|Project Nuclear War Detector|
|Alerts for thermonuclear war and other major radioactive incidents.|
Inspired by a design from Charles Wenzel over at techlib.com, I made a radiation detector designed to react only to very high amounts of gamma rays. It is a simple pin-diode type detector, and although it will respond to natural background radiation, such low levels only elicit a click from the device about once every 15 minutes or so. When exposed to sufficiently ridiculous levels of radiation, it will instead emit an irritating sound, thus hopefully alerting participants present at the space to the eventuality of an unfolding nuclear conflict or similarly unfortunate event. To quote Mr. Wenzel: "Being caught off guard by a nuclear war can be inconvenient. This project should alert the utterly unobservant individual to any significant nuclear exchange or radiation spill in the immediate vicinity, giving the owner time to kiss various body parts goodbye."
The November 2011 issue of Elektor magazine included a somewhat improved iteration of an earlier design for a simple PIN diode radiation detector. I took their circuit, shrunk it down with smd parts, and combined it with a comparator and active buzzer to make a bare-bones radiation detector. It works by reverse-biasing the photodiode in complete darkness. A sufficiently energetic gamma ray will present as a tiny pulse across the diode, which is then amplified by a jfet and a dual opamp. This signal is fed into the comparator, triggering an LED and causing the buzzer to emit a short audible click. Thanks to the active circuitry in the buzzer, a higher count rate will first devolve into a mildly irritating hiss or squeal, subsequently ramping up to a more whiny (and frankly complainatory) note as the device is exposed to increasingly skin-sloughing levels of radiation.
It will emit a barely audible click once every 15 minutes or so during normal operation. This is not cause for alarm. Stronger sources such as a radium watch hands will cause it to click at a rate of up to 60CPM, but only if the source is held directly over the sensor package.
Due to microphonics, any impacts or heavy vibrations will cause the sensor to trigger, but this will only register as short intermittent clicks. The bare-bones comparator design (with a simple voltage divider as reference) does have a slight downside though, as it leaves the detector quite sensitive to input voltage fluctuations. I've set the threshold so that the unit will continue to function up to 5.2V, but above that level the sensor will behave in a manner indistinguishable from its highest alarm condition. This admittedly regrettable flaw in my design may be remedied with a voltage reference at some future date :p
The sensor is complete and functional, all that remains is to build a case for it.