The radionuclide Al-28 emits 1.78 MeV gamma rays with a yield of 1. The energy absorption coefficient for 1.78 MeV photons in air is 0.02434 cm²g⁻¹ and the W-value for air is 33.97 eV.

What is the exposure rate constant (Γ, in units of R cm2 mCi⁻¹ hr⁻¹) for Al-28?

a) 2.6
b) 4.7
c) 8.4
d) 11.5
e) 13.2