Feasibility Study on Quenching Effect Correction in Organic Scintillator for High-LET Particles

The amount of photons emitted from the organic scintillator tends to increase as the LET increases, but the response is non-linear, and the effect of quenching becomes remarkable in the high LET region. This is because ionization occurs locally at high density in the high LET region, and the molecules in the high-density singlet excited state generated in response to this cause quenching by the Förster mechanism. It is known that the emission characteristics of a scintillation depending on LET can be well approximated by the Birks formula and the Chou formula. In our experiment using BC408 scintillator, the amount of scintillation light increased as the LET increased, but it was confirmed that the amount of scintillation light decreased at 10 eV/nm and above due to the quenching effect. In addition, although it could not be uniquely expressed by the Birks formula, the Chou formula allowed a relatively good fitting. On the other hand, it has been found that it is difficult to explain the track structure and photon dynamics in the scintillator by LET alone for heavy ion beams of Si ion or heavier. It is considered that this is because LET gives a one-dimensional energy-giving density on a macro scale, whereas the micro-three-dimensional energy-giving density in the track has a great influence on heavy-ion beams above Si ions. In previous studies, (Z eff /β) ² (Zeff: effective charge of irradiated ions, β: velocity in units of light velocity) is more suitable than LET for expressing the track structure of high-energy ion beams of several hundreds of MeV/u. Therefore, there is a possibility that (Z eff /β) ² can be used as an alternative parameter to LET. In the future, we would like to examine the validity of this method by measuring with different nuclides.