Chapter 24 Applications of Nuclear

Chemistry

Read introduction page 776Quick review of chapter 3 notes

• Most elements and their isotopes found naturally are stable.

• Many radioactive elements and isotopes are man made.

• A few, such as uranium, are found naturally. • The nuclei of unstable elements emit atomic

particles to change the number of protons and eventually become a stable element.

• Radioisotope – a radioactive isotope of an element

• Rubidium (Rb) has two naturally occurring isotopes. (Rb-87 27.85% and Rb-85 72.15%)

• Rb-85 is stable and Rb-87 is radioactive. It emits a beta particle and has a half life of 60 billion years. (show nuclear equation for this decay)

Half-life

• It is the time it take for ½ of a sample of a radioisotope to decay.

• See sample problem on page 780.• Can also use the equation given below• Amount left = (starting amount)(.5)(# of half-lives)

Carbon 14 Dating• C-14 is produced by cosmic rays and atmospheric N-14.

(N-14 absorbs a neutron and ejects a proton)• C-14 is oxidized in atmosphere to 14CO2.• C-14 decays to N-14 by the emitting a beta particle.

(show nuclear reaction)• The C-14 concentration of C-14 in atmosphere is

constant (The production and breakdown is a steady state process)

• C-14 has a half-life of 5730 years.• When C-14 is taken up by plants the decay process is

the same (good for dating once living things).

Nuclear Bombardment Reactions

• Alpha particles can be accelerated with particle accelerators and driven into the nucleus of an atom. This creates an unstable isotope which breaks down.

• Neutrons, because they are neutral) can be absorbed into a nucleus without being accelerated.

Biological Effects of Radiation

• Alpha particles are very weak and not harmful unless produced within the body.

• Beta particles can damage skin• Gamma rays are very penetrating and harmful

• Dosimeter – used to measure the total radiation a person is exposed to in a given amount of time

• Gamma rays (ionizing radiation) cuts through molecules producing ions and free radicals.

• Destruction of tissue – especially rapidly multiplying cells (lymph nodes)

• Marie Curie and her daughter both died of leukemia

• Can also result in genetic damage

Detection of Radiation

• Radiation also ionizes particles in the air and makes it more conductive to electricity.

• Smoke detectors rely on this and so do Geiger counters.

Beneficial Uses of Radioisotopes

• Radiotracers are placed in the body to track the movement and absorption of a particular element. (example I-131 to study thyroid)

• Radiation is often used for cancer treatment because tumors are runaway abnormal cell growth which are more susceptible to radiation.

• Radiation can extend the shelf life of many foods.

Radon – The Hidden Hazard

• Granite bedrock under much of the US contains small amounts of uranium-238.

• One of the decay products in Radon-222 which is a radioactive noble gas.

• This percolates up through the soil into basements.

• While in your lungs it changes into another elements which sticks to the lung and is the second leading cause of lung cancer.

Red – high riskorange – medium risk

yellow – low risk

Nuclear Energy

• Nuclear fission is the splitting of large elements such as uranium into smaller ones.

• A nuclear reactor controls the U-235 fission reaction by controlling the number of neutrons with control rods.

Nuclear Accidents

• Critical mass – the mass of uranium necessary to create and runaway nuclear reaction (atomic bomb)

• The fuel rods in a nuclear reactor do not contain enough uranium to reach critical mass

• 1979 – Three Mile Island, Pennsylvania plant overheated

• 1986 – Chernobly, Ukraine plant had a graphite fire which resulted in meltdown

Nuclear Fusion

• Small atoms such as hydrogen adding to produce larger atoms. (the sun)

• An example is the hydrogen bomb.• Requires very high temps (40 million C) • We do not have the technology as yet to

produce our electricity with a fusion reactor.

E = mc2

• All energy transformations result in a change of mass. The mass change in most situations is so small we cannot measure it.

• The energy given off in nuclear reactions is so great we can detect the change in mass.

• To use this equation E should be in Joules, mass in kilograms, and the speed of light (c) is 3 x 108 meters per second.

Iron sized elements are the most stable

Cold Fusion, the unfulfilled dream, may not be possible.

Fusion could be a way out of our energy dilemma.