, electrons and protons used in radiation therapy [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30]. A commercial radiochromic film (Gafchromic, International Speciately Products, Wayne, NJ, USA) appeared for industrial use in the late 1980s [31]. While this polydiacetylened-based product had a good dose-response, the initial products of Gafchromic film had some issues related to sensitivity, uniformity and reproducibility in color development [32, 33, 34]. These issues have been well solved by continuous improvements of dosimetric properties in subsequently developed models (HD-810, MD-55, HS and EBT series) [20, 22, 35, 36, 34, 25, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75,  
These preferable features of radiochromic films have good potential for application to many other situations other than radiation therapy. The self-developing coloration soon after exposure to any type of radiation would be effectively used for periodical dose verifications of various radiation sources in industry and research. It is also expected that robust, light-insensitive radiochromic films would be desirably used for individual monitoring of occupational radiation exposure of workers who routinely handle high-level radiation sources or those who will be involved in the initial responses to nuclear/radiological emergencies. In these occasions, the ability of a sensitive radiochromic film that can detect in real time a high-dose exposure according to the color change recognized by the naked eye would be helpful for earlier recognition of the occurrence of a radiological accident, which enables us to save the lives of highly exposed casualties by taking necessary medical actions without delays. In the prompt decision on the best medical treatment in such an urgent situation, it is indispensable to know immediately the accurate radiation dose and exposure timings of the individual victim. Though there are several dosimetry techniques applicable to such situations [37; 38; 39; 40], the dose assessments with these techniques are performed in retroactive manners and have limitations for on-site use as the measurements need large, non-portable equipment to read the thermally/optically stimulated luminescence or electron spin/paramagnetic resonance signals from the samples exposed to radiation. Some approaches using biological samples such as tooth enamel and peripheral blood lymphocyte need several days for processing the samples including the elaborate dose calibration. Although real-time monitoring would be possible if the subject carried an electronic personal dosimeter, such small electronic devices cannot accurately respond to pulsed high-dose radiation exposure because of the count-loss problem, which could be averted by using a radiochromic film applicable to a wide dose range. For using radiochromic films for the on-site dosimetry required under such emergency situations, however, the current procedure of measuring films is an issue in terms of practicality, as it requires elaborate tasks for the acquisition of image data using a flatbed scanner and subsequent analyses on color intensities using an image processing software [20; 25; 36]. It would be beneficial if we could measure the color intensities of any radiographic films more simply and shortly with portable devices only.