1Chapter 1
Properties and Sources of Radiation
Mass and energy are the two entities that make up our Universe. At the most ba-
sic level, these two entities represent a single reality that sometimes shows itself as
mass and sometimes as energy. They are intricately related to each other through
Einstein’s famous mass-energy relation,E=mc^2. Just like matter, energy is also
capable of moving from one point in space to another through particles or waves.
These carriers of energy always originate from some source and continue their travel
in space until they get absorbed or annihilated by some material. The term “radia-
tion” is used to describe this transportation of mass and energy through space.
Since the realization of its potentials, radiation has played a central role in our
technological developments in a variety of fields. For example, we all enjoy the
benefits of radiation in medical diagnostics and treatment. On the other hand,
world has also witnessed the hazards of radiation in the form of atomic explosions
and radiation exposure.
Whether we think of radiation as a hazard or a blessing, its study is of paramount
importance for our survival and development. If we looked carefully at the bene-
fits and harms brought in by the use or misuse of radiation, we would reach the
conclusion that its advantages clearly outweigh its disadvantages. Radiation has
unlimited potential and its proper use can open up doors to great developments for
the mankind.
This chapter will introduce the reader to different types of radiation, their prop-
erties, and their sources. The mechanisms through which the particles interact with
matter will be discussed in detail in the next chapter.1.1 TypesofRadiation............................
Radiation can be categorized in different ways, such as ionizing and non-ionizing,
particles and waves, hazardous and non-hazardous etc. However none of these cat-
egorizations draw solid boundaries between properties of individual particles com-
prising the radiation, rather they show the bulk behavior of particle beams. For
example, it will not be correct to assert that an electron always ionizes atoms with
which it interacts by arguing that it belongs to the category of ionizing particles.
All we can say is that if a large number of electrons interact with a large number of
atoms, the predominant mode of interaction will lead to the ionization of atoms.
Sometimes radiation is characterized on the basis of its wave and particle prop-
erties. However, as we will explore in the next section, this characterization is
somewhat vague and can be a cause of confusion. The reason is that, according to