UNFOLDING OF BREMSSTRAHLUNG PHOTONS ENERGY SPECTRA EMITTED FROM 28-GHz ECR ION SOURCE

The aim of present study is to determine end-point energies of the bremsstrahlung photons energy spectra emitted from 28-GHz Electron Cyclotron Resonance Ion Source (ECRIS) by using inverse-matrix unfolding method. Azimuthal angular distribution of the bremsstrahlung photons from 28-GHz ECR ion source were measured at Busan Center of Korean Basic Science Institute (KBSI). Gamma-ray detection system consists of three round type NaI(Tl) scintillation detectors positioned 62 cm radially from the beam axis and another detector placed at the extraction port for monitoring photon intensity along the beam axis. Bremsstrahlung photons energy spectra were measured at six azimuthal angles at RF power of 1 kW to extract ¹⁶O beam with a dominant fraction of O³⁺ and O⁴⁺. Monte Carlo simulation based on Geant4 simulation package was performed to take the geometrical acceptance and energy-dependent detection efficiency into account due to large non-uniformity in the material budget. We extracted true bremsstrahlung energy spectra using the inverse-matrix unfolding method. The unfolding method was based on a full geometry of the Geant4 model of the ECR ion source. The highest end-point energies after unfolding method were found at angles 90° and 330° which both reaches 1.690±0.030 MeV. Therefore, the high end-point energies intensity at angles 90° and 330° were associated with the shape of the ECR plasma.