2-DIMENSIONAL NEUTRON SCINTILLATION DETECTOR WITH OPTIMAL GAMMA-DISCRIMINATION

The gamma sensitivity of a two-dimensional scintillation neutron detec tor based on position sensitive photomultipliers (Hamamatsu R2387 PM) has been minimized by a digital differential discrimination unit. Sinc e the photomultiplier gain is position-dependent by +/- 25 % a discrim ination unit was developed where digital upper and lower discriminatio n levels are set due to the position-dependent photomultiplier gain ob tained from calibration measurements. By this method narrow discrimina tor windows can be used to reduce the gamma background drastically wit hout effecting the neutron sensitivity of the detector. The new discri mination method and its performance tested by neutron measurements wil l be described. Experimental results concerning spatial resolution and gamma-sensitivity are presented.