Re: Half Life of Po-218 (Radium A) -Reply

["Dale E. Boyce" <dale@radpro.uchicago.edu>]

Paul brings up an interesting fact that may not be obvious to everyone.
Look at various sources of half lives for nuclides with half lives in
the several tens to several hundreds of years.  You should find that
they scatter all over the place. Why?....

Because in this range it takes too long to accurately measure the half life
directly by measuring the change in decay rate with time, and you can't get
enough of the stuff to weigh it accurately to calculate the half life
by dividing the activity by the number of atoms.

All in all a 2% variation in a published half life is not unusual. Probably
the least variation occurs for gamma emitters with half lives of weeks
to many months.  Counting system stability can usually be maintained
for multile half lives and count durations modified to maintain
statistical significance.  With short lived species one has to combat
counting system dead time and other error inducing factors.

Dale Boyce
dale@radpro.uchicago.edu