Nuclear & Modern Physics

Relativity, Quantum Mechanics & Nucleogenesis

LOOK FOR “**”…that’s important!

Definitions to grasp-- ** Frame of reference: The perspective from

which a system is observed; two kinds--(a) inertial and (b) non-inertial. An inertial reference frame is one in which Newton's First Law of Motion holds. In a non-inertial reference frame, such as a rotating carousel or a moving car, things appear to accelerate without the forces to cause it.

** Relativity:

Relativity—PREVIEW 1st: Classical Relativity

2nd: ** Special Relativity

3rd: ** General Relativity

Classical Relativity

1,000,000 m/s 1,000,000 m/s

■Based on the astronauts’ frames of reference, how fast is Spaceship A approaching Spaceship B?

■ Both Spaceships see the other approaching at 2,000,000 m/s.

■ This is Classical Relativity.

Two Pillars of 20th Century Physics

Quantum Mechanics is the framework for studying the physics of very short distances.

• Special Relativity is the framework for describing the physics of objects moving at speeds close to the speed of light.

• General Relativity is the extension of this theory to include gravity.

Einstein

Heisenberg

Einstein’s Special Relativity

1,000,000 m/s

0 m/s

300,000,000 m/s

Both spacemen measure the speed of the approaching ray of light. How fast do they measure the speed of light to be?

Special Relativity Stationary man sees light traveling at:

300,000,000 m/s

Man travelling at 1,000,000 m/s sees light traveling at: 301,000,000 m/s? Wrong!

The Speed of Light is the same for all observers

It’s the Law! Absolutely nothing can

move faster than light c = 300,000 km/sec

All observers agree on this speed, regardless of their own motion.

time

space

Special Relativity

The first completed revolution of 20th Century physics: Relativity of

Simultaneity Time Dilation Length Contraction E = mc2

Speed of light as a maximum speed.

M.C. Escher ‘Relativity’

Einstein on a Roll: General Relativity

In General Relativity, gravity is attributed to the curvature of space and time. Slowing of time in

gravitational fields. Bending of light by

gravitational fields. Predicts the existence of

Black Holes.

Essential Q & A What does E = mc2 really mean? Basically that energy and mass are related and

have the same value when mass is multiplied by the speed of light squared.

How does gravity affect light? Bends it. (infinite gravity will mean complete darkness … a

black hole where the gravity is so intense that everything gets sucked in…even light!)

Relativity—SUM UP 1st: Classical Relativity—things are relative to the

frame of reference 2nd: ** Special Relativity—this is special…the

speed of light is NOT relative to the frame of reference. It is what it is not matter who’s looking, no matter from what vantage point.

3rd: ** General Relativity—extending the idea of special relativity to include gravity (gravity’s relationship to space, time, and light)

Quantum Theory & Newtonian Mechanics incorporates wave-particle duality (more on this…) successfully explains energy states in complex

atoms and molecules the relative brightness of spectral lines widely accepted as being the fundamental theory

underlying all physical processes essential to understanding atoms and molecules,

but can also have effects on larger scales

Quantum Theory & Newtonian Mechanics

wave-particle duality Light acts like a wave (reflection, refraction,

diffraction, etc) Light ALSO acts like a particle = photoelectric

effect All electromagnetic waves behave in both ways Look @ 85-87 in review packet…

Heisenberg Uncertainty Principle ** Quantum mechanics tells us there are

limits to measurement – not because of the limits of our instruments, but inherently.

This is because of: the wave-particle duality the interaction between the observing equipment

and the object being observed.

The Heisenberg Uncertainty Principle

Imagine trying to see an electron with a powerful microscope.

At least one photon must scatter off the electron and enter the microscope, but in doing so it will transfer some of its momentum to the electron.

Heisenberg Uncertainty Principle This is called the **Heisenberg

uncertainty principle. It tells us that the **position and

**momentum cannot simultaneously be measured with precision.

Look @ #84 on review packet…

Heisenberg Uncertainty Principle

Heisenberg Uncertainty Principle

The conflict in theories… Quantum Gravity? Absolutely no

candidate theory before the mid 1980’s.

String Theory Summary String theory is the only known theory where

gravity and quantum mechanics co-exist at high energies. Major Lesson of the 20th Century: Relativity and Quantum

Mechanics are almost inconsistent, and so together impose extremely strong self-consistency conditions.

Strings could very well be much longer than the Planck length. Size Matters: much better prospects for eventual

comparison with experiments. We may all be Brane bound.

Important broadening of the low-energy mind.

The Theory of Everything? For the first time in history

we have a candidate which could be a Theory of Everything. It appears to consistently

include gravity down to arbitrarily small distances.

It appears to be so tightly constrained by consistency as to be unique.

It must make contact with experiment, but there is not a time limit so long as progress is made.

Nuclear Energy A nuclear reaction occurs when nuclei collide

and different nuclei are produced In addition to new elements being formed, 3

types of **radiation can be released: **alpha (): a nucleus shoots out two protons/two

neutrons **beta (): a neutron “changes” into a proton, and

an ejected electron …this electron is the **gamma (): a high powered ray that is emitted

without changing the identity of the radioactive material

A Nuclear Reaction Note: Neutrons are very

effective in nuclear reactions.

They nave no charge and therefore are not repelled by the nucleus.

A Nuclear Reaction Once the neutron is in

the nucleus, it is unstable and will break down as shown here.

A fission reaction begins…

Nuclear Fission & Nuclear Reactors The energy release in a

fission reaction is HUGE.

Smaller nuclei are stable with fewer neutrons so several neutrons emerge from each fission.

These neutrons can be used to induce fission in other nuclei, causing a chain reaction.

Radioactive Emissions/Results Visit Wikipedia to see

decay chains and how these particle emissions can create new elements…

http://en.wikipedia.org/wiki/Decay_chain#Radium_series_.28aka_Uranium_series.29

Nuclear Math

He4

2

2+

total mass

total charge

# of protons

Nuclear Math (examples)

A =

Z =

X =

Now you solve:

Nuclear Math (more examples)

He4

2

2+

U238

92 Th___

= + ___

Fission Reactions **Fission: heavy nucleus splits into two

intermediate-sized nuclei **Chain reaction: neutrons emitted in one

fission reaction trigger another, and so on **Critical mass: minimum needed to sustain

chain reaction

Fusion Reactions• **Fusion: the joining of the small nuclei to form

heavier nuclei while releasing energy

• For example: the sequence of fusion processes that change hydrogen into helium in the Sun.

Applications of Nuclear Energy Nuclear reactors use fission reactions Sun’s energy comes from fusion reactions Useful fusion reactor has not yet been built Radiation used in radiation therapy (treating

cancer) Effect of absorbed dose depends on type of

radiation Radiation used in imaging (MRI, NMR)