# 05/09/2011

I did some counts test like:

The distances are:

between PS1 and PS2: 8 cm
between PS1 and n's: 2.5 cm
between PS2 and n's: 1.5 cm
between PS1&2 and n's PMT: 80 cm


The powers were:

PS1 and PS2:  -1000 V (the new power supply C.A.E.N N471)
n's: -1100 V (the old power supply AEC 315 B)


The PMT for n's detectors is PMT HAMAMATSU R580 with supply voltage 1250/1500 V. But I have used the value above, because I though the counts rate was reasonable. See my table below.

The thresholds were:

PS1 and PS2:  -80 mV
n's: -60 mV


Let see what we have. First he CF-243 source is far far away (sealed in the safe):

counts/min (1 min test) counts/min (1 min test) counts/min (5 min test) counts/min (5 min test) avg counts/min
PS1 153 170 132.4 143 149.6
PS2 150 173 175.6 157 163.9
PS1+PS2 3.8 (5 min test) 5.8 (5 min test) 5.8 4.4 4.95
n's 358 378 373.6 354.3 365.9

Second the CF-243 source is somewhere aside (on the table 40 - 60 cm away from detectors. That test supposed to be initially as test without CF243 source and I just put the isotope away from detectors somewhere on the table, but as happened the PS detectors was able to see the source):

counts/min (1 min test) counts/min (1 min test) avg counts/min
PS1 373 362 367.5
PS2 654 656 655
PS1+PS2 2.0 6.0 4
n's 358 358

Third the CF-243 source is on the top of PS1:

counts/min (1 min test) counts/min (1 min test) counts/min (1 min test) counts/min (1 min test) avg counts/min
PS1 364,570 363,477 341,157 341,729 352,733.3
PS2 19,832 19,980 19,384 19,062 19,564.5
PS1+PS2 993 959 908 903 940.8
n's 369 352 375 369 366.3

Now the CF-243 source is on the top of n's detector:

counts/min (1 min test) counts/min (1 min test) counts/min (1 min test) counts/min (1 min test) avg counts/min
n's 362 319 374 398 363.3

What about the PS's detectors. I can concluded that detectors works good, detects the cosmic, and increase the counts as the external source approaches the detectors.

What about the n's detector. The counts rate is basically the same with and without the source CF243. So what we are really detect? Cosmic? Then why the rate does not depend from source. Internal noise of PMT?

I am going to increase the power supply for HAMAMATSU, adjust threshold and see what happens.