<p>This study focuses on developing a dye-based aqueous passive chemical radiation sensor to evaluate the absorbed radiation dose across different pH values in both acidic and alkaline conditions. A qualitative and quantitative investigation was conducted on the gamma-induced behavior of azo Congo red (CR) dye within the dose range of 0–1 kGy using a <sup>137</sup>Cs γ-source with a dose rate of 590 Gy/h. UV–vis spectrophotometric analysis revealed an absorption band maximum (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">${\uplambda }_{\text{max}}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="normal">λ</mi> <mtext>max</mtext> </msub> </math></EquationSource> </InlineEquation>) at 497 nm, characteristic of the anionic monomer form of CR, with an optimized concentration <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$\left[{C}_{0}\right]=40$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mfenced close="]" open="["> <msub> <mi>C</mi> <mn>0</mn> </msub> </mfenced> <mo>=</mo> <mn>40</mn> </mrow> </math></EquationSource> </InlineEquation> mg/L determined from Lambert–Beer’s verification curve. Although a red shift in (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">${\uplambda }_{\text{max}}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi mathvariant="normal">λ</mi> <mtext>max</mtext> </msub> </math></EquationSource> </InlineEquation>) at pH 4 has been previously reported, in this study, it remained unchanged, consistently peaking at 497 nm. The bandgap energy (<InlineEquation ID="IEq4"> <EquationSource Format="TEX">${E}_{\text{g}}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>E</mi> <mtext>g</mtext> </msub> </math></EquationSource> </InlineEquation>) of Congo red was determined to be 5.82 eV, indicating potential applications in spectral sensitization, dark and photoconductivity, and the semiconductor properties of organic dyes. The best sensor performance was observed at pH 5 and 10. The absorption peak at pH 4 is highlighted as particularly suitable for dosimetric studies in various radiation dosimetry applications.</p>

Innovative tuning of pH stability in Congo red dye solutions for enhanced gamma radiation dosimetric accuracy

期刊论文
发表日期：

2026年1月1日

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Mahtab Ali Shehzad,
Nadeem Sabir,
Muhammad Sharif,
Kanwal Younas,
Muhammad Shahbaz,
Syed Wajih ul Hassan,
Imran Shakir,
Taqmeem Hussain

摘要

This study focuses on developing a dye-based aqueous passive chemical radiation sensor to evaluate the absorbed radiation dose across different pH values in both acidic and alkaline conditions. A qualitative and quantitative investigation was conducted on the gamma-induced behavior of azo Congo red (CR) dye within the dose range of 0–1 kGy using a ¹³⁷Cs γ-source with a dose rate of 590 Gy/h. UV–vis spectrophotometric analysis revealed an absorption band maximum ( ${\uplambda }_{\text{max}}$ $λ_{max}$ ) at 497 nm, characteristic of the anionic monomer form of CR, with an optimized concentration $\left[{C}_{0}\right]=40$ $[C_{0}] = 40$ mg/L determined from Lambert–Beer’s verification curve. Although a red shift in ( ${\uplambda }_{\text{max}}$ $λ_{max}$ ) at pH 4 has been previously reported, in this study, it remained unchanged, consistently peaking at 497 nm. The bandgap energy ( ${E}_{\text{g}}$ $E_{g}$ ) of Congo red was determined to be 5.82 eV, indicating potential applications in spectral sensitization, dark and photoconductivity, and the semiconductor properties of organic dyes. The best sensor performance was observed at pH 5 and 10. The absorption peak at pH 4 is highlighted as particularly suitable for dosimetric studies in various radiation dosimetry applications.