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7D10.70 - Alpha Particles with Electroscope

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​7D10.70 - Alpha Particles with Electroscope

Title7D10.70 - Alpha Particles with Electroscope

Observe a nearby alpha source with an electroscope.

Assembly Instructions
Setup Time
Operation Time5
Preview Time5
Operation Instructions

Operation Steps
1   Charge the electroscope negatively with the piezo charger.
2   Leave the projector for a time to show that it is "stable" (holds its charge)
3   Take out the alpha source and place it under the electroscope needle.
4   The electroscope will steadily discharge (due to the incident alpha particles) over about 4 minutes.
Put a charge on the electroscope either positive or negative and show that the charge does not quickly dissapate by letting is set for a minute while you continue the class. Then carefully pick up the electroscope and insert the alpha source, which you should position as close to the internal needle charge deflection plate and away from the tip of the pointer as possible. Allow the apparatus to set and within several minutes the charge will have been completely disapated from the electroscope.

Demo on DimeNo
PIRA 200No
Export Instructions (if different)


Alpha particles are He nuclei (2 protons and 2 neutrons). They are highly ionizing, which is to say that they are very ready to assimilate free electrons.
When we charge the electroscope negatively, we produce a net excess of electrons. However, (on a dry day) they have no where to go from the electroscope.
In the presence of incident alpha particles, these excess electrons readily join the alpha particle to become helium.

Category7 Modern Physics
Subcategory7D - Nuclear Physics
Keywordsalpha radiation radioactive helium electroscope
Construction Information
electroscope - projection scope
alpha source - smoke detector
piezo charger
grounding plate with grounding plug
overhead projector
banana cable