Scanning Electron Microscopy and X-Ray Microanalysis

48

4

direction of the electron travel. In thin specimens where the

beam electron trajectories are nearly aligned, this anisotropy

can result in a different continuum intensity in the forward

direction along the beam relative to the backward direction.

However, in thick specimens, the near-randomization of

the beam electron trajectory segments by elastic scattering

effectively smooths out this anisotropy, so that the X-ray con-

tinuum is effectively rendered isotropic.

0246810

Overvoltage, U = E 0 /Ec

Relative X-ray intensity (thick specimen)

50

40

30

20

10

0

Relati

ve

X-

ray intensit

y

. Fig. 4.9 Characteristic X-ray inten-
sity emitted from a thick specimen;
exponent n = 1.7

Eν=E 0

Eν

. Fig. 4.10 Schematic illustration of
the braking radiation (bremsstrahlung)
process giving rise to the X-ray
continuum

Chapter 4 · X-Rays