Chapter 10 Notes
Radioactivity is the process by which the nuclei of an element transition into nuclei of another element.
When atoms undergo radioactivity, their products are called radio isotopes. Within the nucleus of an
atom, it is the strong nuclear force that keeps all the protons and neutrons tightly packed. In stable
nuclei, the strong nuclear force is able to overcome the repulsive electric forces that the positively
charged protons experience. When a nucleus becomes unstable, the electric forces become stronger
than the nuclear forces, and the atoms experience a change.
Nuclear radiation is the energy released when unstable nuclei break down. There are three types of
nuclear radiation: alpha decay, beta decay and gamma decay.
Alpha decay occurs when nuclei release alpha particles. An alpha particle is a combination of two
protons and two neutrons, and is represented by the symbol α, which is the same as a helium nucleus.
When an element undergoes radioactive decay, its atomic mass decreases by 4, and its atomic number
decreases by 2. Example: 238-U 234-Th + α.
Beta decay occurs when an atom releases the equivalent of an electron, or a beta particle. Remember
that electrons do not have a mass, but they do have one negative charge. When a beta particle is
released, the atomic number of the element increases by 1, but the mass remains the same. The symbol
that represents a beta particle is β. Example: 234-Th 234-Pa + β.
Gamma rays are high energy electromagnetic waves that can be released during nuclear activity.
Gamma decay does not change the mass or the atomic number of the element, it only releases energy.
Normally, gamma decay is accompanied by alpha or beta decay.
Of the three types of nuclear radiation, gamma decay is the most dangerous because the high energy
waves can penetrate surfaces that alpha and beta decay cannot. It is important to protect yourself and
others against excessive forms of nuclear radiation, because it can lead to health and other biological
Nuclear fission is the process by which very large nuclei break down into smaller nuclei. During nuclear
fission, the large nuclei are bombarded by free neutrons, which sparks a reaction and causes the break
down. The critical mass of a nuclear fission reaction is the largest mass that an unstable nucleus can
have before it will break apart. Fission reactions create large amounts of energy from very little atomic
matter, which makes them ideal reactions in the production of energy used to create electricity.
Nuclear power plants rely on controlled fission chain reactions. These power plants cause concern,
because they produce large amounts of radioactive waste, which must be safely stored so as not to
endanger the surrounding population and environment. They also allow the possibility for nuclear
radiation to be released into the atmosphere if the power plant stopped working properly.
Nuclear fusion is the process by which smaller nuclei are combined to make larger nuclei. Fusion
reactions are less efficient than fission reactions, and is a less popular form of producing energy.
However, fusion reactions are safer and can be controlled more than fission reaction, and so it is
becoming important for scientists to create a good fusion reactor for future nuclear energy production.