The atomic proving ground
The Semipalatinsk Test Site (STS), known simply as "The Polygon," covers 18,500 square kilometers of the Kazakh steppe. From 1949 to 1989, this was the Soviet Union's primary facility for testing nuclear weapons. In total, 456 nuclear devices were detonated here. This includes 116 atmospheric tests and 340 conducted underground. The first Soviet atomic bomb, codenamed RDS-1 ("First Lightning"), was tested here at 7:00 AM on August 29, 1949. The device, a 22-kiloton plutonium implosion bomb, was a near-copy of the American "Fat Man" design. The cumulative explosive yield of all tests at the site was over 2,500 times greater than the bomb dropped on Hiroshima.
The immense energy from the surface and atmospheric detonations physically altered the landscape. In the immediate vicinity of these explosions, the intense heat melted the sandy soil, fusing it into a glassy, slag-like material. This substance is analogous to "trinitite," the material created during the 1945 Trinity test in New Mexico. At Semipalatinsk, this atomic glass is sometimes called "kharitonchiki," after Yulii Khariton, a chief designer of the Soviet bomb program. These pieces of black and green glass are concentrated in localized radiation hotspots, physical records of the Polygon's history.
A landscape of isotopes
Each piece of kharitonchiki contains a unique chemical signature. As the molten sand cooled, it trapped radionuclides produced by the nuclear fission and activation processes. These radioactive isotopes—including cesium-137, strontium-90, europium-152, and americium-241—identify the source. By analyzing the specific ratios of these isotopes, particularly plutonium isotopes like Pu-239 and Pu-240, scientists can trace a sample of the glass back to the specific nuclear test that created it. This allows for a detailed reconstruction of the events that transpired across the test site.
One feature within the Polygon is Lake Chagan, or the "Atomic Lake." It was formed on January 15, 1965, by the Chagan test, a 140-kiloton thermonuclear explosion. The device was detonated in a 178-meter-deep shaft in a dry riverbed, creating a crater 400 meters in diameter and 100 meters deep. A channel was later cut to allow the Chagan River to fill the crater, creating the reservoir. The water in Lake Chagan remains radioactive. Another area of intense testing was the Degelen Mountain complex, where 215 underground nuclear tests were conducted in 181 different tunnels bored into the rock.