I tried asking this question in the maths help, but am still stuck. Q. For a simplified model of a proton's charge distribution, (where R can be considered as some characteristic "size" of the proton): [tex] \rho [/tex](r) [tex] \propto [/tex] [tex](1/r)[/tex]Exp(- r / R) where R is some characteristic size of the proton. With some help I've figured the integral to this solution is the exponentialintegral: Ei(-r/R) in the past when I'm asked to normalise something I'd take the limits from infinity to -infinity and find N so the probability is 1, here though the exponential integral can't be normalised from what I can see. Any pointers would be appreciated.