Charged Particles - PowerPoint PPT Presentation

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  1. Charged Particles

  2. Charged particles can come from nuclear decay. Nuclear physics figures into particle detection. Use terminology from nuclear physics. Isotopes share Z Isotones share N Nucleus consists of protons and neutrons. Protons: Z (atomic number) Neutrons: N Nucleons: A = Z + N (atomic mass) Full notation shows A, Z Nuclear Physics

  3. Energy measurements for nuclear an particle physics are built on the electron volt (eV) Energy to move one electron through a volt 1 eV = 1.6  10-19 J Mass is expressed in terms of the rest energy Also atomic mass unit (u) 1 u = 931.5 MeV/c2 Proton, p 938.3 MeV/c2 1.007 u Neutron, n 939.6 MeV/c2 1.009 u Electron, e 0.511 MeV/c2 5.546  10-4 u Energy Measurement

  4. The mass (M) in u is nearly equal to the atomic number (A). Tables of isotope data frequently list D = M – A. Often converted into MeV Data used to calculate energy of decay products. 1H; D = 7.29 MeV 4He; D = 2.42 MeV 56Fe; D = – 60.60 MeV 214Pb; D = – 0.15 MeV 218Po; D = 8.38 MeV 222Rn; D = 16.39 MeV 226Ra; D = 23.69 MeV Mass Difference

  5. Alpha particles are 4He nuclei. Mass approximately 4 AMU Charge is +2 Generally from the decay of heavy nuclei The energy of the alpha particle is due to the mass difference of the daughter nuclei. Typical Problem Calculate the energy of the alpha particle from 222Rn. Answer Get the reaction equation. The energy released is Q = MRn222-MPo218-MHe4 Q = 12.89 MeV Most will go to the alpha. Alpha Particles

  6. Electron decay Nucleus emits an electron and antineutrino Atomic number increases Energy goes to e and n Some include photon as well Positron decay Nucleus emits a positron and a neutrino Atomic number decreases Kinematics like electron decay Same result as electron capture – no beta out Beta Particles

  7. Table of Isotopes

  8. The number of particles decaying in a short period of time is proportional to the number of particles. The decay constant is l. The decay rate or activity is the rate of change. Activity decreases as time increases Decay Rates

  9. Half-Life • The differential equation for decay gives rise to an exponential relation. • Decay constant is fixed for a decay reaction • Decay is usually expressed as a half-life. • Time for half a sample to decay • Remains constant

  10. The SI unit of activity is the Becquerel (Bq). equals one decay/sec (s-1) The older unit is the curie (Ci). Based on the decay of 226Ra Once activity of one gram Now defined by Bq 1 Ci = 3.7  1010 Bq Typical Problem A source of 24Na is marked at 1.16 MBq. How many 24Na atoms are there in the sample? Answer First thing is to look up the half-life for 24Na: T = 15 h = 5.4  104 s Measured Activity

  11. Physical variables are often normalized to the mass. Described as “specific” Specific activity is the activity of a sample divided by the mass. Units Bq g-1 or mCi g-1 In solution expressed per unit volume: pCi L-1 For a pure radionuclide: Normal soil has a few pCi/g Drinking water has a recommended limit of 5 pCi/L of 226Ra + 228Ra. Specific Activity

  12. Particle Physics • Charged particles are measured in particle physics. • Energy scale > 1 GeV • Energetic particles are the results of acceleration or decays.

  13. Unstable particles have a characteristic lifetime. The lifetime t is related to the probability that a particle will survive a given period of time. The survival time is affected by relativity. The probability is an exponential relation: Particle Lifetime

  14. Quarks are fundamental building blocks, but are not detected directly. Binding force too great Stable quarks bind to others Quarks exist in hadrons. Baryons are three quarks Mesons are a quark-anti quark pair. Some baryons proton, p: uud neutron, n: udd lambda, L0: uds lambda-b, Lb0 : udb Some mesons pi-minus, p-: ud k-plus, K+: us J/psi, Y: cc Quarks

  15. Protons are stable hadrons. Charged particles Interact strongly Easy to detect Any other baryon will eventually decay into a proton and other particles. Charged pions are unstable, but relatively long-lived hadrons. Lifetime 26 ns Interact strongly Detectable like protons Pions frequently accompany the decay of other hadrons. Hadrons

  16. Jets • Hadrons that collide at high energy can eject a quark. • When the quark emerges it hadronizes forming a jet of particles. • Most emerging particles are pions High energy pion interaction, Fermilab 1973

  17. Leptons are fundamental particles. Interact weakly Able to exist in isolation Detection of charged leptons is important in many particle physics experiments. Charged leptons: electron, e-: 0.511 MeV/c2 = 1/1836 mp muon, m-: 0.1057 GeV/c2 = 1/9 mp tau, t- : 1.776 GeV/c2 = 1.9 mp Leptons

  18. Electrons are perhaps the most important particle for detection. Stable Charged Lightest charged particle Electrons result from nuclear and particle decays. Electron from W decay Electrons

  19. Muons are charged, long-lived and weakly interacting. Lifetime 2.2 ms Heavy version of the electron. Mass provides greater penetration Muons are naturally created by cosmic rays. Muon from top decay Muons