Radiation–Sensitive Thin Film Dosimeter Based on Polyvinyl Alcohol (PVA)/Hafnium Dioxide (HfO2)/Silver Nitrate (AgNO3) Composite: Colorimetric Characterization and Dose–Response Analysis for Low–Dose Gamma–Ray Applications

The development of sensitive, low–cost, and visually readable dosimeters for low gamma–ray exposures is important for occupational and environmental radiation monitoring and for other low–dose applications. This work investigates a colorimetric and optical thin–film dosimeter based on polyvinyl alcohol (PVA) containing silver nitrate (AgNO3) and hafnium oxide (HfO2). The film was fabricated using a solution–casting technique. The dosimetric response was evaluated over an absorbed–dose range of 22.2–65.2 mGy using diffuse reflectance spectroscopy, Kubelka–Munk (K/S) analysis, CIELAB colorimetry, CMYK image–based analysis, and X–ray diffraction (XRD). Irradiation produced a dose–dependent decrease in visible reflectance and a corresponding increase in optical absorption. The K/S response increased with dose, while CIELAB analysis showed a systematic decrease in lightness and an increase in total color difference (ΔEab∗), reaching approximately 25 at 65.2 mGy. Linear regression of ΔEab∗ over 0–65.2 mGy gave y = 0.399x − 1.0029 with R2 = 0.9845. CMYK analysis also showed a clear dose response, with the yellow channel (ΔY) exhibiting the largest relative change among the chromatic channels. XRD identified monoclinic HfO2 as the dominant crystalline filler phase and showed dose–associated changes in peak intensity, peak position, and the relative prominence of the broad PVA–related feature. At the highest XRD dose, several HfO2 reflections weakened while the broad contribution near 2θ ≈ 19.9–20° became more prominent. These changes are interpreted as dose–dependent structural modification and partial loss of resolved crystalline order rather than definitive evidence of a newly formed crystalline phase. A surface morphology and microstructure analysis was performed on control and γ–ray–irradiated PVA/HfO2/AgNO3 nanocomposite films using scanning electron microscopy (SEM–EDX). The morphological transition to fibrous, tree trunk–like structures seen by SEM is well correlated with the dose–dependent change in composition to higher surface Ag content, supporting the idea that radiation–induced Ag nanoparticle nucleation and growth is the primary degradation mechanism in the irradiated films. The combined optical and colorimetric results demonstrate a measurable response of the PVA/HfO2/AgNO3 formulation in the investigated low–mGy gamma–ray range.