Optimization design of diaphragm of the ¹³⁷Cs irradiator

The Monte Carlo simulation of the flatness and scattering dose for the ¹³⁷Cs radiation was performed with respect to different cone angle of the diaphragm collimator, and the diaphragm collimator was optimized. The flatness by using the diaphragm collimator was compared between the experimental results and calculations. The radiation field with flatness better than 99% and diameter greater than 10 cm is obtained at 1 m from the center of radiation source. The simulated results and measurements for the axial dose of the ¹³⁷Cs radiation were compared with the inverse square theory and the discrepancies were both smaller than 1%. The flatness and axial dose distribution with the diaphragm collimator can meet the requirements of ¹³⁷Cs standard radiation field. (authors)