The trigger scintillators are in our lab at the Asburn, VA GWU campus. As a reminder here is the schematic:
Burnham came to visit us in February, bringing the support stands from JLab and helping us set up one of the scintillators. Here are some pictures: (can click image for fullsize)
Here is the scintillator in the nice support frame (legs have been removed):
Attaching the PMT's:
My first wrapping job!:
Burnham and Allena hard at work:
View of the whole setup:
Here are spectra from when the top and bottom paddles that define the coincidence are placed over the center of the scintillator (X = 110 cm):
TDC Channels:
QDC Channels:
And here are spectra when the top and bottom paddles are placed 20 cm from the left end (X = 20 cm):
TDC Channels:
QDC Channels:
And a table comparing peaks for the TDC and QDC values of the left and right:
Table 1: TDC and QDC peak values (QDC with pedestal subtracted)
| TDC Ch. | X=20 cm | X=110 cm | QDC Ch. | X=20 cm | X=110 cm | ||
| 1 (left) | 380 | 560 | 1 (left) | 3430 | 1901 | ||
| 2 (right) | 744 | 560 | 2 (right) | 1241 | 1860 |
Notice that the change in the TDC channels are both ~180 channels (and in the correct direction)!
Each channel corresponds to 35 picoseconds, so this time difference is 6.3 ns. The difference in distance is 0.9 m, which gives a speed of light in the scintillator of 1.4*10^8 m/s. This gives an index of refraction of 2.1. Note that the index of refraction for diamond is 2.4. It is unlikely that Saint-Gobain sent us diamond instead of BC408, which has n = 1.58.
Using n = 1.58, the speed of light in BC408 is 1.9*10^8 m/s; in 6.3 ns light should travel 1.2 m in BC408. Is it possible that the extra bounces to get into the pmt would effectively increase the distance from 0.9 m to 1.2 m?
See the shielding wall webpage located here.