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PH 103 Dr. Cecilia Vogel Lecture 24
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Review Outline Nuclei decay rate and number of nuclei Matter Particles leptons & quarks More Particles antimatter creation and annihilation baryons & mesons
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Antimatter Properties For every matter particle there is an antimatter particle with the same mass always positive mass!!! the same spin opposite charge
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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.
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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
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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
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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
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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
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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
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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
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Antimatter e+ ( positron) + +
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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
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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
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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
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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
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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
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