CHEM 1405

1. CHEM1405 1 CHEM 1405 Class Meeting 27

2. CHEM1405 2 Assignments and Reminders Quiz today Homework Problems due Today Apr 25th Chapter 10 even numbered Problems 2-8 and 18�30, 36, 38, 42-50 Homework problems due Thursday Apr 27th Chapter 12 even numbered problems 2-18 Exam IV in test center Apr 27th through May 4th Class website http://iws.ccccd.edu/jstankus/

3. CHEM1405 3 Chemistry Help Resources My office hours Tuesdays after class in Lecture room Thursdays 1-2 in Math Lab Free Tutoring through college Students must submit a tutor request form in order to receive detailed information about the available tutoring services.� The form is available on Collin's website and in the following offices: CPC room A108 (ask for Sonia Castillo) PRC room F109 (ask for Shontel Penny or Mary Eldridge) SCC rooms G200 and G141 There�are�group tutoring services available for the following courses: (SUBJECT TO CHANGE!) CHEM 1405, 1411, 1412, 2423, � Also available will be online tutoring in the following courses: (SUBJECT TO CHANGE!) CHEM 1412 & below

4. CHEM1405 4 Objectives What is meant by the half-life of a radioisotope? How are radioisotopes used to date materials? How is this used in archeology and geology? What is transmutation? What is nuclear fission? Nuclear fusion? How are radioisotopes used in medicine?

5. CHEM1405 5 Half-Life Period for one-half of the original elements to undergo radioactive decay Characteristic for each isotope Fraction remaining = n = number of half-lives

6. CHEM1405 6 Half Life Example You obtain a new sample of Cobalt-60 with a half-life of 5.25 years, with a mass of 400 mg. How much cobat-50 remains after 15.75 years (three half-lives)?

7. CHEM1405 7 Half Life Example You obtain a 20.0 mg sample of mercury-190 with a half-life of 20 minutes. How much of the mercury-190 remains after 2 hr?

8. CHEM1405 8 Radioisotopic Dating Use certain isotopes to estimate the age of various items 235U half-life = 4.5 billion years Determine age of rock 3H half-life = 12.3 years Used to date aged wines

9. CHEM1405 9 Carbon-14 Dating 99.9% 12C Produce 14C in upper atmosphere Half-life of 5730 years ~50,000 y maximum age for dating

10. CHEM1405 10 Isotopes Useful in Radioactive Dating

11. CHEM1405 11 Carbon-14 dating example A piece of fossilized wood has a carbon-14 activity that is one-sixteenth (1/16) that of new wood. How old is the artifact? (The half-life of carbon-14 is 5730 years.) solving for n we find that n=4 half-lives Therefore the artifact is 22,920 years old

12. CHEM1405 12 Artificial Transmutation Transmutation changes one element into another Middle Ages: change lead to gold In 1919 Rutherford established protons as fundamental particles Basic building blocks of nuclei

13. CHEM1405 13 Artificial Transmutation Example Write a balanced equation for the nuclear reaction in which potassium-39 is bombarded with neutrons, producing chlorine-36. Mass numbers 39 + 1 = 36 + ? Atomic numbers 19 + 0 = 17 + ?

14. CHEM1405 14 Nuclear Fission �Splitting the Atom� Break a large nucleus into smaller nuclei

15. CHEM1405 15 Nuclear Chain Reaction Neutrons from one fission event split further atoms Only certain isotopes, fissile isotopes, undergo nuclear chain reactions

16. CHEM1405 16 Manhattan Project How to sustain the nuclear reaction? How to enrich uranium to >90% 235U? Only 0.7% natural abundance How to make 239Pu (another fissile isotope)? How to make a nuclear fission bomb?

17. CHEM1405 17 Radioactive Fallout Nuclear bomb detonated; radioactive materials may rain down miles away and days later Some may be unreacted U or Pu Radioactive isotopes produced during the explosion

18. CHEM1405 18 Nuclear Power Plants Provide ~20% U.S. electricity France >70% Slow controlled release of energy Need 2.5�3.5% 235U Problem with disposal of radioactive waste

19. CHEM1405 19 Nuclear Fusion Reaction takes smaller nuclei and builds larger ones Also called thermonuclear reactions

20. CHEM1405 20 Uses of Radioisotopes Tracers Easy to detect Different isotopes have similar chemical and physical properties Physical, chemical, or biological processes

21. CHEM1405 21 Nuclear Medicine Used for two purposes Therapeutic � treat or cure disease using radiation Diagnostic � obtain information about patient�s health

22. CHEM1405 22 Radiation Therapy Radiation most lethal to dividing cells Makes some forms of cancer susceptible Try to destroy cancer cells before too much damage to healthy cells Direct radiation at cancer cells Gives rise to side effects

23. CHEM1405 23 Diagnostic Uses Many different isotopes used See Table next slide Can measure specific things Iodine-131 to locate tumors in thyroid Selenium-75 to look at pancreas Gadolinium-153 to determine bone mineralization

24. CHEM1405 24 Nuclear Medicine Isotopes

25. CHEM1405 25 Computed Tomography (CT scans) Uses X-rays to assemble a 3D image Also known as CAT scan (Computed Axial Tomography)

26. CHEM1405 26 PET Imaging Positron emission tomography (PET) Uses an isotope that emits a positron Observe amount of radiation released Observe g radiation

27. CHEM1405 27 Techniques can be Combined PET scan and CT scan

28. CHEM1405 28 Other Imaging Techniquesnonionizing radiation MRI � Magnetic Resonance Imaging Measures magnetic properties of a nucleus (originally known as Nuclear Magnetic Resonance NMR) Can give chemical information Ultra-Sound Uses reflection of soundwaves to develop an image