1. Radiation enters the GM tube

Radiation (alpha, beta, gamma, or X‑ray) enters a sealed tube filled with gas (usually argon or neon).

The tube has:

• A central wire (anode)
• A cylindrical outer wall (cathode)
• High voltage applied between them

2. Radiation ionizes the gas

When radiation passes through the tube:

• It knocks electrons off gas atoms
• This creates ions (charged particles)
• This process is called ionization

3. Avalanche effect (signal amplification)

The freed electrons are pulled toward the central wire because of the high voltage.

As they move:

• They collide with other atoms
• These collisions free even more electrons

This creates a chain reaction (avalanche).

Result:

• One radiation event → a large electrical pulse

4. Pulse is detected and counted

The detector electronics:

• Detect the pulse
• Count it as one event

This is displayed as:

• CPM (counts per minute)
• CPS (counts per second)

5. Tube resets (quenching)

After each event:

• The tube temporarily becomes inactive
• It must reset before detecting the next event

This is called dead time

Simple Analogy

Think of a GM detector like a light switch that snaps ON when radiation hits it:

• Radiation enters → triggers a spark
• Spark becomes a big signal → counted
• Tube resets → ready again

It counts events, not energy strength.