# Attenuation of Beta Particles

## Background

In this experiment we will study the attenuation of beta particles in aluminium, using a radioactive source and a Geiger counter detector.

The source used is strontium-$$90$$ which undergoes $$\beta^{-}$$ decay into yttrium-$$90$$ with decay energy $$0.546$$ MeV and half-life $$28.79$$ years.

Each decay emits an electron ($$\mathrm{e}^{-}$$) and an electron anti-neutrino ($$\mskip 1.5mu \overline{\mskip-1.5mu \nu_{\mathrm{e}}\mskip-1.5mu }\mskip 1.5mu$$). Neutrinos have negligible probability of interacting with matter. Electrons, however, lose kinetic energy as they interact electromagnetically with matter. So, they can only travel a certain distance, or range, before they come to rest.

## Theory

The absorption of $$\beta$$ rays is given approximately by Beer’s Law

$$I_{x}=I_{0}\,\exp\left(\mu\,x\right)\nonumber \\$$

where: