It is a really bad idea to use gamma as a variable name because you are now stepping on the name of a very useful function in MATLAB.
Regardless, we cannot tell you when you did, since you never give the value for that variable, nor for Rc or the vector l.
Odds are some of those variables are such that the lower limit of integration is relatively large. It need to be too huge for that integral to be zero anyway.
What is the numerical integral of a function that is zero or effectively so over the entire domain of the integral? Even if the interval is infinite in width, integral will return zero.