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Segmented PMTs
Last updated: May 24, 2019
By default, optical photon sensitive surfaces (referred to as PMTs here) are not segmented. In order to enable PMT segmentation, use the following commands
/nDet/detector/setPmtColumns 8
/nDet/detector/setPmtRows 8
These two commands will set the number of columns (along the X-axis or width of the detector) and the number of rows (along the Y-axis or thickness of the detector) of anodes that a segmented PMT has.
When you set more than one PMT columns or rows, you have the ability to specify the gain of each individual PMT anode.
The gain of a PMT anode is used by NEXTSim to set the amplitude of the single photon response in the simulated PMT light response class. By default, the individual gains of the anodes of a segmented PSPmt are all equal to 100%. In some cases, it is necessary to set the gain of each anode individually to better represent a physical detector.
To load a NEXTSim anode gain matrix use the command
/nDet/detector/setGainMatrix gain.dat
where gain.dat is the filename of a tab-delimited ascii file, an example of which
is shown below. Note that the command nDet/detector/update must be called
before you attempt to read in a gain matrix otherwise the command will fail.
78 80 85 88 89 81 89 96
77 84 92 95 96 93 91 98
77 68 78 91 92 83 84 96
78 69 82 95 97 86 83 94
78 70 80 92 97 84 83 95
75 71 79 89 99 85 81 95
70 77 81 87 100 92 96 93
72 73 74 80 90 93 99 92
The gain matrix above is taken from the spec sheet of a Hamamatsu H12700A segmented PMT with 8x8 anodes. All values are given as percentages relative to the gain of the anode with the highest gain. There must be at least as many values in the file as there are anodes in the PSPmt otherwise the command will fail.