Production of a fluorescence probe in ion-beam radiolysis of aqueous coumarin-3-carboxylic acid solution, 2; Effects of nuclear fragmentation and its simulation with PHITS

Maeyama, Takuya*; Yamashita, Shinichi; Taguchi, Mitsumasa; Baldacchino, G.*; Sihver, L.*; Murakami, Takeshi*; Katsumura, Yosuke

Coumari-3-carboxylic acid scavenges OH radical produced in water radiolysis, leading to production of a fluorescence probe at almost constant ratio relative to the amount of the scavenged OH radicals. This was applied in estimation of OH radical yield in water radiolysis especially with therapeutic heavy ions of GeV-class energies, i.e. C beams of 135, 290 and 400 MeV/u. OH yields upstream of the Bragg peaks decreased with increasing penetration depth of the projectile ions while that downstream suddenly jumped up to near the value for low-LET radiations such as -rays. This is due to low-LET secondary fragmentation ions produced during long trajectory of the primary projectile C ion. Quantitative explanation by nuclear fragmentation simulations with PHITS code was attempted and resulted in 15-45% underestimation in the region behind the Bragg peaks, which would be due to the difference in geometries between irradiations of the sample solutions and dosimetry with a small ionization chamber.