The heart of the AL54 radiation sensor is a custom PIN diode covered with a thin aluminum foil to make it insensitive to light. Electrons (beta) and photons (gamma) easily penetrate the aluminum foil. Alpha particles which interact with the aluminum foil generate electrons and photons that can be detected by the PIN diode.  
The analog output of the pulse charge amplifier can be connected to an energy spectrum analyzer to detect radon decay products such as 218Po and 214Po.

An integrated pulse discriminator with temperature compensated threshold provides a true TTL signal output for alpha particles, electrons and photons.
The performance of the AL54 solid-state sensor combined with its extremely low power consumption makes it an excellent choice for physics lab experiments as well as cutting-edge designs.