I had this setup (see attached photo) for the linear gate method in a γγ coincidence experiment. Using a Na22 source. The pulse from the movable detector enables the gate of the MCB, and any corresponding pulse from the fixed detector that arrives within the gate interval will be considered coincident and will be counted in the spectrum. Basically, we wanted the signal from the SCA to enable the input of the MCB at the right time. This was done by connecting the SCA output to the logic shaper, and then the logic output to the gate input of the MCB. However, changing the angle of one detector didn't change the count rate. As the angle between the two detectors was moved either side of 180 degrees we should have seen a reduction in the count rate. However, it generally stayed the same. I'm not really sure why. Everything was connected correctly. I'm hoping someone has conducted this experiment and method before and this isn't too much of an uncommon error as I want to do it again and would rather not have to troubleshoot for hours!