The Nucleus
description
Transcript of The Nucleus
The Nucleus
Physics is Phun
November 2004
Topics:Nuclear structureNuclear radiationUseful radiation effects
The Electromagnetic Spectrum
c = f λ
c = the speed of lightf = frequency
λ = wavelength
E = h fE = photon energy
h = Planck’s constantf = frequency
“Waves” “Photons”
Infrared
Visible light
Ultraviolet
“Members” of the
Electromagnetic Spectrum
Atomic models:1. the “plum-pudding” model
2. the “nuclear” model(tiny nucleus with electrons
in much larger orbits)
Berylliumatom(withoutneutrons!!)
The Nucleus1. Protons (positive charge)2. Neutrons (neutral charge)3. Nuclear Diameter ~10-15 m
(atomic diameter ~10-10 m)The term “nucleon” refers to either a proton or a neutron in the nucleus.
The term “nuclide” refers to a nucleus with a specific number of protons and neutrons.
Stable Nuclides All Known Nuclides
Nuclear models:
1. the “water-drop” model2. the “shell” modelModels tell us aspects of the structure of nucleiand how they behave.
The water-drop model
all nucleons “undifferentiated”
binding energy is equally distributed
Binding Energy
BE = M(Z protons) + M(N neutrons) – M(Nucleus)
BE is the energy required to separate the full nucleus into its
individual protons and neutrons
Average Binding energy per nucleon
Applications of thewater-drop model
1. Nuclear fission (very large nuclei break up)
2. Nuclear fusion(very small nuclei fuse together)
Nuclear fission235U + n –—> small nuclei + neutrons + ENERGY!! n + 235U –—> another fissioncreating a “chain reaction”
NuclearChainReaction
Click title above to see video
Controlled fission:Nuclear reactor
Uncontrolled fission:Atomic bomb
(235U or 239Pu bomb)
Pressurized Water Reactor
From: Joseph Gonyeau, P.E., Virtual Nuclear Touristhttp://www.nucleartourist.com/
Advantages of Nuclear Power:
1. Clean (no air pollution, including greenhouse gases)2. Safe compared with other fuels3. Price competitive with fossil fuels4. 100 year supply of 235U5. Infinite supply of 238U (if we use breeder reactors)
Woolsey-Swanson Rule:
People would rather live with a problem they cannot solve
than accept a solution they cannot understand.
UM Reactor Core
Blue Cerenkov radiation
Average Binding energy per nucleon
Nuclear fusion2D + 2D –—> larger nuclei + LOTS OF ENERGY!!
“Theta Pinch”electromagnetic squeezing
to producefusion
Nuclear Shell ModelDiscrete energy levels
for protons and neutronsand
discrete energies for radiationwhen energy levels change
Radiation types:Alpha particle (2 Ps + 2 Ns: 4He nucleus)
Beta particle (- or + electron)Gamma ray (photon energy packet)
Neutrons
Cosmic Rays
Radiation Exposure
Sources of radiation exposure:1. Natural Exposure2. Man-made Exposure
Natural Exposure:1. Radon gas2. Cosmic Rays3. External Environment4. Internal: The Body
238U Decay Chain
Cosmic Rays:1. Mostly cosmic ray muons2. 14C and other products
Cosmic Radiation
Man-made radiation:1. X-rays2. Nuclear medicine3. Consumer products
(food, etc.)
From: National Institutes of Health
Sources of Radiation Exposure
Useful Radiation Effects INuclear PowerMedical:
Diagnostic scans, tracersMagnetic resonance imagingCancer radiation treatmentPlutonium powered pacemakerMedical, dental sterilization
Useful Radiation Effects IIPolymer cross-linking
Shrink tubing (turkey wrapping)Ultra-strong materials (eg Kevlar)
Tires (replaces vulcanization)Flooring
Food irradiationSterilization of meatDisinfestation of grain and spicesIncreasing shelf life (eg, fruits)
Useful Radiation Effects IIIAbsolute sterilization of food:
hospitals and space travelRadioactive datingInsect controlSemiconductor dopingTesting of space computer technologyEnvironmental studies:
air, global warming, ozone
The Nuclear Waste
Test
Test Question #1 Suppose that all of the electrical energy for the world for the next
500 years were obtained from breeder reactors. Further suppose that all of the nuclear waste from these reactors were dissolved and spread uniformly throughout the
oceans of the world.
Which statement is true:1. The oceans would be a vast wasteland,
unable to support life.
2. Much death and damage to ocean life would be caused.
3. Any effect would be so small that it would be virtually impossible to see
Which statement is true:1. The oceans would be a vast wasteland,
unable to support life.
2. Much death and damage to ocean life would be caused.
3. Any effect would be so small that it would be virtually impossible to see
Test Question #2
Consider all of the people throughout history who have been
exposed to man-made nuclear radiation, such as Hiroshima and Nagasaki, Chernobyl, Three Mile
Island, nuclear bomb tests, accidental spills, etc.
Which number most nearly approximates how many
children conceived and born later to these people suffered
genetic damage due to a parent’s exposure?
1. ~ millions2. ~ thousands
3. zero
Which number most nearly approximates how many
children conceived and born later to these people suffered
genetic damage due to a parent’s exposure?
1. ~ millions2. ~ thousands
3. zero
Reference materials:General:
Nuclear Physics and Society web siteNuclear Reactors and Power:
Joseph Gonyeau's Virtual Nuclear Tourist! Nuclear Plants Around the World
A Nuclear Sunset
We are on the web at
http://www.physics.umd.edu/lecdem/
Animated Gifs compliments of bellsnwhistles.com
The EndSee you in January!