I drove to Chernobyl with health physicist Vadim Chumak at the Research Center for Radiation Medicine at the Health physicist Vadim ChumakAcademy of Medical Sciences of Ukraine and his colleagues. A car shuttles there every week to collect stool samples from workers to test for any plutonium they might have accidentally absorbed. (Science, like journalism, can be a dirty job, but someone has to do it.)
The world is normally bathed in a low level of radiation. In Kiev, where I started my trip, one normally receives 0.1 millionths of a sievert every hour. This is pretty much the level of radiation we saw on the road on the roughly two-hour, 150-kilometer drive into the exclusion zone, but readings on our dosimeter temporarily climb up to 4.76 millionths of a sievert per hour when our car passes through the old path of the radioactive plume from the destroyed reactor.
How safe this area is now after the accident depends on what radioactive material was released and where it went. There are four kinds of radionuclides or radioactive isotopes that are of special concern at the site. Iodine-131 is rapidly absorbed by the thyroid gland and increases the risk of childhood thyroid cancer. Cesium-137 mimics potassium inside the body, seeking out muscle. Strontium-90 acts like calcium, attracted to bone. Plutonium-239 and other isotopes can stay in the body indefinitely, irradiating organs.
These four materials escaped from the explosions to varying distances, given factors such as their mass and melting points. Iodine-131 and cesium-137 were both very broadly transported hundreds of kilometers, while strontium-90 remained in dust just 30 kilometers from the power plant and plutonium traveled only four kilometers or so.
Iodine-131 decays rapidly, and was virtually gone from the environment after only three months, Chumak says. However, cesium-137 and strontium-90 both have approximately 30-year half-lives, meaning they each take roughly three decades for half their material to decay, and plutonium-239, one the main isotopes in nuclear reactors, has a half-life of more than 24,000 years.
There's some really interesting stuff in here. The Chernobyl exclusion zone isn't one monolithic thing, Choi discovers. Some areas are already reasonably safe, while others are places that humans will probably never live again. Even the animal impacts are varied. The creatures that live here are thriving, and don't seem to be passing on genetic mutations. But, Choi points out, the species diversity has gone down significantly since the accident.
Photo: Charles Choi. Taken inside the control room for destroyed reactor No. 4 at the Chernobyl nuclear power plant.