1.4 - Particles And Antiparticles Flashcards
what happens when matter and antimatter particles meet
they destroy each other and radiation is released
how do we make use of this effect
positron emitting tomography (PET) hospital scanner
what is the positron
antiparticle of the electron
what happens when a PET scan is done on the brain
A positron emitting isotope administered to the patient and some of it reaches the brain via the blood system.
Each positron emitted travels no further than a few millimetres before it meets an electron and they annihilate each other.
Two gamma photons, produced as a result, are sensed by detectors linked to the computer and gradually an image is built up from the detector signals of where the positron emitting nuclei are inside the brain.
when does positron emission take place
when a proton changes into a neutron in an unstable nucleus with too many protons
what is the symbol of a positron and what is its charge
+1B positive as it is the antiparticle of the electron
what is a antiproton
the antiparticle of the proton
what is an antineutron
the antiparticle of a neutron
do positron emitting isotopes occur naturally
no
how are positron emitting isotopes made
manufactured by placing a stable isotope ,in a 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 positron emitters
when and who predicted antimatter
1928 by English physicist Paul Dirac before the first antiparticle (positron) was discovered
what happened 20 yrs after Dirac
Einstein had shown that the mass of a particle increases the faster it travels creating the E=mc^2 equation
what did Einstein say that the rest mass of a particle corresponds to
rest energy locked up as mass and showed that the rest energy must be included in the conservation of energy
Dirac predicted the existence of anti particles that would unlock rest energy when ……
a particles and a corresponding antiparticle meet and annihilate eachother
Dirac theory of antiparticles predicted the for every type of particle there is a corresponding anti particle that
- annihilates the particle and itself if they meet, converting there total mass into protons
- has exactly the same rest mass as the particle
- has exactly the opposite charge to the particle if the particle has a charge
what did Dirac also predict
the opposite process of pair production
He predicted that a photon with sufficient energy passing near a nucleus or a electron can suddenly change into a particle - antiparticle pair which would then separate from each other
what is the energy of a particle/antiparticle often expressed in
MeV
what does 1 MeV =
1.60 x 10^-13 J
what is one electron vault defined as
the energy transferred when an electron is moved through a potential of 1 vault
when does annihilation occur
when a particle and a corresponding antiparticle meet and their mass is converted into radiation energy
what is produced for annihilation
2 photons (a single photon cannot ensure a total momentum of 0 after the collision)
how do you calculate the minimum energy of each photon produced
hfmin = E0
the minimum energy of the 2 photon = hfmin
E0 = rest energy of the particle
what happens in pair production
a photon creates a particle and a corresponding antiparticle and vanishes in the process
minimum energy of a photon needed to create pair production
hfmin = 2E0
what can you see the path of an alpha and a beta particle using
a cloud chamber
transparent container containing air saturated with vapour and made very cold like high in the atmosphere
what do ionising particles leave behind them in a cloud chamber
a trail of liquid droplets
in 1932 what did carl Anderson use the cloud chamber to do
take photos of the trails produced by cosmic rays as they passed through a lead plate within a magnetic field
what 2 things should happen to the particles in the cloud chamber
bend towards the magnetic field depending on wether the particles are positive or negative
when the particles are going slower they should bend so should bend ore after going through plate due to loss of kinetic energy
how did Dirac discover the positron
sent a beta particle into the chamber however it bent towards the wrong pole so was therefore a positron
