im not sure, i didnt to that Q or finished the topic. A suggestion is that it would somehow be related to the ionising ability in alpha, beta and gamma, and thus how they are used in medicine/agriculture/industry...hope that helps..
you use that guys equation... ummm... forget his name, but it has rhybergs constant, and you work out the energy if it goes to an infinite quantum number level thingy.
its the energy that's needed to completely remove an electron from an atom.
for this question, you use that equation...yeh i forget the name too...but you put in n(final) as infinity and n(initial) as 1.
now you know the wavelength of the photon needed (which turns out to be 1/-R).
then put that into E=hc/wavelength (it comes out nicely as -hcR) and that should get you -13.6eV