=== Measuring Radiation ===
Background on Space Radiation Measurements
What they found was radiation levels were high (relatively) near the surface of the earth, low levels in the mid-atmosphere, but yet high again near space. What did this mean? The reason was because near Earth radiation had come from radioactive materials emitting energy, but the near space radiation was from the cosmic radiation background. This was a very important finding for space physics.
The experiments which we perform below are an imitation of those famous historical experiments. The difference is we are using modern electronics to record the information for us - no expendable human pilots needed.
More Background - NASA's Mars Science Laboratory
This graphic shows the flux of radiation detected by NASA's Mars Science Laboratory on the trip from Earth to Mars from December 2011 to July 2012. The spikes in radiation levels occurred in February, March and late May of 2012 because of large solar energetic particle events caused by giant flares on the sun. The data were obtained by the Radiation Assessment Detector on Curiosity....The MSL spacecraft structure (which includes the backshell and heatshield) provides significant shielding from the deep space radiation environment, reducing significantly the particle flux observed by the Radiation Assessment Detector.
Clearly, March was a great month for astronauts to eat popcorn.
The Geiger Counter
It requires a 9V battery to power, while current draw is really small. I used a non-rechargeable lithium 9V battery as they are rated down to -40C before failure. A typical battery, including lithiums, will fail by -20C. Just one battery is good for several flights.
Obtaining a Signal from the Geiger Counter
If a gamma or beta ray is detected, it will pulse about ~6 times, spaced at about 8ms per pulse. Your microcontroller simply needs to count all pulses within a specific time (interrupt on rising edge) to record a single ray detection event. If only 2 or 3 pulses are counted, then the microcontroller should just ignore it as a false signal. Below is an image from an oscilloscope of what a single gamma ray detection will look like.
Note that a 4V spike would risk damaging a 3.3V microcontroller, such as the Axon Mote microcontroller (which I used). To correct for this problem, you just need to replace the blue LED with either a green, yellow, or orange LED. This is because different color LEDs have different voltage drops, and these three colors have the voltage drop you need.
Using the Geiger Counter in Space
To test if this would be a problem, I placed our Geiger Counter into a vacuum chamber (available in any professional chemistry lab). Sparks everywhere! As such, without modification, it won't work for space. To solve the problem I covered the high-voltage components with hot glue - a very effective insulator. The following video demonstrates my Geiger Counter tests.
As seen in the above video, the electrical short didn't begin until the vacuum chamber surpassed 30 inches of mercury:
One more picture of everything being tested in the vacuum chamber, just to make sure nothing would fail in a vacuum:
Yea, for a robotics engineer, I can be really dumb sometimes . . .
Anyway, I at least have radiation data from the many pre-launch flights. This first chart is from leaving it sitting on my room floor for four hours. You can see that the radiation trend was very slowly decreasing, but I didn't investigate further about why. Click to enlarge:
This below chart shows what radiation looked like inside my freezer. It doesn't appear that cold temperatures affected radiation readings. Click to enlarge:
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