It decays by isomeric transition with a half-life of 241 years, which makes it unusual, both for its long half-life for an isomer, and that said half-life greatly exceeds that of the ground state of the same isotope.
ɪt dᵻkˈeɪz baɪ ˌaɪsoʊmˈɛɹɪk tɹænsˈɪʃən wɪð ɐ hˈæflˈaɪf ʌv tˈuːhˈʌndɹɪd fˈoːɹɾi wˈʌn jˈɪɹz, wˌɪtʃ mˌeɪks ɪɾ ʌnjˈuːʒuːəl, bˈoʊθ fɔːɹ ɪts lˈɔŋ hˈæflˈaɪf fɚɹən ˈaɪsəmɚ, ænd ðæt sˈɛd hˈæflˈaɪf ɡɹˈeɪtli ɛksˈiːdz ðæt ʌvðə ɡɹˈaʊnd stˈeɪt ʌvðə sˈeɪm ˈaɪsətˌoʊp.