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Laurence & McMillan with 1st cyclotron design, FermiLab (top right) Cern
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”
Hadrons Heavier particles: protons & neutrons Medium size particles Lighter particles: electrons Leptons Baryons Mesons 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 = uud What’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.
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. Force Carriers (Exchange particles) E&M: the photon Gravity: the graviton Strong: the gluon Weak: the boson Faster than light particles are called… tachions Slower than light particles are called… tardions
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. 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”.