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

[FRAMEP@ORAU.GOV]

John Takala wrote:
>I was recently looking up decay information for radon progeny on the 
> National Nuclear Data Center's web program NuDat.  To my surprise
 >it  listed the half life of Po-218 as 3.11 minutes.  
 >The value that I have commonly seen used is 3.05 minutes
> (e.g., Table  of Isotopes - 7th edition, ICRP 38).  This is a change of
>nearly 2%!  Does anyone have any comments on the revised half 
>life of Po-218? What is the reference for it?
     
The 1977 Chart of the Nuclides listed it at 3.05 min, the 1983 Chart listed it
at 3.11 min and the current chart has it at 3.10 min. 

Kocher in 1981 is still listing it at 3.05 so the change seems to have
begun in the 1980-1983 time frame. 

(I believe this helps explain variations in the coefficients found in working
level formulae)   

I remember reading a paper about these measurements that might have
appeared in Health Physics. But for the life of me I can't locate it.   As I
recall, the measurement was particularly tricky. Perhaps the difficulty
related to the  the fact that Po-218 is short lived and produces longer
lived daughters.  In the one pitiful attempt I've made at it, subtracting out
the daughter contributions was a pain so I when I got within 0.5 minutes
of the right answer I was happy.
     
Interestingly, the half life for Ag-108m has recently been revised to 418
years while the latest chart of the nuclides has it at 130 years.  
        
Best wishes

Paul Frame
Professional Training Programs
ORISE
framep@orau.gov