This book is devoted to the use of NAA to be applied for the determination of the qualitative and quantitative elemental analysis of selected samples. It involves the use of the knowledge of nuclear reaction particularly (n, Gamma) reaction and implement its practical applications to determine element types and their concentrations in the sample. In lab, a total of Five different biological and geological samples were studied, four samples were studied for their qualitative and quantitative elemental analysis and one soil sample was studied for its natural radioactivity. Long lived and short lived radionuclides spectra were measured using HPGe gamma detector. Using known values of gamma-ray energies ema- nating from calibrating point gamma sources, an energy calibration curve and full energy peak efficiency curve were determined and plotted. The best fit line matched the data with a least squares fit, R 2 , of approximately equal to 1.