Pu-241
Pu-241 is isotope of Plutonium.
Decay
$ \rm ^{241}_{~94}Pu \xrightarrow[15.4~y]{\beta^-,~ 21\,KeV} {} ^{241}_{~95}Am \xrightarrow[432.7\,y]{\alpha,\, 4.959\,MeV} {}^{237}_{~96}Np \xrightarrow[2.4 \times 10^6\,y]{\alpha,~4.958 \,MeV} \mathrm{^{233}_{91}Pa} ~.\,.\,. $
References
