Cosmic Ray Telescope Construction

2003 SLAC QuarkNet Workshop


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QuarkNET team at the Stanford Linear Accelerator Center team
sand light guide Layers of plastic parts are lightly clamped together to avoid rounding edges during sanding.  A few small pieces of double sided tape are placed between the layers to prevent parts from moving independently and to protect surfaces.  It was found that too much tape makes it difficult to separate the layers when done.  The faces are protected from scratches from the metal clamp faces.  Gloves are worn to protect the plastic from skin oils.  Thomas Glanzman, answers questions.
The edges where light will be transmitted to adjacent parts need to be smoothed with successive 60 to 600 grit wet/dry silicon carbide sandpaper to remove scratches and prepare for gluing. wet sanding
Properly smoothed surfaces have a luster and no noticeable remaining scratches. luster
glide polish The sides of the light guides need to be further polished to reflect light into the photomultiplier tubes.  The lucite light guides can withstand the heat generated by an electric polishing wheel, while the more delicate scintillator plastic is polished by hand.
The shined surface reflects light like a sheet of glass. shine
scintillator plastic The scintillator blocks also need to be smoothed.  The outside edges need to be sanded to 1500 grit and polished to reflect light towards the photomultiplier tube.  The edge to be attached to the light guide needs to be finished to 600 grit to allow a surface for glue adhesion.  The glue will provide a medium for light transmission of about the same index of refraction so that surface needs not be polished.
Preparing Cerium Oxide polish on mole skin. preparing polish
polishing scintillator Carefully polishing a set of scintillator blocks.
cleaning All pieces need thorough cleaning before assembly.
supports The small support blocks are glued with epoxy to the light guide with smoothed ends aligned for attachment to the photomultiplier tube.  Care is taken to avoid getting glue on transmitting ends of blocks.
The mixed optical cement (Stycast 1266) is cycled through an evacuated chamber to remove gas bubbles that could deflect light transmission. outgasing glue
strapping photomultiplier to support The photomultiplier is strapped securely to the support plywood.
The light guide is attached to the photomultiplier tube with epoxy glue making sure there are no bubbles to impede light transmission. gluing light guide to PM tube
glue scintillator to light guide The scintillator is then glued and carefully aligned with the light guide.  The assembly is oriented vertically and held with rubber bands until the glue sets.
The support bases are screwed together and the water closet flange attached. making base
glue pipes The threaded pipe connections are glued to the smaller diameter pipe.
The smaller diameter pipe is inserted into larger plastic pipe and held in position by pipe clamps. adding pipe clamps
This movable arm is attached by long bolts, nuts, washers, lock washers, and wing nuts to the large support pipe.  The whole pipe assembly is placed in the pipe flange but not glued allowing for disassembly, transportation, and storage. stand
assembling mounting The center of gravity of each plywood mount holding the muon detector is located, mounting holes drilled and pipe ends attached by machine bolts.
Meanwhile each glued scintillator and light guide is again cleaned. adding pipe clamps
wrapping tube The light sensitive apparatus is first tightly wrapped in white Tyvek to reflect any escaping light back into the apparatus.  Marvelguard is then folded around the apparatus with silver side inward and black side outward to block any room light.
The cosmic ray detectors and photomultiplier tubes are wrapped with several layers of black tape to further block entry of any room light. taping
Seven completed detectors:  each scintillator, light guide, and photomultiplier tube is fully wrapped. detectors
checking circuit boards Each circuit board is checked to determine if it responds correctly to input signals.
A special photomultiplier base amplifies 5 Volts to a variable high voltage.  Each adjustment Helipot is calibrated by measuring the output voltage for a variety of settings. adding pipe clamps
Inside of a photomultiplier base. voltage amplifier
checking circuit boards
  1. Ionizing radiation such as muons made by cosmic rays pass through both top and bottom detectors
  2. creating light in the scintillators
  3. which generates electric current in both photomultipliers,
  4. which, if both electronic pulses are nearly simultaneous, is counted by the circuit board,
  5. then a summary of the event is sent to the computer and optionally recorded on disk.


The Cosmic Ray Detector construction portion of the 2003 SLAC QuarkNet Teacher's Workshop involved a significant amount of behind-the-scenes "volunteer" work by a number of people. Tom Glanzman and Willy Langeveld, co-conveners for this portion of the workshop, would like to thank the following people for their generous and important contributions:

  • Dave Trapp a participating teacher from Washington for recording this project in text and photographs (including this very page)
  • Harvey Lynch (also a SLAC QuarkNet Mentor) for his enthusiasm and insightful questions and suggestions
  • Michael "MO" Olsen for good advice, providing us a great space to hold this part of the Workshop, scintillator cutting and his ever present good cheer (and MO, we're going to miss you when you return to teaching this Fall!)
  • Karl Bouldin and Jim McDonald for their help rounding up equipment and parts, providing expertise in many areas, and hosting (tolerating?) the "pre-game" and "post-game" activities in the Group C lab areas
  • Stefanie Harvey who provided valuable advice about polishing the scintillator, and provided moleskin
  • Clive Field for being an authority on photomultipliers
  • Ken Martell for setting up a wireless network just for us
  • Anna Pacheco for providing supplies and offering extra drinks
  • Tom Jordan from FermiLab for managing, against difficult odds, to provide crucial parts in time for the Workshop, including such vital items as the logic boards and photo tube bases
  • Finally, a very special thank you is due to a person who despite a very demanding schedule at the End Station always seemed available to help in a variety of ways. Without his careful diversion and storage of surplus scintillator, photomultiplier tubes, cables, and other materials, we would not have embarked upon this project in the first place. He provided us with test materials, electronics, name it. He attended our preparatory meetings and generally wound up volunteering for something unexpected. Terry Tuck, please accept our very sincere thank you!!
  • - Tom and Willy


    to SLAC QuarkNet page

    created 6/25/2003
    revised 8/12/2003
    by D Trapp