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Unit 9: Atomic, Quantum, Nuclear Physics

Hewitt Chapters 31-34Brent Royuk

Phys-109Concordia University

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IntroductionThe more important fundamental laws and facts of physical science have all been discovered, and these are now so firmly established that the possibility of their ever being supplanted in consequence of new discoveries is exceedingly remote.... Our future discoveries must be looked for in the sixth place of decimals. - Albert. A. Michelson, speech at the dedication of Ryerson Physics Lab, U. of Chicago 1894

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Introduction“There is nothing new to be discovered in physics now. All that remains is more and more precise measurement” -Lord Kelvin, 1900

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The Correspondence Principle

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Quantum Introduction• The central quantum idea.

– Waves vs. Particles• What does “quantum” mean?• Uncertainty and randomness• Very Small Things• So if you know what the parts act like (atoms and molecules), you know what the

whole acts like (the universe), right?

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The Photoelectric Effect

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Experimental Results1. Brighter light makes more current.2. The energy of the liberated electrons depends on the

frequency of the light but not its brightness.3. There’s a cutoff frequency. If the light isn’t blue

enough, no current flows.4. Current flows immediately, without a delay.• Result #1 agrees with classical theory. The others are

a problem.• Einstein explained the photoelectric effect by

postulating the existence of massless light particles, called photons.

• Nobel Prize, 1921.

• Energy of a photon:– E = hf– h = 6.63 x 10-34 Js

• The Planck Constant

– Ionizing radiation

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Duality• So is light a wave or a particle?• Why don’t we notice the graininess?• Light propagates as a wave and interacts as a particle.

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Matter Waves• So light is a particle. Guess what…• Louis deBroglie, 1924 doctoral thesis.

There is a wave “associated with” particles, such that

How big is the wave for a baseball? An electron?h = 6.63 x 10-34 Js

What is the nature of this wave?

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Matter Waves• Can matter waves be observed?

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Electron Interference• What passes through the other slit?• What if you cover one slit?• What if you detect which slit?• Can you predict where electrons will hit?

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Heisenberg’s Uncertainty Principle• How do you know where a wave is?

– Wave packets• The Principle:

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The Wave Function• The Schrodinger Equation

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Quantum Collapses• What travels through the slits in the electron interference

experiment? – What hits the screen?

• The Copenhagen Interpretation of Quantum Mechanics– Where is the electron just before it hits?

• The Repeated Measures Argument• What is an orbital?

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The Wave Function• What is an orbital?

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Schrodinger’s Cat

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Schrodinger’s Cat

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Nonlocality

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The QM Worldview• The Four Newtonian Characteristics:1. Atomism

– Reality is composed of atoms.

2. Objectivity– Remove human influence when studying nature.

3. Predictability – Knowledge of the current state of a system allows you to predict future states.

4. Analysis– Break down systems into their components. Study the simplest pieces of the system to

understand the whole system.

• Guess what?

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The QM Worldview• Art Hobson on the significance of QM:• In short, this quantum worldview asserts that the universe

is made of non-material fields, the particles of the microscopic world are merely quantized increments of these fields, the future is inherently unpredictable, and nature is deeply interconnected and indivisible. This is nothing like a machine.

• Despite more than a century of post-Newtonian physics, a post-Newtonian worldview is still not in sight, and the metaphor of the mechanical universe continues to deeply and perhaps inappropriately influence our culture’s view of physical reality. Will we construct a scientifically accurate and human worldview that can sustain us in this post-Newtonian age? Humankind has barely scratched the surface of this task. It might be the critical issue for the modern world.

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Nuclear Classification• Atomic number = # of protons = # of electrons

– Mass number = p + n• Isotopes

– Isotopes have the same atomic number but different mass numbers

• Notation– is a standard notation.

• e.g.

• This is often just written as U-238. The superscript/subscript notation is most often seen in nuclear equations.

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Nuclear Classification• Most elements have several naturally occurring

isotopes. Isotopes can also be created artificially.• Many isotopes are radioactive, especially heavy ones.

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Nuclear Classification• Most elements have several naturally occurring

isotopes. Isotopes can also be created artificially.• Many isotopes are radioactive, especially heavy ones.

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Radioactivity• Henry Becquerel discovers radioactivity, 1896

– Uranium exposes film• Three “Rays”

– Alpha, Beta, Gamma• Oops, Alpha particles are He-4 nuclei, Beta particles are

electrons.

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Nuclear Decay• Radioactive nuclei are unstable. They break

into pieces and change into something else.• Alpha Decay

– A radioactive nucleus spits out an alpha particle and becomes a daughter nucleus

– e.g. • Beta Decay

– A neutron inside the radioactive nucleus changes into a proton and spits out an electron

– e.g.

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Half-Life• Radioactive decay is an utterly random process, governed by

quantum physics. But large numbers of particles follow predictable patterns.

• The half-life is the time during which 50% of some nuclei will decay.

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Half-Life

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Fusion and Fission• Radioactive decay occurs because of instability. Fusion

and fission are nuclear reactions that can occur because of external conditions applied to the nucleus. – I.e., they can be controlled.

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Nuclear Fusion• A basic fusion reaction:

– VERY high temps– occurs only in core of stars– But the reaction is self-sustaining, once it gets going.

• Big problem 100 years ago: What makes the fire in the sun?– The sun isn’t a chemical fire, it’s a nuclear fire. – Wood gets lighter because it vaporizes and loses part

of its mass to gaseous products. Does the sun get lighter?

• There’s only 10 billion years left

• Fusion reactors are being designed and tested. We haven’t passed the “break-even” point yet.– Where will we get the fuel for fusion reactors?– How do you contain such a hot fire?29

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Nuclear Fusion

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Nuclear Fusion

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Nuclear Fission• In fission, a large nuclei splits into two big daughters• One typical equation: • Energy is also released. The daughters are a little bit

lighter than the parent.

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Nuclear Enrichment• The only fissionable naturally occurring isotope is U-

235.• U-235 is only 0.7% of mined Uranium.• 3-5% enrichment for fuel, >90% for weapons

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Chain Reactions• Neutrons cause nuclei to fission, which release

neutrons, which cause nuclei to fission, which…• Controlled fission vs. explosions

– Cd, B control rods in reactor core

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Chain Reactions

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Chain Reactions• Critical mass

– Feynman – U-235: 15 kg (grapefruit); Pu-239: 5 kg (orange)

• Implications for bomb design & proliferation

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Criticality Accident• This article was originally published in The Beaver in their August/September 1995 issue.

Reproduced with permission.

• Louis Slotin And 'The Invisible Killer'• A young Canadian scientist gave his life to save his friends when an experiment

went wrong• By Martin Zeilig• It happened in an instant. A sudden blue glow momentarily enveloped the room before

evaporating. In that moment, as the Geiger counter clicked wildly, scientist Louis Slotin knew that he had received a lethal dose of gamma and neutron radiation from the core of the plutonium bomb he was testing. It was 3:20 P.M. on Tuesday, 21 May 1946, at the secret Omega Site Laboratory in Pajarito Canyon, Los Alamos, New Mexico.

• Slotin had been instructing a colleague, Alvin C. Graves, who was to replace him at the Omega Site. Also present was S. Allan Kline, a 26-year-old graduate of the University of Chicago, who had been called over to observe the procedure. Five other colleagues were close by as Slotin, a Canadian physicist from Winnipeg who had been part of the team that created the atomic bomb, performed the action that would bring into close proximity the two halves of a beryllium-coated sphere and convert the plutonium to a critical state.

• With his left thumb wedged into a cavity in the top element, Slotin had moved the top half of the sphere closer to the stationary lower portion, a micro-inch at a time. In his right hand was a screwdriver, which was being used to keep the two spheres from touching. Then, in that fatal moment, the screwdriver slipped. The halves of the sphere touched and the plutonium went supercritical.

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Criticality Accident• The chain reaction was stopped when Slotin knocked the spheres apart, but

deadly gamma and neutron radiation had flashed into the room in a blue blaze caused by the instantaneous ionization of the lab's air particles. Louis Slotin had been exposed to almost 1,000 rads of radiation, far more than a lethal dose. Kline, who had been three or four feet away from Slotin, received between 90 and 100 rads, while Graves, standing a bit closer, received an estimated 166 rads.

• A surge of heat "swept over the observers, felt even by those some distance from the source," writes Thomas D. Brock, a retired University of Wisconsin biologist who has done extensive research on early atomic-era accidents at Los Alamos. "In addition to the blue glow and heat, Louis Slotin experienced a sour taste in his mouth [and] an intense burning sensation in his left hand. As soon as Slotin left the building, he vomited, a common reaction from intense radiation." Another commentator suggests that it was as though Slotin had been fully exposed to an exploding atomic bomb at a distance of 4,800 feet.

• After arriving at the Los Alamos hospital Slotin told Alvin Graves: "I'm sorry I got you into this. I'm afraid I have less than a 50 per cent chance of living. I hope you have better than that.”

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Criticality Accident• Many volunteers were ready to donate blood for the transfusions doctors

deemed necessary. Sadly, all efforts to save Slotin were futile. He died on 30 May after an agonizing sequence of radiation-induced traumas including severe diarrhea and diminished output of urine, swollen hands, erythema (redness) on his body, massive blisters on hands and forearms, paralysis of intestinal activity, gangrene and a total disintegration of bodily functions. It was a simple case of death from radiation, similar to what American scientists and medical personnel saw in Japan among A-bomb victims.

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By mass, polonium-210 is around 250,000 times more toxic than hydrogen cyanide(the LD50 for 210Po is less than 1 microgram for an average adult compared with about 250 milligrams for hydrogen cyanide).

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Nuclear Power• Power plant fuel usage rates:

– Nuclear: 6.5 oz/minute– Coal: 10 tons/minute

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Nuclear Power

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Nuclear Power

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Nuclear Waste• Spent nuclear fuel is high-level waste. Each full-size power plant

produces about 75 m3/year.– low-level: things that are irradiated and become radioactive

• A nuclear plant is refueled every 18 months• The amount of HLW worldwide is currently increasing by about

12,000 metric tons every year• A coal power plant releases 100 times as much radiation as a

nuclear power plant of the same wattage.• Processing: diluted with twice volume of neutral material: block

of ceramic• Within 600 to 1000 years, high level waste will be back to

Uranium ore levels• Depleted uranium

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Nuclear Power

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E = mc2 : 1 kg = 7 MT

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