For the two crystal materials, XaI(T1) and CsI(Sa), total, photoelectric and photopeak efficiencies are derived at several y-ray energies and crystal thicknesses. The effects of the stochastic variations in photomultiplier pulse production and of multiple Compton events on resolution are combined so as to give the modulation transfer function of gamma cameras without collimators. The effect of a hypothetical Compton discrimination on sensitivity and resolution is discussed.
Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) films were formed without initial nucleation using a coaxial arc plasma gun. The UNCD crystallite diameters estimated from the X-ray diffraction peaks were approximately 2 nm. The Fourier transform infrared absorption spectrum exhibited an intense sp 3 -CH peak that might originate from the grain boundaries between UNCD crystallites whose dangling bonds are terminated with hydrogen atoms. A narrow sp 3 peak in the photoemission spectrum implied that the film comprises a large number of UNCD crystallites. Large optical absorption coefficients at photon energies larger than 3 eV that might be due to the grain boundaries are specific to the UNCD/a-C:H films.
p-Type ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite films were fabricated by pulsed laser deposition using boron-doped graphite targets. Thermal analysis confirmed the occurrence of p-type conduction. The electrical conductivity increased with the doped amount of boron. An activation energy estimated from the Arrhenius plot was approximately 0.1 eV. Near-edge X-ray absorption fine structure spectra revealed that the à C-H peak weakened and the à C-B peak strengthened with an increase in the doped amount of boron. Fourier transform infrared spectroscopy showed that the sp 3 C-H peak weakened with the doped amount of boron. These probably indicate that the hydrogen atoms that terminate the dangling bonds of UNCD crystallites are partially replaced with boron atoms.
The atomic bonding configuration of ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) films prepared by pulsed laser ablation of graphite in a hydrogen atmosphere was examined by near-edge X-ray absorption fine structure spectroscopy. The measured spectra were decomposed with simple component spectra, and they were analyzed in detail. As compared to the a-C:H films deposited at room substrate-temperature, the UNCD/a-C:H and nonhydrogenated amorphous carbon (a-C) films deposited at a substrate-temperature of exhibited enhanced and peaks. At the elevated substrate-temperature, the and bonds formation is enhanced while the C–H and C–C bonds formation is suppressed. The UNCD/a-C:H film showed a larger C–C peak than the a-C film deposited at the same elevated substrate-temperature in vacuum. We believe that the intense C–C peak is evidently responsible for UNCD crystallites existence in the film.
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