▁is om ers , ▁with ▁the ▁most ▁stable ▁being ▁ 1 4 3 m G d ▁( t 1 / 2 ▁= ▁ 1 1 0 ▁seconds ), ▁ 1 4 5 m G d ▁( t 1 / 2 ▁= ▁ 8 5 ▁seconds ) ▁and ▁ 1 4 1 m G d ▁( t 1 / 2 ▁= ▁ 2 4 . 5 ▁seconds ). ▁ ▁The ▁primary ▁decay ▁mode ▁at ▁atomic ▁weights ▁lower ▁than ▁the ▁most ▁abund ant ▁stable ▁is ot ope , ▁ 1 5 8 G d , ▁is ▁electron ▁capture , ▁and ▁the ▁primary ▁mode ▁at ▁higher ▁atomic ▁weights ▁is ▁beta ▁decay . ▁The ▁primary ▁decay ▁products ▁for ▁is ot op es ▁l ighter ▁than ▁ 1 5 8 G d ▁are ▁is ot op es ▁of ▁europ ium ▁and ▁the ▁primary ▁products ▁of ▁heav ier ▁is ot op es ▁are ▁is ot op es ▁of ▁ter b ium . ▁ ▁G ad olin ium - 1 5 3 ▁has ▁a ▁half - life ▁of ▁ 2 4 0 . 4 ▁ ± ▁ 1 0 ▁days ▁and ▁em its ▁g amma ▁radiation ▁with ▁strong ▁pe aks ▁at ▁ 4 1 ▁ke V ▁and ▁ 1 0 2   ke V . ▁It ▁is ▁used ▁as ▁a ▁g amma ▁ray ▁source ▁for ▁X - ray ▁absor pt i ometry ▁and ▁flu ores c ence , ▁for ▁b one ▁density ▁gau ges ▁for ▁o ste op or osis ▁screen ing , ▁and ▁for ▁radi ometric ▁profil ing ▁in