TFP: Radium vs. Sr 90 not distinguished?

[Jeffrey Lahr <jl64@PRISM.GATECH.EDU>]

At 11:59 AM 6/15/01 -0400, Gerald Nicholls wrote:

>There are some details of the analytical procedure used to determine Sr-90 

>in the children's teeth samples in the appendix to the paper listed in the 

>original posting.

>

>It is stated that the analyses are performed by Hari D. Sharma, Professor 

>Emeritus of Radiochemistry.  The teeth are dried at 110 degrees C for 12 

>hours, ground to a powder, weighed and dissolved in nitric acid.  Carriers 

>are added and the Sr and Y precipitated as carbonates and 

>centrifuged.  The precipitate is repeatedly washed with dilute sodium 

>carbonate solution until any coloration is lost.

>

>The precipitate is then dissolved in hydrochloric acid and samples 

>prepared for liquid scintillation counting using a previsously determined 

>window and counting efficiency derived from an NIST standard solution.  A 

>counting efficiency of 1.67 counts/decay of Sr-90 is given.  Samples are 

>counted 4 times at 100 minutes each.  Background was counted for 5000 

>minutes.  No information is given regarding blanks, duplicates or cross 

>checks.  Ca is determined by AA spectrometry.

>

>There isn't enough information here to determine whether or not there is 

>interference from naturally occurring radionuclides.



--------------

There _is_ enough information to say that the carbonate precipitate will carry

not only the calcium and strontium, but also any radium (among other things).

The precipitate is dissolved and counted with no separation of strontium from

these potential interferences.  Check the Th-232 (4n) and U-238 (4n+2) decay

chains to see all the daughters of Ra-228 and Ra-226 which ingrow rapidly and

emit a wide range of beta as well as alpha particles.



Additionally, the 3-sigma uncertainty for the Sr-90 per gram of calcium as

given is higher than the average value for all their locations except Dade 

County.



That appendix is online at:

http://www.radiation.org/ijhs092000_appen.html



Just a few observations,

Jeffrey Lahr

Environmental Radiation Laboratory

Georgia Tech

-----------------------





>Gerald P. Nicholls

>NJ Dept. of Environmental Protection

>609-633-7964

>gnicholl@dep.state.nj.us



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