Physics and Engineering of Radiation Detection

1.5. Sources of Radiation 29

Potassium-40 and Carbon-40 isotopes. However the absorbed dose and the damage
to tissues due to this radiation is minimal.

1.5.B Man-MadeSources........................

Right after the discovery of radiation and realization of its potentials, scientists
started working on developing sources that can be used to produce radiation in
controlled laboratory environments. These sources are made for specific purposes
and generally give off one type of radiation. Common examples of such sources are

medical x-ray machines,

airport x-ray scanners,

nuclear medicines,

particle accelerators, and

lasers.

Out of all these sources, the ones used in medical diagnostics and therapy expose
the public to the most significant amounts of radiation. For example a single chest
x-ray exposes the patient to about 20mremof radiation, which is a significant
fraction of about 360mremof total radiation exposure to general public due to
all types of radiation. Repeated x-rays of patients are therefore discouraged unless
there is absolute medical necessity.
There are also some consumer products that give off radiation although they have
been made for some other purpose. Examples of such sources are

television,

smoke detectors, and

building materials.

As we saw in the section on radioactivity, there are a large number of naturally
occurring and man-made isotopes that emit different kinds of radiation. Depending
on their half lives, types of radiation they emit, and their energies, some of these
radioisotopes have found applications in a variety of fields. In the next section, when
we discuss individual particle properties, we will also look at some of the commonly
used radiation sources made from such isotopes.
Before we go to the next section, let us have a general look at some radioisotopes
that are made in laboratories for specific purposes. A variety of methods are used to
produce radioisotopes. For example a common method is the bombardment of stable
elements with other particles (such as neutrons or protons), a process that desta-
bilizes the nuclides resulting in its decay with emission of other particles. Another
method is to extract the unstable isotopes from the spent fuel of nuclear reactors.
Some of the frequently produced radioactive elements are listed in Table.1.5.1.