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How to Build A Geiger Counter - A Class Project

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  • How to Build A Geiger Counter - A Class Project

    Permission to copy with attribution & not for commercial purposes -




    EXPERIMENT 8: Build a Geiger Counter (A Class Project)

    THINGS YOUR CLASS WILL NEED: Geiger counter components (see parts list and circuit diagram). Gamma ray source.*
    Chances are you?ve heard of a Geiger counter before. This versatile instrument is one of the most useful pieces of equipment ever developed for detecting the presence of radioactive emissions.

    A Geiger counter is a relatively simple device. Its heart is the Geiger tube, a chamber filled with a mixture of special gases and equipped with a pair of internal electrodes that must be charged at high voltage.

    Normally, the gas inside a charged Geiger tube does not conduct electricity. However, if a radioactive emission strikes the tube, the gas is momentarily ionized, and it becomes a conductor for a split second. Thus, a pulse of electric current flows through the tube, from electrode to electrode. The electrical circuit of the Geiger counter is designed so that a click is produced by the headphones each time a pulse of current flows through the tube. Each click you hear means that a radioactive emission has struck the Geiger tube.

    *Your school may have a gamma ray source or a chunk of radioactive ore. If not, try to find an old luminous-dial watch or clock. These time pieces, unlike newer models, have a small amount of radioactive material, radium, mixed in with the dial phosphors. If all else fails, a low level gamma ray source intended for educational use is available by mail order (see inside front cover).

  • #2
    Re: How to Build A Geiger Counter - A Class Project

    Permission to copy with attribution & not for commercial purposes -





    Some Geiger tubes will respond to alpha, beta, and gamma radiation. However, the tube we used has a thin metal envelope that cannot be penetrated by alpha particles. Thus, this instrument detects only beta and gamma rays, along with cosmic rays from outer space.

    The Geiger tube needs about 900 volts to work. And believe it or not, our little unit can generate that voltage from the six-volt battery. But don?t let that high voltage frighten you. The unit is completely safe because it has a very low current output. Nevertheless, don?t touch the Geiger tube or the capacitors. You can get a mild shock if you go looking for trouble.

    How does the unit build six volts into 900 volts? In steps. Tapping the charge button (located on top of the unit) many times allows the voltage to climb with each tap. Eventually the voltage reaches operating level. We?ll say more about this later.

    Build the Geiger counter on a piece of perforated chassis board. Use push-in terminal strips to support the various components. The diagram shows how the parts must be connected. Keep these points in mind as you work:

    The transistors will not operate, and may be damaged, if not connected exactly as shown. This is also true of the silicon rectifiers.
    Try not to overheat the transistors and rectifiers whenyou solder them in place. It?s a good idea to grip eachlead with long-nose pliers when you start to solder (the pliers act as a ?heat sink? to protect the parts).
    All solder joints must be bright and shiny. Gray, dull,grainy solder joints usually mean poor electrical con nections and could prevent proper operation.

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    • #3
      Re: How to Build A Geiger Counter - A Class Project

      Permission to copy with attribution & not for commercial purposes -




      GROUND LINE

      The Geiger tube is so delicate you could deform with your fingers. So mount it gingerly. Use “broom clips,” one at each end. Also, make sure you connect to the right leads on the Geiger tube socket. The Geiger tube pins are numbered on the underside of the base. Pin 1 connects to the main circuit and pin 3 connects to ground. Pin 2 is a dummy pin that is not used.

      Be certain the negative terminal of the battery goes toground.

      Mount the completed package on rubber mounts in an enclosure. Any kind of enclosure will do; we just happened to pick a metal tool box. If you also use a metal
      box, don’t let any of the exposed wiring touch the metal walls.

      Before you install the assembly, cut a large rectangular hole in the wall next to where the Geiger tube will be. The hole will serve as a radiation window. Incidentally, both switches and the headphone pin jacks must be mounted on top of the enclosure.

      Procedure for Charging Geiger Counter

      Needless to say, turn on the power switch (S1).
      Put on the headphones.
      Tap the charge switch (S2) firmly in a rapid-fire manner about 60 times, or until you hear random click ing. This is normal background noise caused by cosmic rays.
      After the unit is charged up, tap the switch occasion-ally to keep it charged. You’ll be able to tell how often this has to be done when you start using the counter. It may range from several seconds to a minute or so
      Assuming you have a gamma source, note that when you bring the source near the Geiger counter, or vice versa, the clicking will increase dramatically.

      If you were fortunate enough to locate more than one source, the counter will indicate their relative strengths by the clicking intensity.

      With the Geiger counter and gamma ray source, you can now do the last part of Experiment 7 (on gamma ray shielding materials).

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      • #4
        Re: How to Build A Geiger Counter - A Class Project

        Geiger Counter Parts List

        Dl, D2 ? Silicon rectifier,
        Rl, R2 ? l.0-ohm, l/2-watt
        1000-volt PIV rating,
        l-ampere (or higher) rated
        current capacity, low reverse
        current (20 microamperes
        or lower)
        carbon resister
        R3 ? 1,500,000-ohm, l/2-watt
        carbon resistor
        R4, R5, R7 ? 560,000-ohm,
        Ql, Q2 ? NPN silicon transistor
        l/2-watt carbon resistor
        (2N3402 or equivalent)
        R6 ? 2700-ohm, l/2-watt carbon
        Headphones ? 2000-ohm high
        resistor
        sensitivity headphones
        Cl ? 0.0033-mfd, 600-volt
        tubular capacitor
        B ? 6-volt battery with screw
        terminals
        C2, C3, C4, C5 ? 0.47-mfd,
        600-volt tubular capacitor
        G ? Geiger tube (A tube and
        bakelite socket are available
        for about $20 from The
        Nucleus Inc., Box R,
        Oak Ridge, Tennessee 37830.
        Ask for tube-socket unit SG-2)
        C6 ? 0.006-mfd, 1600-volt
        tubular capacitor
        C7 ? 0.047-mfd, 250-volt (or
        higher) tubular capacitor
        Perforated chassis board
        T ? 6.3-volt AC, 1.0 ampere
        filament transformer
        Push-in terminals
        S1 ? SPST toggle switch
        Hookup wire
        S2 ? SPST normally open push-
        Suitable enclosure

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        • #5
          Re: How to Build A Geiger Counter - A Class Project

          What a sign of the times this is!
          _____________________________________________

          Ask Congress to Investigate COVID Origins and Government Response to Pandemic.

          i love myself. the quietest. simplest. most powerful. revolution ever. ---- nayyirah waheed

          "...there’s an obvious contest that’s happening between different sectors of the colonial ruling class in this country. And they would, if they could, lump us into their beef, their struggle." ---- Omali Yeshitela, African People’s Socialist Party

          (My posts are not intended as advice or professional assessments of any kind.)
          Never forget Excalibur.

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          • #6
            Re: How to Build A Geiger Counter - A Class Project

            If people have better designs, please post them.

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