Chapter 3: Unit 1: Explain Radioactivity

Explain Radioactivity

(Illustration by Leila Ross)
Radioactivity is  a nuclear phenomenon. Protons and neutrons are attracted by strong nuclear force in the nucleus. In a neutral atom when neutron/proton ratio becomes unstable (usually neutron/proton=1.) then the atomic nucleus spontaneously disintegrates to another new atomic nucleus and radiation is emitted. When the nuclei radiate, both atomic number and mass number change and the element is converted to a completely new element and energy is released as a form of radiation. The reaction takes place in the nucleus of the atom. For example, Uranium decays to Lead by spontaneous emission. This phenomenon is called radioactivity.

Usually the symbol of an atomic nucleus is expressed as:

Z= atomic number
A= mass number

The process through which unstable nuclei become stable is called radioactive Decay. After the radioactive decay, the element becomes a new element (X’)  with new atomic and mass number.

The natural radiation that is always present in the environment, including radiation from the sun, stars and the earth itself. The typical average exposure in the U.S. from background radiation is about 310 millirems per year. Sometimes it is called background radiation. Humans cannot see, smell or feel the radiation, it can be only detected through instruments.

Materials that emit radiation are called radioactive materials. Radioactivity comes from the atomic nucleus composition i.e. ratio between neutron and proton in the nucleus and not from the electron cloud that surround nucleus. For example, ¹⁶₈O is a stable isotope where the nucleus contains 8 protons and 8 neutrons. But ¹⁸₈O is radioactive isotope due to unfavorable neutron/proton ratio. Some isotopes are radioactive, others are stable and do not emit any radiation. Most of the heavy elements after lead(Pb) have radioactive isotopes.

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