1 nuclear chemistry copyright © 2000 by harcourt, inc. all rights reserved

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Nuclear Chemistry

Copyright © 2000 by Harcourt, Inc. All rights reserved.


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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


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


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


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


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


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


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

31

21


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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


Turning Heat into ElectricityBWR:Boiling Water Reactors

PWR:PressurizedWater Reactors


Comanche Peak


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.


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


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


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


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.

1 nuclear chemistry copyright © 2000 by harcourt, inc. all rights reserved

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