▁the ▁exact ▁location ▁of ▁the ▁center ▁of ▁the ▁valley ▁of ▁stability ▁is ▁model ▁dependent . ▁It ▁is ▁widely ▁believed ▁that ▁an ▁island ▁of ▁stability ▁exists ▁along ▁the ▁beta ▁stability ▁line ▁for ▁is ot op es ▁of ▁elements ▁around ▁cop ern ici um ▁that ▁are ▁stabil ized ▁by ▁shell ▁clos ures ▁in ▁the ▁region ; ▁such ▁is ot op es ▁would ▁decay ▁primarily ▁through ▁alpha ▁decay ▁or ▁sp ont aneous ▁f ission . ▁Bey ond ▁the ▁island ▁of ▁stability , ▁various ▁models ▁that ▁correctly ▁predict ▁the ▁known ▁beta - stable ▁is ot op es ▁predict ▁anom al ies ▁in ▁the ▁beta - st ability ▁line ▁that ▁are ▁un ob ser ved ▁in ▁any ▁known ▁nu cl ides , ▁such ▁as ▁the ▁existence ▁of ▁two ▁beta - stable ▁nu cl ides ▁with ▁the ▁same ▁odd ▁mass ▁number . ▁This ▁is ▁a ▁consequence ▁of ▁the ▁fact ▁that ▁a ▁semi - emp ir ical ▁mass ▁formula ▁must ▁consider ▁shell ▁correction ▁and ▁nuclear ▁de formation , ▁which ▁become ▁far ▁more ▁pron ounced ▁for ▁heavy ▁nu cl ides . ▁ ▁B eta ▁decay ▁toward ▁minimum ▁mass ▁B eta ▁decay ▁generally ▁causes ▁is ot op es ▁to ▁decay ▁toward ▁the ▁is obar ▁with ▁the ▁lowest ▁mass ▁( high est ▁binding ▁energy ) ▁with ▁the ▁same ▁mass ▁number , ▁those ▁not ▁in ▁ital ics ▁in ▁the ▁table ▁above . ▁ ▁Thus , ▁those ▁with ▁lower ▁atomic ▁number ▁and ▁higher ▁neut ron ▁number ▁than ▁the ▁minimum - mass ▁is obar ▁under go ▁beta - minus ▁decay , ▁while ▁those ▁with ▁higher ▁atomic