Chapter 9. Radioactivity, Radon, and Nuclear Energy. READ THE CHAPTER CAREFULLY ON RADON

Transcription

1 Chapter 9. Radioactivity, Radon, and Nuclear Energy. READ THE CHAPTER CAREFULLY ON RADON CHEM 3320 Dr. Houston Brown

2 Radioactivity Emission of subatomic particles or high-energy electromagnetic radiation by nuclei Such atoms/isotopes said to be radioactive CHEM 3320 Dr. Houston Brown

3 Its discovery Discovered in 1896 by Becquerel Called strange, new emission uranic rays Since emitted from uranium Marie Curie & hubby discovered two new elements, both of which emitted uranic rays Polonium & Radium Uranic rays became radioactivity CHEM 3320 Dr. Houston Brown

4 CHEM 3320 Dr. Houston Brown

5 Types of radioactivity Rutherford and Curie found that emissions produced by nuclei Different types: Alpha decay Beta decay Gamma ray emission CHEM 3320 Dr. Houston Brown

6 Isotopic symbolism Let s briefly go over it Proton = 1 1p Neutron = 1 0n Electron = 0-1e CHEM 3320 Dr. Houston Brown

7 Types of decay: alpha decay Alpha ( ) particle: helium-4 minus 2e - = 4 2He Parent nuclide daughter nuclide + He U Th + 4 2He Daughter nuclide = parent nuclide atomic # minus 2 Sum of atomic # s & mass # s must be = on both sides of nuclear equation! CHEM 3320 Dr. Houston Brown

8 CHEM 3320 Dr. Houston Brown

9 Alpha decay Has largest ionizing power = ability to ionize molecules & atoms due to largeness of -particle But has lowest penetrating power = ability to penetrate matter Skin, even air, protect against -particle radiation CHEM 3320 Dr. Houston Brown

10 Beta decay Beta ( ) particle = e - How does nucleus emit an e -? neutron changes into proton & emits e - 1 0n 1 1p + 0-1e Daughter nuclide = parent nuclide atomic number plus Cs Ba + 0-1e - CHEM 3320 Dr. Houston Brown

11 Beta decay Lower ionizing power than alpha particle But higher penetration power Requires sheet of metal or thick piece of wood to arrest penetration more damage outside of body, but less in (alpha particle is opposite) CHEM 3320 Dr. Houston Brown

12 CHEM 3320 Dr. Houston Brown

13 Gamma ray emission Electromagnetic radiation High-energy photons 0 0 No charge, no mass Usually emitted in conjunction with other radiation types Lowest ionizing power, highest penetrating power requires several inches lead shielding CHEM 3320 Dr. Houston Brown

14 Problem: Write a nuclear equation for each of the following: 1. beta decay in Bk alpha decay of Ra-224 CHEM 3320 Dr. Houston Brown

15 Cont. In determining nuclear stability, ratio of neutrons to protons (N/Z) important Notice lower part of valley (N/Z = 1) Bi last stable (non-radioactive) isotopes N/Z too high: above valley, too many n, convert n to p, beta-decay N/Z too low: below valley, too many p, convert p to n CHEM 3320 Dr. Houston Brown

16 Magic numbers Actual # of n & p affects nuclear stability Even # s of both n & p give stability Similar to noble gas electron configurations: 2, 10, 18, 36, etc. Since nucleons (= n+p) occupy energy levels within nucleus N or Z = 2, 8, 20, 28, 50, 82, and N = 126 Magic numbers CHEM 3320 Dr. Houston Brown

17 Radioactive decay series CHEM 3320 Dr. Houston Brown

18 Detecting radioactivity Particles detected through interactions w/atoms or molecules Simplest film-badge dosimeter Photographic film in small case, pinned to clothing Monitors exposure Greater exposure of film greater exposure to radioactivity CHEM 3320 Dr. Houston Brown

19 Geiger counter Emitted particles pass through Ar-filled chamber Create trail of ionized Ar atoms Induced electric signal detected on meter and then clicks Each click = particle passing through gas chamber CHEM 3320 Dr. Houston Brown

20 Radioactive decay kinetics Half-life = time taken for ½ of parent nuclides to decay to daughter nuclides CHEM 3320 Dr. Houston Brown

21 Radiometric dating: radiocarbon dating Devised in 1949 by Libby at U of Chicago Age of artifacts, etc., revealed by presence of C-14 C-14 formed in upper atmosphere via: 14 7N + 1 0n 14 6C + 1 1H C-14 then decays back to N by -emission: 14 6C 14 7N + 0-1e; t 1/2 = 5730 years Approximately constant supply of C-14 Taken up by plants via 14 CO 2 & later incorporated in animals Living organisms have same ratio of C-14:C-12 Once dead, no longer incorporating C-14 ratio decreases 5% deviation due to variance of atmospheric C-14 Bristlecone pine used to calibrate data Carbon-dating good for 50,000 years CHEM 3320 Dr. Houston Brown

22 Radiometric dating: uranium/lead dating Relies on ratio of U-238:Pb-206 w/in igneous rocks (rocks of volcanic origin) Measures time that has passed since rock solidified t 1/2 = 4.5 x 10 9 years For ex, if rock contains equal amts of isotopes above, it would be 4.5 billion years old CHEM 3320 Dr. Houston Brown

23 Fission Meitner, Strassmann, and Hahn discovered fission: splitting of uranium-235 Instead of making heavier elements, created a Ba and Kr isotope plus 3 neutrons and a lot of energy Sample rich in U-235 could create a chain rxn To make a bomb, however, need critical mass = enough mass of U- 235 to produce a self-sustaining rxn CHEM 3320 Dr. Houston Brown

24 Nuclear power In America, about 20% electricity generated by nuclear fission Imagine: Nuclear-powered car Fuel = pencil-sized U-cylinder Energy = gallon tanks of gasoline Refuel every 1000 weeks (about 20 years) CHEM 3320 Dr. Houston Brown

25 Nuclear power plant Controlled fission through U fuel rods (3.5% U-235) Rods absorb neutrons Retractable Heat boils water, making steam, turning turbine on generator to make electricity CHEM 3320 Dr. Houston Brown

26 CHEM 3320 Dr. Houston Brown

27 Comparing Typical nuclear power plant makes enough E for city of 1,000,000 ppl and uses about 50 kg of fuel/day No air pollution/greenhouses gases But, nuclear meltdown (overheating of nuclear core) Also, waste disposal: location, containment problems? CHEM 3320 Dr. Houston Brown

28 Comparing OTOH, coal-burning power plant uses about 2,000,000 kg of fuel to make same amt of E But, the coal plant releases huge amounts of SO 2, NO 2, CO 2 CHEM 3320 Dr. Houston Brown

29 Fusion H-bonds utilize fusion (but needs high-temps to react because both positively charged) As does the sun: 2 1 H + 3 1H 4 2He + 1 0n 10 x more energy/gram than fission CHEM 3320 Dr. Houston Brown

30 Transmutation Transforming one element into another In 1919, Rutherford bombarded N-17 to make O-17 The Joliot-Curie s bombarded Al-27 to form P-30 In 30 s, devices needed that could accelerate particles to high velocities: 1. linear accelerator 2. cyclotron CHEM 3320 Dr. Houston Brown

31 Linear accelerator Charged-particle accelerated in evacuated tube Alternating current causes particle to be pulled into next tube Continues, allowing velocity = 90% speed of light! 2 miles long CHEM 3320 Dr. Houston Brown

32 Cyclotron Similar alternating voltage used But applied between two semicircular halves of cyclotron Particle spirals due to magnets Hits target CHEM 3320 Dr. Houston Brown

33 Radiation on life 3 divisions 1. acute radiation 2. Increased cancer risk 3. genetic effects CHEM 3320 Dr. Houston Brown

34 The first Quickly dividing cell at greatest risk: Intestinal lining Immune response cells Likelihood of death Depends on dose/duration CHEM 3320 Dr. Houston Brown

35 2 nd Cancer = uncontrolled cell growth leading to tumors Dose? Unknown Cancer is a murky illness CHEM 3320 Dr. Houston Brown

36 3 rd Causes genetic defects teratogenic CHEM 3320 Dr. Houston Brown

37 Average American 620 mrem/yr (US NRC) CHEM 3320 Dr. Houston Brown

38 Medical Procedures Procedure Dose (mrem) X-Rays-single exposure Pelvis 70 Abdomen 60 Chest 10 Dental 1.5 Hand/Foot 0.5 Mammogram (2 views) 72 Nuclear Medicine 400 CT Full body 1,000 Chest 700 Head 200 CHEM 3320 Dr. Houston Brown

39 Sources: 1) web.clark.edu/aaliabadi/. Accessed 3/1/2016. CHEM 204 lecture. 2) Accessed 3/1/ ) Environmental Chemistry, Baird. Chapter 8. CHEM 3320 Dr. Houston Brown