Nuclear Chemistry

Chapter 25

Radiation

In 1896, Antoine Henri Becquerel discovered radiation by accident.His associates at the time were Marie

and Pierre Curie. Marie Curie gets credit for naming

radioactivity.

Radioisotopes

Nuclei of unstable isotopes are called radioisotopes.

An unstable nucleus releases energy by emitting radiation during the process of radioactive decay

Radiation

Three TypesAlpha Helium NucleusBeta ElectronGamma Light wave

Symbols

He42

42

e0101

Alpha

Gamma

Beta

00

Radiation

Radiation

Nuclear Symbols

Table O

Nuclear Stability

For smaller atoms a ratio of 1:1 neutrons to protons helps to maintain stabilityC-12, N-14, O-16

For larger atoms, more neutrons than protons are required to maintain stabilityPb-207, Au-198, Ta-181

Nuclear Stability

Radioactive Decay

Radioisotopes will undergo decay reactions to become more stable

Alpha Decay Beta Decay Positron Emission

Nuclear Reactions

Unstable isotopes of one element are transformed into stable isotopes of a different element.

They are not affected by outside factors, like temp and pressure. They can not be sped up or slowed down.

General Reaction Format

Reactants Products

Starting Material Ending Material

Science equivalent of Math’s =

Reaction Format

In Math class you might say:A – B = C

In Science, we don’t use subtractionA B + CA breaks into B and C

Decay Reactions

Decay reactions involve one unstable nuclei decaying (breaking down) into 2 (or

more) smaller nuclei.Alpha Decay - one of the products is

an alpha particle

Beta Decay - one of the products is a beta particle

Nuclear Reactions

Reactions must always Balance Mass Numbers have to balance Atomic Numbers have to balance

ThU 23490

42

23892

238 = 4 + 234

92 = 2 + 90

Alpha Decay

AtFr 21685

42

22087

Alpha Decay

ThHeU 22990

42

23392

Alpha Decay

PoHeRn 21884

42

22286

Beta Decay

YSr 9039

01

9038

Beta Decay

SeP 3216

01

3215

Beta Decay

OeN 168

01

167

Positron Emission

FeNe 199

01

1910

Transmutations

Any reaction where one element is transformed into a different element

Two main typesNaturalArtificial

Transmutations

NaturalUsually has one reactantAlpha and Beta Decay

ArtificialUsually has more than one reactantParticle Accelerators

Example

LiHeHBe 63

42

11

94 X

Example

SiHHeAl 3014

11

42

2713 X

Example

BanKrnU 14156

10

9236

10

23592 3 X

Half Life

Amount of time for half of a sample to decay into a new element

Parent AtomsUndecayed atoms

Daughter AtomsDecayed atoms

Half Life

Number of Half-lives

Fraction left

0 1

1 1/2

2 1/4

3 1/8

4 1/16

5 1/32

Half Life

Number of half-lives

T

t t = amount of time elapsed

T = half-life

Example

How many half lives does it take for a sample of C-14 to be 11460 yrs old?

25730

11460

y

y

T

t

Half Life

Fraction Remaining

T

t

2

1t = amount of time elapsed

T = half-life

Example

What fraction of P-32 is left after 42.9days?

8

1

2

1

2

1

2

13

3.14

9.42

d

d

T

t

Example

How long will a sample of Rn-222 take to decay down to 1/4 of the original sample?

282.3

2

1

2

1

4

1

d

X2

82.3

d

x

7.64d

Fraction Remaining

T

t

2

1Mass Left

Original Mass=

Practice

How much Carbon-14 was originally in a sample that contains 4g of C-14 and is 17190 years old?

8

1

2

1

2

143

5730

17190

y

y

x

g

32g

More Practice

How much 226Ra will be left in a sample that is 4800 years old, if it initially contained 408g?

8

1

2

1

2

1

408

31600

4800

y

y

g

x

51g

And One More….

What is the half life of a sample that started with 144g and has only 9g left after 28days?

428

2

1

16

1

2

1

144

9

x

d

g

g4

28

x

d

7d

Fission

Splitting of a larger atom into two or more smaller piecesNuclear Power Plants

One Example:

nKrBanU 10

9236

14156

10

23592 3

Fission

Energy Production

Energy is produced by a small amount of mass being converted to energy

E=mc2

Chain Reaction

Reaction that produces material that can initiate more than one reaction

nKrBanU 10

9236

14156

10

23592 3

Chain Reaction

nKrBanU 10

9236

14156

10

23592 3

Fusion

Joining of two or more smaller pieces to make a larger pieceSun, Stars

One Example:

01

42

11 24 HeH

More Examples:

Fusion

nHeHH 10

32

21

21

nHeHH 10

42

31

21

Fusion

Energy Production

Energy is produced by a small amount of mass being converted to energyMore energy is produced by fusion

than any other source

E=mc2

Fission vs. Fusion

Advantages of FissionProduces a lot of energyCan be a controlled reactionMaterial is somewhat abundant

Fission vs. Fusion

Disadvantages of FissionUses hazardous materialProduces hazardous material

• Long Half Life

Reaction can run out of control.Limited amount of fissionable material

Fission vs. Fusion

Advantages of FusionLighter weight materialEasily available materialProduces waste that is lighter and has

shorter half-lifeProduces more energy than fission

Fission vs. Fusion

Disadvantages of FusionMust be done at very high

temperatures• Only been able to attain 3,000,000K

Have not been able to sustain stable reaction for energy production

Uses of Radioisotopes

Smoke Detectors Food Irradiation Radioactive Dating Medical Tracers Nuclear Power Plants Nuclear Weapons Origin of Elements

Smoke Detectors

Americium produces radiation that is monitored by an electrical circuit

Smoke interferes with the current, triggering the alarm

Food Irradiation

Food is exposed to radiation, killing bacteria and mold

Food is cleaner and lasts longer

Radioactive Dating

Ratio of Parent atoms to Daughter atoms provides an age

ExamplesC-14 used to date organic materialU-238 used to date geological

formations

Medical Tracers

Radioisotopes replace stable isotopes Radiation produced can be detected

by machines Example

I-131 is used for thyroid disordersBarium milk shakesCo-60 for Cancer

Radioisotopes

You must know these radioisotopes and usesI-131

• Diagnosing and treating thyroid disorders

Co-60• Treating cancer

Radioisotopes

You must know these radioisotopes and usesC-14

• Dating living organisms• Compare to C-12

U-238• Dating geologic formations• Compare to Pb-206

Nuclear Power Plants

Nuclear Power Plants

Nuclear Power Plants

Nuclear Weapons

Video

Origin of Elements

YouTube

Stability

Elements 1-26 are made in the core of stars

Elements 27-92, excluding 43 and 61, are made during a Supernova explosion

No element larger than 83 has a stable isotope

No element larger than 92 is made in nature