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!