The capsules, the size of soda cans with small amounts of cobalt-60 - used in X-ray machines and other medical and industrial applications, were stolen in September and found two weeks later in nearby villages, the The New York Times said on Tuesday.
A 30-year-old Iraqi man and a four-year-old boy were found to have symptoms of radiation sickness in one of the villages, the paper quoted officials as saying.
One of the capsules was discovered less than five metres from where a family had their clay oven to bake bread.
US military commanders are certain the villagers looted the
testing site to get scrap metal and not to use or sell the cobalt, which can be used to make "dirty bombs."
The cobalt was housed in eight 23-metre (75-foot) steel poles, three of which were dismantled by the looters, who entered the site with heavy vehicles, the officials said.
The looters left tyre marks on the ground, but US forces
discovered the theft two weeks later.
The lapse in security around the 52-square km radiation testing site in the desert outside Baghdad may have been due to what the official claimed a "work overload among US experts".