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Modern Physics
Model of the atomRadioactivity
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Introduction - Today we expand our discussion of explaining what happens at the nuclear level atoms.
• Radioactivity (substances that give of invisible radiations) and the types of radiations.
• What happens when an atom undergoes radioactivity decay
• Uses for radiation
• The types of reactions that cause nuclear reactions
• The affects of nuclear reactions on energy
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Nucleons
• Are particles occupying the nucleus• Consist of + charged protons and neutral
neutrons• Have almost 2000 time the mass of electrons• Are made of quarks and leptons (building
blocks of matter, elementary particles)
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AtomAtomic mass = protons + neutrons
(number of nucleons)
Atomic number = number of protons
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Isotopes
• Atoms of the same element with different numbers of neutrons (different masses)
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Radioactive Isotopes
• Has an unstable nucleus• Spontaneously emits a particle and decay into
another element.
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Marie Curie – Nobel prize winner• The word radioactivity was
first used by Marie Curie in 1898.
• She used the word radioactivity to describe the property of certain substances to give off invisible “radiations” that could be detected by films.
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Radioactive Decay• Three different kinds of
radiation given off by radioactive materials:– Alpha rays– Beta rays– Gamma rays
• called “rays” because the radiation carried energy and moved in straight lines, like light rays.
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• Radioactivity comes from the nucleus of the atom.
• If the nucleus has too many neutrons, or is unstable the atom undergoes radioactive decay.
• decay - to "break down."
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Atomic Decay• Alpha decay: the nucleus ejects two protons and two
neutrons.• Beta decay: a neutron in the nucleus splits into a proton
and an electron.• Gamma decay occurs because the nucleus is at too high
an energy. The nucleus falls down to a lower energy state and, in the process, emits a high energy photon.
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• Radioactive decay gives off energy. • The energy comes from the conversion of
mass into energy.• Because the speed of light (c) is such a
large number, a tiny bit of mass generates a huge amount of energy.
• Radioactivity occurs because everything in nature tends to move toward lower energy.
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Radiation• The flow of energy through space. • Forms of radiation:
– Light– Radio– Microwaves– X-rays
• Many people mistakenly think of radiation as only associated with nuclear reactions.
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X-ray machines
• X-rays are photons• Used to produce
images of bones and teeth on x-ray film.
• X-ray film turns black when exposed to x-rays.
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X-Rays Uses• High level therapeutic
x-rays are used to destroy diseased tissue, such as cancer cells.
• The beams are made to overlap at the place where the doctor wants to destroy diseased cells.
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CAT scan• Computerized Axial
Tomography• Produced by a computer that
controls an x-ray machine as it takes pictures of the body from different angles.
• Produces three-dimensional images of bones and other structures within the body.
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Radiation Detection
The Geiger counter is a type of radiation detector invented to tell when radiation is present and to measure its intensity.
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Half-life
• The time it takes for half the mass of a radioactive sample to decay.
• Ranges from a fraction of a second to billions of years.
• Is not affected by external conditions.
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Fusion reactions
• Nuclear reaction that combines, or fuses, two smaller nuclei into a larger nucleus.
• It is difficult to make fusion reactions occur because positively charged nuclei repel each other.
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Fission reactions
• A fission reaction splits up a large nucleus into smaller pieces.
• A fission reaction typically happens when a neutron hits a nucleus with enough energy to make the nucleus unstable.
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Nuclear Reactions and Energy
• A nuclear reaction is any process that changes the nucleus of an atom.
• Radioactive decay is one form of nuclear reaction.
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Nuclear Reactions and Energy• If you could take apart a nucleus and separate
all of its protons and neutrons, the separated protons and neutrons would have more mass than the nucleus did.
• The mass of a nucleus is reduced by the energy that is released when the nucleus comes together.
• Nuclear reactions can convert mass into energy.
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• Both these nuclear reactions release a small portion of the mass as large amounts of energy.
• Nuclear fusion is what powers a modern nuclear warhead (hydrogen bomb)
• Nuclear fission (less powerful) occurs in an atomic bomb (like the ones used against Japan in WWII), or in a nuclear power plant.
Nuclear Reactions and Energy