Am currently doing an undergraduate project work on 'estimation of radiological risk pose by U-238, th-232 and K-40 in rock samples' . The instrument I'll use are NaI(TI) crystal for scintilation were the gamma rays from the source(my rock samples) interact with the crystal through photoelectric effect, compton effect & pair production thus releasing photoelectrons, A photomultiplier tube (PMT) optically couple to the detector- to energize the photoelectrons from the detector, multichannel analyzer (MCA) plus an amplify with A-D converter, and a computer with the software winDAS installed to display the spectrum in histogram with count/second on the vertical axis and channel(energy in MeV) on horizontal axis. The radionuclides present in the sample is identified if you trace it's energy on the spectrum, eg K-40 who's E is 1.460MeV will be traced. Now, once the spectra corresponding to K-40 energy is identified how do i CALCULATE the ACTIVITY(Bq) of this nuclide and that of others to be identified?. Thanks in advance!