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Ch. 18: The NucleusCh. 18: The Nucleus
ReviewReview
21.1: Nuclear Stability and Radioactive 21.1: Nuclear Stability and Radioactive DecayDecay
21.2 Kinetics of Decay21.2 Kinetics of Decay
21.3 Nuclear Transformations21.3 Nuclear Transformations
ReviewReview Nucleus contains protons and neutrons Atomic number (Z) - # p+
Mass number (A) - # p+ + # n0
Isotopes- differ in number of neutrons only Same Z but different A
Nuclide- specific type of atom, member of a group of isotopes
Nuclear symbol notation CXAZ146
Radioactivity and StabilityRadioactivity and Stability A nucleus that decomposes forming another A nucleus that decomposes forming another
nucleus and one or more particlesnucleus and one or more particles All nuclides are unstable with 84 pAll nuclides are unstable with 84 p++ or more or more Lightweight nuclides are stable with equal Lightweight nuclides are stable with equal
numbers of nnumbers of n00 and p and p++
Heavy nuclides should have ratio >1 to be Heavy nuclides should have ratio >1 to be stablestable
Radioactivity Radioactivity and Stabilityand Stability
Types of Decay- Types of Decay- AA changes changes
Alpha particle productionAlpha particle production αα particle: helium nucleus particle: helium nucleus
Spontaneous fissionSpontaneous fission Splitting of a heavy nucleus into 2 Splitting of a heavy nucleus into 2
lighter nuclides that are about the lighter nuclides that are about the same sizesame size
ThHeU 23490
42
23892
He42
Types of Decay- Types of Decay- AA is Constant is Constant
Beta Particle ProductionBeta Particle Production ββ particle is an electron particle is an electron Can assume the mass is zero Can assume the mass is zero
Net effect : changing a nNet effect : changing a n00 into a p into a p++
PaeTh 23491
01
23490
e01
Types of Decay- Types of Decay- AA is is ConstantConstant
Gamma Ray ProductionGamma Ray Production γγ ray is collection of high energy ray is collection of high energy
photonsphotons Occurs with other types of decayOccurs with other types of decay
Helps a nucleus release extra Helps a nucleus release extra energy so it can relax to a lower energy so it can relax to a lower energy stateenergy state
00
23490
42
23892 2 ThHeU
Types of Decay- Types of Decay- AA is is ConstantConstant
Positron ProductionPositron Production Occurs for nuclides below the line of Occurs for nuclides below the line of
stabilitystability Positron is a positive particle with Positron is a positive particle with
same mass of electronsame mass of electron Also called antiparticle of electronAlso called antiparticle of electron
Net effect: change pNet effect: change p++ into n into n00NeeTh 22
1001
2211
e01
Types of Decay- Types of Decay- AA is is ConstantConstant
Electron CaptureElectron Capture One of the inner electrons in an atom One of the inner electrons in an atom
is captured by nucleusis captured by nucleus Gamma raysGamma rays always produced always produced
Decay SeriesDecay Series When several types of decay occur until a When several types of decay occur until a
stable nuclide is producedstable nuclide is produced
00
20179
01
20180 AueHg
e01
Writing EquationsWriting Equations
111166C produces a positronC produces a positron
2142148383Bi produces a beta particleBi produces a beta particle
2372379393Np produces an alpha particleNp produces an alpha particle
BeC 115
01
116
PoeBi 21484
01
21483
PaHeNp 23391
42
23793
Writing EquationsWriting Equations
Beta particle (electron)Beta particle (electron) Electron captureElectron capture
PositronPositron Positron productionPositron production
PtAu 19578
19579 ?
ArK 3818
3819 ?
Kinetics of DecayKinetics of Decay
Rate of decay is Rate of decay is directly directly proportional to proportional to number of number of nuclides nuclides availableavailable
All are first orderAll are first order Constant half-lifeConstant half-life
kt
ktN
N
kNRate
693.0
ln
2/1
0
ExampleExample If the half-life of a decay is 67.0 hours, If the half-life of a decay is 67.0 hours,
how much of a 1.000 mg sample will how much of a 1.000 mg sample will remain after 335 hours?remain after 335 hours? 335 / 67 = 5 half-life’s335 / 67 = 5 half-life’s 1.000 1.000 mgmg 0.500 0.500 mgmg 0.250 0.250 mgmg 0.125 0.125 mgmg
0.062 0.062 mgmg 0.031 0.031 mgmg
Nuclear TransformationsNuclear Transformations
Change of one element into anotherChange of one element into another Scientists have been able to use this Scientists have been able to use this
to make the periodic table larger by to make the periodic table larger by creating new elementscreating new elements
Since 1940, have been able to make Since 1940, have been able to make transuranium elementstransuranium elements (93-112) (93-112)
18.4 Detection and Uses of Radioactivity18.4 Detection and Uses of Radioactivity18.5 Thermodynamic Stability18.5 Thermodynamic Stability
18.6 Nuclear Fission and Fusion18.6 Nuclear Fission and Fusion18.7 Effects of Radiation18.7 Effects of Radiation
Carbon-14 DatingCarbon-14 Dating Used to date items made out of natural fibers Used to date items made out of natural fibers Created by Willard Libby in 1940sCreated by Willard Libby in 1940s Based on the decay of naturally existing Based on the decay of naturally existing
carbon-14 isotope by carbon-14 isotope by ββ-particle production-particle production
It is also createdIt is also createdN e C 14
701
146
C H n N 146
11
10
147
Carbon-14 DatingCarbon-14 Dating These happen at the same These happen at the same
rate as long as the plant is rate as long as the plant is alive but when it dies, the alive but when it dies, the decay happens more decay happens more rapidly than the creationrapidly than the creation
Ratio of 14-C to 12-C Ratio of 14-C to 12-C decreasesdecreases
Most accurate for pieces Most accurate for pieces older than 10,000 yearsolder than 10,000 years
Medical ApplicationsMedical Applications RadiotracersRadiotracers
Radioactive nuclides that can be traced in Radioactive nuclides that can be traced in people by monitoring their radioactivitypeople by monitoring their radioactivity
Thallium-201Thallium-201 For assessing heart damage from heart For assessing heart damage from heart
attacksattacks Is taken up by healthy heart tissue onlyIs taken up by healthy heart tissue only
Medical ApplicationsMedical Applications
Iodine-131Iodine-131 For diagnosing thyroid problemsFor diagnosing thyroid problems Patients drink a solution of 131-I Patients drink a solution of 131-I
and the uptake is monitoredand the uptake is monitored
Thermodynamic StabilityThermodynamic Stability Can be determined by calculating the change Can be determined by calculating the change
in potential energy if the nucleus is made in potential energy if the nucleus is made from individual particlesfrom individual particles
We can create energy changes by comparing We can create energy changes by comparing the sum of the masses: the sum of the masses: mass defectmass defect
Mass of Mass of 161688O – mass of (8 O – mass of (8 11
00n + 8 n + 8 1111n)n)
Convert amu on periodic table to g Convert amu on periodic table to g (1amu=1.66x10(1amu=1.66x10-24-24 g) g)
2.65535x102.65535x10-23-23 – [8(1.67493x10 – [8(1.67493x10-24-24) + 8(1.67262x10) + 8(1.67262x10-24-24)])] -2.269x10-2.269x10-25-25 g/nucleus = -0.1366 g/mol : lost g/nucleus = -0.1366 g/mol : lost
when 1 mol of 16-O is formedwhen 1 mol of 16-O is formed
OHn 168
11
10 88
Thermodynamic StabilityThermodynamic Stability Find energy (J) using E=mcFind energy (J) using E=mc22
E = (-1.366x10E = (-1.366x10-4-4kg)(3.00x10kg)(3.00x1088m/s)m/s)22 = -1.23x10 = -1.23x101313J/mol J/mol
Binding energyBinding energy Energy required to decompose this Energy required to decompose this
nucleus into its particles nucleus into its particles Often in MeV / nucleonOften in MeV / nucleon
nucleonMeVnucleons
nucleus
J
MeV
nuclei
mol
mol
J
/98.716
1
1060.1
1
1002.6
11023.11323
13
mass must be in kg!
Thermodynamic StabilityThermodynamic Stability
Nuclear Fission and FusionNuclear Fission and Fusion FissionFission
Splitting a heavy nucleus into 2 smaller Splitting a heavy nucleus into 2 smaller nuclei with smaller mass numbersnuclei with smaller mass numbers
Can use neutrons to create instabilityCan use neutrons to create instability
Neutrons produced are used to cause Neutrons produced are used to cause more fissionmore fission
Produces a huge amount of energyProduces a huge amount of energy
nKrBaUn 10
9236
14156
23592
10 3
Nuclear Nuclear Fission Fission
and and FusionFusion
Nuclear Fission and FusionNuclear Fission and Fusion
FusionFusion Combination of 2 light nuclei to form Combination of 2 light nuclei to form
a heavier, more stable nucleusa heavier, more stable nucleus Stars produce their energy using thisStars produce their energy using this
Requires very high temperaturesRequires very high temperatures Must be shot at each other to get Must be shot at each other to get
close enoughclose enough
eHHH 01
21
11
11
Effects of RadiationEffects of Radiation
Any sort of energy transferred to cells can Any sort of energy transferred to cells can break bonds and cause damagebreak bonds and cause damage
Radioactive species are sources of high Radioactive species are sources of high energy particles so can be very harmfulenergy particles so can be very harmful
TypesTypes Somatic: cause illness, cancer, deathSomatic: cause illness, cancer, death Genetic: produce damage in offspringGenetic: produce damage in offspring
Factors in Effects of Factors in Effects of RadiationRadiation
The more energy, the more damageThe more energy, the more damage How deep it goes into bodyHow deep it goes into body
γγ rays > rays > ββ particles (1 cm) > particles (1 cm) > αα particles particles (skin)(skin)
How easily they attract electrons from How easily they attract electrons from biomolecules (ionization)biomolecules (ionization) γγ rays cause less than rays cause less than αα particles particles
How long it stays inside bodyHow long it stays inside body