Geiger counter.

Geiger counter. Both of these devices are Geiger Counters, using Geiger-Mueller tubes as detectors for emissions from radioactive materials. Both devices have the option of making audible clicking sounds when radiation is detected. Both have meters to indicate 'count rate'. The large heavy older unit, the 'Classmaster', is tube technology, suitable for stationary class demonstrations. The newer light hand-held battery-operated Ludlum Survey Meter is easily portable and sensitive, and the meter reads in millirem/hour. See XX for a brief description of how a Geiger-Mueller tube operates. Classmaster: Turn High Voltage control to 'Off' before plugging in the device. 'Volume' switch should be on maximum. Selector switch should be set to 'Volts' and the high-voltage knob should be adjusted to about 700 volts. Place a radioactive source near the Geiger-Mueller tube. Turn up the voltage slowly until the counter starts counting. Don't raise the high voltage more than 150 volts above where the counting begins. Don't exceed 1000 volts on the tube. See manual for further info. Ludlum Survey Meter: Has 3 linear ranges that vary from 0-50 MR/HR. Uses two standard 'D' cells. There is a battery test switch. The speaker can be switched on or off. The meter can be set to fast (full scale 3 sec) or slow response (full scale 11 sec). The unit has an power supply adjustable from 0 to 1600 volts, if different G-M or scintillator tubes are desired. Use microphone to amplify clicks.