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.