▁beta - dec ay ▁stable ▁nu cl ides ▁are ▁currently ▁known . ▁The oret ically ▁predicted ▁or ▁experiment ally ▁observed ▁double ▁beta - dec ay ▁( if ▁not ▁domin ated ▁by ▁alpha ▁decay ▁or ▁sp ont aneous ▁f ission ) ▁is ▁shown ▁by ▁ar rows , ▁i . e . ▁ar rows ▁point ▁towards ▁the ▁light est - mass ▁is obar . ▁ ▁No ▁beta - dec ay ▁stable ▁nuc lide ▁has ▁pro ton ▁number ▁ 4 3 ▁or ▁ 6 1 ▁and ▁no ▁beta - dec ay ▁stable ▁nuc lide ▁has ▁neut ron ▁number ▁ 1 9 , ▁ 2 1 , ▁ 3 5 , ▁ 3 9 , ▁ 4 5 , ▁ 6 1 , ▁ 7 1 , ▁ 8 9 , ▁ 1 1 5 , ▁ 1 2 3 , ▁or ▁ 1 4 7 . ▁ ▁All ▁beta - dec ay ▁stable ▁nu cl ides ▁with ▁A ▁ ≥ ▁ 2 0 9 ▁were ▁observed ▁to ▁decay ▁by ▁alpha ▁decay ▁except ▁some ▁where ▁sp ont aneous ▁f ission ▁domin ates . ▁With ▁the ▁exception ▁of ▁ 2 6 2 No , ▁no ▁nu cl ides ▁with ▁A ▁ ≥ ▁ 2 6 0 ▁have ▁been ▁definit ively ▁identified ▁as ▁beta - stable , ▁although ▁ 2 6 0 F m ▁and ▁ 2 6 2 No ▁are ▁un conf ir med . ▁ ▁The ▁general ▁patterns ▁of ▁beta - st ability ▁are ▁expected ▁to ▁continue ▁into ▁the ▁region ▁of ▁super he avy ▁elements , ▁though