The penetration depth of charged-pa

The penetration depth of charged-particles is limited to typically less
than 100 below the surface of a material.
While the number of emitted charged-particles relates to the concentration
of the affected material in the object, the energy distribution of
emitted particles is indicative of the depth of emission. Owing to the
short range of charged-particles, this depth profiling technique is limited
to subsurface or thin-layer analysis. Moreover, since the range of
a charge-particle is material dependent, the technique is used to determine
the amount of impurity in an otherwise uniform material, so that
a constant value of the range is maintained. To detect charged-particles,
it is necessary to position the inspected object in a vacuum chamber, to
avoid energy losses in air.
Charged-Particle Emission by Photon
Activation
High-energy photons, as discussed in section 8.3, can penetrate a nucleus
and release some of its protons. Some of the possible reactions are:
the reaction, as in those listed in Table 8.9, the reaction, as
in and the reaction, as in The
emitted protons can in principle be used for depth profiling, employing
the principle exemplified by Eq. (8.8). The emitted protons can exit a
sample for subsequent detection, but only if the sample is quite thin.
For such a thin sample, the incident high-energy photons will hardly
suffer any interactions, for the activation to take place. Nevertheless,
photonuclear activation can produce reaction products that decay by
emitting high-energy beta-particles, either in the form of electrons or
positrons. For example, produces which decays by emitting
beta-particles with a maximum energy of 3.51 MeV and 0.81 s half-life.
Similarly, the reaction produces a beta-emitter that decays
with half lives of 0.84 s with maximum beta-particle energy of 13 MeV,
while the reaction gives rise to a positron emitter that decays
with a 2.56 s half-life and a maxim positron energy of 4.39 MeV [13].
These reactions have threshold-energies of 12 MeV for 19 MeV for
and 15.24 MeV for The high-energy of emitted betaparticles
and their low mass give them higher penetrability than heavier
charged-particles, thus can be used for the analysis of lithium, beryllium
and sulfur [259]. The short-half life of the reaction products either enables
on-line (immediate) detection, or requires a rapid transfer system
for delayed analysis away from the photon source.
Electrons can also be emitted from the atom by Compton scattering
and the photoelectric effect. Therefore, electrons emitted by a material
exposed to x-rays can be used to radiograph its surface. Most of the