Answer
4.0 Gy.
Work Step by Step
Use equation 31–10b to relate Sv to Gy.
$$effective\;dose\;(Sv)=dose\;(Gy)\times \;RBE$$
The table on page 901 shows that the Relative Biological Effectiveness (RBE) of $\gamma$ rays is 1.
For gamma rays, the number of Sv equals the number of Gy.
4.0 Sv = 4.0 Gy
