1. The problem statement, all variables and given/known data A beam of thermal neutrons (10^12 neutrons per cm^2 second) strikes a 1cm thick water target normal to its surface. The target is a round disk with diameter 20cm. Find the exposure rate (R/second) 100cm beyond the water target (the middle of the disk) from only the 1H(n,gamma)2H reaction. Ignore attenuation in water and air. Atomic density is 6e23 atoms/gram. 2. Relevant equations The only real equation I know if for dose calculation, not exposure. D(n,gamma) = 1.6e-13 (J/MeV) * Flux * Number atoms (given) * cross section of hydrogen * Energy gamma * AF 3. The attempt at a solution I can get a value for the dose rate created from the (n, gamma) reaction, but am unsure how to get exposure 100cm past that point. The above formula gives a Dose rate absorbed in the water shield (we often used water as a substitute for tissue anyway). Would it be logical to create a secondary equation with the water disk as a disk source of radiation that is irradiating the point 100 cm away from its center? If so, how would a number in Gy/s be converted back to something usable to calculate exposure.