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Cosmic Ray Detector Problems

  1. Oct 9, 2011 #1
    I am building a cosmic ray detector and I am following these designs:

    http://www.lbl.gov/abc/cosmic/documentation/CosmicDetector2-0.pdf [Broken]

    I have a few questions for those who may be familiar with this.

    a) In the parts page (http://www.lbl.gov/abc/cosmic/parts.html) I see that the price for the "integrated base and photomultiplier tube" is very expensive, so I opted for the separate base and PMT. My question is will I be able to use a different PMT tube for this detector than the one that is linked in the parts page? Also where exactly could I find the "base" that it is talking about. I would essentially just like to know exactly what the PMT that I choose would have to have in order to be compatible with this design. (ex. # of pins, brand, etc.)

    b) Is it possible for me to find or make some of the other materials for a much cheaper price and still be compatible with the design? I am primarily talking about the 2 scintillator parts (plastic and paddle) and the optical cement.

    I really like the design for this, but the prices for their linked parts are exorbitant. I feel like I am fine with the construction of the circuit board and its design, but I would just like to know more about the rest of the design (scintillator paddles and PMT) and if there is maybe a simpler circuit board and design that I could use. Any other information you have or can find on this topic is also extremely appreciated.

    I hope I put this in the right place, but it seems like an engineering problem to me.

    Thanks in advance for all of the help!
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Oct 9, 2011 #2
    I was at Berkeley as a grad student 50 years ago, and I made and used these phototube scintillator combinations for detecting particles from accelerators. Our favorite 2" end-window tubes were an RCA 6342(?) (10 stage) and an RCA 6810 (14 stage). The RCA 931 is a good side-window 9-stage tube and should work well. I don't know about the sensitivity of the 1P21 in the blue. I would never buy a used or NOS photomultiplier tube, unless it comes in its original box, because they can be "burned out" inside by exposure to light with the voltage on.

    I am a little confused by switch S2 in the schematic (page 44). I think it must be a 3-way switch with center off for proper pulse coincidences. The most important components in the schematic are U3 and U12 comparators, and the U4 B, C, D coincidence circuit. In all cases, U3 and U12 want anode signals (negative going pulses), so this means negative high voltage on the PMTs.

    I see no mention of the two required high voltage supplies for the PMTs.

    Here is pinout of the RCA 931:

    Last edited: Oct 9, 2011
  4. Oct 9, 2011 #3
    Yeah. I was thinking the same thing as I have read more about how the PMTs work. I am scared of buying one that may be burned out, but I don't really see any other options as I am a high school student on a tight budget and I just can not afford to buy a $150+ PMT when I also have to buy the other materials.

    I have at most $200 to spend on this project and I think that I will be fine with everything except for the scintillator and PMT as far as price and knowledge goes.
  5. Oct 10, 2011 #4
    Besides the cost of two PMTs with bases, the cutting and polishing of the scintillator and light pipes requires a special skillset. Berkeley (Lawrence Radiation Lab when I was there) had a special group that did that exclusively. You might consider starting out with two or three Geiger-Muller tubes in coincidence. The counting rate will be a lot lower, but so is the cost. Look for example at this simple cosmic ray GM coincidence circuit:


    The first time I built a coincidence circuit for cosmic rays (1957), I used vacuum tubes. ICs are a lot simpler.
  6. Oct 10, 2011 #5
    The reference web site you gave has proven to be very interesting. I was looking around the site and came across this:


    Do you think that this would be better (i.e. more economical and useful for gathering data) than the scintillation paddle detector or the Geiger-Muller detector that you referenced?

    Would it be better to use that design (http://hardhack.org.au/scintillator_detector) and take my data from it or use the GM design(http://hardhack.org.au/geiger_muller_detector).

    If this(http://hardhack.org.au/detector-outline) design was stable, I think I might would use it.

    My main objective for this project is to build a muon detector and gain useful data from it without spending exorbitant amounts of money.

    In addition, if I were to use the scintillator design that I referenced earlier(http://hardhack.org.au/scintillator_detector) what type of scintillation material would you recommend? Any other thoughts would be useful. Thank you for your help.

    EDIT: I have found this paper that seems to pertain to exactly what I need:


    The only problem is that I can not seem to find some of the parts and I am not exactly sure how the electronics portion of this design works and how I could get useful data. I would greatly appreciate any advice on this design as it is made with monetary implications in mind and seems perfect for what I need. Any thoughts on this are welcome.
    Last edited by a moderator: Apr 26, 2017
  7. Oct 10, 2011 #6
    The SLAC circuit (1995 era) looks interesting. You should look carefully at the theory and calculation of counting rates, even if you decide to use GM tubes. If you can get the scintillator and 931A's with base cheaply (as shown in SLAC TM), it might be worth a try. For information on the circuit board etc. contact Helen Quinn at quinn@slac.stanford.edu or

    MS 81 SLAC
    2575 Sand Hill Rd
    Menlo Park, CA 94025
    United States of America

    The important part of the circuit are the uA733 (video amp) and LM360 (comparator) chips. The 74123 (monostable multivibrator) with a 1 millisecond output pulse can drive earphones or light LEDs (as shown).

    I suspect you are looking at $500 to $1000 to build the SLAC design.
  8. Oct 10, 2011 #7
    Thanks for the input. I may have found some cheap scintillator and 931A's but I can't find the bases for the 931A's as they are discontinued. Would you recommend any other PMTs and bases or is the design specifically for that model from Hamamatsu?
  9. Oct 10, 2011 #8
  10. Oct 10, 2011 #9
    I have found a website that actually seems to sell the 931A (http://www.elexs.com/7Photo.htm [Broken]) but I would need the base. Could I buy 2 of these 931A's and buy a power supply that is linked on the right side Hamamatsu page (http://sales.hamamatsu.com/fr/products/division-tube/detecteurs/photomultiplier-tubes/part-931a.php) and use it or would I also have to buy the "socket + bleeder + HV circuit" that you mentioned for it to work? Would this be the same as buying a "base" for the 931A? It would be really helpful if I could buy 2 of the linked 931A's at $73.00 USD and then buy the bases. Do you think that this would work? I am sorry for all of this pedantry but I am not as familiar with some electrical problems as others.
    Last edited by a moderator: May 5, 2017
  11. Oct 10, 2011 #10
    The Hamamatsu web page on the 931A states "This product has been discontinued". I recommend you purchase a (wired) socket plus bleeder plus HV supply for each PMT tube you decide to purchase.
  12. Oct 10, 2011 #11
    Thanks for the help!
  13. Nov 1, 2011 #12

    I am on the same project here in Italy, is someone willing to share experiences?

    I bought all the pieces for about $450 (electronics + scintillator material + used PMT/ HV bases). I can provide all the details for the parts purchase.

    Currently I am prototyping and testing the circuit on a solderless breadboard, before soldering the final one.

    I do have a quick question about the 7 segment leds, I noticed that in the design they are powered with +12V. But from the data sheets of this component:
    the correct voltage seems 4/5 Volts.

    Am I missing something?
  14. Nov 1, 2011 #13
  15. Nov 1, 2011 #14
    Use current limiting-resistors on every cathode connection to limit current to 30 milliamps maximum. For 12 volts, use 510 ohm, 1/2 watt resistors.
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