2Nuclear ChemistryPictures of human heart before and after stress using gamma rays from radioactive Tc-99m
3Why do you care? PET scans Nuclear Power Space travel Smoke Detectors (Am-241)Ionizing Radiation and X-raysNeutron ActivationExposure (pilots, nuclear accidents, Radon)Carbon DatingNuclear Weapons
4Nuclear RadiationThe Process of emitting energy in the form of waves or particles.Comes from the Nucleus of the AtomThe NeutronsInstability – Binding EnergyE=mc2Non-conservation of Mass
5ATOMIC COMPOSITION Protons positive electrical charge mass = x grelative mass = atomic mass units (amu)Electronsnegative electrical chargerelative mass = amuNeutronsno electrical chargemass = x grelative mass = amu
6IsotopesAtoms of the same element (same Z) but different mass number (A).Boron-10 (10B) has 5 p and 5 n: 105BBoron-11 (11B) has 5 p and 6 n: 115B10B11B
7RadioactivityOne of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie ( ).She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.
10Nuclear Reactions Alpha emission Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2.Nucleons are rearranged but conserved
11Nuclear Reactions Beta emission Note that mass number (A) is unchanged and atomic number (Z) goes up by 1.How does this happen?
12Other Types of Nuclear Reactions Positron (0+1b): a positive electron207K-capture: the capture of an electron from the first or K shellAn electron and proton combine to form a neutron.0-1e + 11p --> 10n
14Stability of NucleiHeaviest naturally occurring non-radioactive isotope is 209Bi with 83 protons and 126 neutronsThere are 83 x 126 = 10,458 possible isotopes. Why so few actually exist?
15Stability of NucleiUp to Z = 20 (Ca), n = p (except for 73Li, 115B, 199F)Beyond Ca, n > p (A > 2 Z)Above Bi all isotopes are radioactive. Fission leads to smaller particles, the heavier the nucleus the greater the rate.Above Ca: elements of EVEN Z have more isotopes and most stable isotope has EVEN N.
16Stability of Nuclei Even Odd Z N 157 52 50 5 Suggests some PAIRING of NUCLEONSSomething inside the nucleus gives each atom a probability of radioactive decay
17Band of Stability and Radioactive Decay 24395Am --> 42a Npa emission reduces Zb emission increases Z6027Co --> 0-1b NiIsotopes with low n/p ratio, below band of stability decay, decay by positron emission or electron capture
18Binding Energy, EbEb is the energy required to separate the nucleus of an atom into protons and neutrons.Use E=mc2Find the mass of the isotope.Sum the masses of the nucleons.For m, use the DIFFERENCE between those masses.
19Calculate Binding Energy For deuterium, 21H: H ---> 11p nMass of 21H = g/molMass of proton = g/molMass of neutron = g/mol∆m = g/mol = 2.39x10-6 kg/molc = 3x108 m/secFrom Einstein’s equation:Eb = (∆m)c2 = 2.15 x 1011 J/molHow much binding energy is there per nuclear particle?Eb per nucleon = Eb/2 nucleons= 1.08 x 108 kJ/mol nucleons
20Half-LifeHALF-LIFE is the time it takes for 1/2 a sample to disappear.The rate of a nuclear transformation depends only on the “reactant” concentration. It does not depend on any factors outside the nucleus.Half-life is a property that can be used to identify an element.Half-life cannot predict the likelihood a single atom will decay
21Half-LifeDecay of 20.0 mg of 15O. What remains after 3 half-lives? After 5 half-lives?
22Kinetics of Radioactive Decay Activity (A) = Disintegrations/timeN is the number of atomsDecay is first order, and soln (A/Ao) = -kt orln (A) – ln (Ao) = -ktThe half-life of radioactive decay ist1/2 = 0.693/k
23Radiocarbon DatingRadioactive C-14 is formed in the upper atmosphere by nuclear reactions initiated by neutrons in cosmic radiation14N + 1on ---> 14C + 1HThe C-14 is oxidized to CO2, which circulates through the biosphere. There is a constant % of C-14 in the atmosphere. While a plant is alive, it has the same % of C-14 in it as the atmosphere.When a plant dies, the C-14 is not replenished.But the C-14 continues to decay with t1/2 = 5730 years.Activity of a sample can be used to date the sample.
25Man-made Eyes to See Small Things Humans needed to find a way to extend their senses, to gather knowledge about things beyond our physical constraints.Light can be thought of as a piece of information sent between matter.The wavelength/frequency/energy of light determines how it interacts with matter and also predicts where it came from.Certain materials can “see” light that our eyes cannot.Using these materials we learn about the elements in space and on earth.
26Human LimitationsThe molecules in our eyes only work within a very specific range of wavelengths.
28Extending Our VisionCommon detector materials that interact with light:Sodium Iodide crystal:Plastic scintillator:Germanium Crystal:Silicon:
29Cosmic RaysSuper fast particles from the sun and outer space (protons and ions)---Strike the atmosphere and become pions (positively charged fundamental particle), then muons (heavy electrons).Built a detector to “see” them using a plastic scintillator.
30Cosmic Rays Obtainable info: Direction of radiation Shielding effects Protonfrom sunCosmic RaysMolecule inatmosphereObtainable info:Direction of radiationShielding effectsPyramids exampleDepth inside EarthSolar activity levelsPionMuonNeutrinoLightAtom ofHydrocarbon200 muons/m2/secondPhotomultiplier Tube (PMT)
31Cosmic rays are the source of C-14 used in radiocarbon dating!
32Terrestrial Radiation Uses gamma ray spectroscopy to “see” light that comes from matter in the groundObtainable info:Naturally occurring radioactive isotopes can be identified.Composition of isotopes in rocks is compared to rocks from around the world.Background radiation in the air can be measuredInvestigation of radiation in the ground.
33SummaryCertain materials interact with the light that our eyes don’t detect.Devices made from these materials have lead to the field of spectroscopy, meaning “seeing light.”All modern devices convert a light signal into an electrical signal.The electrical signal is arranged in a way that allows us to ‘see’ what is going on with our eyes.
34Bubble ChambersAlpha, Beta, and Gamma Particles rip through a supercooled gas,ionizing them, and forming bubbles.
35Artificial Nuclear Reactions New elements or new isotopes of known elements are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- or even a much heavier particle such as 4He and 11B.Radioisotopes used in medicine are often made by these n,g reactions.
36Neutron Activation Applications: Shoot neutrons into a substance, stuffing them into a nucleus to make it unstable. They will then decay in a special way that we can “see” what is in them.Applications:Test for the presence of heavily shielded dangerous nuclear material.Create small amounts of elements (alchemy)Find approximate percent compositions of elements in a substance.
37Transuranium Elements Elements beyond 92 (transuranium) made starting with an n,g reaction23892U n ---> U + g23992U > Np b23993Np ---> Np b
40Nuclear Fission Fission chain has three general steps: 1. Initiation. Reaction of a single atom starts the chain (e.g., 235U + neutron)2. Propagation. 236U fission releases neutrons that initiate other fissions3. Termination.
42Nuclear Fission & POWER Currently about 104 nuclear power plants in the U.S. and about 400 worldwide.17% of the world’s energy comes from nuclear fission.What are would be the benefits and drawbacks to using nuclear FUSION instead of nuclear fission?
44BNCT Boron Neutron Capture Therapy 10B isotope (not 11B) has the ability to capture slow neutronsIn BNCT, tumor cells preferentially take up a boron compound, and subsequent irradiation by slow neutrons kills the cells via the energetic 10B --> 7Li neutron capture reaction (that produces a photon and an alpha particle)10B + 1n ---> 7Li + 4He + photon
45Food IrradiationFood can be irradiated with g rays from 60Co or 137Cs.Irradiated milk has a shelf life of 3 mo. without refrigeration.USDA has approved irradiation of meats and eggs.
46Effects of Radiation Rem: Quantifies biological tissue damage Usually use “millirem”