Cloud Chamber and Radioactivity

Cloud chamber: 

It is used to identify whether it is alpha, beta, gamma rays or alpha and beta both.

We have a box, at the lower part of the box we have dry ice. Below the dry ice, we have sponge/form to support the dry ice. To press the dry ice closer to the bottom of the box.

The function of dry ice is to cool down the air in the upper part to very low temperature. The condensation point of dry ice is -78.5 degree Celsius. The two corners have rings soaked in alcohal that it will release alcohal vapour into the box.

Since temperature is low, the alcohol vapours can form droplets easily. Very very saturated, very low temperature 

So if we place the radioactive source inside the upper part, the alcohol will form liquid droplets — there is lamp to shine on the droplet. There is plastic lead so you can observe from a buffer is transparent.

When viewed from above, you can see the track of alcohol droplet. Because a radioactive source will form a track of the droplet — lamp will help you see it. 

How to identify the particles?

Alpha track

Why alpha’s track is thick? Because it has high ionisation power. Can ionise lot of air molecules and then form a lot of alcohol vapours. Why it’s track is straight? Because the mass of alpha particles is very high, so it hardly gets deflected by other molecules. Only occasionally it will be deflected by air. 

Beta track

Thin, does not move in straight line — it is deflected by other molecules. Beta particle is electron, very small when it will collide with the air, it will be deflected. So it will move in random directions. 

Gamma track

Thin but not connected — it’s continuous.

So by identifying the track, you can identify alpha, beta, gamma.