1 nuclear chemistry copyright © 2000 by harcourt, inc. all rights reserved
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Nuclear Chemistry
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Comparison Of Chemical and Nuclear ReactionsChemical Reactions1No new elements can be produced.
2Usually only the outer most electrons participate
3Release or absorb relatively slight amounts of energy.
4 Rate of reaction depends on factors such as concentration, pressure, temperature, and catalysts.
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Comparison Of Chemical and Nuclear Reactions
Nuclear Reactions1Elements may be converted from one to
another.
2Particles within the nucleus are involved.
3Release or absorb immense amounts of energy.
4 Rate of reaction is not influenced by external factors.
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Beginning of Nuclear Science
1896 - Henri Becqurel– discovers radioactivity in U salts
1898 - Marie and Pierre Curie– discover two new radioactive elements– Po and Ra
1898 - Ernest Rutherford– discovers that radioactivity has two forms
a and b radiation
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Radioactive decay (transmutation)
During nuclear reactions atoms can change into new elements through radioactive decay
When balancing reactions make sure the mass numbers and atomic numbers before and after the arrow are equal
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Several types of radioactive decay4 Nuclide too large – alpha or
4 Too many neutrons Beta minus (electron) or
4 Too many protons, Beta plus (also called a positron or electron capture) or
He42 42
01- e01-
01 e0
1
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Other types of particles used during radioactive decayNeutron
Proton or
Gamma (high energy including x-rays)
heavy proton
n10
p11 H1
1
00
H21
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Examples
1) 218Po + ?
2) 253Es + ? +
3) 142Pm + ? 142Nd
• 7 = instead of + + + + + +
• Try 4
He42
42 n10
n10 n1
0 n10n1
0 n10n1
0 n10 n1
0 71 x 7
0 0 x 7
He42
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Main Types of Radiation
4 Alpha (2 protons and 2 neutrons) or
4 Beta (electron) or
4 Gamma (including x-rays)
He42 42
01- e01-
00
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Radiation Interaction with Matter
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Alpha particles – first to be discovered
Radium-226 Radon-222 alpha particle
Mass number must = 4
Atomic number must = 2
So an alpha particle is 2 protons and 2 neutrons, and has a charge of +2.
The element Helium has a mass of 4 and an atomic number of 2, so the alpha particle is just like a helium atom without any electrons
4
?? Pb Ra ????
22286
22688
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Beta particles
Carbon-14 Nitrogen-14 beta particle
Mass number must = 0
Atomic number must = -1
The electron has a mass of zero and a charge of -1, so the beta particle is just like an electron;
Beta particles are produced when a neutron changes into a proton; an electron is ejected from the nucleus
?? N C ????
147
146
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Gamma rays – last to be found
Uranium-238 thorium-234 alpha particle gamma ray
Mass number must = 0
Atomic number must = 0
The gamma ray has no mass and no charge;
Gamma rays usually occur with alpha and beta radiation
They account for most of the energy lost during radioactive decay
?? He ThU ????
42
23490
23892
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Alpha particles (+ charge) deflect towards the negative plate
Beta particles (- charge) deflect towards the positive plate
Gamma rays (no charge) are not deflected at all
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Detecting Radiation
What do you need in order to detect radiation?– Material for interaction– Method of measuring the interaction
4 Typical detectors include– Gas filled counters, semiconductor based
(Geiger counters)– Luminescent film (Photographic detection)– Florescent detection (Scintillators absorb energy
and then emit visible light)
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Fission and Fusion
Nuclear fission (fizzing like pop rocks or shaking a coke) – splitting of a heavy nucleus into two lighter
nuclei
Nuclear fusion (fusing two things together)– combining two light nuclei into one heavier
nucleus
Both processes generate enormously large amounts of energy
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Fusion Merge (makes heavier
products)
Release tremendous amounts of energy
Produces no radioactive waste
Hydrogen + Hydrogen Helium
Involves changes in the atom at the subatomic level
Currently not feasible
Fission
Split up (makes lighter products)
Release tremendous amounts of energy
Produces radioactive
waste
Uranium lots of smaller radioactive elements
Involves changes in the atom at the subatomic level
Used at nuclear reactors
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Nuclear Fusion
Fusion is the most energetic process in nature.– energy source of stars, fusion reaction is in the
main sequence of stars– produces chemical elements– potential energy source for humans
Thermonuclear or hydrogen bombs have been in existence since the 1950’s
energy n He H H 10
42
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Nuclear Fusion (Thermonuclear) EnergyControlled nuclear fusion
– must occur at temperatures of »10 million oC
Fusion reactors must contain this temperature and not melt!
Some fusion reactors exist around the world– Although none can currently generate a
sustainable fusion reaction
Possible energy source for the 21st Century
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Nuclear Fission
Most nuclides with atomic numbers greater than 80 are able to undergo fission – They split into nuclei of intermediate (smaller)
masses and emit one or more neutrons
Some fission reactions are spontaneous while others require activation, usually by neutron bombardment (hit by a neutron).
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Nuclear Fission – chain reaction
Some possible fission paths for 235U are (after bombardment by a neutron)
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Nuclear Reactors (Fission)
Electricity can be generated from steam heated by nuclear fission reactions. Nuclear power is a cost effective and relatively safe way to produce power
Greatest danger of nuclear reactors is core meltdown.
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Serious nuclear reactor accidents:– Three Mile Island, PA (1979) Nuclear reactor
malfunctioned – no meltdown, but some radioactive contamination. Affected a 25 mile radius
– Chernobyl , Russia (1986) Nuclear reactor’s cooling system failed – meltdown. Released thirty times the radioactivity of the atomic bombs dropped on Hiroshima and Nagasaki. 31 lives were lost immediately. Radiation in soil & atmosphere still presents significant health risks.
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– Japan (2011) After the earthquake and tsunami that hit Japan in 2011. The cooling system of the nuclear power plant in Fukushima failed causing the reaction to spiral out of control. The heat produced by the reaction caused the Uranium to decay to Cesium 137, a very unstable atom that caused most of the environment to become radioactive. This has caused the area to become a dead zone.
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Nuclear Reactors (Fission)
Fuel - 235UO2 or 239PuModerator – a material usually graphite or water that
slows neutrons from fast to thermalControl Rods - removes neutrons and slows the chain
reaction– usually made of boron, efficient neutron absorber
Shielding - protection from radiation– lead and concrete are commonly used
Cooling Systems - reactor core must be cooled to remove heat– possible coolants: water, helium, and liquid sodium
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Turning Heat into ElectricityBWR:Boiling Water Reactors
PWR:PressurizedWater Reactors
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Comanche Peak
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Radiation all around us4 Naturally occurring radiation
– K-40, Thorium, Radium– Cosmic
4 Radiation in household products– Fiestaware
• (1936 – 1959) used U • (1959 – 1973) used depleted U
– Fire Detectors• Uses Americium-95
– Antique Clocks and watches• Used Radium which glows in the dark• 1917 – women who worked at the U.S. Radium Factory were told
that the Ra was harmless. They ingested deadly amounts of Ra and in turn became incredibly ill. This is an important time in history for labor rights
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Health concerns
Acute radiation to cells causes them to divide and grow without control – this creates a tumor (cancer)
*More harmful to children than adults
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Health benefits
Radiation can be used to actually destroy cancerous growths
Medical Field - Wide spread use in medical imagining and diagnostics. – CT Scans– PET Scans– X-rays– Cancer Treatments– Radioactive barium used in “milkshakes” for
colon exams.
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More benefits
Many uses of nuclear radiation in industry, agriculture, space research– used in archaeology, biology, physics,
chemistry, cosmology
Food Industry– Food is sometime irratdiated to kill the bacteria
that causes food to spoil
Crime Scene Investigations
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Radioactive DatingCarbon dating can be used to estimate the ages of
items of organic origin. 14C is produced continuously in the upper atmosphere
by the bombardment of 14N by cosmic-ray neutrons:
14C atoms then react with O2 to form CO2
– CO2 then is incorporated into plant life by photosynthesis.
After material dies 14C content decreases from radioactive decay ~ 14C half-life is 5730 years.
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Half life the amount of time it takes for half of a sample to decay.
Ex. the half life of carbon-14 is 5730 years. – This means that if you start with 24 grams of
carbon 14, 5730 years later you will have 12 grams, 5730 years after that you will have 6 grams, 5730 years after that you will have 3 grams.
Half Life
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Mythbusters
● Myth #1
Americans get most of their yearly radiation dose from nuclear power plants
●Dental X-ray ~ 1 mrem●Natural Radiation ~ 30 mrem per yr●3 hour flight ~ 1.5 mrem●Living within 50 miles of a Nuclear plant ~0.01 mrem
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Mythbusters
Myth #2● A nuclear power plant can explode like
a nuclear bomb
–It is impossible for a reactor to explode like a bomb.– Bombs require much, much, much higher levels of fuel enrichment and must be configured in a specific geometry– Neither of which are present in a power plant
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Mythbusters
Myth #3● The smoke you can see from a cooling
tower is radioactive
– The `smoke' is actually water vaper. The water is very clean and has no detectible radiation
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Mythbusters
Myth #4● An event similar to Chernobyl can
happen in the USA
– The Chernobyl design is vastly different than what is operating in the US– Chernobyl used graphite as a moderator not water– Graphite has postive reactivity coefficient, water has a negative reactivity coefficient– Chernobyl did not have containment, American reactors have 3 levels of containment
Fuel Rod, Reactor Vessel, and Containment building
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Nuclear science has been one of the driving forces of science in the 20th Century.