Detecting Ionising Radiation

Detecting Ionizing Radiation

In this topic I’ll discuss how to detect the ionizing radiation. There are two ways by which we can detect this radiation. These are as following:-

1. Photographic film
2. Geiger Muller tube

Photographic Film

Long ago, scientists used to believe that when some uranium is placed over a photographic film and exposed to sunlight, the uranium will emit x-rays. But on an experiment, it showed that x-rays are being emitted even when uranium over the photographic film isn’t exposed to sunlight. That is, when an ionizing radiation is exposed on a photographic film, there is an image formed on the photographic film because ionizing radiation can make the photographic film fogged.

Uses of photographic film to detect radioactivity

In radioactive places like in nuclear reactors, scientists or technicians who work with radioactive materials, wear a badge with a photographic film inserted in it. If the film becomes fogged, they understand that the scientists or workers are exposed to certain excess amount of radiation. Then they move out from there.

Geiger Muller tube

The diagram of a Geiger Muller tube is drawn above. There is history behind the invention of Geiger Muller tube which you’ll find in the web. The GM tube has a thin window made of mica. The GM tube contains a special mixture of gases at very low pressure. This gas molecules or atoms are ionized when ionizing radiations get in and interact with them and produce a pulse of current. This pulse of current passes to the detecting circuit and detecting circuit gives us the count rate.

Activity

Number of disintegration per second is known as activity.

Unit of activity is Becquerel (Bq).

Background Radiation

Background radiation is a low level ionizing radiation that is produced all the time. Like if a Geiger Muller tube is placed over a table inside a room and switched on, it will start counting the rate of radiation because the color paint on the wall contains uranium and even if there is a human, from his body the ionizing radiations can be produced because there are also chemical reactions going on inside the human body and some chemicals might be unstable that can be ionizing. So even there are some natural and artificial radiations going on that we can’t see because radiations cannot be seen directly by clear human eyes. But ionizing radiations occur all the time and the Geiger Muller tube can count these radiations. Some sources of background radiations and the % effect of them are given below.

Source                                                                                             Effect

Radon gas……………………………………………………………………… 50%

Ground and Buildings………………………………………………………14%

Medical…………………………………………………………………………..14%

Cosmic ray………………………………………………………………………10%

Food and drinks………………………………………………………………11.5%

Nuclear reactor……………………………………………………………....0.3%

Others…………………………………………………………………………….0.2%