04-20-2015
Started testing detector 4 again.
Fake stop time
Discriminator width was decreased from 40 ns (255 on discriminator display) to 6.3 ns (10 on discriminator display)
Discriminator threshold is set to 100 mv
The delay for the fake stop is set to 800 ns
CODA/CODAreader/ROOT_V5.30/R1DC/evio2nt -fr4516.dat > /dev/null
R1DC->Draw("(evt.TDC1190[1][6]-evt.TDC1190[2][6])/10>>(4096,-4096,4096)");
Run 4536
Below is a picture of the typical 800 ns fake stop pulse that should appear as a second hit in the Multihit TDC.
Now decrease delay of fake stop to 400 ns
Terminator test
Change discriminator threshold with terminators in
PMT detector #4 HV at -1000 Volts
Run 4537 had a discriminator threshold set to 100 mv and the terminators were in. I see very few multiple hits in Detector 4
Now change threshold to 30 mv
Run 4538
I see two pulses from the discriminator but only one from the delayed fake stop (perhaps our delay module Ortec 416A is ignoring the second pulse)
Now change threshold to 16 mv
Run 4539
Change discriminator threshold with terminators out
PMT detector #4 HV at -1000 Volts
Run 4540 had a discriminator threshold set to 16 mv and the terminators were out.
Run 4541 had a discriminator threshold set to 30 mv and the terminators were out.
Run 4541 had a discriminator threshold set to 60 mv and the terminators were out.
Run 4542 had a discriminator threshold set to 100 mv and the terminators were out.
clearly one can turn up the threshold high enough to get rid of the ring with the terminators out.
But are the terminators reducing the ring effect by attenuating or by reducing reflections (the ring) in the output pulse.
Using the scope I did not observe an attenuation of the PMT output by more than a factor of two when inserting 50 ohm terminators on both ends of the cable.
I still see the ring when the discriminator is set to 60 mV and the terminators are out. If I insert the terminators I do not see the ring at a discriminator threshold of 16 mV.
Unless the 50 Ohm terminators are attenuating the signal by more than a factor of 2, the attenuators appear to also be removing some of the "ring" output of the PMT base.