Topic Content:
- Meaning of Radioactivity
- Properties of Radioactive Radiations
- Deflection in a Magnetic Field
- Penetration of Matter
- Types of Radioactivity
- Natural
- Artificial
- Radioactive Elements
What is Radioactivity?
Radioactivity is the spontaneous decay or disintegration of the nucleus of the atom of a radioactive element during which radiations, alpha, beta and gamma particles (α, β and γ-particles) and sometimes neutrons and energyEnergy is the ability to do work. Energy exists in several forms such as heat, kinetic or mechanical energy, light, potential energy, and electrical energy. Units of Energy: The SI unit... More are emitted.

Radioactive elements are elements that are capable of spontaneous decay with the emission of radiation and energy. Examples of such elements are uranium, boron, thorium, radon, cobalt, radium, etc.
The phenomenon of radioactivity was discovered by Henry Becquerel in 1896.
Properties of Radioactive Radiations:
α-particles | β-particles | γ-particles | ||
1. | Effect of electric field | Deflected towards the –ve plate | Deflected towards the +ve plate | Unaffected |
2. | Effect of magnetic field | Deflected toward the south pole | Deflected towards the north pole | Unaffected |
3. | Nature of charge | Positively charged | Negatively charged | Neutral |
+2e (+3.3 × 10-19 C) | -e (-1.6 × 10-19 C) | |||
4. | Mass | Massive (heavy) | Less massive | No mass |
5. | Momentum | High momentum | Low momentum | No momentum |
6. | Penetrating power | Low penetration power | High penetration power | Very high penetration power |
7. | Nature of the atom | Helium nucleus | High energy electrons | Electromagnetic radiation of short wavelength |
8. | Ionization power | High ionization power | Low ionization power | No ionization |
9. | Fluorescence | Cause Fluorescence in ZnS | No Fluorescence in ZnS |
Deflection in a Magnetic Field:

These three forms of radiation can be separated by a magnetic field since positively charged alpha particles bend in one direction, negative beta particles bend in an opposite direction, and electrically neutral gamma radiation doesn’t bend at all.
Alpha particles move towards the negatively charged plate. Since they are attracted to a negative charge, this shows us that alpha particles carry a positive charge.
Beta particles move towards the positively charged plate. Since they are attracted to a positive charge, this shows us that beta particles carry a negative charge.
Gamma rays are unaffected. Gamma rays are uncharged, so are unaffected by the positive and negatively charged plates.
Penetration of Matter:
The alpha particle is the shortest in range because of its strong interaction with matter. The electron of beta radioactivity strongly interacts with matter and has a short range, but its penetrating power is 100 times greater than that of alpha. The electromagnetic gamma ray is extremely penetrating, even penetrating considerable thicknesses of concrete.

Types of Radioactivity:
There are two types of radioactivity namely natural radioactivity and artificial radioactivity.
Natural Radioactivity:
Natural radioactivity is the splitting or breakdown of nuclei of elements on their own without any stimulation from man, during which α-particles, β-particles, γ-rays, or a combination of any of these are released with accompanied energy.
Artificial Radioactivity:
Artificial radioactivity is achieved by bombarding ordinary materials with radioactive particles to give radioactive elements radiation and energy. E.g.
\( \scriptsize \underset{aluminium}{_{13} ^{27} \textrm {Al}} + \underset{helium}{\: _{2} ^{4} \textrm {He}} \rightarrow \: \underset{phosphorous}{_{15} ^{30} \textrm {P}}\: + \: _{0} ^{1} \textrm {n} \rightarrow \: \underset{silicon}{_{14} ^{30} \textrm {S}}\: + \: _{1} ^{0} \textrm {e} + energy\)
When aluminium is bombarded with helium or alpha particles, it gives rise to an unstable phosphorus nucleus (radioactive phosphorus) which disintegrates further spontaneously into a stable silicon atom.
Neutrons, protons and alpha particles are used as very effective bombarding particles for disintegrations of nuclei of elements.
Radioisotopes are isotopes made artificially by bombarding neutrons or protons or deuterons at elements.
Radioactive Elements:
Radioactive elements are elements that spontaneously emit radiation from their nucleus. It has been established that elements of atomic number greater than 83 are radioactive, i.e., they undergo spontaneous decay. e.g.
- Uranium
- Thorium
- Protactinium
- Neptunium
- Americium
- Radium
- Radon
- Polonium
- Bismuth
- Curium
- Actinium
- Berkelium, etc