Particles and radiation
- Created by: RebeccaCass
- Created on: 19-05-18 18:51
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- Particles and Radiation
- Atomic structure
- Nucleon number (mass number)- The number of protons and neutrons in the nucleus. (A)
- Proton number (atomic number)- The number of protons in the nucleus. Same as the number of electrons. (z)
- Specific Charge- Ratio of an a particles mass compared to it's charge (CKg-1)
- Isotopes- Atoms with the same number of protons but a different number of neutrons.
- Isotopic data-The relative amounts of different isotopes of an element present in a substance
- Stable and Unstable Nuclei
- Forces acting on the nucleus are the electromagnetic force, the gravitational force and the strong nuclear force.
- The strong nuclear force
- At small separations (>0.5fm) it is repulsive.
- As separation increases (0.5-3fm) nuclear attraction increases to maximum attraction value and decreases
- the force extends indefinitely
- The strong nuclear force
- Nuclear Decay
- Alpha decay
- Only happens in big atoms as they are too big for the strong force to keep them stable.
- They emit an alpha particle (4,2 A) from their nucleus.
- proton number decreases by two, nucleon number decreases by 4.
- They have a short range. Can be seen in a cloud chamber or detected by a Geiger or spark counter.
- Beta decay and the hypothesis of neutrinos
- 1930- Wolfgang Pauli suggested another particle was emitted during as part of beta decay. this took the energy.
- Alpha decay
- Beta-minus decay
- The emission of an electron from the nucleus along with an antineutrino particle.
- Happens in isotopes that are neutron rich.
- beta particles have a larger range than alpha particles
- A neutron becomes a proton, the antineutrino carries away energy and momentum
- Forces acting on the nucleus are the electromagnetic force, the gravitational force and the strong nuclear force.
- Antiparticles and photons
- Electromagnetic radiation
- Radio waves Microwaves Infrared Visible light Ultraviolet X-rays Gamma Rays
- Down-increasing frequency Up-increasing wavelength
- the higher the frequency the higher the energy
- Radio waves Microwaves Infrared Visible light Ultraviolet X-rays Gamma Rays
- Photons
- Einstein suggested EM waves and their energy could only exist as discrete packets of energy called photons
- Energy of photon= the frequency of light dived by Planck's constant
- Frequency= speed of light in a vacuum (c)/ Wavelength in m.
- Antiparticles
- Each particle has an antiparticle with the same mass and energy but opposite charge.
- Particles are matter. Antiparticles are antimatter
- pair production
- Einstein's theory, energy can turn into mass and mass into energy
- When energy is converted into mass it creates equal amounts of matter and antimatter.
- E.g if two protons with a large amount of KE collided a proton and antiproton might form.
- The minimum energy needed is known as the total rest energy. The minimum energy needed is equal to two times the rest energy of a particle
- Annihilation
- Happens when a particle meets it's antiparticle.
- All the mass is converted back into energy, antiparticles don't exist in normal matter as this happens
- Minimum energy of photon produced=rest energy of particle type annihilated
- PET scanners work by putting a positron emitting isotope in the bloodstream and detecting the gamma ray produced by the annihilation that occurs.
- Electromagnetic radiation
- Hadrons and leptons
- Hadrons- made up of baryons and mesons
- particles that feel the strong force are called hadrons
- Baryons
- All baryons except a free proton are unstable and so will decay. Eventually to become a proton.
- Antibaryons- not found in normal matter
- baryon number- a quantum number that must be conserved
- proton and neutron B=+1 Antibaryons B=-1 Other Particles B+0
- Neutron Decay- caused by weak interaction
- n= p+ e-+ Ve
- mesons
- Interact with baryons via the strong force. All mesons are unstable
- Pions are the lightest meson. There are 3 types, all with different charges
- Kaons are heavier and more unstable. Have a short lifetime and decay into pions.
- Detection of mesons Cosmic rays(contain lots of high energy particles) can be observed in a cloud chamber or detected by two Geiger counters with a piece of lead in between.
- leptons
- Fundamental particles that don't feel the strong force. They interact with other particles through the weak force
- Electron, muon and electron neutrino and muon neutrino. Each also have an anti particle
- Lepton number- a quantum number that must be conserved. Two different types for electron and muon
- Hadrons- made up of baryons and mesons
- Strange particles and conservation of properties
- Strange particles
- Have a property called strangeness, they're created via the strong force in which the strangeness must be conserved.
- Strange particles decay via the weak force where strangeness can change by 1
- Conservation of properties
- Charge must always be conserved
- Baryon number must always be conserved
- Lepton numbers must be conserved seperately
- Strangeness only has to be conserved via the strong force.
- Strange particles
- Quarks and antiiquarks
- Quarks
- There are 6 types of quarks, up, down and strange and their antiquarks.
- A combination of 3 up and down quarks make up protons and neutrons.
- All mesons are made up of one quark and one antiquark. Only kaons have strangeness
- Quark confinement- a single quark cannot be confined
- Weak interaction
- Beta minus decay- a neutron is changed into a proton. A d quark becomes an up quark.This is known as changing a quarks characteristics
- Beta plus decay- Unstable isotopes may decay by B+ decay and so a proton becomes a neutron. This means an u quark becomes a d quark.
- Searching for particles- a theory is created based on observations and then are tested. Due to funds large numbers may have to get together to do this.
- Quarks
- Atomic structure
- Particle interactions
- Repulsion
- Particles are pushed away from each other as an exchange particle is passed between them as it carries momentum.
- Attraction
- As an exchange particle is passed between two particles they are pushed together.
- Strong force exchange particle is the pion- affects hadrons
- Electromagnetic exchange particle is the virtual photon and only affects charged particles.
- The size of the exchange particle determines the range of the force.
- Repulsion
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