4.3 Interactions with Particulate Radiation
47
also be the same. The relationship between range and energy has been expressed
empirically as follows:
Range = 0.318E
3
2
(4.1)
where range (expressed in cm) is the distance traveled by an α-particle in air at one
atmospheric pressure and 15
◦ C, and E the initial energy of the α-particle in MeV.
4.3.2 β-Particles
β-particles can be either negatively charged or positively charged (known as positron).
Positron is an electron with a positive charge; it falls in the category of particles along
with electrons, as they have similar masses. Since they have equal masses and opposite charges, they lose their kinetic energy by a similar mechanism. However, the
main difference is that a positron is annihilated with an electron of the interacting
materials into an electromagnetic radiation of 0.511 MeV/particle.
Normally, a β-particle loses its energy in a large number of ionization and excitation events in a manner analogous to the α-particle. Owing to its small mass (and
hence higher velocity at a given energy) and charge, there is a lower probability of a
β-particle interacting in a given medium. Consequently, specific ionization is lower
and the range at which the β-particle can penetrate into the interacting material is
considerably greater than that of an α-particle of comparable energy.
Unlike α-particles, β-particles possess a continuous spectrum of energies, because
decay energy of the nuclei is conserved between a neutrino and a β-particle. In other
words, a β-emitter isotope emits β-particles of energies anywhere from zero to a
maximum energy value, known as E max (Fig. 2.1). E max is the characteristic value
for a particular radioactive nucleus. That is to say that a β-emitting radioactive isotope
can be identified by measuring its E max value because no two radioactive isotopes
have the same E max value.
4.4 Interaction with Electromagnetic Radiation
4.4.1 Electromagnetic Radiation
This group of radiations includes both X -rays and γ -rays. However, these two radiations differ only in their origin of formation and not in their mechanism of interaction.
Here, only γ -radiation is discussed. γ -radiation is emitted from the nucleus with the
velocity of light, has zero rest mass, and no electric charge. The specific ionization
produced by this radiation is very small. The absorption of γ -rays in matter occurs
by mechanisms which are completely different from the absorption of particulate
47
also be the same. The relationship between range and energy has been expressed
empirically as follows:
Range = 0.318E
3
2
(4.1)
where range (expressed in cm) is the distance traveled by an α-particle in air at one
atmospheric pressure and 15
◦ C, and E the initial energy of the α-particle in MeV.
4.3.2 β-Particles
β-particles can be either negatively charged or positively charged (known as positron).
Positron is an electron with a positive charge; it falls in the category of particles along
with electrons, as they have similar masses. Since they have equal masses and opposite charges, they lose their kinetic energy by a similar mechanism. However, the
main difference is that a positron is annihilated with an electron of the interacting
materials into an electromagnetic radiation of 0.511 MeV/particle.
Normally, a β-particle loses its energy in a large number of ionization and excitation events in a manner analogous to the α-particle. Owing to its small mass (and
hence higher velocity at a given energy) and charge, there is a lower probability of a
β-particle interacting in a given medium. Consequently, specific ionization is lower
and the range at which the β-particle can penetrate into the interacting material is
considerably greater than that of an α-particle of comparable energy.
Unlike α-particles, β-particles possess a continuous spectrum of energies, because
decay energy of the nuclei is conserved between a neutrino and a β-particle. In other
words, a β-emitter isotope emits β-particles of energies anywhere from zero to a
maximum energy value, known as E max (Fig. 2.1). E max is the characteristic value
for a particular radioactive nucleus. That is to say that a β-emitting radioactive isotope
can be identified by measuring its E max value because no two radioactive isotopes
have the same E max value.
4.4 Interaction with Electromagnetic Radiation
4.4.1 Electromagnetic Radiation
This group of radiations includes both X -rays and γ -rays. However, these two radiations differ only in their origin of formation and not in their mechanism of interaction.
Here, only γ -radiation is discussed. γ -radiation is emitted from the nucleus with the
velocity of light, has zero rest mass, and no electric charge. The specific ionization
produced by this radiation is very small. The absorption of γ -rays in matter occurs
by mechanisms which are completely different from the absorption of particulate