Beta particles are much more penetrating than alpha particles . Very high energy beta particles can penetrate to a depth of about a centimeter in tissue. Eye and skin damage is possible if the source is strong. Therefore beta sources do present an external radiation hazard . They are, however, relatively easy to deal with by shielding.
If the beta emitter is taken into the body it presents a far greater hazard, though generally less so than the alpha emitters .
Beta particles emitted by any given beta emitter have a range of energies with
a maximum which is characteristic of the emitting
nuclide . Fig. 2.11
shows the beta energy spectrum emitted by
Sr.
Figure 2.11: Beta energy spectrum of
Sr
The maximum energy of beta radiation from the majority of nuclides lies in the range 0.5 to 3.5 MeV but some have energy above and below this range.
Materials with high atomic number , such as lead, are the most effective in stopping beta particles. However, high energy beta particles produce x-rays known as bremsstrahlung when absorbed, and this effect is more pronounced in heavy and dense absorbers. For this reason lighter materials such as lucite or plywood are preferred as absorbers.
The penetrating ability of beta particles in air as a function of energy is
shown in Fig. 2.12
. When beta particles have lost their energy they
join the free electron population as ordinary electrons.
Figure 2.12: Range of beta particles in air