of S or EUS for the major sources of exposure
for 2006. The percent values have been rounded to the nearest 1 %. The
total for S is 1,870,000 person-Sv and the total for EUS
is 6.2 mSv, using a U.S. population of 300 million for 2006. The other
background category consists of the external (space and terrestrial) and
internal subcategories [see Table 8.1 for the values of S
(person-sievert) and EUS (millisievert)].