, ▁ 1 1 8 ) ▁have ▁one , ▁and ▁the ▁remaining ▁ 2 2 ▁have ▁two . ▁From ▁ 1 2 4 ▁to ▁ 1 5 4 , ▁only ▁one ▁( 1 4 0 ) ▁has ▁one , ▁six ▁have ▁three , ▁and ▁the ▁remaining ▁ 9 ▁have ▁two . ▁From ▁ 1 5 6 ▁to ▁ 2 6 2 , ▁only ▁eigh teen ▁have ▁one , ▁and ▁the ▁remaining ▁ 3 6 ▁have ▁two , ▁though ▁there ▁may ▁also ▁exist ▁some ▁und isc over ed ▁ones . ▁ ▁All ▁prim ord ial ▁nu cl ides ▁are ▁beta ▁decay ▁stable , ▁with ▁the ▁exception ▁of ▁ 4 0 K , ▁ 5 0 V , ▁ 8 7 R b , ▁ 1 1 3 C d , ▁ 1 1 5 In , ▁ 1 3 8 La , ▁ 1 7 6 Lu , ▁and ▁ 1 8 7 Re . ▁ ▁In ▁addition , ▁ 1 2 3 Te ▁and ▁ 1 8 0 m T a ▁have ▁not ▁been ▁observed ▁to ▁decay , ▁but ▁are ▁believed ▁to ▁under go ▁beta ▁decay ▁with ▁an ▁extremely ▁long ▁half - life ▁( over ▁ 1 0 1 5 ▁years ). ▁ ▁All ▁elements ▁up ▁to ▁and ▁including ▁no bel ium , ▁except ▁te ch net ium ▁and ▁prom eth ium , ▁are ▁known ▁to ▁have ▁at ▁least ▁one ▁beta - stable ▁is ot ope . ▁ ▁List ▁of ▁known ▁beta - dec ay ▁stable ▁is ob ars ▁▁ 3 5 0