[ RadSafe ] A novel use of I-131

[Geo>K0FF]

Info per a client:
Municipal water well drilling in Florida has changed in the last decades. Once a well would only need to be a 
few hundred feet deep.
Now that the population has grown, naturally the water table has dropped from overuse. 
Today a well will go down 1500 feet, and be of 36 inch diameter. 
The actual hole is much deeper than that, at least 2000 feet deep.

Water pumped from the well is still saline, but not as salty as the ocean.Desalination plants process the
water into drinking water and brine.Instead of pumping the waste brine into the ocean for disposal, it is pumped back down the 
well, all the way to the bottom of the hole. By doing so, the water table is maintained at a higher level. Being much denser than 
the source water, the brine is supposed to stay at the bottom of the hole.

During the well proofing process, that is after construction but before turning it over to the end users, a radioactive
I-131 tracer  is metered into the brine flow down into the well. Simultaneously a 25 foot long tool containing  7 scintillator
gamma detectors is lowered into the well, monitoring any leaks of high pressure brine into the supply pipeline, and the relative position that the brine takes up in the water table.

A normal medical dose of I-131 in liquid form is used, from Cardinal Health Services. 

I-131 has a radiological half life of 8.040 days and decays to stable Xe-131 (NUDAT 2) with a 1.2% branch to radioactive Xe-131m, T/2 11.840 days (C. Hacker)
I-131 beta minus  decays 100% with an 81% probability of a 364.5 gamma ray (and others at lower %). 

After 7 half-lives, any isotope is reduced to only 1% of the original dose.
http://web.ead.anl.gov/marssim/doc/docs/Radiation_Basics.pdf


After each 5 years of use, the above tests are repeated.

Such uses or radioactive materials are numerous and are excellent examples of the risk/benefit ratio theory. 


George DowellNLNLNew London Nucleonics Lab56791 Rivere Au Sel Pl.New London, MO 63459GEOelectronics at Netscape.com573-221-3418