# X-ray Visualization and Quantification Using Fibrous Color Dosimeter Based on Leuco Dye
## 3 Results and Discussion

Table 1: Experimental conditions, viscosities of the polystyrene (PS) solutions, and fiber diameters. Figure 1: SEM images for the fibrous color dosimeters using the composite fibers prepared using the conditions specified in Table 1.  
to the MBTT/Black305 1.0/1.0 and 2.0/2.0 _w/w_ samples were insufficient, because the obtained \(\Delta E\) values are below 10 at any dosages, meaning these color changes color cannot be visually identified in this region. On the other hand, based on the sensitivity criterion, a sufficient sensitivity of 33.28 Gy \(\oplus\)\(\Delta E\) = 10 was obtained for the fibrous color dosimeter with the MBTT/Black305 ratio of 1.0/3.0 _w/w_. Consequently, it is suggested that the Black305 concentration should be at least 30 wt% for the MBTT concentration of 10 wt% for recognizing the color change of the fibrous color dosimeter. In addition, an examination of the morphologies of the composite fibers also shows that these fibers are bead-free, as was found for the experiments in which the dependence on the Black305 concentration was examined. These results suggest that the viscosity of the PS solution controls the fiber morphology regardless of the concentrations of Black305 and MBTT. When the fibrous color dosimeters obtained using increased concentration of MBTT were examined, it was found that the rise of the dose-response curves was improved, and as a result, the sensitivity was successfully improved to 15.36 Gy \(\oplus\)\(\Delta E\) = 10. It is suggested that this improvement in sensitivity is based on the reaction mechanism described below that was first described in our previous study [27]. A kinetic model considering a two-step consecutive first-order reaction for the color-changing in this fibrous color dosimeter was proposed as follows  
\[ \begin{split}\text{MBTT}&\overset{X-ray}{\to} \text{MBTT}+\text{Cl}\\ \text{Cl}+\text{RH}&\text{(polystyrene)}\overset{k_{ 1}}{\to}H^{+}\text{Cl}^{-}+R\\ H^{+}\text{Cl}^{-}+\text{Black305}&\text{( colorless)} \overset{k_{2}}{\to}\text{Black305}-\text{H}&\text{(black)}+ \text{Cl}^{-}\end{split} \]  
At the first step in the reaction scheme, the MBTT in the fibrous color dosimeter directly absorbed the X-rays. Most of the irradiated X-rays are lost due to transmission; however, the MBTT absorbs a small fraction of the irradiated X-rays because of its X-ray absorption property, and radical generation occurs to produce a free radical (Cl\(\bullet\)). Subsequently, the generated Cl\(\bullet\) immediately reacts with the polymer matrix RH (polystyrene) to generate a proton in the second step. This radical-generating reaction has been reported by [PERSON] et al. [34]. The produced H\({}^{+}\) diffuses and reacts with Black305 to cleave the lactone ring of the colorless leuco-form in Black305, and give the black colored dye-form Black305-H in the third step. As a result, the absorbed exposure area gradually changes to a black  
Figure 2: Dose-response curves at 20 \({}^{\circ}\)C for the fibrous color dosimeters using the composite fibers prepared under the conditions specified in Table 1. The black dashed line indicates the point at which the color change can be visually observed. The color bar indicates the color tone corresponding to \(\Delta E\). color according to the absorbed dose, and this color change can be visually observed. In the previous study, we developed a composite resin dosimeter (CRD) film containing a scintillator YAP:Ce that emits ultraviolet light inside the film that was the driving force for the radical generation from the MBTT. However, this CRD film contains a powdery inorganic scintillator YAP:Ce in the film and is unsuitable for use as a fabric because of its low mechanical strength. Furthermore, the sensitivity can be improved by heating based on the proposed thermodynamic mechanism. Figure S3 shows the thermal gravimetric analysis (TGA) curves of the fibrous color dosimeter with a MBTT/Black305 ratio at 3.0/3.0 _w/w_, Black305, MBTT, and PS fiber in air.