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Nuclear Reactions vs.
Normal Chemical Changes
 Nuclear reactions involve the nucleus
 The nucleus opens, and protons and
neutrons are rearranged
 The opening of the nucleus releases a
tremendous amount of energy that
holds the nucleus together – called
binding energy
 “Normal” Chemical Reactions involve
electrons, not protons and neutrons
The Nucleus
 Remember that the nucleus is comprised of
the two nucleons, protons and neutrons.
 The number of protons is the atomic number.
 The number of protons and neutrons together
is effectively the mass of the atom.
Isotopes
 Not all atoms of the same element have the same
mass due to different numbers of neutrons in those
atoms.
 There are three naturally occurring isotopes of
uranium:
 Uranium-234
 Uranium-235*
 Uranium-238
Isotopes
Two Categories
 Unstable – isotopes that continuously
and spontaneously break down/decay in
other lower atomic weight isotopes
 Stable – isotopes that do not naturally
decay but can exist in natural materials
in differing proportions
Radioactivity
 It is not uncommon for some
isotopes of an element to be
unstable, or radioactive.
 We refer to these as radioisotopes.
 There are several ways radioisotopes
can decay and give off energy known
as radiation.
Types of Radioactive Decay
Alpha Decay
Loss of an -particle (a helium nucleus)
4
2
238
92
U

He
234
90
4
2
Th+ He
Types of Radioactive Decay
Beta Decay
Loss of a -particle (a high energy electron)
0
−1
131
53
I

0
or −1
131

54
e
Xe
+
0
−1
e
Types of Radioactive Decay
Gamma Emission
Loss of a -ray (high-energy radiation that almost
always accompanies the loss of a nuclear particle)
0
0

Penetrating Ability
Radioactive Particle
alpha
Nuclear Symbol
4
He
Pertinent Information
helium atom without
any electrons
2
beta
0
e
high energy electron,
no mass with a
negative charge
γ
high energy ray with
no mass and no
atomic number
-1
gamma
0
0
positron
0
e
+1
mass of an
electron but a
positive charge
Nuclear Reactions
 Alpha emission
Note that mass number goes down by 4
and atomic number goes down by 2.
Nucleons (nuclear particles… protons
and neutrons) are rearranged but
conserved
Nuclear Reactions
 Beta emission
Note that mass number is unchanged
and atomic number goes up by 1.
Write Nuclear Equations!
 Write the nuclear equation for the alpha
decay of radon-222
222Rn
86

218Po
84
4He
+
2
 Write the nuclear equation for the beta
emitter Co-60.
60Co
27

60Ni
28
+
0e
-1
Growth/Decay curves for radioactive elements
Radioactive Decay
Proportion of daughter atoms remaining
120
120
% Proportion of daughter atoms
% Proportion of parent atoms remaining
Proportion of parent atoms remaining
100
80
60
40
20
0
100
80
60
40
20
0
0
1
2
3
Time
4
5
6
0
1
2
3
4
Time
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5
6
Half-Life
Parent
Daughter / Radiation
Half-Life (Y)
3H
3He
+
0β-1
12.3
14C
14N
+
0β-1
5730
87Rb
87Sr
+
0β-1
49 X 109
210Pb
206Pb
238U
234Th
+
+
4α+2
4α+2
20.4
+γ
4.5 X 109
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Element
Uranium
Uranium- 238 series
U-238
4.5*109 y
Proactinium
Thorium
Th- 232 series
U-234
245500 y
U-235
7.0*108 y
Pa-234
1.2 min
Th-234
24.1 d
Pa-231
32800 y
Th-230
75400 y
Th-232
1.4*1010 y
Actinium
Radium
U-235 series
Th-228
1.91 y
Ac-228
6.1 h
Ra-226
1600 y
Ra-228
5.75 y
Th-231
25.5 h
Th-227
18.7d
Ac-227
21.8 y
Ra-224
3.7 d
Ra-223
11.4d
Pb-208
stable
Pb-207
stable
Francium
Radon
Rn-222
3.8 d
Astatine
Polonium
Po-218
3.1 min
Po-214
0.00014 s
Bismuth
Lead
Bi-214
19.9 min
Pb-214
26.8 min
α-decay
Z: -2
N: -4
Po-210
138 d
Bi-210
5.0 d
Pb-210
22.3 y
Pb-206
stable
β-decay
Z: +1
N: +/-0
Decay
series of
short
lived
nuclides
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Radioactive Series
 Large radioactive
nuclei cannot stabilize
by undergoing only
one nuclear
transformation.
 They undergo a series
of decays until they
form a stable nuclide
(often a nuclide of
lead).
Detection of Isotopes
Existence of ISOTOPES
confirmed by Aston using
the first mass spectrometer
in 1919.
Analysis of Neon gas
achieved separation of 3
stable isotopes:
20
10
Ne
90.9%
21
10
Ne
0.3%
22
10
Isotope Ratio MS
Magnetic
sector
Ion
Source
Faraday cups
Detection
system
Ne
8.8%
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Chart of the Nuclides
100
90
 A nuclide = an isotope
 Narrow band of stability
 For stability, N/P ratio
rises with mass
Number of neutrons, N
80
70
60
β- emission
50
40
30
20
10
0
0
 All nuclides outside the
band and with Z > 83 are
radioactive
 Elements can have from
0 – 10 stable Isotopes
10
20
30
40
β+ emission
50
60
Number of protons, Z
70
80
90
100
The Clocks in the Rocks
 In the beginning was the BIG BANG
 Solar system / earth condensed from dust and
gas
 Radioactive elements decay to daughters
(Parent : Daughter ratio changes with time)
 With half-life can calculate the age of the earth
Geologic Time
 Radioactive Isotopes used in Geologic Dating
 Parent
Daughter
half-life (y)
 U-238
Lead-206
4.5 billion
 U-235
Lead-207
713 million
 Thorium 232 Lead 208
14.1 Billion
 K-40
Argon-40
1.3 billion
 R-87
Sr-87
47 billion
 C-14
N-14
5730
 Half-life = time it takes for 1/2 of the parent mass to decay into
the daughter mass
Dating with Isotopes
Process:
120
 Select suitable isotope
Percent parent
100
80
Parent C-14
60
Daughter N-14
40
20
 Clearly the
0
system is useless …..
beyond 40,000 years
87Sr
14N
–
system
is fine for 60M to
400G years!
0
5000
10000 15000 20000 25000 30000 35000
Time years
120
100
Percent parent
 The
87Rb
14C
80
Parent Rb-87
60
Daughter Sr-87
40
20
0
0
100
200
300
400
500
600
Time (billions of years)
700
800
Process:
 Ideally the crystals in the
rock should contain no Sr
(eg: Mica in Granite)
 All subsequent Sr arises from
Rb decay
 Earliest rocks on Earth are
4G years old
 On melt, the clock is reset
when new igneous rock is
formed
Strontium Dating – the Forensic
Application
 Sr has 4 stable isotopes
0.715 ----
0.730 ----
 As a result of 87Rb decay, 87Sr levels
will rise with time

87Sr
/
86Sr
is highest in oldest rock
 Sr has similar chemistry to Calcium
and ends up in BONE
88Sr
7%
87Sr
10%
86Sr
82%
84Sr
1%
87Sr
/ 86Sr ratios:
0.703 in young rock
0.750 in oldest rock
Strontium Dating – Tracing Adam
 Sept 2001, torso of 5 yr old boy
recovered from Thames
 Suspected ritual killing
 Gut contents suggested poisoning
and UK as place of murder
 Bone 87Sr/86Sr was high – PreCambrian levels
 Police search for relatives in rural
area between Benin City and
Ibadan, Nigeria…arrest made in
Dec 2003
Carbon Dating

14C
half life = 5730 yrs
Cosmic radiation
 Excellent for dating organic
material from 0-40,000
yrs*
Nitrogen-14
Carbon-14
Neutron capture
Why is there any 14C left, &
how does it work?
14C
is absorbed along with
and 13C into the tissue
of living organisms in a
fairly constant ratio
12C
 Assume 14C is continually
being produced at the same
rate.
 Whilst alive, 14C levels
remain constant. Only on
death does the level start to
drop
 However, calibration is
needed to get accurate
dates
Soil
When an organism dies 14C converts back to 14N by beta decay
Carbon-14
Beta decay
Nitrogen-14
Geologic Time
14Carbon
Dating
 Dating is accomplished by determining the
ratio of 14C to non-radioactive 12C which is
constant in living organisms but changes
after the organism dies
 When the organism dies it stops taking in
14C
which disappears as it decays to 14N
Forensic 14Carbon Cases
Nuclear testing during 1955-63 put large amounts of 14C
into the atmosphere which was incorporated into the
enamel of human teeth. Because such testing stopped
the 14C input ended and the 14C in the teeth decayed at a
fixed rate allowing dating of the teeth
Forensic 14Carbon Cases
 Dead Sea Scrolls – 5-150 AD
 Stonehenge – 3100 BC
 Hezekiah’s Tunnel - 700 BC
Forensic 14Carbon Cases
● King Arthur’s Table in
Winchester Castle,
England 14C dated to
13th century AD
● Cave painting at
Lascaux, France 14C
dated to 14,000 BC
● Rhind Papyrus on
Egyptian math 14C
dated to 1850 BC
Forensic 14Carbon Cases
●The Shroud of Turin was
14C
dated
1260-1390 AD which suggests that it is a
fake
●However, recent evaluation shows that
the sample measured was from a
medieval patch and or that it was
seriously contaminated with molds,
waxes, etc
Measuring Radioactivity
 One can use a device like this Geiger counter to
measure the amount of activity present in a
radioactive sample.
 The ionizing radiation creates ions, which conduct
a current that is detected by the instrument.
Trafficking Nuclear Materials
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Man-made Radioactive
Isotopes
 Smuggled Plutonium – can
identify the reactor type in
which the fuel was originally
radiated and the type of plant
where the material was
subsequently reprocessed
In 1997, two pieces of
stainless steel
contaminated with
alpha-emitters were
found in a scrap metal
yard in Germany.
Source was identified as a
fast-breeder reactor in
Obninsk, Russia
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Weapons-grade Plutonium
 The isotopic composition of
plutonium can indicate
INTENT
In 1994, a small lead
cylinder discovered in a
garage in Tengen on the
Swiss-German border
was found to contain
plutonium metal,
isotopically enriched to
99.7%
Weapons-grade Pu-239
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Radioactive Fingerprints
 Preserving the
conventional chain of
evidence whilst dealing
with radioactive samples
can be problematic
The first ever radioactive
fingerprint has recently been
identified on an object
contaminated with alphaemitting isotopes
For example – lifting
fingerprints and swiping
for radioactive
contamination cannot
both be carried out
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Nuclear Fusion
 nuclear fusion is a nuclear reaction
in which two or more atomic nuclei
join together, or "fuse", to form a
single heavier nucleus.
 During this process, matter is not
conserved because some of the mass
of the fusing nuclei is converted to energy which is
released.
 Fusion is the process that powers active stars.
 Fusion would be a superior method of generating
power.
 The good news is that the products of the reaction are not
radioactive.
 The bad news is that in order to achieve fusion, the material
must be in the plasma state at several million kelvins.
 Weapons whose explosive output is
exclusively from fission reactions are
commonly referred to as atomic bombs
or atom bombs
 misnomer because the energy actually
comes from nucleus
 Many fission products are either highly
radioactive (but short-lived) or
moderately radioactive (but long-lived),
and as such are a serious form of
radioactive contamination if not fully
contained. Fission products are the
principal radioactive component of
nuclear fallout.
 Thermonuclear bombs work by
using the energy of a fission
bomb to compress and heat
fusion fuel.
 When the fission bomb is
detonated, gamma rays and Xrays emitted first compress the
fusion fuel, then heat it to
thermonuclear temperatures
 Tsar Bomb
Nuclear Fission
 How does one tap all that energy?
 Nuclear fission is the type of reaction carried
out in nuclear reactors.
Nuclear Fission
 Bombardment of the radioactive nuclide with
a neutron starts the process.
 Neutrons released in the transmutation strike
other nuclei, causing their decay and the
production of more neutrons.
 This process continues in what we call a
nuclear chain reaction.
 If there are not enough radioactive nuclides in the
path of the ejected neutrons, the chain reaction
will die out.
 Therefore, there must be a certain minimum
amount of fissionable material present for the
chain reaction to be sustained: Critical Mass.
Nuclear Reactors
In nuclear reactors the heat generated by the
reaction is used to produce steam that turns a
turbine connected to a generator.
Nuclear Reactors
 The reaction is kept in
check by the use of
control rods.
 These block the paths of
some neutrons, keeping
the system from reaching
a dangerous supercritical
mass.