Human radiation exposure is measured by the amount of radioactive energy deposited in a body's tissue in rad units (or in the international unit, a gray). Since different tissues have different mass and molecular structure, the same radioactive source of energy will, therefore, cause different rad doses. Some radioactive materials deposit in specific organs. Iodine-131, for example, deposits in the thyroid gland where it can cause thyroid cancer and hypothyroidism. Other radioactive materials like Cesium-137 are more generalized and are absorbed into the body's soft tissues where they can cause a variety of cancers.¹

Data in the table and graph below show the 1945 levels of exposure to Iodine-131 from drinking milk. The data is organized by gender for various age groups and for exposure Zone 1, closest to Hanford, and for Zone 2, further from the site. The ages represent the low end of an age group. For example, "0" represents ages 0 to 1; "1" represents ages 1 to 5, and so on. The exposure values are the mid range value for each age group.