Nuclear Chemistry:
Like regular chemistry, only different.

Nuclear reactions involve the atomic nucleus. Regular chemical reactions involve only the outer electrons of atoms. In a chemical reaction, elements do not change from one to another. When an atomic nucleus changes, it is very probable that the products will be different elements than the reactants.

The energy needed to change an atomic nucleus is much greater than the energy needed to rearrange the valence electrons of atoms. While we are surrounded by many naturally occuring radioactive materials, the nuclear chemist must use accelerators and reactors to achieve the extreme energies needed for their reactions.

Fission is a nuclear reaction in which a very heavy nucleus is split into two approximately equal fragments. This process, known as a chain reaction, releases several neutrons which in turn split more nuclei. If it is not controlled, a nuclear explosion can occur. The photograph above is a ground explosion of twenty pounds of plutonium releasing the energy equal to 70 million pounds of TNT. See an air burst equal to 2,180 million pounds of TNT.

	Man's first controlled nuclear reaction - December 2, 1942, at 3:25 p.m.
	Man's first atomic explosion - July 16, 1945, at 5:29:45 a.m.

Background Questions:   In what year was radioactivity discovered? "Little Boy" and "Fat Man" are the only nuclear weapons to have been used as weapons of war. When were they used? How many nuclear detonations were done by the U.S between 1961 and 1962? What happened at Chernobyl? What happened at Three-mile Island?

Day 2

 

Fusion is a nuclear reaction in which two or more small nuclei are forced together to form one larger nucleus. The energy released during a fusion reaction is much greater than in a fission reaction. Transmutation - a change in the number of protons in the nucleus producing an atom with a different atomic number.

Click on the drawing to tour the accelerators at Fermilab.

Transmutation can be represented with a nuclear equation. The earliest artificial transmutation was performed by Lord Rutherford in 1911. Nitrogen-14 was bombarded with alpha particles, producing Oxygen-17 and protons. The nuclear equation for this reaction looks like this:

14   7

N +

4 2

He

17   8

O +

1 1

H

This is a nuclear chemical symbol:

The element is represented by its chemical symbol.
The top number is the mass number - total protons and neutrons.
The bottom number is the atomic number - number of protons, or positive charges.

Homework Assignment:
This assignment must be turned in by the beginning of class tomorrow to receive credit.

 

1. Complete and balance the following equations:

 

a.	7 3	Li     +	1 1	H	4 2	He
b.	3 1	H     +	2 1	H	1 0	n
c.	14   6	C	14   7	N
d.	9 4	Be     +	4 2	He	12   6	C
e.	26 12	Mg     +	1 0	n	0 +1	e
f. lead-214 decays by beta emission
g. bismuth-214 decays by beta emission
h. polonium-214 decays by alpha emission

Day 3

Not all isotopes of an element are equally stable. A completely stable isotope is one whose nucleus will not spontaneously decay. A completely unstable isotope would be one whose nucleus spontaneously decays completely. Most isotopes fall somewhere in between. It is possible to predict which isotopes will be the most stable using the following general rules:

• The greater the binding energy per nucleon, the more stable the nucleus.
• Nuclie of low atomic numbers with a 1:1 neutron to proton ratio are very stable.
• The most stable nuclei tend to contain an even number of both protons and neutrons.

Half-life: The length of time it takes for one-half of the atoms of a radioactive nuclide to disintegrate. The rate of disintegration is measured in a unit called a becquerel, Bq.

Nuclear Decay Calculator

Radiation and living things:

All radiation, whether particles or waves, has an effect on living things. If the radiation has enough energy, it can penetrate living cells and disrupt their processes. This is particularly dangerous if DNA or RNA molecules are affected. Very small changes in this genetic material can cause mutations and cancer. Large amounts of radiation released into the upper atmosphere can quickly travel around the world. This map shows how wind carried the radiation from Chernobyl in 1986. Because of the dangers involved, the measurement of radiation around living things is important. Radiation used to be measured in rads and rems. These units have been changed to fit within the International System of Measurement. The amount of radiation being produced by a source is now measured grays, Gy. One gray is equal to the transfer of one joule of energy to one kilogram of living tissue. The damage to tissue is better indicated by the absorbed dose of radiation, which is measured in sieverts, Sv. A sievert is equal to a gray multiplied by factors that determine how much of the energy transferred was actually absorbed by the tissue.

We are always being exposed to radiation found naturally in our environment. This radiation is known as background radiation and is equal to about 0.001 Sv/year. Here is a general idea about radiation amounts:

• A single medical X-ray produces about 0.2 mSv (0.0002 Sv)
• Nuclear reactor workers are permitted to receive up to 0.05 Sv/year
• An exposure of 1 Sv/hour results in radiation poisoning
• Exposure to 3 to 5 Sv/hour results in death in 50% of the cases

Food Irradiation:

It has been found that food spoilage can be prevented by exposing it to gamma radiation from   ⁶⁰₂₇Co. Depending on the dose level, irradiated food may last for weeks or even years without refrigeration and with no change in the taste or consistency of the food. The U.S. Food and Drug Administration has approved the irradiation of some foods with dosages up to 1000 grays.

Care to guess which of these has been exposed to radiation?

Portfolio Assignment:

1. Batteries used in heart pacemakers contain plutonium-238. The half-life of plutonium-238 is 27.1 years. If your original sample contains 2.57 x 10⁹ atoms of   ²³⁸₉₄Pu, how much time will pass before the amount is reduced to 5.02 x 10⁶ atoms?
2. Do a quick Internet search for "radiation sterilization". Write one paragraph giving your ideas about the safety of food irradiation.
3. Commercial fusion reactors have been a dream for years because of their "clean" fuel (hydrogen) and waste (helium). The problem has been the cost of containing the reaction. While an experimental fusion reactor as been in operation at Princeton University for years, it takes more electricity to run the reactor than the reactor can produce. A group of scientists from the U.S., Japan, Russia, and other European countries is working on a new reactor design at a site in California. Do an Internet search for "International Thermonuclear Experimental Reactor". What is the status of this project?

Research Links:

• Atomic Structure Timeline - Watertown Unified School District
• Enrico Fermi - University of Chicago
• Nuclear Information - International Nuclear Safety Center
• Nuclear Information - National Nuclear Data Center, Brookhaven National Laboratory (BNL)
• Map of Nuclides - T-2 Nuclear Information Service, Los Alamos National Laboratory
• Nuclear Forces Guide - Federation of American Scientists
• Fusion Energy Science - Princeston Plasma Physics Laboratory
• Radiation and Health Physics - University of Michigan Student Chapter of the Health Physics Society
• What Is Fusion? - General Atomic Fusion Group
• Fusion Energy Education - General Atomics Fusion Group
• Uranium - Uranium Information Center, Melbourne Australia
• Nuclear Energy - World Nuclear Association
• Plutonium Disposal - The Nuclear Control Institute Washington, DC
• Radioactive Waste - RadWaste.Org
• Smashing Atoms - Stanford Linear Accelerator Center
• Chernobyl, 1986 Nuclear Accident - World Nuclear Association
• List of All U.S. Nuclear Weapons - The High Energy Weapons Archive
• Remembering Nagasaki, August 10, 1945 - The Exploratorium
• Nuclear Power - Solcomhouse Types of  Nuclear Reactors and locations
• Nuclear Reactions - CHEMystery Project
• Nuclear Waste Transportation Routes - State of Nevada, Nuclear Waste Project Office