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