Radioactivity and Gold Leaf Electroscope

What is the use of gold leaf electroscope? 

To detect presence of charge suppose you’ve an object carrying negative charge , it will push the electrons to go down and gold leaf opens.

If object carries positive charge, the electroscope will attract the electrons upward, leaving the positive charge at bottom and gold leaf opens again.

So if object is placed closed to the dish, and the gold leaf opens, the object carries a charge. 

So it’s purpose is detection of charges and it too can detect radioactive emissions. Can only detect alpha particles because beta and gamma are lower in ionisation.

Detection of alpha particles by gold leaf electroscope 

Charge the gold leaf electroscope 

How we can charge gold leaf by induction? Both positively and negatively charged electroscope will do. 

When charged, gold leaf will open, in 10-20 minutes it will close- if surrounding is dry, gold leaf will take more time to dry. In humid surrounding, it will close faster.

If you bring an alpha particle source near the gold leaf electroscope, the gold leaf will close very fast. The more intense the radiation, the faster the leaf falls. The higher rate of radiation, the faster the gold leaf falls.

Ionisation of air produces positive and negative particles. If gold leaf electroscope is charged positively, tye electrons will be attracted towards the plate. The positive charger will be repelled. The electrons neutralises the positive charge of gold leaf and hence the leaf closes. That’s how alpha particles cause gold leaf to close.