11

Nuclear ChemistryNuclear Chemistry

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Radioactivity Radioactivity

Emission of subatomic particles or high-Emission of subatomic particles or high-energy electromagnetic radiation by nucleienergy electromagnetic radiation by nuclei

Such atoms/isotopes said to be Such atoms/isotopes said to be radioactiveradioactive

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Its discoveryIts discovery

Discovered in 1896 by BecquerelDiscovered in 1896 by Becquerel Called strange, new emission Called strange, new emission uranic raysuranic rays Cuz emitted from uraniumCuz emitted from uranium Marie Curie & hubby discovered two new Marie Curie & hubby discovered two new

elements, both of which emitted uranic rayselements, both of which emitted uranic rays Polonium & RadiumPolonium & Radium

Uranic rays became radioactivityUranic rays became radioactivity

44

55

Types of radioactivityTypes of radioactivity

Rutherford and Curie found that emissions produced Rutherford and Curie found that emissions produced by nucleiby nuclei

Different types:Different types: Alpha decayAlpha decay Beta decayBeta decay Gamma ray emissionGamma ray emission

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Isotopic symbolismIsotopic symbolism

Let’s briefly go over itLet’s briefly go over it Proton = Proton = 11

11pp

Neutron = Neutron = 1100nn

Electron = Electron = 00-1-1ee

77

Types of decay: alpha decayTypes of decay: alpha decay

Alpha (Alpha () particle: helium-4 bereft of 2e) particle: helium-4 bereft of 2e--

= = 4422HeHe

Parent nuclide Parent nuclide daughter nuclide + He-4 daughter nuclide + He-4238238

9292U U 2342349090Th + Th + 44

22HeHe Daughter nuclide = parent nuclide atomic # minus Daughter nuclide = parent nuclide atomic # minus

22 Sum of atomic #’s & mass #’s must be = on both Sum of atomic #’s & mass #’s must be = on both

sides of nuclear equation!sides of nuclear equation!

88

99

Alpha decayAlpha decay

Has largest Has largest ionizing powerionizing power = ability to ionize molecules & atoms due to = ability to ionize molecules & atoms due to

largeness of largeness of -particle-particle But has lowest But has lowest penetrating powerpenetrating power = ability to penetrate matter= ability to penetrate matter Skin, even air, protect against Skin, even air, protect against -particle -particle

radiationradiation

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Beta decayBeta decay

Beta (Beta () particle = e) particle = e--

How does nucleus emit an eHow does nucleus emit an e--?? neutron changes into proton & emits eneutron changes into proton & emits e --

1100n n 11

11p + p + 00-1-1ee

Daughter nuclide = parent nuclide atomic Daughter nuclide = parent nuclide atomic number plus 1number plus 1

1371375555Cs Cs 137137

5656Ba + Ba + 00-1-1ee--

1111

Beta decayBeta decay

Lower ionizing power than alpha particleLower ionizing power than alpha particle But higher penetration powerBut higher penetration power Requires sheet of metal or thick piece of wood Requires sheet of metal or thick piece of wood

to arrest penetrationto arrest penetration more damage outside of body, but less in more damage outside of body, but less in

(alpha particle is opposite)(alpha particle is opposite)

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Gamma ray emissionGamma ray emission

Electromagnetic radiationElectromagnetic radiation High-energy photonsHigh-energy photons 00

00 No charge, no massNo charge, no mass Usually emitted in conjunction with other radiation Usually emitted in conjunction with other radiation

typestypes Lowest ionizing power, highest penetrating power Lowest ionizing power, highest penetrating power

requires several inches lead shieldingrequires several inches lead shielding

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Problems Problems

Write a nuclear equation for each of the Write a nuclear equation for each of the following:following:

1. beta decay in Bk-2491. beta decay in Bk-249

2. alpha decay of Ra-2242. alpha decay of Ra-224

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Cont.Cont. In determining nuclear In determining nuclear

stability, ratio of neutrons stability, ratio of neutrons to protons (N/Z) importantto protons (N/Z) important

Notice lower part of valley Notice lower part of valley (N/Z = 1)(N/Z = 1)

Bi last stable (non-Bi last stable (non-radioactive) isotopesradioactive) isotopes

N/Z too high: above valley, N/Z too high: above valley, too many n, convert n to p, too many n, convert n to p, beta-decaybeta-decay

N/Z too low: below valley, N/Z too low: below valley, too many p, convert p to ntoo many p, convert p to n

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Magic numbersMagic numbers Actual # of n & p affects nuclear Actual # of n & p affects nuclear

stabilitystability Even #’s of both n & p give Even #’s of both n & p give

stabilitystability Similar to noble gas electron Similar to noble gas electron

configurations: 2, 10, 18, 36, etc.configurations: 2, 10, 18, 36, etc. Since Since nucleons nucleons (= n+p) occupy (= n+p) occupy

energy levels within nucleusenergy levels within nucleus N or Z = 2, 8, 20, 28, 50, 82, and N or Z = 2, 8, 20, 28, 50, 82, and

N = 126N = 126 Magic numbersMagic numbers

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Radioactive decay seriesRadioactive decay series

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Detecting radioactivityDetecting radioactivity

Particles detected through interactions Particles detected through interactions w/atoms or moleculesw/atoms or molecules

Simplest Simplest film-badge dosimeterfilm-badge dosimeter Photographic film in small case, pinned to Photographic film in small case, pinned to

clothingclothing Monitors exposureMonitors exposure Greater exposure of film Greater exposure of film greater exposure to greater exposure to

radioactivityradioactivity

1919

Geiger counterGeiger counter

Emitted particles pass Emitted particles pass through Ar-filled chamberthrough Ar-filled chamber

Create trail of ionized Ar Create trail of ionized Ar atomsatoms

Induced electric signal Induced electric signal detected on meter and then detected on meter and then clicksclicks

Each click = particle passing Each click = particle passing through gas chamberthrough gas chamber

2020

Radioactive decay kineticsRadioactive decay kinetics

Half-lifeHalf-life = time taken for ½ of parent nuclides = time taken for ½ of parent nuclides to decay to daughter nuclidesto decay to daughter nuclides

2121

Radiometric dating: radiocarbon Radiometric dating: radiocarbon datingdating

Devised in 1949 by Libby at U of Devised in 1949 by Libby at U of ChicagoChicago

Age of artifacts, etc., revealed by Age of artifacts, etc., revealed by presence of C-14presence of C-14

C-14 formed in upper atmosphere via:C-14 formed in upper atmosphere via: 1414

77N + N + 1100n n 1414

66C + C + 1111HH

C-14 then decays back to N by C-14 then decays back to N by --emission:emission:

141466C C 1414

77N + N + 00-1-1e; te; t1/21/2 = 5730 years = 5730 years

Approximately constant supply of C-Approximately constant supply of C-1414

Taken up by plants via Taken up by plants via 1414COCO2 2 & later & later incorporated in animalsincorporated in animals

Living organisms have same ratio of Living organisms have same ratio of C-14:C-12C-14:C-12

Once dead, no longer incorporating Once dead, no longer incorporating C-14 C-14 ratio decreases ratio decreases

5% deviation due to variance of 5% deviation due to variance of atmospheric C-14atmospheric C-14

Bristlecone pine used to calibrate dataBristlecone pine used to calibrate data Carbon-dating good for 50,000 yearsCarbon-dating good for 50,000 years

2222

Radiometric dating: uranium/lead Radiometric dating: uranium/lead datingdating

Relies on ratio of U-238:Pb-206 w/in igneous Relies on ratio of U-238:Pb-206 w/in igneous rocks (rocks of volcanic origin)rocks (rocks of volcanic origin)

Measures time that has passed since rock Measures time that has passed since rock solidifiedsolidified

tt1/21/2 = 4.5 x 10 = 4.5 x 1099 years years For ex, if rock contains equal amts of isotopes For ex, if rock contains equal amts of isotopes

above, it would be 4.5 billion years oldabove, it would be 4.5 billion years old

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FissionFission

Meitner, Strassmann, and Hahn discovered fission: Meitner, Strassmann, and Hahn discovered fission: splitting of uranium-235splitting of uranium-235

Instead of making heavier elements, created a Ba and Instead of making heavier elements, created a Ba and Kr isotope plus 3 neutrons and Kr isotope plus 3 neutrons and a lot of energya lot of energy

Sample rich in U-235 could create a Sample rich in U-235 could create a chain rxnchain rxn To make a bomb, however, need To make a bomb, however, need critical mass = critical mass =

enough mass of U-235 to produce a self-sustaining enough mass of U-235 to produce a self-sustaining rxnrxn

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Nuclear powerNuclear power

In America, about 20% electricity generated by In America, about 20% electricity generated by nuclear fissionnuclear fission

Imagine: Imagine: Nuclear-powered carNuclear-powered car Fuel = pencil-sized U-cylinderFuel = pencil-sized U-cylinder Energy = 1000 20-gallon tanks of gasolineEnergy = 1000 20-gallon tanks of gasoline Refuel every 1000 weeks (about 20 years)Refuel every 1000 weeks (about 20 years)

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Nuclear power plantNuclear power plant

Controlled fission through Controlled fission through U fuel rods (3.5% U-235)U fuel rods (3.5% U-235)

Rods absorb neutronsRods absorb neutrons RetractableRetractable Heat boils water, making Heat boils water, making

steam, turning turbine on steam, turning turbine on generator to make electricitygenerator to make electricity

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Comparing Comparing

Typical nuclear power plant makes enough E Typical nuclear power plant makes enough E for city of 1,000,000 ppl and uses about 50 kg for city of 1,000,000 ppl and uses about 50 kg of fuel/dayof fuel/day

No air pollution/greenhouses gasesNo air pollution/greenhouses gases But, nuclear meltdown (overheating of nuclear But, nuclear meltdown (overheating of nuclear

core)core) Also, waste disposal: location, containment Also, waste disposal: location, containment

problems?problems?

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Comparing Comparing

OTOH, coal-burning power plant uses about OTOH, coal-burning power plant uses about 2,000,000 kg of fuel to make same amt of E2,000,000 kg of fuel to make same amt of E

But, releases huge amts of SOBut, releases huge amts of SO22, NO, NO22, CO, CO22

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Fusion Fusion

H-bonds utilize fusion H-bonds utilize fusion (but needs high-temps (but needs high-temps to react cuz both to react cuz both positively charged)positively charged)

As does the sun: As does the sun: 2211H + H +

3311H H 44

22He + He + 1100nn

10 x more energy/gram 10 x more energy/gram than fissionthan fission

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Transmutation Transmutation

Transforming one element into anotherTransforming one element into another In 1919, Rutherford bombarded N-17 to make O-17In 1919, Rutherford bombarded N-17 to make O-17 The Joliot-Curie’s bombarded Al-27 to form P-30The Joliot-Curie’s bombarded Al-27 to form P-30 In ’30’s, devices needed that could accelerate In ’30’s, devices needed that could accelerate

particles to high velocities:particles to high velocities: 1. linear accelerator1. linear accelerator 2. cyclotron2. cyclotron

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Linear acceleratorLinear accelerator

Charged-particle accelerated Charged-particle accelerated in evacuated tubein evacuated tube

Alternating current causes Alternating current causes particle to be pulled into particle to be pulled into next tubenext tube

Continues, allowing Continues, allowing velocity = 90% speed of velocity = 90% speed of light!light!

2 miles long 2 miles long

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Cyclotron Cyclotron

Similar alternating Similar alternating voltage usedvoltage used

But applied btwn two But applied btwn two semicircular halves of semicircular halves of cyclotroncyclotron

Particle spirals due to Particle spirals due to magnetsmagnets

Hits targetHits target

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Radiation on lifeRadiation on life

3 divisions3 divisions 1. acute radiation1. acute radiation 2. Increased cancer risk2. Increased cancer risk 3. genetic effects3. genetic effects

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The firstThe first

Quickly dividing cell at greatest risk:Quickly dividing cell at greatest risk: Intestinal liningIntestinal lining Immune response cellsImmune response cells Likelihood of deathLikelihood of death Depends on dose/Depends on dose/ durationduration

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22ndnd

Cancer = uncontrolled cell growth leading to Cancer = uncontrolled cell growth leading to tumorstumors

Dose? UnknownDose? Unknown Cancer is a murky illnessCancer is a murky illness

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33rdrd

Causes genetic defects Causes genetic defects teratogenicteratogenic

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Average American 360 mrem/yrAverage American 360 mrem/yr

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Good siteGood site

http://www.deq.idaho.gov/inl_oversight/radiatihttp://www.deq.idaho.gov/inl_oversight/radiation/radiation_guide.cfmon/radiation_guide.cfm

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Let’s try the handoutLet’s try the handout

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More factsMore facts 20 rem 20 rem decreased white blood decreased white blood

cell count after instantaneous cell count after instantaneous exposure exposure

100-400 rem 100-400 rem vomiting, vomiting, diarrhea, lesions, cancer-risk diarrhea, lesions, cancer-risk increaseincrease

500-1000 500-1000 death w/in 2 months death w/in 2 months 1000-2000 1000-2000 death w/in 2 weeks death w/in 2 weeks Above 2000 Above 2000 death w/in hours death w/in hours

4141

Diagnostic and therapeutic radiationDiagnostic and therapeutic radiation

Radiotracer = radioactive nuclide in brew to Radiotracer = radioactive nuclide in brew to track movement of brew in bodytrack movement of brew in body

Tc-99 Tc-99 bones bones I-131 I-131 thyroid thyroid Tl-201 Tl-201 heart heart F-18 F-18 heart, brain heart, brain P-31 P-31 tumors tumors

4242

PETPET

Positron emission tomographyPositron emission tomography Shows both rate of glucose metabolism and Shows both rate of glucose metabolism and

structural features of imaged organstructural features of imaged organ F-18 emits positronsF-18 emits positrons Positron and ePositron and e-- produce two gamma rays produce two gamma rays Rays detectedRays detected ImagedImaged

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Radiotherapy Radiotherapy

Using radiation to treat cancerUsing radiation to treat cancer Develop symptoms of radiation sickness: Develop symptoms of radiation sickness:

vomiting, diarrhea, skin burns, hair lossvomiting, diarrhea, skin burns, hair loss

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Other applicationsOther applications

Irradiating foodsIrradiating foods Nuking bugs like fruit flies and screw-worm Nuking bugs like fruit flies and screw-worm

fliesflies