Longest half-life

Longest half-life
Who
tellurium-128
What
2,200,000,000,000,000,000,000,000 total number
Where
Not Applicable
When
n/a

The element tellurium is classed as a metalloid, which sit on the periodic table between metals and non-metals. Its isotope tellurium-128 has a half-life of 2.2 x (10 to the power of 24) years, which is around 160 trillion times the age of the Universe. It decays via double beta decay, in which a pair of protons change into neutrons or vice versa. In one gram of tellurium-128 you would only witness a double beta decay event every 674 years.

The previous record holder, bismuth-209, still has the longest half-life via alpha decay.