nuclear chemistry & radioactivity

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Nuclear Chemistry & Radioactivity. So I think it is kind of fun…. 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?. - PowerPoint PPT Presentation


Nuclear Chemistry & Radioactivity

So I think it is kind of funNuclear Chemistry&Radioactivity1Who Am I?Mark Vander PolM.Div. Westminster Seminary California, 2009Waiting for a call to the ministryGraduated from CCHS in 1995I think I set a record in the Physics Olympics I wonder if it is still standing?2Why Am I Here?B.A. Trinity Christian College, 1999 Minor: BiologyMajor: Chemistry3Where Was I?S.E.T. Environmental, Inc., 1999-2002Hazardous Materials ChemistArgonne National Laboratory, 2002-2005Chemical Technology DivisionAnalytical Chemistry LaboratoryRadiochemical Analysis GroupI was a radiochemist analyzing and working with radioactive materials4What is Nuclear Chemistry?Study of the change/transformation of the atomic nuclei of isotopesWhat are isotopes?Atoms of an element that differ in their atomic mass (same number of protons, different number of neutrons).RadioactivityWhat is emitted from a change in an atoms nucleusA 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.5Radioactive RadiationThere are three main types of radiation that result from radioactive decay.Alpha - Beta -Gamma There are other ways that nuclei can transformElectron Capture K-CapturePositron emission + SF Spontaneous FissionIT Isomeric Transition6Measuring RadiationDisintegration EventsOne decay per second = 1 Becquerel (Bq)1 Curie = 3.7x1010 BqGeiger Counters used to measure activityEnergies, , and radiation occur with various energiesSpecialized detectors are made for each type of radiation The energies of a sample can be plotted on a spectrogram7 RadiationThe biggest type of radiationContains 2 protons and 2 neutronsWhat would this be the nucleus of?Because of its size it cant pass through much. Paper can stop 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 would become234Th 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 mass8- RadiationAn electron being emittedSmaller than so it isnt 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 same137Cs decaying by - would become137Ba why?Cesiums 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) 9 RadiationElectromagnetic RadiationNot 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 radiationit is energy emitted as a result of another nucleus transformation (i.e. or decay).10Half-LifeThe amount of time it takes for a particular radioactive material to decrease by halfCould 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 1:15:00At 1:15:45 you will have how many grams?At 1:16:30?At 1:17:15?What about at 1:30:00?11What Isotopes Are Radioactive?Easier/Quicker answer: What Isotopes arent radioactive?All the elements have isotopes that will undergo radioactive decayHydrogen only has one, 3H, tritium: t1/2 12.32 years, - decayThe 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 isotopesApproximately 650 isotopes with t1/2 > 60 min.At least 2,350 isotopes with t1/2 < 60 min.12


14Natural RadioisotopesThere are 65 radioactive isotopes that are found in natureSome are continually formed in the atmosphere by interactions with cosmic raysMany 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 - radiation because of naturally occurring 40K! (The abundance of 40K is only o.0117% and the t1/2 is 1.27 billion years)15


17Man-Made RadioisotopesNuclear Fission ReactionsFission 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 radioactiveEnergy can be harnessed and converted to electricity (p. 716)BombardmentIn a fission reaction sometimes neutrons are absorbed and larger elements are created (by - decay)Other particles can be bombarded onto targets to create other isotopes18Why Is Nuclear Chemistry Important?Its practicalSmoke alarms use 241Am to ionize the airIts dateable14C dating helps archeologists determine dates of organic materialIts for your healthMany 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 onNuclear fission reactions help produce electricityIt can keep you warmOkay, not really. However, 238Pu heat sources provide electricity to unmanned spacecraft

19Thanks!Any Questions?20




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