Time-integrated radiotoxicity index for study of transmutation of long-lived nuclides

Radiotoxicity of actinides is investigated based on the Annual Limit on Intake (ALI). A new radiotoxicity index, which takes the radiotoxicity of a parent and its all daughters into account, is defined. Three time-integrated radiotoxicity indices are also introduced for three time intervals of 0 to ∞ (ultimate), 0 to 1 × 10⁴ years (short-term) and 1 × 10⁴ to 1 × 10⁸ years (long-term). For 29 actinides, these indices are calculated theoretically and numerically. The ultimate indices of the actinides are almost the same. The long-term indices, however, show a wide range of values. Neptunium-237 and Am-241 have the largest long-term indices. On the contrary, Pu-240, Pu-242 and Pu-244, Cm-244 and Cm-246 have very small values which are 1/50 to 1/100 of those of Np-237 and Am-241. If these indices are used in the study of transmutation, one can examine and compare easily radiotoxicity and its time dependence for any material.