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Count Accumulator for Radiation Levels (CARL)

2017-01-18 05:02  
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Count Accumulator for Radiation Levels (CARL)
The CARL device is an add-on numerical counter that plugs into the headphone jack of 1960s vintage geiger counters such as the Victoreen CDV700 and CDV700-6B. It should also work with the Lionel ENI/LENi counters, and any other geiger counter that has a headphone output pulse greater than -5V. Vintage 1960s era geiger counters don't actually count, they use an analog meter with an integrator circuit to give short-term averaged readings of radiation detections (clicks). The CARL circuit keeps track of the total number of clicks for a period of either 60 or 600 seconds (1 or 10 minutes). This provides a way to get a long-running count of low-level radiation from sources such as radon gas, rock samples and background radiation. The CARL circuit allows for the measurement and comparison of radioactive sources that are of levels that don't produce measurable readings on analog geiger counter meters. In my Colorado location, the CARL counter shows background radiation levels of 15-20 clicks per minute upstairs and 20-25 clicks per minute in basements where radon gas is present. As a collector of rocks, my interest in making this device was to find all of the radioactive minerals in my collection, and remove them from my living space. I found quite a few rocks that registered above the background level, fortunately, I did not find anything super-hot. I have also used the meter to compare background levels in various geographical locations.