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Nuclear ChemistryIntroduction, goals, and review. Chapter OutlineNuclear decayFusion and FissionRelation between mass and energyLots of interesting applications along the way

Real life Explanation GoalsNuclear Medicine: various applicationsSmoke detectorsGeiger CountersNuclear BombsNuclear PowerRadioactive dating

SymbolsXAZA is the Mass number#protons + #neutrons

Z is the Atomic numbernumber of protons, or in case of beta particles and positrons, its chargemass-atomic number g/mol, amu see note page. 4ExamplesFor each example name the number of protons, neutrons and electronsU23592Li73B853 protons3 electrons7-3=4 neutrons5 protons5 electrons8-5=3 neutrons92 protons92 electrons235-92=143 neutronsIntroduction to radioactive decay processesLearning OutcomesIntroduce the concept of radioactive decay. Identify the particles that are frequently discussed in nuclear chemistry. Radioactive Decay ProcessessummarySpontaneousTypically measured in half-life with bulk amountsImpossible to estimate when one particle will decayFollows first order kineticsWell discuss 5 types.

A nuclei decays and becomes two particles or a particle and energyParticlese-0-1e+01p+11n10Namealpha

Electron, beta particle

Positron

Proton

Neutron GammaHe4 2Mass (amu)4.0026033

0.00054857990

0.00054857990

1.00727647

1.00866490

0

Other symbols

Radioactive Decay Processes (that we will cover)Alpha: Emits an alpha particle

Beta: emits a beta particle

Positron: emits a positron

Gamma: emits gamma radiation

Electron Capture: brings an electron into the nucleusHe4 2e-0-1e+01ReviewThere are many types of radioactive decay processes. In the coming videos we will focus on five of them. Many of the atomic particle have a couple of ways of noting them. Youll want to be aware of all of them, even if you only choose to use your favorite. Alpha DecayLearning GoalsDefine alpha decay. Review what an alpha particle is. Determine what is left over after alpha decay. Describe how alpha decay is used in smoke detectors. Describe how alpha particles creates mineable heliumAlpha DecayUsually restricted to heavier elements (Z=83+ typically)

Occurs when Proton:Neutron ratio is too large

Example

Loses an alpha particleAlpha Decay: ExampleYou Try: Fill in the A, Z and element symbol.

Loses an alpha particle241-423795-293NpFind on periodic tableAlpha Decay: ExampleWrite the equation for the alpha decay of Seaborgium-263Name of element tells you proton number.

Loses an alpha particleAlpha decay in the worldFire DetectorsAm-241 decays and ionizes surrounding air.Smoke lessens current and alarm sounds

Natures helium productionUranium and Thorium undergo alpha decay leaving underground deposits to be mined.

Reviewa decay occurs when a heavy atom loses a particle with two neutrons and two protons from its nucleus. Balance neutrons and charges to find out what particle is left over. There are many places that a decay occurs, two of which are It is used in smoke detectorsoccurs in the ground allowing us to mine helium. B decay (b- and b+)Learning ObjectivesDefine b- and b+ decay.Complete nuclear equations involving b- and b+ decayDiscuss applications of b- and b+ decayBeta DecayOccurs in proton deficient nuclei

Example

Note: Be careful, this is a packet of negative charge coming from the NUCLEUS, not the outside electrons. Transforms neutrons into a proton, emits electron aka beta particleBeta DecayFill in the A and Z values for S

Transforms neutrons into a proton, emits electron aka beta particle32-03215-(-1)16Beta DecayFinish the equation for b- emission

Transforms neutrons into a proton, emits electron aka beta particleBeta Decay: 90SrTreat eye and bone cancer- - Strontium-90: Strontium 90 is a bone seeker, like calcium. Provides targeted radiation treatment.

Played a role in the Partial nuclear test ban treaty. Children born in 1963 had 50x higher level of 90Sr

Oddly enough strontium 90 also causes bone cancer. 25Positron DecayOccurs when neutron to proton ratio is too small

A proton turns into a neutron and a positronThe positron is ejected

Example

Positron DecayRadioactive tracer isotope (PET, positron emission tomography, scans)- +Limitation due to short half lives of radioactive material- need to be near medical cyclotron

Dr Marcus RaichleIn the first one (uppermost image), an individual was hearing a text, in order to learn a new language task.

In the second condition (lowermost image), the same individual has now learned the language task and is spelling out.27Reviewg DecayLearning OutcomesDefine g decayComplete nuclear equations using g decayDiscuss applications of g decayGamma EmissionOccurs AFTER or decay an excited nuclide is formed. (Meta stable state is formed after decay, decay lets it reach stable state)

Example

Energy is released in form of photon in the portion of the EM spectrumFirst decaySecond decayGamma Emission: ExampleNickel-56 is produced by supernovae. It decays to Cobalt-56 and then to Iron-56. This produces a light curve that astronomers can detect. Assume at each stage a metastable nuclide is formed. Write the 3 nuclear reactions involved in going from 56Ni to 56Fe.

Energy is released in form of photon in the portion of the EM spectrumApplications of Gamma EmissionTechnetiuum-99m Imaging

Cobalt-60gamma knife: destroys brain tumors.

Ok not really

33Reviewg emission occurs after another decay process. It allows a high energy arrangement of the nuclei to relax to a low energy arrangement. Electron capture. Learning OutcomesDefine electron captureComplete nuclear equations involving electron capture. Electron CaptureNucleus captures a surrounding electronEffectively turns proton into neutron. Atomic number decreases by one. Mass number doesnt change

Example of two types(dont worry about knowing kinds at a general chem level, its just FYI)Example: Electron CaptureWhat products occur after electron capture on the following:Cobalt- 57

B) Arsenic-73

ReviewElectron capture occurs when the nucleus captures an electron and pulls it into the nucleus. This effectively changes a proton into a neutron. Radioactive decay process summary, practice, review and connectLearning OutcomesUsing part of a nuclear reaction, complete the missing link. By doing the above, decide what type of decay occurred. Discuss how Geiger counters work. Practice ProblemsPredict the products of the followingElectron emission by 14C

Alpha emission by 210Rn

Practice ProblemsComplete the following nuclear equations.

Geiger CounterRadiation ionizes low pressure gasIonized gas allows circuit completionElectricity can be read out, or translated to audible clicking noise. Works best with a and b particles, not so much gAnd yes, in case you were wondering: there is an app for that-

Radiation in:

ReviewGiven part of a nuclear reaction you can complete the rest simply by balancing the mass and charge numbers Then if needed using a periodic table to determine the proper element that is leftOR use what we know of sub atomic particles to decide what particle must have been absorbed or emitted. Nuclear FissionLearning OutcomesDefine FissionLearn how fission is used for powerState common problems and solutions for using nuclear power. Learn how fission is used for nuclear weapons. Spontaneous FissionOccurs with Z=90+

Typically will also eject some neutrons

Example:

Nuclei split into daughter nucleiPlutonium 239 has a very high spontaneous fission rate compared to the spontaneous fission rate of uranium 235. Must consider the spontaneous fission rate of each material when designing nuclear weapons. 48Spontaneous Fission

How does this relate to nuclear weapons?

What about spontaneous fission properties of nuclei must scientists take into account when designing nuclear weapons? Nuclei split into daughter nucleiPlutonium 239 has a very high spontaneous fission rate compared to the spontaneous fission rate of uranium 235. Must consider the spontaneous fission rate of each material when designing nuclear weapons. 49

Spontaneous Fission: QuestionsNuclei split into daughter nucleiAnd often release neutrons.

Must have critical mass but then a chain reaction can occur.Plutonium 239 has a very high spontaneous fission rate compared to the spontaneous fission rate of uranium 235. Must consider the spontaneous fission rate of each material when designing nuclear weapons. 50Neutron Induced FissionBombard radioactive nuclei with neutrons to start a chain reaction.

Now I am become Death, the destroyer of worlds.-Ghagavad Gita, Hindu scripture51HiroshimaNagasakiLittle BoyFat ManFissionFissionUraniumPlutonium

FYI the specifics of the bomb constructions wont be tested. https://www.youtube.com/watch?v=LLCF7vPanrY

Controlled Neutron Induced Fission

Same as Neutron induced, except that excess neutrons are absorbed. Creates controlled nuclear power. 53

Problems and Solutions for Nuclear ReactorsNeed to keep neutrons at slow pace to split 235UH2O or D2ONeed to control the reactionControl Rods keep chain reaction in check. Huge cooling systems neededBuild by water, use water to create steam- turns turbine. Radioactive waste: No good solutionopinions?Burial, bottom of the ocean burial, cavernous land forms, shoot it to the sun . What are the problems with these?54ReviewFission is the splitting of nuclei. This generally produces neutrons. If a critical mass of fission-able material is bombarded with neutrons, a chain reaction can occur. If uncontrolled this is a bomb. If controlled it can be used for power. Nuclear FusionLearning OutcomesDefine fusion.Identify how fusion creates power in the sunIdentify why we cant use fusion for powerDescribe how bombs using fusion work. Nuclear FusionCombines small nuclei into more stable large ones

Occurs constantly on the sun

Nuclear Fusion as PowerNo radioactive wasteMore energy than fissionFuel is 2H which is very cheapSo why cant we use this for power?Million degrees Celsius neededIn plasma stateHow do we contain large quantities of this?

The Hydrogen BombAtomic bomb (fission) is used to set off the hydrogen bomb (fusion)No critical mass for the fusion bombLess radioactive exposure to the environment (some is present from the fission part of the bomb)More powerful in smaller packageNever deployed in warfare

a) Warhead before firing; primary (fission bomb) at top, secondary (fusion fuel) at bottom, all suspended in polystyrene foamb) High-explosive fires in primary, compressing plutonium core into supercriticality and beginning a fission reaction.c) Fission primary emits X-rays which are scattered along the inside of the casing, irradiating the polystyrene foam.d) Polystyrene foam becomes plasma, compressing secondary, and plutonium sparkplug begins to fission.e) Compressed and heated, lithium-6 deuteride fuel produces tritium and begins the fusion reaction. The neutron flux produced causes the U-238 tamper to fission. A fireball starts to form.60Review. Fusion is when nuclei come together (think about what fuse means to remember this)This is in contrast to fission which is when nuclei splitFusion creates more energy than fission, but harnessing it is difficult due to the high heats required for it to happen. Hydrogen bombs use a fission bomb to get to the high heats required to allow fission to happen. Movie of H-bomb test

Ended here Thursday. 62Binding EnergyQuestion: What sub-atomic particles are present in the nuclei?Protons and neutrons. What are their charges?Positive and neutralAre these naturally attracted to each other? Nope, positive charges repelSo what holds them together? Learning OutcomesExplain how nuclei manage to stay together. Calculate the mass defect. Calculate the nuclear binding energy of a nucleus. Calculate the binding energy per nucleon of a nucleus and comment on its relation to the stability of the nucleus. Einstein Mass-Energy RelationshipConserves massenergyTotal mass of nuclei is always less than sum of components.The difference in mass is the mass defectNuclei held together with nuclear binding energyF is atomic number 9 so it has 9 protons and 9 electrons and 10 neutrons. 66Calculate the mass defect:Nuclei held together with nuclear binding energy (massenergy)The difference in mass is the mass defectQuestion: The mass of 19F is 18.9984 Given that the mass of a hydrogen atom (1proton and 1 electron) is 1.007825 amu and a neutron is 1.008665 amu find the mass defect.

9 neutrons10 protons and electrons (9 x 1.007825) + (10 x 1.008665)=19.15708 amu

18.9984 - 19.15708= -0.1587 amu

F is atomic number 9 so it has 9 protons and 9 electrons and 10 neutrons. 67Einstein Mass-Energy RelationshipMass defect is related to nuclear binding energy. Useful conversions1kg=6.022x1026 amu1J=1 kg m2/s2Use mass defect to find binding energyFor a more useful comparison amongst different nuclei, divide binding energy by the number of nucleons

"Reality is merely an illusion, albeit a very persistent one. Albert EinsteinE=mc2 Example: Find the binding energy of 19FPreviously we found the mass defect of 19F to be 0.1587amuConverting:

Filling in to E=mc2 (remember m will be negative, take the absolute value of it before filling it in)

2.368x10-9 JBinding Energy (total)Example:Given that the mass of a hydrogen atom (1proton and 1 electron) is 1.007825 amu and a neutron is 1.008665 amu find the mass defect, binding energy and binding energy per nucleon in 7Li (7.01600 amu)

4 neutrons 3 protons and electrons (4 x 1.007825) + (3 x 1.008665)=7.058135 amu

7.01600-7.058135= -0.04135 amu = mass defect

Binding Energy and StabilityThe higher the binding energy per nucleon the more stable the nuclei.

AtkinsFusionFission71Review.Binding energy is calculated by finding the difference in mass between the actual and expected values for the nuclei. The higher the binding energy per nucleon the more stable the nucleus. Nuclear StabilityLearning OutcomesUse the rules for nuclear stability to determine which type of decay an isotope is likely to undergo. General Trends in StabilityMagic numbers 2, 8, 20, 28, 50, 82, 126 protons or neutrons are more stable

Nuclei with even # of protons and neutrons are more stable than odd #s

All elements with Z=83+ are radioactive. All isotopes of Tc and Pm are radio active. Radioactive decay changes N/Z to increase stability

Stability is determined by the proton to neutron ratio. As atomic mass increases, the ration of neutrons to protons must also increase. This will give a larger binding energy, which as we learned in the last video, gives us increased stability. The extra neutrons counteract the repulsions of the higher number of protons.

Radioactive decay will occur in a way that gets the atom closer to the band of stability, you can see this as the dark band running through the isotopes above. Lets zoom in and see what this means for the type of decay nuclei will undergo. 75

Reaching Stability BandSpecies above band are neutron rich, convert neutrons into protons by emmissionNuclei in proton rich areas below stability band, by emitting a positron, capturing an electron, or emitting a proton. Here we have a very zoomed in version of the graph. If species are above the stability band, that means they have too many neutrons per proton. They will undergo a beta minus emission which effectively changes a neutron into a proton, lowering the ratio.

For atoms that are below the stability band there are several ways which they can undergo decay to reach a stable nuclei. Emitting a positron will effectively change a proton to a neutron, decreasing the ratio of protons to neutrons. Proton emissions will also lower the ratio.

Since we wont always have a full chart too zoom in on, and the charts are typically quite difficult to read precisely, generally the stable nuclei are reported by idea mass to proton ratios or neutron to proton ratios. We can guess the likely radioactive decay that will occur based on whether it is proton rich or neutron rich. 76Examples: Predicting Radio Active DecayPredict whether the nuclei listed is more likely to undergo beta decay or positron emission.The stable isotopes of magnesium are 24, 25 and 26amu. Mg-28

Mg-22

Too heavy= high neutron ratio= Need to lower protons so b - decayToo light= low neutron ratio= Need to raise protons so b+ decayReviewFor a given atom there is an ideal ratio of protons to neutrons.Nuclei will decay in a way that brings them closer to the ideal ratio. Neutron rich nuclei tend to undergo beta decay while neutron poor nuclei tend to undergo positron decay.

Nuclear Decay KineticsKinetics of Radioactive DecayFirst order kinetics (only one reactant)Recall: Rate=K*[A]Aka: t=N (t=rate at a time t, is the decay constant, N is number of radioactive nuclei at time t)Written as the integrated rate law ln(Nt/No)=-tHalf life equation t(1/2)= 0.693/

Radioactive Decay ExampleAfter 500 years a smple of radium-226 has decayed to 80.4% of its original mass. Find the half-life of radium-226. First Order Kinetic equations: ln(Nt/No)=-Ktln(Nt/No)=-Ktt(1/2)=1590yearsWhen 14N is bombarded with cosmic rays, it forms 14C.

Plants take up this 14C in the form of CO2 and incorporate it into life, as then do the animals that eat the plants. Starts radioactively decaying after death.

The fraction of 14C left in a sample gives an estimate of the age of the sample.

Radioactive Decay and Atomic Clocks

Problems with Radio Carbon DatingPreviously- had to count radioactive decayLong half-life led to only a few disintegrations per minute equaling large statistical errors. This is mostly fixed via mass spectrometry- allows for direct counting of isotopesLimited to 100,000)

Radiocarbon Dating ExampleAncient footprints exist in Nicaragua. They were left in volcanic ash and mud by a group of up to 15 people. Soil samples were taken from underneath the footprints. A mass spectrometer showed that 22.62% of the 14C atoms had decayed. How old are the footprints? (t1/214C=5,730 years)ln(Nt/No)=-Kt