05/10/2011
continue...the same set up as before, the distances are the same:
First I change the power supply for HAMAMATSU PMT to the new 2 channel one C.A.E.N N471
The powers are:
PS1 and PS2: -1000 V (the old 2-channel TENNELEC TC952) n's: -1100 V (the new 2-channel C.A.E.N N471)
The thresholds are:
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 | 187 | 160 | 166 | 160.8 | 168.4 |
| PS2 | 187 | 170 | 180.4 | 184.4 | 180.4 |
| n's | 205 | 204 | 201.2 | 202.4 | 203.2 |
Interesting. The same power for HAMAMATSU PMT, but different counts result (see my test on 05/09/2011).
Now I increased the power supply for HAMAMATSU PMT (-1500 V as specified in the data sheet [1]) and adjusted the threshold (-500 mV). All other parameters are the same.
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 (1 min test) | counts/min (1 min test) | avg counts/min | |
|---|---|---|---|---|---|
| PS1 | 158 | 168 | 151 | 175 | 163 |
| PS2 | 194 | 166 | 162 | 176 | 174.5 |
| n's | 224 | 213 | 197 | 201 | 208.7 |
Now 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 | 378,893 | 378,612 | 377,909 | 378,665 | 378,519.7 |
| PS2 | 22,729 | 22,819 | 22,572 | 22,530 | 22,662.5 |
| PS1+PS2 | 1044 | 1021 | 1023 | 975 | 1015.7 |
| n's | 200 | 210 | 228 | 219 | 214.2 |
So the same results as before:
PS detectors probably detect the cosmic and very sensitive the radioactive source.
The counts rate for n's detector 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?