From key@physics.utoronto.ca Fri Mar 21 22:03:37 2008 Date: Fri, 21 Mar 2008 22:03:35 -0400 From: Tony Key To: key@physics.utoronto.ca Subject: SNV and Problem Set > I was wondering what are some examples of internal radiation procedures > that affect all of the body? Also, if the organ was the lungs, for > absorbed dose, would you need to take into consideration that there is air > in it and not just only tissue mass? Answer: In the written problem set, I discuss Radon222 - it is an alpha emitterand when it is breathed in, it can quickly be carried by the blood toall points of the body where it decays. Also C14 which is in all of our bodies, and any otherrelatively long-lived radioisotope that is ingested with out food. Of course cosmic rays affect all of our body also. The density given for lungs includes the fact that they are filled with air. tissue density is about that of water, but the air-filled lung has about 1/3 of that density. The tissue weighting factor takes that into account also I imagine. > I just have one thing for now that I'd like clarify based on your > response. In the case of our problem set answers then, as long as we > determine our answer based on reasonable assumptions, it will be okay even > if it may not necessarily be the same as whatever answer key the T.A.s > have? Answer: Yes that will be my instructions. Even your TA won't know your mass! > > > > > > 1. For question B, I couldn't find the value of the alpha particle > > > energy on the wikipedia site. Is this just the MeV value listed? If > > > so, I calculated the alpha particle energy similar worked problem > > > 3.3 (B) and I didn't get the same value as wikipedia(the quoted MeV > > > was equal to my disintegration energy). Isn't the kinetic energy > > > of the alpha particle just its energy? Am I supposed to assume energy > > > of the daughter is negligible? > > > Answer: The point of many of these questions is to encourage you to make your own assumptions, and to figure out how to use information from different sources - or to look for other information if you need to. Up to now, many of your physics problems have been "set-up" in the sense that they are designed to focus your attention on one concept. This often means that they are rather artificial, usually tell you exactly what assumptions to make, and include only the information you need. In this last section of the course, I wanted to give you a more sophisticated set of problems, which are more like the ones you meet in the real world, where you have to search for information you need, and decide on what assumptions you need to make. Indeed many of these problems were ones I set myself because I wanted to find out the answer - the chest X-ray one I did in class is a good example. Of course, in tests and exams, I can't expect this level of sophistication, but in the MP problems, and particularly in a group assignment, I can! In this case I think the fact that the Worked Problem 3.3(B) is pretty much exactly the same problem as Question B gives you all sorts of support to decide how you want to answer the question. Just explain clearly what you are doing and what you assume. > > > 2. For question C, I think I know how to do it, but I'm stuck on the > > > mass part, since absorbed dose is J/kg but no mass is given. (I'm > > > guessing it's an assumption we have to make?). In general though, for > > > internal radiation, are only some parts of the material > > > in the body irradiated depending on where the radioisotopes are? > > > If so, how do you know how much mass is being affected? Answer: Well, you are one of the few people in the world who knows your own mass! Certainly in some procedures, only some organs are affected by the radiation. Usually "average" values of mass are used, since we don't often know the mass of our own organs! These are available on many Web sites - just Google it! > > > 3. For chain reactions where A -> B -> C, if energy is conserved, can > > > it just be written A -> C to calculate energy? Answer: Yes, as long as all the energy available in B goes to C. > > > 4. Are we allowed to use additional values that aren't given but that > > > may be in the Supplementary Notes? For example, half life of K-40? Answer: Yes, use whatever you need to solve the problem. If you don't trust the SN, find values on the Web or in Knight, etc. Just quote your sources. TonyK > > >