If I'm not getting the proper pulse do I need to replace the OP amp?
No if you are not getting proper pulses then you have to find out why.
Only one reason is a faulty op-amp and that is not so likely. A more likely reason is that it is wired up wrong or no pulses are coming out of the photo multiplier.
This could be that your crystal is not scintillating, there is poor optical coupling between your crystal and photo multiplier or your photo multiplier is not working.
There are more things to go wrong than the sum of the components in your project.