Abstract: The detector has a certain geometric structure. If the radiation intensity of different distance directly is measured, the result should deviate greatly from the theoretical value. In the test of the experiment for inverse square law between γ-rays intensity and distance, a suitable collimator for the detector can reduce efficiently the influence of the incident angle difference of γ-rays which can bring the distance measuring uncertainty, which improves greatly the accuracy of result. We use Monte Carlo method to design the experiment and collimator and use simulation experiment to determine the radius, thickness, aperture size of the collimator. Finally, we conduct the experiment with the collimator of this kind, detector and radioactive source, test whether it accords with the inverse square law.

Key words: collimator, MCNP, inverse square law