Thermally Controllable Decolorization of Reusable Radiochromic Complex of Polyvinyl Alcohol, Iodine and Silica Nanoparticles (PAISiN) Irradiated with \(\gamma\)-rays  
[PERSON]  
1 Department of Radiation Biophysics, Research Institute for Radiation Biology and Medicine,  
Hiroshima University, Hiroshima 734-8553, Japan 1  
2 Advance Radiation Research, Education, and Management Center, Tokushima University,  
Tokushima 770-8501, Japan; [EMAIL_ADDRESS]  
2  
[PERSON]  
2 Advance Radiation Research, Education, and Management Center, Tokushima University,  
Tokushima 770-8501, Japan; [EMAIL_ADDRESS]  
2  
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material to the fingertips, a worker using any radiation source could continuously monitor her/his hand exposure in real time and prevent excessive radiation exposure as necessary by stopping work soon after detecting a change of its color. A material employed for this objective at a variety of workplaces needs to satisfy the following requirements:  
* Good usability: The monitor should be small, lightweight, robust and easily manageable, so that the work would be undisturbed;
* High detectability: Radiation-induced color change should be easily recognized soon after exposure of a few Gy (i.e., threshold dose level of major deterministic effects on human health);
* Stability: It should be stable in terms of dosimetric properties for a month (i.e., the general period for recording individual doses of workers);
* Safety: It should be non-hazardous for both humans and the biosphere;
* Sustainability: It should be reusable so that it would not produce waste.  
With consideration of these requirements, the authors surveyed relevant studies on radiochromic materials that were developed and tested based on similar concepts [7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30]. As a consequence, the authors focused on a complex composed of polyvinyl alcohol (PVA), iodide (I) and silica nanoparticles (SiNP), named \"PAISiN\" here. This complex was developed and investigated with 30 kV X-rays by [PERSON] et al. [17]. They found that the addition of SiNP as a reductant worked as a radiation sensitizer for enhancing the radiochromic reaction. They also observed that the color of PAISiN changed from white to red immediately after irradiation with >0.5 Gy X-rays, and the coloration reverted to the initial state in 24 h by the reducing action of SiNP. The distinct color change was considered to be more easily detected by the naked eye than other radiochromic materials using ferric ions or dye. In addition, its reusability was thought to be desirable in views of both practicality and sustainability. It is known that similar radiochromic materials having the PVA-I matrix show notable natural coloration under room temperature due to auto-oxidation [27; 29], which would be a critical shortcoming for routine monitoring of personal doses which are performed on a monthly basis in general. Furthermore, this complex has an economic advantage since it can be made of inexpensive reagents and inorganic materials used in an ordinary laboratory environment. However, the dosimetric properties of PAISiN for commonly used forms of radiation such as \(\gamma\)-rays and the thermal stabilities of its coloration/decolorization processes are yet to be examined.