CAO Xing-Zhong()

Bao-Yi( ) MA Yan-Yun( ) WANG Ping( ) CAO Xing-Zhong( ) QIN Xiu-Bo( ) ZHANG Zhe( ) YU Run-Sheng( ) WEI Long( ) 1)

Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when a magnetic field is applied parallel to the sample plane. By combining X-ray absorption near the edge structure spectrum and positron annihilation lifetime spectroscopy, Ti3+—VO defect complexes (or clusters) have been identified in annealed crystals at a high vacuum. We elucidate that the unpaired 3d electrons in Ti3+ ions provide the observed room-temperature ferromagnetism. In addition, excess oxygen ions in the TiO2 lattice could induce a number of Ti vacancies which obviously increase magnetic moments.

CsI film has been one of the most extensively used scintillators for indirect X-ray imaging because of its needle-like micro-structure. The purpose of this paper is to investigate the imaging performance of CsI screen as a function of thickness and radiation quality. Four multilayer scintillation screens with microcolumnar CsI:Tl film (thicknesses of 50 µm, 100 µm, 200 µm and 300 µm) included were prepared and coupled to an optical imaging sensor. The modulation transfer function (MTF), normalized noise power spectrum (NNPS) and detective quantum efficiency (DQE) of these screens were evaluated based on the standard IEC 62220-1, and the results indicated that, in the medium spatial frequency range (1-6 lp/mm), the MTF of CsI screens with the same thickness was lower when the incident X-ray photon energy was higher, possibly owing to scattering and K-fluorescence re-absorption effects. The NNPS in the higher spatial frequency range (above 8 lp/mm) is dominated by stochastic noise while the entrance surface air Kerma (ESAK) decreases. For 100 µm, 200 µm and 300 µm thick CsI screens, the DQE under RQA7 and RQA9 is lower than that under RQA3 and RQA5 due to low absorption efficiency.