The Thermal Neutron Cross Section of a Proton Is 0

The thermal neutron cross section of a proton is 0.33 bn. If this cross-section were to represent the circular cross-sectional area of the proton presented to the neutron beam, what would be the radius of the proton?

A) 1.2 x 10^-15 m
B) 1.6 x 10^-15 m
C) 3.2 x 10^-15 m
D) 4.1 x 10^-15 m
E) 5.2 x 10^-15 m