**Aim**
This experiment shows the way in which gamma-rays are absorbed in matter and under the particular conditions of this experiment gives a rough estimate of the gamma-ray energy. Precise measurements would be carried out using a gamma scintillation counter.

**Safety Assessment**
- Wear lab coat, safety glasses and gloves, and handle all the sources with tweezers

__Theory__
__Total Absorption__
The total absorption follows an exponential law of the form

*I = I*0e-μx, where

*I* and

*I*0 are the transmitted and incident gamma ray intensities, x is the absorber thickness and μ is the total absorption coefficient. This exponential behaviour only holds for ‘good’ geometry, i.e. when the source, absorber and counter are widely spaced so that no scattered radiation is detected. The ‘half thickness’ (x½) is defined as the thickness of absorber necessary to reduce the gamma-ray intensity by a factor of 2, i.e. when I/I

0 = ½.

Experimental procedure for the absorption of gamma rays
Questions