June,18,2007 Teachers in lab
Experimenters:
- Jenette Briggs
- Keith Quigley
- Bettie Keetch
- Tony Forest
Monday, June 18, 2007
Out Quarknet Teachers had their first seesion experimenting with a coscmic ray test stand made up of two scintillators. Each scintillator was attached to a single PMT. A voltage of -900 Volts was applied and signals were observed using an oscilloscope.
First Cosmic ray scope pictures using PMT + Scintillator
First scope picture on a single detector
now look for a coincidence signal between two PMT detectors
Tuesday , June 19, 2007
Today our team of experimenters setup a discriminator (LeCroy Model 821) to determine which of the PMT outputs would be used to define the presence of a charged particle passing through the scintillator. The discriminator takes a signal from the PMT that is above the threshold (-30mV to -9V)and returns a voltage of -lV square pulse.
The voltage for each channel was set so that the trigger rates from the discriminator were the same (about 21 pulse/second).
Channel A voltage -1075V, Discriminator threshold -30mV,
Channel B voltage -1001V, Discriminator threshold -30mV.
Tuesday , June 20, 2007
The goal for our team of experimenters today was to repair the PMT devices to be used in the cosmic ray telescope as well as check for light leaks. We began the day by checking the rate of coincidence pulses in a ten minute interval. Beginning at 10:32 AM we counted 35 pulses after 10 minutes, averaging 3.5 coincidences per minute. Voltage rates and discrimimator thresholds were fixed from the previous day (Channel A -1075 V; Channel B -1001 V; Discriminator Threshold of -30mV for both)
After making some repairs to the PMT we checked them with devices previously known to work and found our repairs to be sucessful.
During the light leak test which involved using a dark room and roaming the cosmic ray detector with a flashlight. Using a -900V source, we saw no evidence of noise outside of our normal contraints.
Our final goal for the day was to determine appropriate distances to place the detectors within the telescope.
Cosmic Ray camera detector separation tests
Finger scintillators with PMTs set to :
PMT N714 HV= -1008 Volts
PMT N715 HV = -1025 Volts
| Paddle Separation (cm) | Rate (counts/hour) | Statistical Error in Rate (Counts/min) |
|---|---|---|
| 0 | 100 | 9 |
| 1 | 0 | 0.09e3 |
| 2.5 | 1:15 | 0.01e3 |
| 3 | 0 | 0.02e3 |
| 4 | 0 | 0.08e3 |
| 5 | 0 | 0.02e3 |
| 6 | 0 | 0.005e3 |