Tantalum
Isotopes

Natural tantalum consists of two stable isotopes: Ta (0.012%) and Ta (99.988%). Ta (m denotes a metastable state) is predicted to decay in three ways: isomeric transition to the ground state of Ta, beta decay to W, or electron capture to Hf. However, radioactivity of this nuclear isomer has never been observed, and only a lower limit on its half-life of 2.9 × 10 years has been set. The ground state of Ta has a half-life of only 8 hours. Ta is the only naturally occurring nuclear isomer (excluding radiogenic and cosmogenic short-lived nuclides). It is also the rarest primordial isotope in the Universe, taking into account the elemental abundance of tantalum and isotopic abundance of Ta in the natural mixture of isotopes (and again excluding radiogenic and cosmogenic short-lived nuclides).

Tantalum has been examined theoretically as a " salting " material for nuclear weapons (cobalt is the better-known hypothetical salting material). An external shell of Ta would be irradiated by the intensive high-energy neutron flux from a hypothetical exploding nuclear weapon. This would transmute the tantalum into the radioactive isotope Ta, which has a half-life of 114.4 days and produces gamma rays with approximately 1.12 million electron-volts (MeV) of energy apiece, which would significantly increase the radioactivity of the nuclear fallout from the explosion for several months. Such "salted" weapons have never been built or tested, as far as is publicly known, and certainly never used as weapons.

Tantalum can be used as a target material for accelerated proton beams for the production of various short-lived isotopes including Li, Rb, and Yb.
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