Measurement of the occupation lengths of channeled 17-MeV electrons and 54-MeV electrons and positrons in silicon by means of channeling radiation

Abstract

The occupation length of channeled 17-MeV electrons and 54-MeV electrons and positrons in silicon has been determined by measuring the intensity of the emitted channeling radiation. For 17-MeV electrons the measured 1/e occupation lengths are approximately 16 pm for the (100) plane and 20 pm for the (110) plane. For 54-MeV electrons the occupation lengths are 24 pm for the (100) plane and 36 pm for the (110) plane. For 54-MeV positrons the occupation lengths are 40, 60, and 42 pm for the (100), (110), and (111)planes, respectively. In all cases, the bound-state populations remain equal relative to one another throughout the thickness of the crystal. Multiple scattering appears to modify positron channeling radiation spectra slightly, but multiple scattering has no perceptible inhuence upon electron channeling radiation spectra.

Theory of Low Energy Channeling Radiation: Application to a Germanium Crystal

“…which agrees with the empirical behavior intensity observed by Nething [26] (for diamond) and Kephart et al [25] (for silicon). For diamond or silicon the occupation length should be smaller than that of germanium for an electron beam energy of 9.0 MeV, since the continuum potential of germanium is deeper than the one of diamond or silicon.…”

“…He found that the intensity of the 1±0 transition is proportional to 1 À exp Àzal occ which is in agreement with the findings of Kephart et al Nething has calculated the occupation length for a silicon crystal by scaling the measured values of diamond according to the atomic number of the channeling crystal and the energy of the electrons. The estimated occupation lengths were about three or four times larger than those published by Kephart et al [25]. Andersen et al [27] have determined theoretically the dependence of the channeling states (bound and quasi-free) using the process of feeding and depopulating the electronic states in the crystal.…”

“…This reflects the strong scattering of the bound states which results from the high transition probability. For states with k x ga2, the 142 K. Chouffani and H. Ûberall These values are about five times larger than that proposed by Gary [39] for germanium, which was derived by scaling the occupation length determined by Kephart et al [25] for silicon. The asymptotic form of the population (Eq.…”

“…Kephart et al [25] have determined experimentally the population as a function of the crystal thickness by using the expression…”

Asymmetry in generation of near-surface X-rays by 33MeV electrons at grazing interaction with a thin Si plate in magnetic field

“…The electrons were captured in the crystal volume [5] in the bound states of channeling mode. The channeling electrons can emit X-rays into a narrow cone with opening about $c À1 , c -the Lorentz-factor, due to their spontaneous transitions between the bound states of transverse motion [6], and generate also bremsstrahlung due to interactions with the nuclei of atoms of atomic plane or axis. The bands and spot of intensity of this pattern defined by channeling electrons are much narrower than the cone of ordinary bremsstrahlung because in the case of 33 MeV electrons c À1 = 15 mrad, and the width of ordinary bremsstrahlung cone is about 40 mrad.…”