b'P ROVING THE P RINCIPLErock, and it should contain plenty ofRadioactive Half-Life clay. Workers should be able to dig ver-tical-walled trenches and not have themcollapse. Naturally, the area neededR adioactivity is a natural characteristic of elements like radium and uranium. It good surface drainage and couldnt bealso is a characteristic of many elements that have absorbed neutrons while in upstream of any reactor sites. The IDOa nuclear reactor. wanted to be able to get to the landfillwithout having to build a long, expen-The nuclei within radioactive atoms are unstable. They disintegrate (decay) by sive road. 4throwing off one or more of their constituent particles spontaneously.As timepasses, the material actually changes from one element or isotope into another, The USGS suggested a one-hundred-one atom at a time.acre area about two miles southwest ofEBR-I and five miles west of CentralNo one can predict when a specific atom will decay, only the probability that a Facilities. The site met most of the crite-certain percentage of atoms will disintegrate within a certain period of time. ria. The depth of sediment above thelava rock, having been blown by thePhysicists decided that the half-life of a radioisotope would be a convenient wind for thousands of years, was notway to describe the decay of a substance: the time required for one half of the uniformly twenty feet. However, the soilatoms to disintegrate. contained clay, which provided goodion-exchange and absorptive capacity.The process of decay takes place regardless of the temperature, the pressure, or Any moisture that managed to saturatechemical conditions surrounding the substance. Different authorities identify the waste and suspend radioactive iso-slight differences in half-life depending on the method used to count. The num- topes would travel into the soil, whereber following the name of the element identifies a specific isotope that is chemical reactions would tend toradioactive. It is the combined number of neutrons and protons in the nucleus of remove radionuclides from the watereach atom. and bind them to the soil. The waterR a d i o i sot o p e H a lf -l i f e Ra diois oto p e Haf would move on, albeit slowly, becausel -l i fefissures in the lava rock had filled withSilver-110 24.6 seconds Krypton-85 10.73 years sediments, and this too would retard theIndium-114 1.198 minutes Hydrogen-3 (Tritium) 12.32 years movement of contaminants. The desertBarium-137 2.6 minutes Strontium-90 25 years climate, which contributed about eightLanthanum-140 1.687 days Cesium-137 30 years inches of precipitation per year over theCadmium-115 2.228 days Americium-241 432.2 years Site, was an ally of the landfill plan, asRuthenium-97 2.44 days Radium-226 1599 years very little moisture sank deeply into theIodine-131 8.040 days Carbon-145715 years soil. The geologists noted that it wasu n l ik l , but possible, that water reach-Niobium-95 34.97 days Plutonium-239 24,400 years e yHafnium-181 45 days Iodine-129 1.72 x 10 7 years ing the soil could carry contaminationdownward to the water table (of thePolonium-210 138.38 days Uranium-238 4.46 x 10 9 years Snake River Plain A quif) 5Cobalt-60 5.271 years Uranium-235 7.04 x 10 8 years e r . The IDO accepted the USGS recom-mendation and in May 1952 fenced offthe first thirteen acres of the controlledaccess area that soon became known asthe NRTS Burial Ground. In July work-7 6'