It is in addition to a jail term, both to make sure that such an individual is no longer a threat to society as well as to take away what these brutes most prize - their manhood. That can also be the punishment for other particularly brutal rape cases. I believe that this will be a bigger deterrent than even the death penalty since many rapists are asserting their manhood(in their pathetic minds) by the act of rape.
Then I am with you. Chemical castration with rigorous jail term, say, for ten to twelve years for raping children and minor girls which are open and shut cases. But so far as this gang rape case is concerned, it has crossed all the limits of cruelty, inhumanity and in such open and shut cases, death penalty is a must.