x ray machines have a reletivley short half life
It doesn't have a half life at all.
Half life is the property of a radionucleide, i.e. an atom that is unstable, and going (at some point) to emit some radiation in the form of a particle or electromagnetic gamma wave with very high energy / short wavelength).
The radiation itself keeps on travelling until it gets absorbed by something.
If there are particles involved, they can knock into and then break up or stick to an atom they hit, resulting in the atom changing into a different element. This new atom may in itself be unstable and hence radioactive.
If there are gamma waves involved, they also can affect a nucleus because of their small wavelength (comparable to a necleus) and high energy.
Whereas, although an X-Ray is an electromagnetic wave, it is not produced by a nuclear process but rather by an electronic one. It has relatively low energy compared to a gamma and relatively large wavelength compared to a nucleus, so does not cause nuclear changes in things that are hit.
Their wavelength is more comparable to the size of an atom as a whole, and they do have enough energy to ionise an atom, (as in knock out an electron from it) thereby disrupting the chemistry. So they are harmful, which is why only the minimum possible exposure consistent with the required task is used. However they do not make things radioactive.
pb