Isotopes of niobium

Naturally occurring niobium (₄₁Nb) is composed of one stable isotope (⁹³Nb). The most stable radioisotope is ⁹²Nb with a half-life of 34.7 million years, followed by are ⁹⁴Nb at a half-life of 20,400 years and ⁹¹Nb at 680 years. Other radioisotopes that have been synthesized range from ⁸²Nb to ¹¹⁰Nb; these have half-lives that are less than two hours, except ⁹⁵Nb (34.991 days), ⁹⁶Nb (23.35 hours) and ⁹⁰Nb (14.60 hours).

The most stable of the meta states is ^93mNb with excitation energy 31 keV and a 16.1 year half-life; this is produced in the decay of ⁹³Zr. The primary decay mode before stable ⁹³Nb is electron capture to zirconium isotopes and the primary mode after is beta emission, with delayed neutron emission starting at ¹⁰⁴Nb, leading to molybdenum isotopes.

Only ⁹⁵Nb, along with ⁹⁷Nb (72 minutes) and heavier isotopes (seconds) are fission products in significant quantity, as the other isotopes are shadowed by stable or very long-lived (93) isotopes of the preceding element zirconium from the usual mode of production through beta decay of neutron-rich fission fragments. ⁹⁵Nb is the decay product of ⁹⁵Zr (64 days), so disappearance of ⁹⁵Nb in used nuclear fuel is slower than would be expected from its own 35-day half-life alone.