Chapter 19 – Nuclear Chemistry – Study of the nucleus
Chemical reaction: CH4 + O2 → CO2 + H2O
Nuclear reaction:
230
90
Th →4 He +
2
226
Ra
88
Nuclear Decay – nucleus of an element changes to another element because
the nucleus is unstable. Elements that are unstable are also called
Radioactive.
These elements try to become more stable by emitting nuclear particles and/or
energy.
Types of particles:
1. Alpha particle Decay – (He nucleus)
symbol: α
4He
2
230
90
Th →
4
He +
226
2
Ra
88
Write an alpha decay equation for:
222
Rn
86
2. Beta Particle Decay – (electron)
symbol:
0β
-1
214
82
Pb → 0β +
-1
Write a beta decay equation for:
210
83
Bi
214
83
Bi
or
0e-1
1n
3. Neutron decay: symbol
0
4. Proton decay
1p
1
Radiation: Emission of particles and/or energy
Particles: alpha, beta, protons, neutrons…
Energy: Light
Non-ionizing radiation: (e.g. Visible light, radio waves)
low energy light
e.g. H2O + non ionizing radiation → H2O
Ionizing radiation (e.g. U.V., X-Rays, gamma (γ) Rays)
high energy light, particles
e.g. H2O + ionizing radiation → H+ + OH-
Body tissue + ionizing radiation →
?
Unit to measure radiation include RAD, REM (Roentgen Equivalent for Man)
Background Radiation: ionizing radiation that is present from
radioactive sources around us.
normal background radiation is around 126 mRem/year
dental x-ray = 20 mRem
chest x-ray = 50 mRem
Radon Gas
Half Life - time required for ½ of a radioactive isotope to decay into something
else.
Long half life – low radiation level but radioactive for a long period.
Short half life – high radiation level but radioactive only for a short period of time.
Transuranium (man-made) element – Elements larger than Uranium are all
man-made.
238
92
239
92
→ 239 U + γ
U + 1n
0
U →
239 Np
93
239
94
92
239
Np +
93
0β
t ½ = 24 minutes
-1
→ 239 Pu +
94
Pu → 4He +
2
0β
-1
235
92
U
t ½ = 2.4 days
t ½ = 24,000 years
Fermilab particle accelerator in Batavila Illinois
Radiocarbon dating:
emission.
14C
6
t1/2 = 5730 years and decays by β
1 gram of fresh biological tissue emits 15.3 β per minute.
(round to 16)
Problem: How old is a 1 gram
fossil emitting 8 beta particles
per minute?
2 gram fossil emitting 8 beta
particles per minute?
Problem: How old is a fossil
that emits 12.5% of the
radiation that it originally
emitted?
Medical uses of radioisotopes –
Tracer – radioactive isotope
injected into a person, used to
diagnose a problem.
I-131 is taken up by a healthy
thyroid.
Tl-201 combines with healthy heart
tissue
Cu-64 is absorbed by brain tumors
Radiation therapy
1. X-Rays
2. Radiation source implanted next to tissue, or swallowed.
Food Irradiation:
By shining X-Rays through food, the food is sterilized.
No bacteria can survive this treatment. Since energetic
light is being used, no radiation is retained by the food.
Nuclear Energy:
Energy and mass are inter-related, so if mass is lost through a reaction,
energy is created.
The sun is getting lighter every day.
226
88
Ra
→
225.9771 grams
222
86
Rn
+
4
2
He
221.9703 grams + 4.0015 grams
= 225.9718 grams
Missing mass = .0053 grams (called the mass defect)
An element will give off energy if its daughter nuclide weighs less than the
parent nuclide.
Light elements fuse to become larger elements and give off energy – fusion
Heavy elements split to become lighter elements and give off energy fission
Fission – splitting heavy nuclei with a subsequent release of energy.
Decay products can be:
144Cs
55
90Sr
38
+
139Ba
56
Chain Reaction
Critical Mass
90Rb
37
+ 2 1n
143Xe
54
+ 31n
94Kr
36
+ 31n
+
+
0
0
0
Uncontrolled fission – atomic bomb
Controlled fission – nuclear energy
Nuclear Reactor Core
Nuclear Reactor
Nuclear Waste: There are over 100 decay
products produced from nuclear reactors.
Most are highly radioactive.
Where can we safely store these wastes for
thousands of years?
Decay products can be:
144Cs
55
90Sr
38
+
139Ba
56
90Rb
37
+ 2 1n
143Xe
54
+ 31n
94Kr
+ 31n
+
+
36
0
0
0
Nuclear Fusion:
2
1
H +
3
1
H →
4
2
He +
1
n
0
Tokamak Nuclear Fusion Reactor
= 1.7 x 1012 J/mole
Fusion Bomb (Hydrogen Bomb)
fusion from Li-6 and H-2 (Lithium Deuteride)
fusion energy is initiated by a plutonium fission bomb.