A picture is worth ...
Here I've posted a few pictures from the assembly of the CRD and tried to include some problems I overcame during the process. The LBL assembly manual is a good starting point but since components vary, (expecially electronics parts numbers) so will your assembly. Pay special attention to instructions for your PMT's since they're the most expensive parts of the detector. The P30CW5 model I used required a 50 ohm terminator for a signal lead of over 200 mm and used coaxial cable. An improper connection of the coaxial cable caused problems with coincidence counting by creating excessive noise in the signal and created continuous counting on the display. Again it's always best to double-check your connections and your instructions. |
The polished plastic scintillator as ordered, cut, polished, and wrapped in tape. When handling the plastic you should use rubber gloves to prevent oil and fingerprints from getting on the scintillator. |
The lucite "cookies" where the scintillator will attach to the PMT with optical cement. Be sure to have all the bubbles out between the half circles and the flat sheet.
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An overhead view of the PMT showing electrode through the quartz window..
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Since the scintillator face was oval and the PMT window was round, the white bezel on the PMT window had to be carefully trimmed with an exacto knife in order for it to fit.
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Clamps and stands were used to hold the paddles together while they dried for 48 hours.
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The scintillator with the masking tape removed just before it's wrapped for assembly. The cardstock shown will go over the foil layer and then be covered with tape.
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Aluminium foil is wrapped around the scintillator to help reflect photons back into the PMT.
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The finished scintillator paddle is wrapped with several layers of black gaffer's tape to block exterior light and protect the joint. Since my case does not support the end opposite the PMT, lots of tape was used.
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A standard, midtower ATX style PC case was used for the housing. The plexiglass side panel allows for easy access, mounting the circuit board and adds to cool factor.
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The paddles were mounted to the disk drive bays using existing holes and some automotive hose clamps for adjustment or removal.
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The printed circuit board as recieved from Dr. Matis @ LBL. Numbered areas correspond to components on the parts list.
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The resistors soldered to the board.
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Switches, sockets for IC chips, and the LED's attached. The advantage to sockets, is that you can easily replace the IC chips if they fail and not have to worry about burning them with the soldeirng iron.
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The completed circuit board.
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My report shows the detector failing to count due to a faulty input signal. To fix this the IC 7ns comparators were replaced and a 50 ohm terminator (bottom) was put in line with the signal from the PMT's. The coax cable is required to recieve a viable signal and the braided ground must be insulated from the signal wire (shown top). Be sure to consult your PMT manual.
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A completed signal header with the shielded black ground wire (top) and the second signal header with terminator under the pink insulation before the ground wire is soldered on to the braid (bottom).
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The completed and finally assembled detector.
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