4.3 CHAPTER 4. ATOMICNUCLEI
few people to receive two Nobel Prizes.4.3 Radioactivity and Types of Radiation
ESBAF
In Section 4.1, we discussed that when a nucleus is unstable it can emit particles and energy. This
process is called radioactive decay.DEFINITION: Radioactive decay
Radioactive decay is theprocess in which an unstable atomic nucleus loses energy by
emitting particles or electromagnetic waves. These emitted particles orelectromag-
netic waves are called radiation.When a nucleus undergoes radioactive decay, itemits radiation and thenucleus is said to be radioac-
tive. We are exposedto small amounts of radiation all the time. Even the rocks around us emit
radiation! However some elements are far moreradioactive than others.Even within a single element,
there may be some isotopes that are more radioactive than others simplybecause they contain a larger
number of neutrons. Radioactive isotopes are called radioisotopes.Radiation can be emitted in different forms. There are three main typesof radiation: alpha, betaand
gamma radiation. Theseare shown in Figure 4.1, and are described below.paper aluminium leadalpha (α)
beta (β)gamma (γ)Figure 4.1: Types of radiationAlpha (α) particles and alpha decay ESBAG
An alpha particle is made up of two protons andtwo neutrons bound together. This type of radiation
has a positive charge. An alpha particle is sometimes represented using the chemical symbol He2+,
because it has the samestructure as a Helium atom (two neutrons and two protons) ,but without the
two electrons to balance the positive charge ofthe protons, hence theoverall charge of +2. Alpha
particles have a relatively low penetration power. Penetration power describes how easily the particles
can pass through another material. Because alpha particles have a low penetration power, it means
that even something asthin as a piece of paper, or the outside layer ofthe human skin, will absorb
these particles so that they can’t penetrate any further.