Answer
144 rads of slow neutrons.
Work Step by Step
The biological damage is measured by the effective dose, equation 31–10a.
$$effective\;dose\;(rem)=dose\;(rad)\times \;RBE$$
The table on page 901 shows that the Relative Biological Effectiveness (RBE) of slow neutrons is 5, while that of fast neutrons is approximately 10.
In other words, 1 rad of fast neutrons does about the same biological damage as 2 rads of slow neutrons.
Therefore, 72 rads of fast neutrons does about the same damage as 2(72 rads) = 144 rads of slow neutrons.
