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The following archive was created by hippie-mail 7.98617-22 on Fri Aug 21 1998 - 17:20:11 ADT
Dave Emery (die@pig.die.com)
Tue, 7 Jul 1998 14:35:57 -0400
On Mon, Jul 06, 1998 at 09:12:34PM -0400, Dave Emery wrote:
>
> Perhaps I'm missing something big time, but it seems to me that
> one could time the interval between radioactive events detected by the
> GM tube using a fast binary hardware counter counting a clock signal
> from a stable quartz crystal oscillator, a counter that would be
> expected to count many tens of thousands to many millions of counts
> between events and then use some hash function of the low order few bits
> of the count as several bits of random entropic data, thus harvesting
> several to many bits per decay. While there are some extremely subtle
> biases that could in theory sneak into such a scheme if not carefully
> engineered [GM tube dead time and non random noise in the signal
> processing electronics following the tube come to mind], my
> understanding of radioactive decay is that it is a truly random process
> and the interval between events detected by an ideal detector should
> therefore be a random interval. And the art of measuring time intervals
> with high precision and repeatablity is a very well developed and mature
> technology.
>
I need to confess to serious stupidity for not qualifying this
proposal a bit more carefully. Anything based on time intervals
between radioactive decays or any other random event will show a subtle
bias due to the fact that the probability of a time interval count of n
is always greater than the probability of a count of n+1. This causes
a very slight bias even in the low order bits of a count. True it
would not be large, but would be there. Hashing might eliminate this
error, but actually time stamping events by capturing the value of
a continously rolling counter at the time a decay was detected would
yeild random values in the low bits free of that bias.
My head was clearer during my lunch time constitutional...
-- Dave Emery N1PRE, die@die.com DIE Consulting, Weston, Mass. PGP fingerprint = 2047/4D7B08D1 DE 6E E1 CC 1F 1D 96 E2 5D 27 BD B0 24 88 C3 18
The following archive was created by hippie-mail 7.98617-22 on Fri Aug 21 1998 - 17:20:11 ADT