What do you think of this fact?
Some elements are famous for being radioactive. Uranium, plutonium, radium. Bismuth is not on that list. It’s a heavy, silvery metal that textbooks long described as completely stable. Turns out the textbooks were wrong.
The stable atom that wasn’t
For decades, bismuth-209 was considered the heaviest isotope in nature that never decays. Theorists had actually predicted more than 50 years earlier that it should slowly fall apart, according to Science News. But experiments between 1949 and 1972 found nothing, and the idea faded.
Then, in 2003, a team at the Institut d’Astrophysique Spatiale in Orsay, France, published the proof in Nature. Bismuth-209 does decay: it spits out an alpha particle and turns into thallium-205.
Slower than slow
The catch is the timing. The team measured a half-life of about 19 billion billion years. That’s how long it takes for half of a pile of bismuth-209 atoms to decay. Science News puts it at roughly 1.4 billion times the current age of the universe. Guinness World Records lists it as the longest half-life by alpha decay ever measured.
So how do you catch something that rare? With a lot of atoms and a very cold detector. The researchers used a bolometer, a sensor that registers tiny bursts of heat, cooled to 20 millikelvin, just a hair above absolute zero. A crystal containing bismuth absorbs an alpha particle, warms up by a minuscule amount, and the sensor turns that into a signal. Across two runs with 31 and 62 grams of bismuth, the team counted 128 such events in 5 days.
Bonus fact: Nobody was even looking for this. The team was hunting for dark matter and noticed the unexpected decays during a routine check of their detectors for contamination.
The result doesn’t make bismuth dangerous. Physics World notes that the alpha particles carry very little energy, which is one reason the decay was so hard to spot. The metal behaves as stable for every practical purpose. It just isn’t, technically. Forever turned out to be a little shorter than advertised.