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Transcript of Elementary Particles
Positron and Antiparticles
Particle Accelerators & Detectors
The Meson and Strong Nuclear Force
Classification of Elementary Particles
By: Priyal, Isha, Vanessa, Kashnishaa
Elementary particles are particles with no measurable internal structure; they are not composed of other particles
The 3 main groups of elementary particles are
photon, lepton and hadron
Over 200 such particles have been established
Radioactive decay occurs when the nucleus of an atom spontaneously breaks down, resulting in to the release of energy and matter
Radioisotopes have an unstable nuclei because they don't have enough binding energy to hold the nucleus together
In order to stabilize, they need to transform into a new element, this process is called
Transmutation is the change of one element into another as a result of changes within the nucleus
The decaying process results into the emission of three particles:
-> Alpha particles, Beta particles and Gamma rays
ejected at a high speed but have a range of only a few centimeters in air
actually the nuclei of helium ions; represented as
the atomic number
decreases by 2, since two protons are lost
the atomic mass number
decreases by 4, since two protons and two neutrons are lost
Streams of high-energy electrons
Ejected at various speeds, sometimes approaching the speed of light
Have a charge of -1, but a negligible mass
In the decay process, a neutron disappears and a proton appears
at the same time
in the nucleus and a beta particle is emitted
Therefore, the atomic number increases by 1, but the atomic mass number remains constant
electromagnetic radiations with very short wave lengths
wavelengths and energies can vary
consists of photons that have no mass or electric charge
gamma rays don't effect the atomic number or mass number of the nucleus
represented by the symbol
As we know there are four forces in nature: gravity, the electromagnetic force, the weak nuclear force, and the strong nuclear force.
As the name implies, the strong nuclear force is the strongest of all four forces.
The strong nuclear force is the force that binds protons and neutrons in the nucleus of an atom.
The Meson is a particle that has a rest mass between an electron and a proton that transfers the strong nuclear force that binds the nucleons together in the nucleus.
The idea of the meson was proposed by a Japanese physicist, Hideki Yukawa.
Elementary particles are arranged in groups based on their chemical properties.
The groups are known as: photon, leptons, and hadrons (mesons, baryons, and hyperons).
Photon: has no rest mass and is only involed in electromagnetic interactions
Leptons: are involved only with the weak force, leptons are the electron, the muon, and the two neutrinos (electron neutrino and muon neutrino).
Hadrons: interact by the strong nuclear force, include the neutron, proton, pion, and other particles with large rest masses.
Hadrons are divided again based on spin into the mesons, the baryons, and the hyperons.
Conservation Laws Applied to Alpha and Beta Decay
-The Law of Conservation stated
that a phenomenon of nature is symmetrical and looks the same whether observed directly or in a mirror. E=mc^2
- The energy of an alpha particle can be determined from the mass of the original radioactive nucleus, the mass of the alpha particle, and the mass of the final nucleus.
- If the same law was applied to the beta decay the particles emitted from the identical radioactive nuclei should each have the same energy but this was not the case.
- In each beta decay there was a certain loss of mass which should have been equivalent to the kinetic energy of the emitted beta particle, however it was found that the kinetic energy of the beta particle had a range of values, though never greater than the energy equivalent of the mass decrease.
- According to the Law of Conservation of Energy, no beta particle should have a kinetic energy LESS than the energy equivalent of the mass decrease ( the max kinetic energy of the beta particle should also be the min kinetic energy) therefore, the law failed for beta.
The Pauli Exclusion Principle
-The Pauli Exclusion Principle stated
that only two electrons of opposite spin may occupy the same orbit.
-Pauli suggested that if the beta particle did not carry off all the available energy, the remainder might be given to a second particle.
- When a neutron is broken down into a proton and electron, the loss in mass is equal to approximately one half of the mass of an electron. Calculations were made and it became clear that like a photon, it had a rest mass of zero which concluded that Pauli’s particle was a mass less particle, neutral particle.
- It was then named a neutrino (little neutral one) . Symbol : v
- In beta decay the neutron, proton and electron all have spins of either +1/2 or -1/2
- To conclude, the neutrino is required in order to save no less than 3 conservation laws,
those of energy, linear momentum and angular momentum.
Carl Anderson called the positively charged electron positron (antielectron)
The positron and electron are known as the negative electron and positive electron: e- and e+
In 1934, the radioactive atomic nuclei produced positrons when they were decayed
Frederic and Irene Joloit Curie discovered that it was possible to create artificial radioactive elements from stable elements
Ex: They bombarded aluminum with alpha particles as the radioactive product is phosphorous which emitted positrons as it decayed into silicon
Neutrino: is a tiny subatomic particle that has a tiny mass and no charge as it is made through radioactive decay
Beta Negative Decay: neutron decays into an electron, proton, and antineutrino
Beta Positive Decay: proton decays into an neutron, positron, and neutrino
Pair Production: The photon can disappear and reappear as both positive and negative electron pair. The photon must be equivalent to the mass of the two electrons. The mass of one electron is equivalent to 0.511MeV of energy which is from Einsteins equation: E=mc^2. In order to produce two electrons the photon energy must be 1.022MeV
Pair Annihilation: Conversion into two photons when a particle and antiparticle collides
Gravity: Attractive force between all particles with mass. Based on massive objects, gravity is the most powerful force, however, when you apply gravity to the atomic level, it has a little effect since the mass of subatomic particles are small
How strong is it:
Weak: Where a neutron within the nucleus changes into an electron and proton that is ejected from the nucleus. It is responsible for radioactive decay
Range: Less than 10^-11m
How strong is it: 10^25m
Carrier: W and Z Bosons (W+, W-, Z)
Electromagnetic: Force between electrically charged particles as it can be attractive or replusive. Responsible for keeping the electrons around the nucleus
Range: Infinite range
How strong is it: 10^36
Strong: Binds the protons and neutrons together.
How strong is it: 10^38
• The first scientist to use high-energy particles to explore the atom was Ernest Rutherford.
Constant- voltage Accelerators
: First successful experiments with accelerated ions were performed by J.D Cockcroft and E.T.S. Walton in 1932 at Cambridge University, England.
• Another physicist by the name of Robert J. Van De Graaff constructed the first belt charged electrostatic high- voltage generator.
• Today many of Van de Graaff generators are used as two-stage (tandem) accelerators.
• These generators are used in nuclear physics to bombard atomic nuclei, in order to produce artificial nuclear reactions.
• The first cyclotron was built by Lawrence in 1931 at the University of California.
• For this accelerator to work is that the orbits of the ions are in a uniform magnetic field which are called isochronous. This means that the time taken for particles with the same mass and charge to make one complete cycle is the same at any speed or energy.
• Today many cyclotrons are used in medical and biological research however the major use is in nuclear physics.
• Given its name because it accelerates beta particles.
• The electrons are accelerated in a doughnut-shaped, evacuated chamber located between the poles of a magnet.
• Betatrons are used for high-energy x-rays. They are used in treatment for cancer and in industrial applications such as checking for flaws in metal castings
the four leptons (the electron, the muon and the two neutrinos) were purely elementary particles because they did not break down into smaller particles, however, hadrons did
after being analyzed under high-energy proton beams, it was discovered that nucleons were made up of even smaller elementary particles because they have three separate centres of charges inside of them
- in the proton, they combined to form a single quantum of
-in the neutron, they combined to balance out and create a
net charge of zero
after this discovery, it was concluded that hadrons were made up of six sub-particles, called
the six quarks exist in pairs of three
-up (u) and down (d)
-charm (c) and strange (s)
-top (t) and bottom (b)
for each quark, there is a corresponding