The paper by Wetherbee, Gregory A. et al was published online on February 22, 2012 ahead of the print, on Environmental Science and Technology.
Abstract, from Environmental Science and Technology (emphasis is mine):
Using the infrastructure of the National Atmospheric Deposition Program (NADP), numerous measurements of radionuclide wet deposition over North America were made for 167 NADP sites before and after the Fukushima Dai-ichi Nuclear Power Station incident of March 12, 2011. For the period from March 8 through April 5, 2011, wet-only precipitation samples were collected by NADP and analyzed for fission-product isotopes within whole-water and filterable solid samples by the United States Geological Survey using gamma spectrometry.
Variable amounts of 131I, 134Cs, or 137Cs were measured at approximately 21% of sampled NADP sites distributed widely across the contiguous United States and Alaska. Calculated 1- to 2-week individual radionuclide deposition fluxes ranged from 0.47 to 5100 Becquerels per square meter during the sampling period. Wet deposition activity was small compared to measured activity already present in U.S. soil. NADP networks responded to this complex disaster, and provided scientifically valid measurements that are comparable and complementary to other networks in North America and Europe.
The map above the abstract at Environmental Science and Technology indicates cesium-137 deposition between 0.8 to 240 becquerels/square meter. But without seeing the paper I have no idea how the numbers on the map are related to the numbers in the abstract. (My guess is that the numbers in the abstract, particularly the high number, include iodine-131.)
For more about the paper, here’s USGS webpage on the NADP.
USGS press release on February 22, 2012 regarding the paper is here.
Open-File Report detailing the results and methodology is here.
Here’s an interesting map at USGS page on the NADP. Green dots represent the NADP sites, and “Dot size represents relative deposition amounts. Fallout amounts measured in precipitation by USGS provide a clearer picture of fission-product wet deposition across the USA.”