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  #31  
Old November 3rd, 2011, 08:01 AM
ericfarmer ericfarmer is offline
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Originally Posted by iCountNTrack View Post
Quatum randomness based on quantum events are the most random occurrences known to date, which means nobody has been able to discern any patterns so far.
I tried something like this many years ago as something of a science project. I yanked the chunk of Americium out of a First Alert brand smoke detector, and placed it next to a radiation monitor (http://www.aw-el.com/) that was linked to the serial port on my PC. Each detection caused a modem status register (MSR) interrupt, at which point I used the time stamp counter (rdtsc instruction) to record the time of the detection.

The idea is that the Americium decays, emitting alpha particles as a Poisson process, meaning that the random times between decay events are independent and identically (*) distributed. If two consecutive intervals between successive decay events are measured, then the first interval is equally likely to be longer or shorter than the second... yielding one random bit (e.g., 1 if the first interval is longer, 0 if it is shorter). Slow but effective.

(*) But the pairs of intervals are not quite identically distributed. As the Americium decays, the Poisson rate (\lambda) very slowly decreases, which causes a slight bias toward 0 bits in the above approach. A simple band-aid for virtually eliminating this first-order bias is to simply reverse the sense of the comparison for every other bit.

Finally, this is nothing new. I think the HotBits site (a web source of random numbers, which strikes me as a spectacularly bad idea) used this approach, and a quick search yields a page describing almost exactly the same setup here: http://www.etoan.com/random-number-g...ion/index.html.
  #32  
Old November 3rd, 2011, 10:21 AM
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aslan aslan is offline
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Quote:
Originally Posted by ericfarmer View Post
I tried something like this many years ago as something of a science project. I yanked the chunk of Americium out of a First Alert brand smoke detector, and placed it next to a radiation monitor (http://www.aw-el.com/) that was linked to the serial port on my PC. Each detection caused a modem status register (MSR) interrupt, at which point I used the time stamp counter (rdtsc instruction) to record the time of the detection.

The idea is that the Americium decays, emitting alpha particles as a Poisson process, meaning that the random times between decay events are independent and identically (*) distributed. If two consecutive intervals between successive decay events are measured, then the first interval is equally likely to be longer or shorter than the second... yielding one random bit (e.g., 1 if the first interval is longer, 0 if it is shorter). Slow but effective.

(*) But the pairs of intervals are not quite identically distributed. As the Americium decays, the Poisson rate (\lambda) very slowly decreases, which causes a slight bias toward 0 bits in the above approach. A simple band-aid for virtually eliminating this first-order bias is to simply reverse the sense of the comparison for every other bit.

Finally, this is nothing new. I think the HotBits site (a web source of random numbers, which strikes me as a spectacularly bad idea) used this approach, and a quick search yields a page describing almost exactly the same setup here: http://www.etoan.com/random-number-g...ion/index.html.
The Dilbert comic on your link was so funny, I couldn't resist putting it here for all who don't follow the link to see.

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