Question about interpreting the Milk results

4/13/2011 8:40pm: Major revision note: We just performed a major revision of our preliminary milk measurements. Our activity measurements for milk with a "best by" date after 4/4/2011 were accidentally calculated for the "best by" date itself, rather than an earlier date such as the purchase date. Since milk can be on the shelves starting almost 18 days before the "best by" date, our numbers after 4/4/2011 did not accurately reflect the maximum activity that the radioisotopes could have at the time of purchase. Incidentally, our first two milk measurements were not corrected at all and therefore reflect the activity at the time of measurement. The original numbers are at the bottom of the page for reference.

In order to make a valid comparison between all milk samples, we decided to correct all milk samples to represent the activity at their time of bottling -- this is 18 days before the "best by" date. This revision does not change the Cs-134 or Cs-137 numbers since they have long radioactive half-lives. The I-131 activity increases by factors of 2 to 5 because of its 8 day half-life. Please note that though all I-131 activities have increased due to this revision, the levels are still very low -- one would have to consume at least 1,900 liters of milk to receive the same radiation dose as a cross-country airplane trip.

In addition, two new milk measurements were added to the table. The Cs-134 and Cs-137 levels are very low but are trending upward. This trend is probably due to a combination of the uptake rate by both the cow and grass. We'll continue to watch the milk levels to see how the iodine and cesium end up concentrated or dispersed with time.