Outline: 4/20/07 • Chem seminar today @ 4pm • One week to go… • Practice final exams online… Today: Chapter 22 (cont’d) Nuclear Chemistry - Nuclear Applications… Fission devices, Radiodating, Nuclear medicine...
Let do some CAPA questions: #8 – A radioactivity counter gives a reading of 385 counts per minute, for a 15.1-mg sample of cobalt(II)chloride, partially enriched with 60Co (half-life = 5.26 yr). What percentage of the cobalt atoms in this sample are 60Co? • Calculate the decays per minute you expect from pure 60CoCl2 • Divide 385 cpm by the expected to get percentage…
Let do some CAPA questions: What is k? • 0.693 = k t1/2 #8 – half-life of 5.26 years: • k = 0.1318 1/y • 1 y / 525,600 min Units of 1/min… k = 2.508 10-7 1/min What is N0? 0.0151 g CoCl2 1 mol/131 g 6.022e23 = 6.941e19 atoms 60Co
Let do some CAPA questions: t = 1 min #8 – N = N0 e-kt • N = 6.941e19 exp (-2.508 10-7) N = 6.940998 e19 What is N0-N? 1.741e13 Therefore, not much 60Co present: (385 / 1.741e13)100% = 2.212e-9 %
Nuclear Reactions: Radon • 238U a + 234Th • 238U • Natural series: Uranium • 234Th b- + 234Pa • 234Pa b- + 234U • 234U a + 230Th • 230Th a + 226Ra • 226Ra a + 222Rn • 222Rn a + 218Po • a b b a b b a + 208Pb
N/N0 = e - k t or ln(N/N0) = - k t • ln(34.6/103.7) = - k t1/2 • t = 9080 yrs • Radiodating… • e.g. : If 10.0 g of Kennewick Man bone has 34.6 dpm of 14C, and a present-day 10.0 g bone has 103.7 dpm, how old is Kennewick Man?
Medical Diagnosis & Treatment:Nuclear Medicine X-rays/CAT, Tracers, PET, beam therapy, brachytherapy
a b g Why nuclear effects? High energy, sub-atomic (small) : highly penetrating High energy: highly ionizing
What effect does it have on biology? Mutation….mutagenisis, Cancer….tumorigenisis. Does it make atoms radioactive? No…ionization is a chemical process, not a nuclear process. Consider Food Irradiation….
Handout: Benign Hamburger + Listof questions to be answered in class on Monday Everybody has a different selection of questions. Read the “case”. Look for answers in the textbook, look for references in the library/on the web.