PH 103 Dr. Cecilia Vogel Lecture 24

Review Outline  Nuclei  decay rate and number of nuclei  Matter Particles  leptons & quarks  More Particles  antimatter  creation and annihilation  baryons & mesons

Antimatter Properties  For every matter particle there is an antimatter particle with  the same mass  always positive mass!!!  the same spin  opposite charge

Antimatter Matters  Antimatter is just accounting:  Lepton # = The number of leptons minus the number of antileptons is constant.  two electrons: lepton # is 2  an electron and a positron: lepton # is zero  two positrons: lepton # is -2  ALSO  Baryon # = (The number of quarks minus the number of antiquarks)/3 is constant.

Antimatter Matters  Imagine that Augustana currently has 50 more female students than male  & they decide to keep it that way forever  Then, if Augustana wants to admit a female,  would also have to admit a male  If a female student drops out or graduates  would also have to lose a male student  That’s how matter and antimatter work

Antimatter Matters  Antimatter is just accounting:  You can’t create a lepton  without creating an anti-lepton.  You can’t create a quark  without creating an anti-quark.  Note: you need to have enough energy to create the mass of both particle & antiparticle  Example: beta-plus decay  You can’t create a positron alone,  because, if you create anti-lepton (positron), you have to create a lepton, too.  Thus a positron is created, and so is a neutrino

Antimatter Matters  Antimatter is just accounting:  You can’t lose a lepton without losing an anti-lepton.  You can’t lose a quark without losing an anti-quark.  Example annihilation  If a particle meets its antiparticle,  the two can both disappear.  mass is lost!  The mass energy turns into other forms of energy  such as photons

PET  PET = Positron Emission Tomography  Beta-plus emitter emits a positron  which immediately annihilates with an electron  (electrons are everywhere)  mass of electron and positron disappears  two photons are produced  energy of photons =hf 1 +hf 2  Comes from the energy of the positron and electron = KE + 2m e c 2

PET  The two photons are detected.  Like with binocular vision,  if you have two rays, you can tell direction and distance!  3-D image observed It came from here

Antimatter  Symbols for antimatter  For charged leptons, just show the opposite charge in superscript.  example e +,  +.  For all others, put a bar over the symbol  example  e,  u

Antimatter e+ ( positron)  +  +

Quark Content  The charge of a particle made of quarks  is the sum of the charges of the quarks  The baryon # of a particle  also comes from adding the baryon #’s of the quarks  Quark content of a few particles can be found in text  otherwise figure it out from quark properties adding up

Baryons  Particles made up of three quarks  are called baryons  ex: proton is a baryon  made up of quarks uud  charge 2/3 + 2/3 - 1/3 = 3/3 = +1  baryon # =1/3 + 1/3 +1/3 = 1    ex: neutron is a baryon  made up of quarks udd  charge 2/3 - 1/3 - 1/3 = 0/3 = 0  baryon # =1/3 + 1/3 +1/3 = 1

Mesons  Particles made up of a quark and an antiquark  are called mesons  ex:  + is a meson  made up of u  d  charge 2/3 + 1/3 = 3/3 = +1  baryon # = 1/3 -1/3 =0

Integer Charge  Baryons all have integer charge  Any combination of 3 quarks will make -1, 0, +1, or +2  -1/3 - 1/3 - 1/3 = -1  -1/3 - 1/3 + 2/3 = 0  -1/3 + 2/3 + 2/3 = +1  +2/3 + 2/3 + 2/3 = +2

Integer Charge  Mesons all have integer charge  Any combination of quarks and anti- quark will make -1, 0, or +1  -1/3 - 2/3 = -1  -1/3 + 1/3 = 0  +2/3 - 2/3 = 0  +2/3 + 1/3 = +1