Chemistry for Changing Times11th Edition

Hill and Kolb

Chapter 4Nuclear Chemistry

John SingerJackson Community College, Jackson, MI

©2007 Prentice Hall

Background Radiation

• 3/4ths of all exposure to radiation comes from background radiation.

• Most of the remaining ¼ comes from medical irradiation such as X-rays.

Radiation Damage to Cells

• Radiation is capable of removing electrons from cells, forming ions; hence the term ionizing radiation.

• Molecules can also splinter into neutral fragments called free radicals. Free radicals can disrupt cellular processes.

Radiation Damage to Cells

• Radiation often affects the fastest growing cells and tissues such as white blood cells and bone marrow.

• Ionizing radiation call also disrupt DNA, causing mutations.

Radiation Damage to Cells

Nuclear Equations

In nuclear equations, we balance nucleons (protons and neutrons). The atomic number (number of protons) and the mass number (number of nucleons) are conserved during the reaction.

Nuclear Equations

Alpha Decay

Nuclear Equations

Beta Decay

Nuclear Equations

Beta Decay

Nuclear Equations

Nuclear Equations

Positron Emission: A positron is a particle equal in mass to an electron but with opposite charge.

Nuclear Equations

Electron Capture: A nucleus absorbs an electron from the inner shell.

Nuclear Equations

Nuclear Equations

Nuclear Equations

Half-Life

Half-life of a radioactive sample is the time required for ½ of the material to undergo radioactive decay.

Half-Life

Half-Life

Fraction Remaining = 1/2n

Radioisotopic Dating

Radioisotopic Dating

Carbon-14 Dating: The half-life of carbon-14 is 5730 years. Carbon-14 is formed in the upper atmosphere by the bombardment of ordinary nitrogen atoms by neutrons from cosmic rays.

Radioisotopic Dating

Tritium Dating: Tritium is a radioactive isotope of hydrogen. It has a half-life of 12.26 years and can be used for dating objects up to 100 years old.

Artificial Transmutation

Bombardment of stable nuclei with alpha particles, neutrons, or other sub-atomic particles cause new elements to form. This process is known as artificial transmutation.

Uses of Radioisotopes

Tracers: Radioisotopes can be easily detected through their decay products. Therefore they can be used to trace their movement.– Detect leaks in underground pipes.– Determine frictional wear in piston rings.– Determine uptake of phosphorus and its

distribution in plants.

Uses of Radioisotopes

Irradiation of Food: Radioisotopes can destroy microorganisms that cause food spoilage.

Nuclear Medicine

• Radiation Therapy: Nuclear radiation can be used to kill cancerous cells. Radiation is most lethal to fastest growing cells. Radiation is aimed at the cancerous tissue. Patients undergoing radiation therapy often experience nausea and vomiting, which are early signs of radiation sickness.

Nuclear MedicineDiagnostic Uses of Radiation

Nuclear Medicine

• Gamma Ray Imaging: Technetium-99m emits gamma radiation. It can be used to image the heart and other organs and tissues.

Nuclear Medicine

• Positron Emission Tomography (PET): A patient inhales or is injected with positron-emitting isotopes such as carbon-11 or oxygen-15. When positrons encounter electrons, they emit two gamma rays, which exit the body in opposite directions. PET scans can be used to image dynamic processes.

Penetrating Power of Radiation

• Alpha radiation is least penetrating and can penetrate the outer layer of skin. Alpha radiation is stopped by a sheet of paper.

• Beta radiation can penetrate through a few cm of skin and tissue. Beta radiation is stopped by a sheet of aluminum foil.

• Gamma radiation will pass right through a body. Gamma radiation requires several cm of lead to stop.

Penetrating Power of Radiation

Penetrating Power of Radiation

Penetrating Power of Radiation

Two means of protecting oneself from radiation are distance and shielding.

Distance: Move away from the source. The intensity of radiation decreases with increasing distance from the source.

Shielding: Lead is a commonly used shield for radiation.

Energy from the NucleusBy 1905, Albert Einstein had developed his famous mass-energy equation:

E = mc2

E = Energy

m = mass

c = speed of light

Energy from the Nucleus

When protons and neutrons combine to form a nucleus, a small amount of mass is converted into energy. This is known as binding energy.

Binding Energy

The Building of the BombNuclear Fission: Fission occurs when larger nuclei split into small nuclei.

Nuclear Chain Reaction

Fission of one nucleus produces neutrons that can cause the fission of other nuclei, thus setting off a chain reaction.

Manhattan Project

The Manhattan Project was launched by President Roosevelt in 1939. It consisted of 4 separate research teams attempting to:

a. Sustain the nuclear fission reaction.

b. Enrich uranium.

c. Make fissionable plutonium-239.

d. Construct a fission atomic bomb.

Manhattan Project

Replicas of “Little Boy” (dropped on Hiroshima) and “Fat Man” (dropped on Nagasaki).

Manhattan Project

Mushroom cloud over Nagasaki from the detonation of “Fat Man,” August 9, 1945.

Radioactive Fallout

Many radioactive isotopes are produced in a nuclear bomb blast. Some are particularly harmful to humans. Among these are strontium-90 and iodine-131.

Strontium-90: Half-life = 28.5 years, chemically similar to calcium. Obtained from dairy and vegetable products and accumulates in bone.

Iodine-131: Half-life = 8 days. Concentrates in the thyroid glands.

Nuclear Power Plants

Civilian nuclear power plants use less enriched uranium (2.5-3.5% uranium-235 rather than 90% for weapons-grade).

The nuclear chain reaction is controlled for the slow release of heat energy. The heat is used to make steam, which turns a turbine to produce electricity.

Thermonuclear Reactions

Nuclear fusion is a thermonuclear reaction. Smaller atomic nuclei are fused into larger nuclei in such a reaction. The principle reaction on the sun is one such reaction.

The Nuclear Age