Bohr’s model has shells or energy levels for electrons

Hydrogen Spectrum

Laurence & McMillan with 1st cyclotron design, FermiLab (top right) Cern

Japan’s KEKB

We’ve observed protons turning into neutrons and vice versa by emitting or absorbing a pi meson.

A set of small particles seem to be able to combine and interact to form heavier particles like protons and neutrons. These small particles are electrons, photons and 18 types of

“quarks”

Heavier particles: protons & neutrons

Lighter particles: electrons

Medium size particles

Baryons Mesons Leptons

Hadrons

Hadrons: all experience the strong nuclear force when smashed close together. Fermions don’t. Baryons: all are made of only 3 quarks. Mesons are all made up of 1 quark + 1 antiquark. Leptons are truly fundamental (nothing found inside…..so far); the most common little leptons are the electron and the neutrino.

The nuclear strong force• Only is appreciable when hadrons are very

close…10-14 meters….around size of nucleus.• Holds nucleus together: makes protons (and other

hadrons) stick, and is therefore stronger than electromagnetic repulsion.

• Large atoms need lots of neutrons to provide the strong force interaction to hold protons together.

• When particles merge into a nucleus they lose mass and create “binding energy” of the order

E= mc2.

The nuclear weak force

• Holds quarks and leptons together to create hadrons and mesons.

Annihilation: a particle and its anti-particle collide; mass all become energy: E = mc2

Mass: 1 proton = 1 amu

Each quark has a mass of 1/3 amu

Charge: proton = +1 electron = -1

Quarks have - 1/3 or +2/3 charge

You can make baryons and mesons from quarks:

What’s in a proton ? = +1

=+2/3 +2/3 –1/3 = uudWhat’s in a neutron?= 0

- 1/3 –1/3c + 2/3 = ddu

Antiparticles….

Have the same mass but opposite charge.

Are symbolized with a line on top.

Use the Regents particle chart to find the charge on

a) an anti-top quark b) an antiproton

- 2/3 + 1

1. Describe: a) an anti-proton b) an anti-electron c) an anti-neutron

2. The K meson or “kaon” ( K0) consists of a down quark and an anti-strange quark: determine it’s mass and charge.

3. “An anti-up quark is NOT a down quark”. Explain.

Discoverers of the Antineutron: Wenzell, Cork, Lambertson, Piccioni, 1956Courtesy Lawrence Berkeley National Laboratory

Neutron = UDD

Antineutron = UDD

It’s the fundamental particles that are opposite in charge.

Force Carriers (Exchange particles)

• There is an alternative to the field approach to understanding forces….forces arise when particles exchange force particles

• None of these are on the Regents Exam.

E&M: the photonGravity: the graviton

Strong: the gluon

Weak: the boson

Faster than light particles are called… tachions

Slower than light particles are called… tardions

It’s been observed that quarks can change “color” and “flavor”, that is they can change into one of the other 18 particles by emitting or absorbing a “gluon”.

Quantum Chromodynamics

Up, down and strange are the 3 flavors of quarks. Each flavor quark comes in 3 colors (RGB) which it carries as a type of “color charge” that is also conserved.