From internet resources, $α$ particles can only travel few distance in air (or few range in air), is that because it been absorbed in air?


1 Answer 1


Wikipedia states:

Because of their charge and large mass, alpha particles are easily absorbed by materials, and they can travel only a few centimetres in air. They can be absorbed by tissue paper or by the outer layers of human skin. They typically penetrate skin about 40 micrometres, equivalent to a few cells deep.

Absorbed means crash into, slow down and obtain electrons.

An alpha particle is a fast moving (5% the speed of light) helium nucleus. Once it slows down by bouncing off other molecules and obtains some electrons (from the environment) it is just an atom of helium and completely harmless. Since the alpha particle is quite large the chance of it hitting something in air is quite high. As it has a charge this is increased as it will tend to attract and be attracted to any other molecules that happen to be negatively ionized, or deflected by those positively ionized, and a near miss will still transfer some momentum.

  • 1
    $\begingroup$ Don't forget Blackett's discovery of the 14N($\alpha$,p)17O nuclear reaction in 1924 using a cloud chamber. $\endgroup$
    – Jon Custer
    Nov 12, 2020 at 18:06

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.