Investigation of the projectile ion velocity inside the interaction media by the x-ray spectromicroscopy method

Abstract

A method for space resolved measurements of the fast heavy ion velocity during the interaction with matter are presented. The main idea is based upon the fact that the characteristic radiation from ions traveling in the stopping media undergoes the Doppler shift, which varies along the ion beam trajectory due to the ion deceleration. High spectrally (λ/Δλ=1000–3000) and spatially (up to 30–100 μm) resolved x-ray K-shell spectra of Ca projectile ions as well as of the ionized stopping media have been obtained using focusing spectrometers with spatial resolution (FSSR). Spherically bent crystals of quartz and mica with small curvature radii R=150 mm and large apertures (15×50 mm) have been used as dispersive elements. Fast Ca+6 ions with energies of 5.9 and 11.4 MeV/u were stopped in quartz, SiO2 aerogels and CaF2 targets. High spectral and spatial resolution of the spectra allowed measuring the velocity of heavy projectile ions at different points along the beam trajectory. A method based on the utilization of two equal spectrometers at different angles of observation (along and downstream the ion beam propagation direction) is proposed to measure the absolute values of ion velocity inside the stopping media. The use of aerogel targets with extremely low volume density (0.15 g/cc) increases the ion stopping range up to 50 times in comparison to solid quartz. This provides the resolution of the stopping process dynamics. Experimentally it was found that Ca+6 ions with the initial energies of 5.9 or 11.4 MeV/u propagate in solid dense matter as Ca+17–Ca+19 down to the energies of 2.0–2.2 MeV/u.