A plant growth simulation algorithm was proposed for optimizing source pencil deployment for a 60Co irradiator.A method used to evaluate the calculation results was presented with the objective function defined by relative standard deviation of the exposure rate at the reference points

and the method to transform two kinds of control variables

i.e.

position coordinates xj and yj of source pencils in the source plaque

into proper integer variables was also analyzed and solved.The results show that the plant growth simulation algorithm

which possesses both random and directional search mechanism

has good global search ability and can be used conveniently.The results are affected a little by initial conditions

and improve the uniformity in the irradiation fields.It creates a dependable field for the optimization of source bars arrangement at irradiation facility.