7. The dose rate in free space (intensity) of a radiation therapy treatment beam is 267 cGy/min at a distance of 150 cm from the source. The dose rate in free space at a distance of 80 cm from the source is -cGy/min. (You do not need to know what cGy/min is to do this problem. It is suffi- cient to know that it is a measure of intensity.) inW 8. The intensity of a linear accelerator radiation beam is 1.00 unit at a dis- tance of 100 cm from the source of radiation. a. Use the rule of thumb to estimate the intensity at a distance of 110 cm. b. Use the Inverse Square Law to calculate the intensity at a distance of 1 10 cm to two significant digits. Fanid 9. The radiation emitted by Co-60 has an HVL of 1.2 cm in lead. a. What is the linear attenuateon coefficient of lead for Co-60 radiation in units of cm-? b. What is the average distance that Co-60 photons travel in lead before interacting? c. If a 5.0 cm thick cast block is fashioned from lead, what percent of Co-60 radiation will be transmitted through this block? Assume narrow beam geometry