“My sister in law has thyroid issues and she grew up in that area....”
How old was she in 1962?
About 4-5 years old.
~~~~~~~~~~~~~~
She was still growing rapidly. The body is very susceptible to toxins and ionizing radiation at that time -- and absorbs them "like a sponge"...
"Research from the United States National Cancer Institute (PDF) shows that the Sedan test released about 880,000 curies of Iodine-131 <SNIP>. The fallout reached parts of Iowa, Nebraska, South Dakota and Illinois. According to a 1999 National Cancer Institute report, the Sedan test was the second most fallout-intensive nuclear test of all U.S. continental tests after the 'Harry' test of 19 May 1953."https://www.ctbto.org/specials/testing-times/6-july-1962-sedan-massive-crater-massive-contamination/
One of the fallout nucleotides was Iodine-131, a radioactive isotope of Iodine -- which is readily absorbed by the thyroid.
(That's one of the reasons that Russian people near the latest accident/release rushed to their pharmacies to buy (non-radioactive) Iodine -- which is drunk in water and absorbed by the thyroid.)
Theoretically, if the thyroid has more Iodine than it needs, it won't absorb more -- making the body reject (excrete) the radioIodine, rather than absorbing it.
~~~~~~~~~~~~~~
It's a shame the government didn't provide iodine (or, at the very least publicize the self-administered therapy) to the populace in the areas affected by the Sedan test fallout... :-(
Your S-I-L has my prayers.
TXnMA