real random numbers

Hi,

i read following in an article:
" Numbers that are really random could be generated with expensive add on computer cards that use radioactive sources as a method of collecting really random data. However, pseudo-random-numbers are much more convenient for the purposes of simulation. "

just curious to know how do these computer cards work ? what makes them give real random numbers ?

thanks,
Vinay

It has been observed that the time between radioactive decays forms an exponential distribution with a predictable mean. Such cards use devices similar to geiger counters for their input to make random numbers. This creates never-repeating, completely unpredictable random numbers. For almost all applications, pseudo-random number generators are just as good. For many applications in simulation, they are better because you can record your random number seeds to make your results repeatable.