There's something that bothers me about radioactive decay being random. 
A given chunk of radioactive material will trigger a detector at some 
average rate and the time between events will seemingly form something 
like a gausian around that rate (I don't know if it would be a 
symmetrical gausian, in fact I doubt it). For instance, I was observing 
a piece of uranium glass with a geiger counter and got something like 1
count per second. So, a list of the time between each count (lets count 
to three decimals) will peak around 1 second and there will be very very 
few periods of 000 or even .010 sec, lots more of .500 sec and 1.5 sec, 
way more 1.000 sec, and  very few of 10.000 sec (though perhaps more 
than 0.000 sec)   I would see many more counts at 2.000 then 0.000sec 
(hence the asymmetry) This doesn't seem completely random to me.

Now, if one ran a 100k cps clock and counted only the last four 
decimals, then I would expect no such "bias" i.e. equal chance of 
xx.xx0000sec as xx.xx9999sec as xx.xx5000sec

So, what would be the names of the two different sorts of randomness?
I don't think that you would want the first example as a random number 
generator if you were building a slot machine.

I am sure you would see the same sort of "peaky-ness" with counting the 
number of decays per second with a fast source, but somehow it "feels" 
like the gausian may be more symmetrical.

I'll bet a doughnut that I am somehow showing a great bit of ignorance 
here  :-)  .

So, how would one build a radio decay based random number generator 
without the fast clock and counter - to save power? Perhaps generate a 
voltage like a survey meter does, but that will have the "peaky-ness" 
centered at a function of the average rate. I guess one could use just 
the last few decimals of the AtoD?

Well, I'll be double da#$d, I just this minute went out to my car to get 
my Geiger counter and found out why the car alarm went off last night - 
someone stole my Geiger counter!!! Bummer I really liked it - it will be 
expensive to replace!!
-- 

Looking forward,
Al Shinn



-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist