  A high efficiency, low background counting setup has been made at TIFR
consisting of a special HPGe detector ($\sim$ 70%) surrounded by a low activity
copper+lead shield. Detailed measurements are performed with point and extended
geometry sources to obtain a complete response of the detector. An effective
model of the detector has been made with GEANT4 based Monte Carlo simulations
which agrees with experimental data within 5%. This setup will be used for
qualification and selection of radio-pure materials to be used in a cryogenic
bolometer for the study of Neutrinoless Double Beta Decay in $^{124}$Sn as well
as for other rare event studies. Using this setup, radio-impurities in the rock
sample from India-based Neutrino Observatory (INO) site have been estimated.
