Chapter 18 (DP)
Chapter 28 (Honors Regents)
The Nucleus:
A Chemist’s View
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1
The zone of
stability.
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3
Characteristics of Some Ionizing Radiations
Property
Alpha Radiation
Beta Radiation
Gamma
Radiation
Composition
Helium Nucleus
Free Electron
High Energy EM
Radiation
Symbol
4
2
He
0
1
e
0
0

Charge
+2
-1
0
Mass (amu)
4
1/1837
0
Common Source
Radium-226
Carbon-14
Cobalt-60
Energy
8 x 10-13 J
8 x 10-15 J
1.8 x 10-13 J
Penetrating Power
Low
(0.05 mm body tissue)
Paper, clothing
Medium
(4 mm body tissue)
Metal Foil
High
(goes through the body)
Lead & Concrete
Shielding
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4
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5
Effect of Charge on Nuclear Particles
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6
Nuclear Transmutation
(artificial shown here)
The change of one element into another.
27
13 Al
249
98 Cf

4
30
2 He  15 P

18
263
8 O  106 X


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1
0n
1
40 n
7
Types of Radioactive Decay
(natural transmutation)
alpha production (): helium nucleus, 24 He
238
4
U

92
2 He

234
90Th
beta production (): 10 e
234
234
90Th  91Pa

0
1e
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More Types of Radioactive Decay
(natural transmutation)
gamma ray production ():
238
4
234
0
U

He

Th

2
92
2
90
0
positron production:
0
1e
22
0
Na

11
1e

22
10 Ne
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9
Check Regents Table O for Nuclear Chemistry Symbols!!!
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10
Practice Balancing Nuclear Rxns
27
13
Al + He  Si + ?
4
2
214
83
27
14
30
14
Bi  He + ?
4
2
Si  e + ?
0
-1
Cu  Zn + ?
66
29
66
30
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11
Decay Series
A radioactive nucleus reaches a
stable state by a series of steps.
series of decays 208
232
 82 Pb
90Th  
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12
The decay
series from
U to Pb.
238
92
206
82
Rate of Decay
rate = kN
The rate of decay is proportional to the
number of nuclides. This represents a firstorder process.
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Half-Life
. . . the time required for the number of nuclides to
reach half the original value (N0/2).
ln(2) 0.693
t1/ 2 

k
k
Check Regents Reference Table N for Half-Lives!
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15
Simplified Half-Life Equation:
 A

A
 0
 1
   
2



n
Where A0 = original sample mass
A = final sample mass
n = number of half-lives
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16
The decay of a 10.0-g sample of strontium-90 over
time. Note that the half-life is a constant 28.8 years.
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17
238
92
The change in the amount of
Mo with time (t1/2 = 67 h).
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18
19
Researcher
taking a bone
sample
for carbon-14
dating at an
archeological
site in Egypt.
Atom “Smashers”
Schematic diagram of a linear accelerator.
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21
A schematic diagram of a cyclotron.
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22
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23
An aerial view of Fermilab, a high energy
particle accelerator in Batavia, Illinois.
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24
Energy and Mass
When a system gains or loses energy it also
gains or loses a quantity of mass.
E = mc2
E
2  m
c
m = mass defect
E = change in energy
If E =  (exothermic), mass is lost from the system.
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25
Nuclear Fission and Fusion
Fusion: Combining two light nuclei to form a
heavier, more stable nucleus.
3
2 He
 11H  24 He  01e
Fission: Splitting a heavy nucleus into two
nuclei with smaller mass numbers.
1
0n

235
142
U

92
56 Ba

91
36 Kr
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 301 n
26
Fission Processes
A self-sustaining fission process is called a
chain reaction.
Neutrons
Causing
Event
Fission
subcritical
<1
critical
=1
supercritical
>1
Result
reaction stops
sustained reaction
violent explosion
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27
On capturing a neutron, the nucleus
undergoes fission to produce two lighter
nuclides, free neutrons (typically three), and a
large amount of energy.
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28
Representation of a fission process in which each event
produces two neutrons, which can go on to split other nuclei,
leading to a self-sustaining chain reaction.
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29
If the mass of fissionable material is too small, most of
the neutrons escape before causing another fission
event, and the process dies out.
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30
Key Parts of a Fission Reactor
Reactor Core: 3% U-235 plus moderator +
control rods
Moderator (slows down neutrons – carbon or D2O)
Control Rods (captures neutrons - cadmium based
steel)
 Coolant (deuterium oxide = heavy water or molten
sodium)
 Containment
Shell (concrete & lead)
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A schematic of a
reactor core.
The position of
the control rods
determines the
level of energy
production by
regulating the
amount of
fission taking
place.
A schematic diagram of a nuclear power plant.
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33
Breeder Reactors
Fissionable fuel is produced while the reactor
runs ( 235
is
split,
giving
neutrons
for
the
U
92
creation of 239
):
94 Pu
1
0n

238
239
92 U  92 U
239
239
U

92
93 Np

239
239
93 Np  94 Pu

0
1 e
0
1 e
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36
Biological Effects of Radiation
. . . depend on:
1.
2.
3.
4.
Energy of the radiation
Penetration ability of the radiation
Ionizing ability of the radiation
Chemical properties of the radiation source
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37
A schematic representation of a
Geiger-Müller counter.
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38
After consumption of Na131l, the patient's thyroid is
scanned for radioactivity levels to determine the
efficiency of iodine absorption. (left) A normal
thyroid. (right) An enlarged thyroid.
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39
The two models for radiation damage. In the linear model, even a small
dosage causes a proportional risk. In the threshold model, risk begins
only after a certain dosage.
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43
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44
Ionizing Radiation Used to Cure Cancer
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45
Skin Cancer From Sunlight
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46