A negatively-charged electron (beta minus) or positively-charged electron (beta plus) is more penetrating than an alpha particle as it is 8000 times lighter. By attraction or repulsion, it will remove thousands of electrons and will stop after passing through one of the following materials:

	a sheet of aluminium,
	1 cm of water,
	2 cm of living tissue,
	2 m of air.

(These examples give a rough guide only because the thicknesses penetrated depend on the energy of the particles).