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