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Types of Radiation


Studies have shown that radiation from radioactive decay are of three types: alpha rays; beta rays; and gamma rays.

Alpha rays (α, 42He)

Alpha rays have been found to be positively charged particles, having a mass of 4 and charge of +2 (they are actually helium ions). The emission of an α - particle causes an atom to lose four units of mass and two positive units of charge. Hence, the mass number drops by 4 and the atomic number by 2.

Example, 23892U - α23490Th

Characteristics of α-rays:

1. They have very little penetrating power – they are sufficiently absorbed by sheet of paper or air of about 8 cm thick.

2. They have high ionizing power – due to their relative large masses and high charge, they ionize gases when they collide with gaseous molecules.

3. They are positively charged particles – this is shown by their deflection to the negative plate of an electric or magnetic field.

Beta rays ( β-rays)

Beta rays have been found to be electrons in rapid motion. They may be positively (positrons) or negatively charged, although the term beta rays refer usually to negatively charged particles. Beta decay results in the loss of one unit of negative charge, but the mass is unaffected (electrons do not have masses).

The number of protons correspondingly increases by one unit, hence, the atomic number increases by one. Positron decay results in the loss of a unit of positive charge, thereby reducing the atomic number by one.

Example, 23490Th → 23491Pa (β- decay)

116C → 115B (β+ decay) – positron decay.

Characteristics of beta rays:

1. They have a very high penetrating power.

2. They have less ionizing power than a - particles.

3. They are charged particles – (mostly negative), and are deflected to the positive plate of an electric or magnetic field.

Gamma rays (γ-rays)

Gamma rays are electromagnetic rays of the same nature as light or x – rays, but they are of shorter wavelength and higher frequency. They are found to be produced when an excited nucleus that has emitted either an α or a β particle returns to its ground state. There is no change in mass or atomic number of an atom which undergoes γ -decay.

Example, 23491Pa → 23491Pa + γo

Characteristics of gamma rays:

1. They have no charge and are therefore undeflected by an electric or magnetic field.

2. They have extremely high penetrating power (higher than that of β - rays) - they can only be absorbed by thick block of lead.

Summary of The Effects of Radiation

- It affects photographic plates; causes gases to ionize; initiates chemical reactions (polymerization); and it makes certain substances (e.g., crystalline ZnS) to fluoresce.

- It can cause physiological effects in someone who is exposed to it. Intense exposures could cause irreparable damage to cells. Cancerous growth can be induced from exposures to the highly penetrating ones, especially gamma rays.


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