Chapter 32 - Nuclear Physics and Nuclear Radiation - Problems and Conceptual Exercises - Page 1154: 59

$1.0\times 10^3rad$

We know that $dose \space in \space rem=dose \space in \space rad\times RBE$ $\implies dose \space in \space rem=(50rad)(20)=1.0\times 10^3rem$ Now $Dose \space in\space rad=\frac{dose\space in\space ram}{RBE}$ $\implies Dose \space in\space rad=\frac{1.0\times 10^3rem}{1}=1.0\times 10^3rad$