Author: Jay Howson
The Concept of an Alpha Spark Detector is simple; High voltage is applied between a thin wire or mesh grid and and parallel ground plane a few mm below it.
The voltage is set such that a breakdown does not occur. However, if an alpha particle ionizes the air between the grid and ground plane.
(an alpha particle will leave a trail of ionized particles as it collides with air molecules and sheds energy until coming to rest)
A break down (spark) will occur where that ionization took place, and only where the ionization took place. Giving a quality visual indicator that an alpha particle was present.
I find the device to be a very useful tool for demonstrating how far alpha particles can travel in air, and how they are easily stopped by thin materials like kitchen plastic wrap. I regularly use it to perform demos for kids, etc.