Berkelium (97Bk) is an artificial element, and thus a standard atomic weight cannot be given.
Like all artificial elements, it has no stable isotopes.
There are twenty known radioisotopes, from 233Bk and 233Bk to 253Bk (except 235Bk and 237Bk), and six nuclear isomers.
The longest-lived isotope is 247Bk with a half-life of 1,380 years.
No fission products have a half-lifein the range of 100 a–210 ka ... ... nor beyond 15.7 Ma[9]