  We present the design and optimization of a Tomographic Gamma Scanning (TGS)
collimator based on Monte Carlo simulations using MCNP5 computer code. In these
simulations, an accurate Monte Carlo model of TGS was built and the collimator
radius, collimator deep and collimator shape of the TGS are optimized. The
simulation results reveal that the collimator aperture radius of 3.1 and depth
of 18.6 cm are the high sensitivity when FWHM choose 26.7cm, the rotated
hexagon is the optimal shape. Our design shows a significantly improved
performance of the TGS system.
