[ RadSafe ] TFP - next questions

[James Salsman]

> At some point several years ago, there was a semi-detailed
> description of the method being used by the tooth fairy
> project to analyze teeth for Sr.  Can anyone point me to this post?

The following is quoted from pp. 23-24 and 49 of:
  http://mtafund.org/prodlib/radiation_health/final_report.pdf

"Upon receipt of envelopes containing teeth, RPHP data managers assign 
a unique control number to each tooth and logs it into a computerized 
data base. Teeth are periodically sent in batches to REMS, Inc., a 
radiochemistry laboratory in Waterloo, Ontario, Canada. Laboratory 
personnel document Sr-90 concentrations by separately measuring Sr-90 
activity (in picocuries) and calcium mass (in grams) in the teeth. 
REMS personnel, headed by radiochemist Dr. Hari Sharma, are blinded 
from any information about each tooth.

"A tooth is dried for 12 hours at 110 degrees centigrade, then ground 
to a fine powder.  Approximately 0.1 gram of the powder is weighed in 
a vial, then digested for a few hours with 0.5 milliliter of 
concentrated nitric acid along with solutions containing 5 milligrams
of Sr2+ and 2 milligrams of Y3+ carriers at about 110 degrees 
centigrade on a sand bath. The solution is not evaporated to dryness. 
The digested powder is transferred to a centrifuge tube by rinsing 
with tritium-free water. Carbonates of Sr, Y, and Ca are precipitated 
by addition of a saturated solution of sodium carbonate, then 
centrifuged. The carbonates are repeatedly washed with a dilute 
solution of sodium carbonate to remove any coloration from the 
precipitate. The precipitate is dissolved in hydrochloric acid, and 
the pH is adjusted to 1.5 to 2 to make a volume of 2 milliliters, of 
which 0.1 milliliter is set aside for the determination of calcium. 
The remaining 1.9 milliliters are mixed with 9.1 milliliters of 
scintillation cocktail Ultima Gold AB, supplied by Packard Bioscience 
BV in a special vial for counting. A blank with appropriate amounts 
of Ca2+, Sr2+, and Y3+ is prepared for recording the background.

"The activity in the vial with the dissolved tooth is counted four 
times, 100 minutes each time, for a total of 400 minutes, with a 
Wallac WDY 1220X Quantulus low-level scintillation spectrometer. 
The spectrometer has special features so that the background 
count-rate in the 400 to 1,000 channels is 2.25 plus or minus 0.02 
counts per minute. The background has been counted for over 5,000 
minutes so that the error associated with the background measurement 
is about 1 percent . The overall uncertainty or one sigma associated 
with the measurement of Sr-90 per gram of calcium is plus or minus 
0.7 picocuries per gram of calcium.

"The efficiency of counting was established using a calibrated 
solution of Sr-90/Y-90 obtained from the National Institute of 
Standards and Technology, using the following procedure. The 
calibrated solution is diluted in water containing a few milligrams 
of Sr2+ solution, and the count-rate from an aliquot of the solution 
is recorded in channel numbers ranging from 400 to 1,000 in order to 

determine the counting efficiency for the beta particles emitted by 
Sr-90 and Y-90. It is ensured that the Y-90 is in secular 
equilibrium with its parent Sr-90 in the solution. The counting 
efficiency was found to be 1.67 counts per decay of Sr-90 with 1.9 
milliliters of Sr-90/Y-90 solution with 25 milligrams of Ca2+, 5 
milligrams of Sr2+, 2 milligrams of Y3+, and 9.1 milliliters of the
scintillation cocktail.

"The calcium content was determined using a Varian A-A 1475 atomic 

absorption spectrophotometer by flame spectroscopy at a wave length 
of 422.7 nanometers, using acetylene plus air as fuel."

Please see also:
  http://dx.doi.org/10.1016/S0048-9697(03)00439-X

Sincerely,
James Salsman

P.S. What is "secular equibrium"?  It sounds like something that 
might happen on Dick Cheney's secret energy task force.