Discuss the below:
1. Consider a beam of monoenergetic photons incident on a slab of water as depicted below. The energy per photon is 5 MeV and the indicent photon fluence rate is φ =108mm -2 sec-1.
2. At a depth of one mean free path (mfp) determine the rate of Compton interactions, photoelectric absorption interactions, coherent scatter interactions and pair production interactions in the pill box shaped volume (orange in figure below) of cross sectional area A=3 mm2 and thickness Δx=1cm. Estimate the power (watts) that is generated as bremsstrahlung because of these interactions.
3. A 60Co radiation therapy unit is equipped with a 1000 Ci source. The source to skin distance is 100 cm. Estimate how many photons per second are incident on a 1 mm x 1 mm area of the skin of a patient. Neglect air attenuation.
4. A fission reactor accident evaporates 5 x 106 Ci of 90Sr (T1/2 = 27.7 yr) into the air. The 90Sr falls out uniformly over an area of 104 km2 How long will it take the activity of the 90Sr to reach the agriculturally "safe" level of 2 μCi/m2
5. Calculate the energy of the Compton scattered photon at θ=90o for incident photons of energies 100 keV and 5 MeV.
6. A sample of a radioactive isotope is found to have an activity of 115 Bq immediately after it is pulled from the reactor that formed it. Its activity 2 hours and 15 min later is measured to be 85.2 Bq. (a) Calculate the decay constant and the half-life of the sample. (b) How many
radioactive nuclei were there in the sample initially? Supplementary Material
Rest mass energy of an electron = 0.511 MeV
1 Ci = 3.7 ×1010 Bq
1 eV = 1.602 ×10-19 J
1 watt = 1 J/sec
1 amu = 931.5 MeV/c
