The maps below show the activity concentration of Xe-133 at ground-level on March 31, 2011 (top) and May 10, 2011 (bottom)
http://enenews.com/almost-entire-ground-level-northern-hemisphere-covered-radioactive-fission-product-after-311-study-impact-fukushima-radioxenon-releases-worldwide-xe-133-background-be-investigated-graphic