Die absolute Intensität der durch Elektronenstoß in einer dicken Wolfram-Antikathode erzeugtenL _α -Strahlung

Abstract

The number$N_{L_\alpha }^{dir}$ (produced) ofL _α -photons produced by electron-bombardment in a thick target of tungsten per incident electron has been measured absolutely with the Ross-filter method and relatively with the crystal-spectrometer method in the energyregion up to the 3.6 times theL _III-ionization energy$E_{L_{III} }$. The result can be presented in the following empirical form:$N_{L_\alpha }^{dir}$ (produced)=4π·ŧ·(U ₀−1)ⁿ with ŧ=0.52·10⁻⁴±5% andn=1.44±0.02$(U_0 = E_0 /E_{L_{III} }< 3.6)$. Out of this the number$n_{L_{III} }$ ofL _III-ionizations per electron which is slowed down to the energy$E_{L_{III} }$ within the target, has been evaluated. The computation of$n_{L_{III} }$ out of the elementary process by usingBethe's non-relativistic formulae for totalL _III-ionization cross sectionQ _L and energy loss-dE/ds is in full agreement with experiment in the region 2<U ₀<3.6, if the constants in$Q_{L_{III} }$ are chosen as follows:$B = 4E_{L_{III} } , b_{L_{III} } = 0.25 \cdot 5.89$. By comparison of this result for$b_{L_{III} }$ with the corresponding value ofb _K in the totalK-ionization cross-sectionQ _K for copper (b _K=0.35·2.26) it is concluded that$Q_{L_{III} }$ is considerably higher than predicted by theory.

The necessary correction factors as e.g. loss ofL _III-ionizations by rediffusion of electrons and portion of indirectly producedL _α -radiation-radiation are determined for tungsten quantitatively.