Page 6 - Professorial Lecture - Prof Oyedele

Director of Ceremony, I should mention that this is the project that led to the
title of this Professorial inaugural lecture.

1.2 RADIOACTIVITY

In the late 1800s, some scientists such as Marie and Pierre Curie observed
that certain elements emitted radiation without any external stimulus unlike
in the case of X-rays. This phenomenon was later called radioactivity (Martin
and Harbison, 1987; Bryan, 2009; Turner, 2012). These elements occur in
nature and they could also be produced artificially. When the elements
occur naturally, the phenomenon is called natural radioactivity. These
elements or radiation sources are naturally around us and so the radiation
they emit is always in our environment. In fact, human beings have always
lived with natural radioactivity. The natural background radiation comes
from two main sources: Cosmic radiation and terrestrial sources of radiation.

Cosmic rays which are high energy particles (primarily protons and alpha
particles) originating in outer space continually bombard the earth. They
interact with atoms of the atmosphere and thereby produce radioactive
14
nuclei (e.g. carbon-14 or C). The energies of the cosmic rays and the
radioactive nuclei they produce are high enough that many reach the
surface of the earth.

The soil and rocks of the earth contain various amounts of naturally
occurring radionuclides such as Thorium-232 (and the radionuclides in its
series). As the radionuclides decay they emit radiation. The more the
concentrations of the radionuclides or elements, the more the radiation
emitted. It is well known that the radiation emitted has many useful
applications in different fields such as Science, Agriculture, Engineering and
Medicine. However, the radiation could, in general, be hazardous. It is
therefore necessary to determine or monitor the level of radiation in the
environment and thereby control or reduce the exposure of the public to
radiation.

In this lecture, I will first discuss the basics, threats and applications of nuclear
radiation and UNAM’s nuclear science programmes. I will then talk about
my studies on natural radioactivity and radiation levels of different cities and
towns in Namibia.