Inverse-square law and absorption of gamma or beta rays with the Geiger-Müller counter

Principle

The inverse square law of distance is demonstrated with the gamma radiation from a 60-Co preparation, the half-value thickness and absorption coefficient of various materials determined with the narrow beam system and the corresponding mass attenuation coefficient calculated.

Benefits

• Basic experiment in nuclear physics
• Showing two fundamental laws: Inverse square law and absorption
• Classical version with GM Counter for better understanding

Tasks

1. To measure the impulse counting rate as a function of the distance between the source and the counter tube.
2. To determine the half-value thickness d1/2 and the absorption coefficient of a number of materials by measuring the impulse counting rate as a function of the thickness of the irradiated material. Lead, iron, aluminium, concrete and Plexiglas are used as absorbers.
3. To calculate the mass attenuation coefficient from the measured values.

Learning objectives

• Radioactive radiation
• β-decay
• Conservation of parity
• Antineutrino

• g- quants

• Half-value thickness

• Absorption coefficient
• Term diagram
• Pair formation
• Compton effect
• Photoelectric effect
• Conservation of angular momentum
• Forbidden transition
• Weak interaction
• Dead time