Estimations of relative biological effectiveness of secondary fragments in carbon ion irradiation using CR‐39 plastic detector and microdosimetric kinetic model

PurposeTo estimate relative biological effectiveness (RBE) ascribed to secondary fragments in a lateral distribution of carbon ion irradiation. The RBE was estimated with the microdosimetric kinetic (MK) model and measured linear energy transfer (LET) obtained with CR‐39 plastic detectors.MethodsA water phantom was irradiated by a 12C pencil beam with energy of 380 MeV/u at the Gunma University Heavy Ion Medical Center (GHMC), and CR‐39 detectors were exposed to secondary fragments. Because CR‐39 was insensitive to low LET, we conducted Monte Carlo simulations with Geant4 to calculate low LET particles. The spectra of low LET particles were combined with experimental spectra to calculate RBE. To estimate accuracy of RBE, we calculated RBE by changing yield of low LET particles by ±10% and ±40%.ResultsAt a small angle, maximum RBE by secondary fragments was 1.3 for 10% survival fractions. RBE values of fragments gradually decreased as the angle became larger. The shape of the LET spectra in the simulation reproduced the experimental spectra, but there was a discrepancy between the simulation and experiment for the relative yield of fragments. When the yield of low LET particles was changed by ±40%, the change of RBE was smaller than 10%.ConclusionsRBE of 1.3 was expected for secondary fragments emitted at a small angle. Though, we observed a discrepancy in the relative yield of secondary fragments between simulation and experiment, precision of RBE was not so sensitive to the yield of low LET particles

Simulation study on transverse laser cooling and crystallization of heavy-ion beams at the cooler storage ring S-LSR

Multi-dimensional laser cooling of heavy-ion beams at the cooler storage ring S-LSR in Kyoto University is studied numerically using the molecular dynamics simulation technique in which the stochastic interaction between ions and laser photons is incorporated. The purpose of the study is to find out how low-temperature we can achieve using actual experimental parameters and to verify the observation result in the experiment. In these proceedings, the characteristics of the ion beam lasercooled in S-LSR are reported. It has been confirmed that, in spite of the limitation in the experimental conditions such as a single laser beam, low power, fixed detuning and short laser-cooling section, the three-dimensionallylow-temperature beam is obtained through resonant coupling at a low intensity of 104 ions in the ring, which is consistent with the experimental result. It is also demonstrated that a string crystalline state of the beam can be formed at a further lower intensity

Parameter optimization for multi-dimensional laser cooling of an ion beam in the storage ring S-LSR

S-LSR is a compact ion cooler ring built in ICR, Kyoto University, aiming at creating ultra-low temperature ion beam by laser cooling. In order to approach lowest possible temperature at S-LSR in an experiment, parameters of laser cooling should be carefully chosen by simulation. This paper mainly concerns optimization of laser cooling parameters and prediction of possible low limit of beam temperature at S-LSR. Firstly, the adiabatic capture process of ion beam is introduced and studied.Then, different laser profile parameters are compared and an optimized value is chosen. After that, optimized solenoid field strength for 3-D coupling is proposed. At last, by choosing the parameters proposed, the lowest beam temperature achievable for S-LSR is predicted to be 10 K in transverse direction and 0.05 K in longitudinal direction

Latest results of experimental approach to ultra-cold beam at S-LSR

Utilizing S-LSR which has a super-periodicity of 6 and is designed to be tough against resonant perturbation to the circulating beam, we have tried to approach as low as possible temperature with laser cooled 40 keV 24Mg+ ion beam. With the use of theoretically proposed Synchro-Betatron Resonance Coupling scheme, we have experimentally demonstrated the capability of active indirect transverse laser cooling. At first, the achieved transverse cooling efficiency was limited due to heating caused by intra-beam scattering (IBS). For the purpose of reduction of IBS heating, we have established a scheme tocontrol the circulating ion beam intensity down to ~104 by scraping the outskirt of the beam with the use of a horizontally moving scraper, which enabled us to cool down the transverse beam temperatures down to 20 K and 29 K for horizontal and vertical directions, respectively for the operation tune without H-V coupling. They were modified to be 40 K and 11 K by the horizontal and vertical coupling with the difference resonance with an excitation of a solenoid of 22.5 G, which were further improved to 7.0 K and 2.1 K adding deceleration by an induction accelerator of 6 mV/m using a -26 MHz detuned laser