Characteristics of the three kinds of emissionCopy

 Learning Objectives

• Discuss the random nature of radioactive emission
• Identify α-, β- and γ-emissions by recalling
  –– their nature
  –– their relative ionizing effects
  –– their relative penetrating abilities
• Describe their deflection in electric fields and in
  magnetic fields
• Interpret their relative ionizing effects
• Give and explain examples of practical applications of α-, β- and γ-emissions

Contents to learn

Alpha rays
Experiment show that alpha-rays consist of doubly ionized helium atoms. These rays possess the following properties.

1. The mass of an alpha particle is four times the mass of hydrogen nucleus.
2. An alpha particle carries a positive charge equal to +2e, where e is the charge on an electron.
3. The ionizing power of alpha-particle is very high.
4. Penetrating power of alpha particles is very low.
5. Alpha rays produce fluorescence in certain substances.
6. When allowed to pass through a thin metal foil, such as gold foil, some of the rays are scattered through large angles.
7. Alpha ray scan induce artificial radioactivity inverain nuclei.
8. Alpha rays produce burns and sores on human body.
9. Alpha rays get absorbed after covering a short distance in air.

Beta rays
These rays consist of fast moving electrons. They possess the following properties:

1. The kinetic energy of beta-rays is less than that of alpha-rays.
2. Beta-rays affect the photographic plate.
3. These rays produce fluorescence easily, especially in barium platinocynide.
4. The ionizing power of beta-rays is very low.
5. The penetrating power of beta-rays is greater than that of alpha-rays.

Gamma – rays
Experiments show that gamma- rays are uncharged radiations. Their properties are given below:

1. Gamma-rays carry no charge as they are not affected by electric and magnetic fields.
2. Gamma-rays travel with the speed of light, therefore, they are electromagnetic radiations, similar to X-rays.
3. Gamma rays are highly energetic radiations as their frequencies are extremely high.
4. The penetrating power of Gamma rays is very large. It is about 100 times larger than that of Beta –rays. They can
5. penetrate through several centimeters thick block of lead.
6. Gamma- rays produce feeble florescence when incident on a screen coated with barium platinocynide.
7. Gamma rays eject electrons when incident on metal.
8. Like alpha-rays, these rays also get absorbed in various materials.