Download Homework 8 (due 4/2)

Homework Assignment #8
Physics 397
(due 4/2/12)
Reading
How Things Work (HTW) : 16.3 (Medical Imaging and Radiation)
Questions/Problems
1. An X-Ray technician can adjust the energy of the X-ray photons produced by a
machine by changing the voltage drop between the X-ray tube’s cathode and the anode.
Please explain.
2. Lead, with 82 electrons per atom, is an excellent source of X-rays. Why?
3. Electric charge is strictly conserved in our universe, meaning that the net charge of an
isolated system cannot change. Why doesn’t the production of an electron-positron pair
in a patient cause a change in the patient’s charge?
4. Gallium 67 (67Ga) is a radioactive isotope with a half-life of 3.26 days. It’s used in
nuclear medicine to locate inflammations and tumors. Accumulations of 67Ga in a
patient’s tissue can be detected by looking for the gamma rays it emits when it decays. A
radiologist usually begins looking for the 67Ga about 48 hours after administering it to a
patient. What fraction of the original 67Ga remain after 48 hours?
5. Two weeks after 67Ga was administered to the patient in Problem 4, what fraction of
the 67Ga nuclei remain?
Project Paper due on Monday April 2, 2012!