Complex sentence: The most stable radioisotopes are Nb-92 with a half-life of 34.7 million years, Nb-94 (half life: 20300 years), and Nb-91 with a half life of 680 years.
Split into simpler sentences: The most stable radioisotope is Nb-92 with a half-life of 34.7 million years. The next longest-lived niobium nuclides are Nb-94 (half life: 20,300 years), and Nb-91 with a half life of 680 years.