1.4 Particles and antiparticles Flashcards
What is the universe made up of?
» Antimatter and matter
What happens when antimatter and matter meet?
» When antimatter and matter meet they destroy one another and radiation is released
What does PET scanner stand for?
» PET Positron emitting tomography - uses this effect for a scanner
How does a PET scanner work?
» A positron-emitting isotope is administered to the patient and some of it reaches the brain via the blood system
» Each position emitted travels no further than a few millimetres before it meets an electron and they annihilate each other
» Consequently 2 gamma photons is produced and are sensed by detectors linked to a computer - gradually an image is built up from the detector of where the nuclei are inside the brain
When does positron emission take place?
» Takes place when a proton changes into a neutron
What is the positron the antiparticle of?
» An electron
What is the equation of when a proton changes into a neutron?
Positron + neutrino released ( which is uncharged)
How are positron-emitting isotopes made?
» They do not occur naturally
» Manufactured by placing a stable isotope in liquid or solid form - in the path of a beam of protons - some of the nuclei in the substance absorb extra protons and become unstable position - emitters
What is rest energy?
» Rest energy is the mass of a particle when it is stationary corresponds to rest energy locked up as mass
What is the notation for rest energy?
» m(o)c^2
What must be included in the conversation of energy?
» Rest energy must be included in the conversation of energy.
» Dirac predicted the existence of antimatter particles that would unlock the rest energy when they would meet and annihilate
What did Dirac’s theory of antiparticles predict?
For every type of particle there is a corresponding antiparticle that:
» Annihilates the particles and itself if they convert their total mass into photons
» Has exactly the same rest mass as the particle
» Has exactly the opposite charge to the particle if the particle has a charge
What is pair production?
» Dirac predicted that a photon with sufficient energy passing near a nucleus or an electron can suddenly change into a particle-antiparticle pair ,which would then separate from each other
What is 1 MeV equal to?
» 1.60 x 10^-13
What is the definition of one electron volt?
» Defined as the energy transferred when an electron is moved through a potential different of 1 volt
When does annihilation occur?
» occurs when a particle and a corresponding antiparticle meet and their mass is converted into radiation energy
What is produced as a result of annihilation?
» 2 photons are produced in this process
Can a single photon be produced?
» No as a single photon cannot ensure a total momentum of zero after the collision
What is the minimum energy of each photon in annihilation?
» hf(min) = E(o) where E(o) is the rest energy of the particle
» Energy of photon = hf, and Energy = Mc^2, when mass is 0 Energy = Energy(o)
What is the minimum energy of photon needed in pair production?
» hf(min) = 2E(o)
What are the four fundamental forces?
» Gravity
» Electromagnetic
» Weak force
» Strong nuclear
What are forces between particles caused by?
» Exchange particles
What is the rest energy of an electron in MeV?
» 0.511 MeV
Describe the changes that take place in a proton-rich nucleus when it emits a positron?
» Proton changes into a neutron
» And a positron and neutrino is released
What are the 2 ways in which pair production of a positron and an electron differs from positron emission?
» No photon involved in positron emission
» In pair production only photons are emitted, no neutrinos
Why is the energy after collision more?
» The energy associated with the rest masses
must be added
If the kinetic energy is greater what is the effect on the subatomic particles produced?
» Be more massive
» Have greater kinetic energy
