HV and Threshold calibration

Procedure for the neutron array HV and threshold calibration

Main considerations -

• calibrate all neutron bars to equal gains.
• set gains as low as posibble, to reduce current on PMT's.
• set threshold energy as low as possible to increase efficiency.
• set threshold energy low enough to remove minimum ionizing electrons.

 optimum was chosen at threshold = 5 MeV = 300 channels - need to re-check.

 this is equivalent to 1 MeV = 60 channels
 

Calibrations steps -

• Test-area calibration using cosmic muons

Use top-buttom bar trigger, to obtain vertical minimum ionizing muons with known energy deposit.

adjust HV, so that the muon peak will be at-

10.0 cm bar -> E=20 MeV -> channel=1200

12.5 cm bar -> E=25 MeV -> channel=1500

15.0 cm bar -> E=30 MeV -> channel=1800

25.0 cm bar -> E=50 MeV -> channel=3000

• Beam calibration using the H(e,e'p) reaction.

Use the H(e,e'p) reaction to create 1 GeV/c protons which will have energy loss of 32 MeV for a 10cm wide bar, calibrate the gain cofficients, so these events will be at channel=1920