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Large doses of ionizing radiation delivered to tumors at ultra-high dose rates (i.e., in a few milliseconds) paradoxically spare the surrounding healthy tissue while preserving anti-tumor activity (compared to conventional radiotherapy delivered at much lower dose rates). This new modality is known as “FLASH radiotherapy” (FLASH-RT). Although the molecular mechanisms underlying FLASH-RT are not yet fully understood, it has been suggested that radiation delivered at high dose rates spares normal tissue via oxygen depletion followed by subsequent radioresistance of the irradiated tissue. To date, FLASH-RT has been studied using electrons, photons and protons in various basic biological experiments, pre-clinical studies, and recently in a human patient. However, the efficacy of heavy ions, such as swift carbon ions, under FLASH conditions remains unclear. Given that living cells and tissues consist mainly of water, we set out to study, from a pure radiation chemistry perspective, the effects of ultra-high dose rates on the transient yields and concentrations of radiolytic species formed in water irradiated by 300-MeV per nucleon carbon ions (LET ~ 11.6 keV/μm). This mimics irradiation in the “plateau” region of the depth-dose distribution of ions, i.e., in the “normal” tissue region in which the LET is rather low. We used Monte Carlo simulations of multiple, simultaneously interacting radiation tracks together with an “instantaneous pulse” irradiation model. Our calculations show a pronounced oxygen depletion around 0.2 μs, strongly suggesting, as with electrons, photons and protons, that irradiation with energetic carbon ions at ultra-high dose rates is suitable for FLASH-RT.

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Monte Carlo track chemistry simulations were used to investigate the effects of multiple ionization (MI) of water on the yields (<i>G</i>-values) of the ferrous sulfate (Fricke) dosimeter which was irradiated with low-energy α and lithium ion recoils from the ¹⁰B(<i>n</i>,α)⁷Li nuclear reaction as a function of temperature from 25 to 350 °C. Calculations were performed individually for 1.47 MeV α-particles and 0.84 MeV lithium nuclei with dose-average linear energy transfer (LET) values of ~196 and 225 keV/μm at 25 °C, respectively. The total yields were obtained by summing the <i>G</i>-values for each recoil α and Li ion weighted with its fraction of the total energy absorbed. At room temperature, our <i>G</i>(Fe³⁺) values calculated under aerated and deaerated conditions only agreed well with the experimental results, provided the multiple ionization of water was incorporated in the simulations. This strongly supports the importance of the role of MI of water molecules in the high-LET radiolysis of water. We also simulated the effects of MI of water on <i>G</i>-values for the primary species of the radiolysis of deaerated 0.4 M H₂SO₄ aqueous solutions by ¹⁰B(<i>n</i>,α)⁷Li recoils. As with the Fricke dosimeter, the best agreement between experiment and simulation was found at 25 °C when the MI of water was included in the simulations. It was also shown that <i>G</i>(Fe³⁺) decreases slightly as a function of temperature over the range of 25–350 °C. However, at elevated temperatures, no experimental data were available with which to compare our results.

Biomaterials offer alternative opportunities to build sustainable environment compared to synthetic polymeric materials. Here, we utilized a naturally occurring and plentiful biopolymer, chitin, for the studies on interactive phenomena of a reactive textile dye, Remazol Orange (RO), from aqueous solution. The functional groups and crystallinity of chitin were examined by Fourier transform infrared spectroscopy (FT-IR) and x-ray diffraction (XRD) study. Scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were employed for the exploration of morphology and thermal stability of chitin. In order to investigate the effects of pH, contact time and initial RO concentration, batch studies were performed at room temperature of 25°C. Chitin exhibited a highly pH controlled reversible interaction with RO. RO was bounded 116.3 milligram per gram of chitin at pH 2.0 within 90 minutes of continuous shaking whereas 98.45% (w/w) RO were immediately unbounded from the chitin surface when the in-situ environment was changed at pH 10. Langmuir adsorption isotherm and pseudo-second order kinetic plot indicate homogeneous chemisorption and uniform monolayer of dye molecules on chitin surface. The findings from this study will certainly add value to analytical research leading to advanced applications in separation science and technology.