The pulse height gains are used to correct for gain mismatches among the phototubes on the different cells of the detector. A spectrum for each cell is obtained from the geometric mean of the pulse heights from each end of the detector . A minimum ionizing cosmic ray will deposit 21 MeV in 10 cm of BC-517s liquid scintillator and 23.6 MeV in BC-408 plastic scintillator. Therefore the spectra should have a cutoff at 21 MeV for the first three planes, and 23.6 MeV for the last plane, followed by a peak and a long Landau tail. A sample spectrum is shown in figure .
Figure: Sample pulse height spectrum from cell NC02 (third plane, third cell). The dotted line at 21 MeV represents the energy of a minimum ionizing particle would deposit when traversing the cell.
The pulse height gain factors are adjusted in the software so that all the spectra for all the cells give the correct energy deposition.