Sunday, August 16, 2009



Radioactivity is the spontaneous emission of alpha particles, beta particles and / or gamma rays by an unstable nucleus to become stable.

There are three common types of emissions:

i. Alpha particles

ii. Beta particle, and

iii. Gamma rays.

In an alpha decay, the nucleus emits an alpha particle. An alpha particle is a helium nucleus, made up of two protons and two neutrons.

In beta decay, the nucleus emits a beta particle. A beta particle is a fast moving electron.

In gamma decay, the nucleus emits gamma rays. Gamma rays are electromagnetic radiation of very high frequency.

Radioactivity detectors that work because of the ionizing ability of the radiations are :

(a) Geiger- Muller tube (G-M tube)

(b) Electroscope

(c) Spark counter

(d) Cloud chamber

They can be used to differentiate between alpha, beta and gamma radiations.

The nature of radioactivity was discovered by husband and wife scientists, Marie Curie (1867-1934) and Pierre Curie (1859- 1906).

Cloud chamber

The track patterns formed in the cloud chamber can be used to differentiate between alpha, beta and gamma radiations.

Alpha radiation produces thick, straight tracks. The tracks are thick because of their high ionizing ability. Straight tracks are due to their large mass, making alpha particle difficult to deflect (high inertial).

Beta radiation produces thin; twisted tracks. The thin twisted tracks are due to the weak ionizing ability of the beta particle. Twisted tracks are due to their small mass, making beta particles easier to deflect.

Gamma radiation produces short, thin and scattered tracks. This is due to the extremely weak ionizing ability of gamma rays.

Spark counter

When a radioactive source which produces alpha particles is brought near, the air between the gauze and the wire is ionized by it.


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