Download and Preview : L 36 Modern Physics 3 The University Of Iowa
Report CopyRight/DMCA Form For : L 36 Modern Physics 3 The University Of Iowa
L 35 Modern Physics 3Nuclear Physics L 35 Nuclear structure L 36 Nuclear energy what s inside the nuclear fissionnucleus nuclear fusion. what holds it together nuclear reactors isotopes nuclear weapons radioactivity half life Structure of the nucleus.nucleus electron proton neutron 0 The diameter of the nucleus is about 10 5times smaller than the diameter of the atom 3 The atom and the nucleus. the electron and proton have the same chargevalue but the electron is and the proton is Qe Qp charge value is 1 6 10 19 C the neutron has no charge Qn 0 the attractive force between the protons and.the electrons holds the atom together the neutron and proton have about the same mass and are about 2000 times more massive than the mp mn mp 2000 me 1 67 10 27 kg the nuclear mass is about 99 9 of the atoms mass. What role do the neutrons play Nuclear Terminology Atomic number Z the number of protons inthe nucleus which is equal to the number ofelectrons in the atom since atoms are electrically.neutral The atomic number is what distinguishesone chemical element from another Neutron number N the number of neutrons inthe nucleus atoms with the same Z but differentN s are called isotopes. Atomic mass number A Z N the numberof protons neutrons A determines the mass ofthe nucleus Symbol for the nucleus of element XNumber of protons.and neutrons examplesNuclei having the same number of protons butdifferent numbers of neutrons are called isotopes Hydrogen 11Hproton 0 neutrons. Deuterium 21H 1 proton 1 neutron TritiumH1 proton 2 neutrons Alpha particle 42 He 2 protons 2 neutrons Carbon.C C 6 protons 6 6 7 8 neutrons Uranium 235Uhas 235 92 143 neutrons What holds the nucleus together .The nuclear glue The nucleus containspositively charged protons all stuck in a very smallvolume repelling each other. so what keeps the nucleus the nuclear force glue this is where the neutronsplay a role the nuclear strong force. protons and neutrons exert 300an attractive nuclear force on 250each other when they are 200very close to each other However the nuclear force of.the protons alone isn t 100enough to hold the nucleus 50together but the neutrons 0add more nuclear glue 0 20 40 60 80 100without adding the repulsive Atomic Number Protons .electric force Since the proton and neutron have stable light Z 50 nuclei roughly the same mass the Nuclearmass is about the mass of the protonshave as many neutrons asplus the mass of the neutrons Nuclei.protons with the same number of protons and stable heavy nuclei Z 50 neutrons lie on the straight line As Zhave more neutrons than Increases N increases more rapidly protons often many more 9 What is radioactivity . in some nuclei there is a very delicatebalance between electric repulsion andnuclear attraction forces some nuclei are just on the verge of fallingapart and need to release some excess.energy an unstable nucleus an unstable nucleus can disintegratespontaneously by emitting certain kinds ofparticles or very high energy photonscalled gamma rays s radioactivity 10. Natural radioactivity some nuclei are naturally radioactive andgive off either alpha rays He nucleus bets rays electrons or gamma rays highenergy photons randomly. the particles are classified in terms theirability to penetrate matter gammas arethe most penetrating and alphas the leastpenetrating Gammas can go right throughseveral inches of lead . how do we detect these particles using aGeiger counter 11 Geiger Counters a gas filled metal cylinderwith a positively charged.wire down the center the or ray ionizesthe gas and the resultingelectrons are collectedby the positive wire. the result is a pulse blip ofcurrent which is convertedto a sound pulse Geiger tubeElectronic. Alpha beta and gammas in a magnetic fieldAlpha and beta particles are charged so they are deflected bya magnetic field Gammas are photons which are not deflected Half Life of radioactive nuclei the decay of radioactive nuclei is a random.process If you have a sample of manyunstable nuclei you cannot predict whenany one nuclei will disintegrate if you start with No radioactive nuclei now the HALF LIFE T1 2 is defined as the time.for half of the nuclei present to disintegrate Half Life T1 2After one Half life N0After two Half lives N0 After three Half lives N0 . December 2 2011T1 2 2 5 min0 1 2 3 4 5TIME minutes Nuclear reactions.Rn decays to Po by emitting an alphaparticle He with a half life of 3 8 days86 Rn 84 Po 24 He If we started with 20 000 atoms of Rn 222 thenin 3 8 days we would have 10 000 atoms of Rn .222 and 10 000 atoms of Po 218 In 7 6 days we would have 5000 atoms of Rn 222 in 11 4 days 2500 Rn 222 s etc Cobalt 60 T1 2 5 27 years decays by emittingbetas and gammas. Smoke detectors use radioactivitySmoke detectors havea radioactive alphaemitting source Thealpha particles ionize.the air in the detectorcreating a current If smoke particles enterthe detector they caninterfere with the.current causing it todrop which sets off theAmericium 241 Carbon Dating As soon as a living organism dies it stops taking.in new carbon The ratio of carbon 12 to carbon 14 at the moment of death is the same as everyother living thing but the carbon 14 decays and isnot replaced The carbon 14 decays with its half life of 5 700.years while the amount of carbon 12 remainsconstant in the sample By measuring the ratio of carbon 12 to carbon 14in the sample and comparing it to the ratio in aliving organism it is possible to determine the.age of a formerly living thing fairly precisely Natural Radioactivity Radon gas 222occurs in soil and canleak into basements It.can attach to dustparticles and be cosmic rays energeticparticles from thecosmos enter the.atmosphere and decay Nuclear activationSome nuclei that are stable can beactivated made unstable bybombarding them with neutrons .stable nucleus Cyclotron facility at UIHC Nuclear medicine A cyclotron is a device whichaccelerates charged particles.producing beams of energetic These protons are used tobombard materials to produceradioisotopes unstable nucleiwith a short half life. The radioisotopes areimplanted in patients for eitherdiagnostic purposes or forcancer treatment.The University of Iowa Other titles Arial Symbol Verdana Wingdings Default Design MathType 5.0 Equation L-35 Modern Physics-3 Nuclear Physics PowerPoint Presentation Structure of the nucleus The atom and the nucleus Nuclear Terminology PowerPoint Presentation examples What holds the nucleus together?