Nuclear Chemistry & Radioactivity

1. Nuclear Chemistry&Radioactivity So I think it is kind of fun…

2. Who Am I? • Mark Vander Pol • M.Div. Westminster Seminary California, 2009 • Waiting for a call to the ministry • Graduated from CCHS in 1995 • I think I set a record in the Physics Olympics… I wonder if it is still standing?

3. Why Am I Here? • B.A. Trinity Christian College, 1999 • Minor: Biology • Major: Chemistry

4. Where Was I? • S.E.T. Environmental, Inc., 1999-2002 • Hazardous Materials Chemist • Argonne National Laboratory, 2002-2005 • Chemical Technology Division • Analytical Chemistry Laboratory • Radiochemical Analysis Group • I was a radiochemist analyzing and working with radioactive materials

5. What is Nuclear Chemistry? • Study of the change/transformation of the atomic nuclei of isotopes • What are isotopes? • Atoms of an element that differ in their atomic mass (same number of protons, different number of neutrons). • Radioactivity • What is emitted from a change in an atom’s nucleus • A material is “radioactive” when it is contains isotopes which are decaying and emitting certain types of radiation. • When I was working at Argonne my group determined what isotopes were present in a sample. We usually did this by measuring the energies of the various types of radiation.

6. Radioactive Radiation • There are three main types of radiation that result from radioactive decay. • Alpha - α • Beta – β- • Gamma – γ • There are other ways that nuclei can transform • Electron Capture – “K-Capture” • Positron emission – β+ • SF – Spontaneous Fission • IT – Isomeric Transition

7. Measuring Radiation • Disintegration Events • One decay per second = 1 Becquerel (Bq) • 1 Curie = 3.7x1010 Bq • Geiger Counters used to measure activity • Energies • α, β, and γ radiation occur with various energies • Specialized detectors are made for each type of radiation • The energies of a sample can be plotted on a spectrogram

8. α Radiation • The biggest type of radiation • Contains 2 protons and 2 neutrons • What would this be the nucleus of? • Because of its size it can’t pass through much. Paper can stop α radiation and even a few inches of air can cause it to loose its energy. • However, because it is so big and heavy it can do a lot of damage. • Comes from the decay of the larger isotopes (106Te, really 144Nd) • Causes the isotope to drop its atomic number by 2 and its atomic weight by 4. • 238U decaying by α would become… • 234Th – why? • Uranium is atomic number 92. Loosing 2 protons gives it an atomic number of 90, which is Thorium. • Loosing 2 neutrons as well makes 4 nucleons lost. 238-4=234 which is the new atomic mass

9. β- Radiation • An electron being emitted • Smaller than α so it isn’t as easily stopped, but it is still a particle. Stopped by low density material (wood, plastic, etc.) • Essentially a neutron turns into a proton and emits an electron. The atomic number increases by 1, but the atomic mass stays the same • 137Cs decaying by β- would become… • 137Ba – why? • Cesium’s atomic number is 55. Adding a proton would make the atomic number 56 which is Barium. • The atomic mass stays the same because all that was lost was an electron (negligible difference)

10. γ Radiation • Electromagnetic Radiation • Not a particle, but is a wave like light, x-rays, radio waves, etc. • Very hard to stop. Usually need heavy metals like lead. • Nothing “decays” by γ radiation—it is energy emitted as a result of another nucleus transformation (i.e. α or β decay).

11. Half-Life • The amount of time it takes for a particular radioactive material to decrease by half • Could be hundreds of thousands of years or milliseconds (p.723) • The shorter the half-life the more radiation the material is emitting (because it is decaying faster). • Example: • 212Po : t1/2 = 45 seconds (decays to stable 208Pb) • Start with 100 grams at 1:15:00 • At 1:15:45 you will have how many grams? • At 1:16:30? • At 1:17:15? • What about at 1:30:00?

12. What Isotopes Are Radioactive? • Easier/Quicker answer: What Isotopes aren’t radioactive? • All the elements have isotopes that will undergo radioactive decay • Hydrogen only has one, 3H, tritium: t1/2 12.32 years, β- decay • The larger the nucleus the more unstable it is and the more likely to have decay properties. • Decaying allows the nucleus to get to a more stable state. • Around 266 stable isotopes • Approximately 650 isotopes with t1/2 > 60 min. • At least 2,350 isotopes with t1/2 < 60 min.

15. Natural Radioisotopes • There are 65 radioactive isotopes that are found in nature • Some are continually formed in the atmosphere by interactions with cosmic rays • Many are the part of “decay chains” from naturally occurring 232Th, 235U, and 238U. (See p. 717) • These decay to stable isotopes of Pb (208, 206, and 207 respectively) • The remaining are just radioactive! • Foods with a lot of potassium have detectable amounts of β- radiation because of naturally occurring 40K! (The abundance of 40K is only o.0117% and the t1/2 is 1.27 billion years)

18. Man-Made Radioisotopes • Nuclear Fission Reactions • Fission is the splitting of a large atom (235U or 239Pu) with neutrons into smaller atoms along with enormous amounts of energy being released. (p.714) • The “Fission Products” generated are varied and very radioactive • Energy can be harnessed and converted to electricity (p. 716) • Bombardment • In a fission reaction sometimes neutrons are absorbed and larger elements are created (by β- decay) • Other particles can be bombarded onto targets to create other isotopes

19. Why Is Nuclear Chemistry Important? • It’s practical • Smoke alarms use 241Am to ionize the air • It’s dateable • 14C dating helps archeologists determine dates of organic material • It’s for your health • Many radioisotopes can be used as tracers to determine the functionality of various bodily organs. • Also used to help kill cancer cells. • It can keep the lights on • Nuclear fission reactions help produce electricity • It can keep you warm • Okay, not really. However, 238Pu heat sources provide electricity to unmanned spacecraft

20. Thanks! Any Questions?