Trinitite – November 18, 2020


Sharing a photo of a rather unusual “rock” seen at the National Museum of Nuclear Science & History in Albuquerque, New Mexico. On July 16, 1945, the world’s first atomic device (“Gadget”) was tested at the Trinity Site, about 30 miles southeast of Socorro, New Mexico, on government-owned land that was part of the Alamogordo Bombing Range (now the White Sands Missile Range). The test was the culmination of the Manhattan Project’s extensive scientific research and experimentation – as well as the precursor to an implosion-design plutonium bomb soon to be dropped on Nagasaki, Japan.
Detonators ignited explosives around the large, steel, globe-shaped Gadget on a 100-foot tower. The explosion prompted a fission chain reaction in the plutonium inside the globe, with the resulting nuclear blast releasing an explosive force of 21 kilotons (equivalent to 21 thousand tons of TNT). It created a blinding flash of light, a thunderous sound, and a mushroom cloud 38,000 feet tall.
After rupturing, the plutonium atoms transformed into a host of radioactive elements. Those still present in the sandy soil of Trinity in significant quantities today will stick around for a long time, such as cesium-137, europium-152 and europium-155. One particularly long-lived isotope has a half-life of 24,100 years!
The green glass-like solid pictured here is called trinitite. It was originally thought that trinitite was created when the heat of the fireball liquefied the sand on the ground. A study published in 2005, however, indicates that upon explosion of the device, the ground was pushed down initially, then rebounded which forced the sand into the fireball. The sand then “rained” down in the form of trinitite droplets of nearly pure melted silica, olivine and feldspar minerals. Most trinitite is light green (due to the iron-bearing olivine mineral), while other collected samples looked black given they incorporated iron from the tower on which Gadget was detonated, or red, as they contained copper from the electrical wires.
The bomb crater measured nearly 2,400 feet across and was 10 feet deep in some places. Trinitite up to a ½ inch thick coated the entire crater! In the 1950s, most of the trinitite was removed and the crater was filled with soil.
So, is it still radioactive? Trinitite does contain radioactive fission products. On the surface, this is minimal – only about 0.3 mR/hr (these units are milliroentgen per hour), equivalent to the radiation dose rate per hour of flight at typical commercial airline flight altitude (35,000 feet). The level of radioactivity on the case surrounding the sample is indistinguishable from normal Albuquerque background radiation.