bismuth of 209/83Bi is stable because?

Question

nuclei even or odd # of nucleons. which one is stable?

Answer 1

209 happens to be the only isotope of Bi that is not radioactive. It is also the largest stable nucleon of any kind. The reasons for is stability are quite complicated. Some attribute it a nuclear "shell model" and the fact that 126 (the number of neutrons) is one of the "magic numbers" of nuclear physics that are unusually stable. Other magic numbers are 2,8,20,50,and 82.