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Rarest nucleus reluctant to decay

Tantalum-180m’s half-life is more than a million times universe’s age

9:00am, October 3, 2016
High Activity Disposal Experimental Site

LONG WAIT  Scientists searched for the decay of nature’s rarest type of atomic nucleus, tantalum-180m, at the High Activity Disposal Experimental Site, or HADES, laboratory (shown above) located 225 meters underground in Mol, Belgium. 

Nature’s rarest type of atomic nucleus is not giving up its secrets easily.

Scientists looking for the decay of an unusual form of the element tantalum, known as tantalum-180m, have come up empty-handed. Tantalum-180m’s hesitance to decay indicates that it has a half-life of at least 45 million billion years, Bjoern Lehnert and colleagues report online September 13 at arXiv.org. “The half-life is longer than a million times the age of the universe,” says Lehnert, a nuclear physicist at Carleton University in Ottawa. (Scientists estimate the universe’s age at 13.8 billion years.)

Making up less than two ten-thousandths of a percent of the mass of the Earth’s crust, the metal tantalum is uncommon. And tantalum-180m is even harder to find. Only 0.01 percent of tantalum is found in this state, making it the rarest known long-lived nuclide, or variety of atom.

Tantalum-180m is a bit of an

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