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:

1. The transistors will not operate, and may be damaged, if not connected exactly as shown. This is also true of the silicon rectifiers.
2. 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).
3. All solder joints must be bright and shiny. Gray, dull,grainy solder joints usually mean poor electrical con nections and could prevent proper operation.