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Spark Counter

Hi, I was wondering as how to how the potential difference across the air gap in a spark counter varies as the radioactive source is moved towards the wire gauze. Thanks

Reply 1

uberteknik

Original post by Shiv7

Hi, I was wondering as how to how the potential difference across the air gap in a spark counter varies as the radioactive source is moved towards the wire gauze. Thanks

The p.d. across the gap between the gauze and the h.v. electrode will be maintained at several thousand volts (perhaps 8kV to 10kV).

When the alpha source is brought to within a few centimetres of the gauze, emitted alpha particles ionise air molecules between the hv gap and the electrode. This causes the air dielectric insulation resistance to breakdown, such that a cascade of electrons can now jump from the electrode to the gauze.

At that instant and for the period that current flows across the gap, the p.d. will have fallen to a few tens of volts before recovering to full hv potential.