Berkelium-248

Main isotopes of berkelium

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct 245Bk syn 4.94 d ε 245Cm α 241Am 246Bk syn 1.8 d α 242Am ε 246Cm 247Bk syn 1380 y α 243Am 248Bk syn >300 y α 244Am 249Bk syn 330 d α 245Am SF – β− 249Cf

Berkelium (₉₇Bk) is an artificial element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was ²⁴³Bk in 1949. There are 20 known radioisotopes, from ²³⁵Bk to ²⁵⁴Bk, and 6 nuclear isomers. The longest-lived isotope is ²⁴⁷Bk with a half-life of 1,380 years.

No fission products
have a half-life
in the range of
100–210 k years ...

... nor beyond 15.7 M years

Legend for superscript symbols
₡  has thermal neutron capture cross section in the range of 8–50 barns
ƒ  fissile
m  metastable isomer
№  naturally occurring radioactive material (NORM)
þ  neutron poison (thermal neutron capture cross section greater than 3k barns)
†  range 4–97 y: Medium-lived fission product
‡  over 200,000 y: Long-lived fission product

...
Wikipedia