HV and Threshold calibration

Procedure for the neutron array HV and threshold calibration

Main considerations -

• calibrate all neutron bars to equal gains.
• set threshold voltage as low as posibble (50 mV), 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 - still need to verify this.

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=1500 12.5 cm bar -> E=25 MeV -> channel=1875 15.0 cm bar -> E=30 MeV -> channel=2250 25.0 cm bar -> E=50 MeV -> channel=3750

• 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, so these events will be at channel=2000

• Gain calibration cross check using the C(e,e'p) reaction, by indentifying the punch-through point of the protons.

The punch-through energy in a 10cm wide bar is 120 MeV. The TOF vs. ADC of the C(e,e'p) events should have the following shape -