emitted electrons would arise from

emitted electrons would arise from near the surface exposed to radiation,
due to the poor penetrability of electrons in matter. A film placed
on the surface, on the same side as the x-ray source, can then be used
to radiograph the surface of the object exposed to x-rays. This method
is known as electron-emission radiography [134]. The amount of electrons
emitted depends on the electron-density of the material, thus the
method can be used to image variations in material and their concentration
near the surface of an object. This method is similar in principle to
the electron-transmission method discussed in section 6.6.3. Therefore,
the same requirements of high-energy x-rays, close proximity of the film
to the object and the use of slow (fine grain) films, are also applicable
to electron-emission radiography, for the same reasons discussed in
section 6.6.3. However, electron-emission can be applied to image the
surface of a thick object, and to detect the presence of metallic content
in a non-metallic objects.
Charged-Particles Emission by Neutron
Activation
Neutron-induced charged-particle emission relies on the or (n,p)
reactions introduced by thermal-neutrons in some elements [263]. These
are the same reactions used in neutron detection, see chapter 4; that
is, the and reactions. Table 8.10
lists the main properties of these reactions, along with other reactions
that have a reasonably high cross-section. Theses reactions are exothermic,
releasing energy ( value) that is distributed among the emitted
charged-particle and the heavier product nucleus, in reverse proportion
to their mass. For example, the value of the is
2.310 MeV (96% of the time), of which is carried by the alpha-particle
(1.470 MeV) and the rest (0.840 keV) by
The technique is primarily used for analyzing boron content, which is
widely employed in the semiconductor industry. Boron is used to dope
silicon wafers to create p-type semiconductors, and is also used in manufacturing
borophosphislicate glass, employed as insulating layers on integrated
circuits. The high abundance of the highly neutron-absorbing
(19.9 % in natural boron, the rest being makes boron a natural candidate
for direct use in neutron depth-profiling. However, the technique
requires a neutrons flux in the order of neutrons/ s to produce
high sensitivity to changes in concentration. Therefore, this technique
is usually employed in conjunction with research reactor facilities [264].