Abstract:
Secondary electron (SE) emission from thin carbon foils induced by 1-20 keV positrons has been investigated over a range of nominal foil thicknesses from 1.0 to 5.0 μg/cm2. The measurement of SEs was carried out in forward geometry using a microchannel plate as a detector. The SE yield has been measured as a function of beam energy and compared with some Monte Carlo simulation results. The material parameter and the emitted SE energy spectra were present as well. We also present measurements of energy loss and energy loss straggling for 1-10 keV positrons passing through those thin carbon foils. The stopping power and positron transmission coefficient have also been investigated as a function of incident positron energy and foil thickness.
Titanium dioxide nanotube arrays fabricated by anodization of titanium foil and annealed at different temperatures were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and positron annihilation spectroscopy (PAS). The crystallization process and morphological change of the nanotubes have been discussed.
A new design of the lifetime positron beam based on the SE emission is proposed. The observed experimental results and simulation results make it possible to construct a new type of high resolution (<250ps) lifetime positron beam.