The Pion Beta Decay Experiment and A Remeasurement of the Panofsky Ratio

7.2.1 On-line Gain Matching

Prior to data taking the gains of the individual channels of both calorimeters were equalized. This was done in an iterative way using the 129.4 MeV photon peak. With a 12-bit ADC channel full scale of 4096, a position at 3000 was chosen to provide sufficient dynamic range. The actual peak position of the i-th detector module whenwas determined by building the sums

(7.a)

where N is the number of modules (44 in the case of the CsI-array and 64 in the case of NaI-wall), x_j the channel number of the j-th module and p_j the pedestal value. The obtained peak was fitted using a Gaussian curve with an exponential tail. For each channel the necessary decrease or increase for the supply voltage was calculated and applied on demand. After about five iterations, a similar peak position for each channel was achieved, as well as an improved energy resolution.