Tracking Photons with G3sim

Plastic scintillator based detectors are commonly used in cosmic ray, high 
energy and nuclear physics experiments for study of charged radiation due 
to their fast response time (~1 ns), rugged nature and reasonable cost. 
The advent of wave-length shifting fibers has provided numerous options to 
explore newer designs and improved performance for these detectors. 
However, design of a new detector starting with a prototype is an 
expensive and time consuming option. On the other hand, if realistic Monte 
Carlo simulations could be performed to evaluate the performance of   
scintillator detector, then that could result in considerable savings in 
effort, time and cost. The G3sim is a realistic Monte Carlo code, 
developed entirely in-house, to aid the design of new scintillator 
detectors for the expansion of the GRAPES-3 air shower array at Ooty. It 
has successfully reproduced the measurements of photon yield, surface 
uniformity and the response time for different scintillator designs. G3sim 
is compact (~1000 lines of C++ code) with a simple input format, making it 
easy to understand and use. We have made it available to the scientific 
community on request. In this talk, I will discuss various features of 
G3sim and its validation for the GRAPES-3 scintillator detector followed 
by a small demonstration on its usage.