Method for releasing carbon foils from substrates

The performance of a carbon foil (C-foil) as a charge stripper in an accelerator is directly affected by its condition and quality. C-foils are fabricated by evaporating carbon onto a substrate. Therefore, a suitable technique must be established for depositing and removing C-foils from substrates. The selection of appropriate releasing agents is crucial for the removal process. C-foils with thicknesses less than 0.1 mg/cm2 were produced using the arc discharge method, wherein chloride materials were used as releasing agents. The magnetron sputtering method is suitable for manufacturing C-foils thicker than 0.1 mg/cm2 using appropriate releasing agents, such as fluorine-based or silicon-based agents. The contact angle analysis demonstrates a negative relationship between the C-foil thickness and the wettability of the substrate treated with an appropriate releasing agent. The possibility of using ionic liquids as novel releasing agents is also investigated

Organic-Gelatin-Free Nanocomposite Fricke Gel Dosimeter

We report a nanocomposite Fricke gel (NC-FG) dosimeter prepared using only Fe²⁺ and nanoclay in water, without any organic gelling agents. This dosimeter gels due to its thixotropic properties and exhibits linear energy transfer (LET)-independent radiological properties under carbon ion beam irradiation. The radiation sensitivity of this dosimeter was 1.8 [s^–1 kGy^–1], which is three times higher than that reported previously (0.6 [s^–1 kGy^–1]) for a similar dosimeter containing gelatin. The Fe³⁺ yield was determined to be 0.19 μmol/J by evaluating the difference in spin–lattice relaxivity between Fe³⁺ and Fe²⁺. A further increase in the radiation sensitivity was observed upon addition of the hydrated electron scavenger N₂O, suggesting the reduction of Fe³⁺ by a hydrated electron. LET-dependent variations of the contributions of OH radicals and hydrated electrons compensate each other in the oxidation yield of NC-FG. This is the main mechanism of the suppression of LET effects in the Bragg peak compared to conventional Fricke dosimeters. The radiation-induced oxidation yield <i>G</i>(Fe³⁺) can be described by the stoichiometric equation {<i>G</i>(Fe³⁺) = <i>G</i>(OH) – <i>G</i>(e_aq^–) + 2<i>G</i>(H₂O₂) + <i>G</i>(H)} with the reported LET dependence of the primary yield of water decomposition radicals. The calculated results are in approximate agreement with the absolute value of the experimental oxidation yield of NC-FG. The effects of the addition of small amounts of radical scavengers (nitrate, selenate, or cadmium) are also evaluated. The sensitivity was divided into two types, and influences of intermediate radicals after scavenging reaction are indicated

Development of a high-density highly oriented graphite stripper

High-density highly oriented graphite sheets provided by Kaneka Corporation have been applied as stripper disks for heavy-ion acceleration at RIKEN RI Beam Factory since 2014. The graphite sheets withstand increasing amounts of beam intensity. We observed the graphite sheets after beam irradiation with an electron microscope and their lifetime was discussed

Heavy-ion-induced mutations in the gpt delta transgenic mouse: Effect of p53 gene knockout

The influence of the loss of p53 gene on heavy-ion-induced mutations was examined by constructing a new line of transgenic mice, p53 knockout (p53-/-) gpt delta. In this mouse model, deletions in lambda DNA integrated into the mouse genome are preferentially selected as Spi- phages, which can then be subjected to molecular analysis. Mice were exposed to 10 Gy of whole-body carbon-ion irradiation. The carbon ions were accelerated to 135 MeV/u by the RIKEN Ring Cyclotron. The p53 defect markedly enhanced the Spi- mutant frequency (MF) in the kidneys of mice exposed to C-ion irradiation: the Spi- MF increased 4.4- and 2.8-fold over the background level after irradiation in p53-/- and p53+/+ mice, respectively. There was no significant difference in the background Spi- MF between p53-/- and p53+/+ mice. Sequence analysis of the Spi- mutants indicated that the enhancement of kidney Spi- MF in p53-/- mice was primarily due to an increase in complex or rearranged-type deletions. In contrast to the kidney, the p53 defect had no effect on the Spi- MF in liver: Spi- MF increased 3.0- and 2.7-fold after the irradiation in p53-/- and p53+/+ mice, respectively. Our results suggest that p53 suppresses deletion mutations induced by heavy-ion irradiation in an organ-specific manner

Whole Three-Dimensional Dosimetry of Carbon Ion Beams with an MRI-Based Nanocomposite Fricke Gel Dosimeter Using Rapid T1 Mapping Method

MRI-based gel dosimeters are attractive systems for the evaluation of complex dose distributions in radiotherapy. In particular, the nanocomposite Fricke gel dosimeter is one among a few dosimeters capable of accurately evaluating the dose distribution of heavy ion beams. In contrast, reduction of the scanning time is a challenging issue for the acquisition of three-dimensional volume data. In this study, we investigated a three-dimensional dose distribution measurementmethod for heavy ion beams using variable flip angle (VFA), which is expected to significantly reduce the MRI scanning time. Our findings clarified that the whole three-dimensional dose distribution could be evaluated within the conventional imaging time (20 min) and quality of one crosssection

Whole Three-Dimensional Dosimetry of Carbon Ion Beams with an MRI-Based Nanocomposite Fricke Gel Dosimeter Using Rapid T1 Mapping Method

MRI-based gel dosimeters are attractive systems for the evaluation of complex dose distributions in radiotherapy. In particular, the nanocomposite Fricke gel dosimeter is one among a few dosimeters capable of accurately evaluating the dose distribution of heavy ion beams. In contrast, reduction of the scanning time is a challenging issue for the acquisition of three-dimensional volume data. In this study, we investigated a three-dimensional dose distribution measurement method for heavy ion beams using variable flip angle (VFA), which is expected to significantly reduce the MRI scanning time. Our findings clarified that the whole three-dimensional dose distribution could be evaluated within the conventional imaging time (20 min) and quality of one cross-section