> de_a_I131:=diff(a_I131(t),t)=-l_I131*a_I131(t)+0.778*l_I131*a_Te131m(t)+1*l_I131*a_Te131(t);

> sys_131:={de_a_Xe131m,de_a_I131,de_a_Te131,de_a_Te131m,a_Xe131m(t0)=core_Xe131m,a_I131(t0)=core_I131,a_Te131(t0)=core_Te131,a_Te131m(t0)=core_Te131m};

> sol_131:=evalf(value(dsolve(sys_131,[a_Xe131m(t),a_I131(t),a_Te131(t),a_Te131m(t)])));