Unit: Nuclear Chemistry

Fission, Fusion, and Applications of Nuclear Chemistry

Day 4 –

Notes

After today you will be able to…

• Describe what happens in a nuclear chain reaction.• Differentiate between fission

and fusion reactions.• Identify examples of how

radioisotopes are used in everyday life.

Recall, during transmutations an atom can be converted into a different atom through radioactive decay or by bombarding a nucleus with particles.Today, we will focus on the

latter by learning about fission and fusion.

Nuclear FissionFission: occurs when a nucleus is split into smaller pieces.• This process begins by colliding a

nucleus with particles such as neutrons.

• The resulting nucleus is highly unstable and decays.

• This causes a chain reaction where particles emitted from the initial reaction bombard other nuclei, causing them to break apart.

Example: Uranium-235

ENERGY

n10 U235

92

U23692

n10

n10

n10

Kr9136

Ba14256

A neutron collides with the U-235 atom.

The U-236 atom is unstable and decays.

U-236 is formed.

The neutrons released from the decay of U-236 will collide with

other U-235 atoms,

repeating this process all over again (chain

reaction).

Nuclear Fission• Uranium-235 and

Plutonium-239 are the only fissionable isotopes.

• These reactions release a large amount of energy.

Nuclear FusionFusion: occurs when nuclei combine (or fuse together) to produce a new nucleus of greater mass.• Example: Production of

energy from the sune0

+1H11 H

e42 energ

y++4 2

Nuclear Fusion• Releases far more

energy than fission reactions.

• These reactions require very high temperatures in order to occur (~40,000,000°C).

Real-World Applications: C-14 Dating

Scientists often find the age of an object that was once living by measuring the amount of carbon-14 it contains.• Recall, C-14 has a half-life of

5730 years.• This is its nuclear decay:

C146 N14

7 e0-1+

Real-World Applications: C-14 Dating

• All living things contain C-12 and C-14 in a fixed ratio.

• Once an organism dies, the ratio of C-14:C-12 changes, which allows archeologists to estimate its age.

Real-World Applications: C-14 Dating

• The most accurate way to examine the C-14 content is through use of a mass spectrometer.

• First, the carbon in the sample must be converted into graphite or carbon dioxide.―This is can be done by burning a

portion of the sample.

Real-World Applications: C-14 Dating

• The sample is then injected into a mass spectrometer and ionized.

• Due to the different masses of carbon having different angles of deflection, a scientist can count the individual C-14 atoms in the sample.

Mass Spectrometer:

Real-World Applications: U-238

But what if all of the C-14 in a sample has decayed or the sample is non-living?• Similar to carbon-14, uranium-

238 is used to date specimens.• Uranium is naturally found in

most rocks, seawater, and in Earth’s crust.

• It has a half-life of 4.5 billion years.

• U-238 is specifically used in dating rocks and fossils.

Real-World Applications: I-131

Radioisotopes can be used to diagnose medical problems or treat diseases.• Specifically, iodine-

131 is a radioisotope given to patients to check for abnormal thyroid function.

• Patients are given a drink containing the radioisotope (Na131I).

Real-World Applications: I-131

• Since the thyroid extracts iodide ions from the bloodstream, the ions are absorbed and its radioactivity is used to create an image on a screen.

• From the image, doctors can examine the amount of iodine absorbed and determine if a person has hyperthyroidism or thyroiditis.

Real-World Applications: Co-60

The strong penetrating power of gamma rays allows it to be useful in the treatment of cancer.• Cobalt-60, which is

produced in particle accelerators, emits both beta and gamma radiation.

Real-World Applications: Co-60

• The Co-60 is placed into a gun that is used to direct the radiation to where the tumor is located.

• The cells of the tumor are destroyed and it decreases in size.

• However, gamma radiation can also destroy healthy cells making those treated very ill.

Questions?Begin

WS4