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Transcript of Nuclear Physics
and the interactions that occur. The nucleons that forms the nucleus are held by attractive forces called the strong nuclear force. The time it takes for half of the radioisotope's nucleus to decay is called the half-life. Another way for transmutation to occur is by striking the nucleus with another particle. Introduction It's the branch of physics that examines the behaviour and structure of the atomic nuclei All matter is composed of atoms
and all atoms contain a heavy core
called the nucleus. The nucleus is the core of the atom and it's
composed of neutrons and protons. Neutrons are particles that have no charge and protons are particles that have a positive charge. These particles that are known as nucleons because
they make up the nucleus. Atoms An atom is described by its atomic number and
atomic mass number The atomic number describes the number of electrons and protons. The atomic mass number describes the number of nucleons(number of protons and neutrons) This expression describes the atomic number (B), atomic mass number (C) and the atom (A). C
B A Particles The masses of atoms and particles
are measured in unified atomic mass
units (u). This unit is based on a scale that defines
the mass of a carbon to be 12u For a stable nucleus that contains
protons and neutrons, it has lesser
mass when combined than the sum of
individual nucleons because of an
In nuclear physics, it's known as a mass
defect. These forces attract proton-proton, proton-neutron, neutron-neutron together within a short range (approximately 1.5X10^15m). The fault with these is that because of the electrical
force of the proton-proton repulsion, it can overcome the strong nuclear force and cause the nuclei to be unstable. This will only occur if the atomic number is greater than 82 because at this range, high number of neutrons cannot produce a stable nuclei. Radioactivity Radioactivity is defined as the rapid decay of
an atomic nuclei using the emission of radiation
and particles. Scientists like Ernest Rutherford state that there
are three types of radiation emission called alpha particles, beta particles and gamma particles. In 1898, Marie Curie concluded that the process of radiation derives from a nucleus, through a series of experiments with radium and polonium Transmutation Emission of radiation have a tendency to
change an element and transform it to a
new element. This process is called transmutation Alpha Decay During alpha decay, a nucleus of an element emits an alpha particle to form a new element called the daughter nucleus. An alpha particle has atomic mass number of 4u, consists of two protons and two neutrons and a atomic number of 2. An alpha particle is equivalent to a helium nuclei The general equation for alpha decay can be written as C B A A C-4 B-4 + He 4 2 Beta Decay(Electron Emission) When an isotope becomes unstable, it has too many neutrons. One way to counteract this problem, is that when a neutron decays, a proton is produce along with the emission of an electron. During beta(-) emission, the emitted Neutrino and Antineutrino During beta(-) emission, the emitted electron's kinetic energy is less than expected based on the laws of conservation of mass and energy. In 1930, a scientist known as Wolfgang Pauli suggested that the excess energy lost from the electron was given to a second particle known as the neutrino, a neutral particle that has a very small,rest mass. Neutrino's have an antiparticle called antineutrinos which is also emitted along with the electron during beta(-) decay. Beta (+) decay positron emission In this situation, the unstable isotope has not enough neutrons in the nucleus for the
strong nuclear forces to occur and stabilize the nucleus. To achieve stability, a proton must decay to form a neutron by emitting a positron(e+) and a neutrino. Gamma Decay and Electron Capture Electron Capture is an event where the electron
that orbits the nucleus very closely that it gets
absorbed; this causes a proton to change to a neutron. Like beta (+) decay, this occurs when there is not enough neutrons in the nucleus. A neutrino is also emitted during the electron capture. When the electron is absorbed by the nucleus, the nucleus becomes excited and has extra energy; with this extra energy, the nucleus will release it as gamma rays. Mathematically, half-life can be expressed by this equation N=N (1/2)^1/T 0 1/2 Activity The number of radioisotope nuclei that decay per second is called the activity. It is measured by becquerels (Bq) named after Henri Bequerel, a french physicist. Like the half equation, activity can be expressed by this equation. A=A (1/2)^1/T 0 1/2 Radioactive Dating Radioactive dating is the process of using carbon-14 to determine the age of artifacts and relics. Carbon-14 is a radioactive isotope that is created in the upper atmosphere when a neutron from cosmic radiation interacts with nitrogen in the upper atmosphere. Also the hydrogen is emitted during this reaction. C + n 12 6 1 0 C + H 14 6 1 1 Eventually, Carbon-14 can decay back to nitrogen along with releasing an electron. This two reaction balance the amount of carbon-14 in the upper atmosphere. Carbon-14 reacts with oxygen in the atmosphere to form carbon dioxide. Plants absorb the carbon dioxide along with the stable carbon dioxide, and humans absorb the carbon dioxide by eating plants. Since the half-life of carbon-14 is 5730 years, it last longer than a persons' lifetime. Therefore, all organisms have a ratio of carbon-14 and carbon-12, and this ratio increases until the organism dies. By determining the ratio of carbon-14 and carbon-12, scientist can analyze the age of the artifact. Artificial transmutation is the process through human interaction, an element can transform into a new element. In 1919, Rutherford struck nitrogen with alpha particles and the reaction formed oxygen and emitted a proton. Elements that have a atomic number over 82 are unstable and when neutrons interacts with other elements like uranium and form new elements that decay rapidly. Leptons A group of particles that are unaffected by the strong nuclear force(i.e. electrons) but are affected by weak nuclear forces. Leptons are grouped into three pairs, one with a charge and one with no charge.
Electron, Electron Neutrino
Muon, Muon Neutrino
Tauon, Tauon Neutrino The Neutrinos have a very small mass and speed that travels very close to the speed of light. All subtomic particles have antiparticles of the same mass, but opposite charge. Particles with neutral charges are there own antiparticle. Leptons only make the small portion of the
matter Quarks Protons and neutrons have a very complex structure that is made up of fundemental particles called quarks Quarks have a charges of +1/3e and +2/3e _ _ Hadrons Quarks are made up of subatomic particles
called hadrons. There are two kinds of hadrons: Baryons and Mesons. Baryons are made up of three quarks and mesons are made up of a quark and a antiquark. The binding energy of quarks in nucleons are so strong that scientist can only seperate them through experiments. Nuclear binding energy Einstein's energy equation,E=mc^2 In other for a nucleus to be broken down into protons and neutrons ,energy must be supplied. This energy is called the total binding energy. The average binding energy per nucleon can
be calculated by dividing the total binding energyof the nucleus by the total number of nucleons it has. This occurs because the binding energy of the heavier nuclei is weaker than smaller nuclei. Scientists are able to split the nucleus by striking it using slow moving neutrons or thermal neutrons. After striking the nucleus, it gets excited and starts to deform into a ellipitical shape Electrical force of repulsion overcomes the strong nuclear force and splits the nucleus into 2 nuclei and 2 neutrons. A chain reaction can occur if there is enough neutrons and if the nuclei are available. A chain reaction is a process where the nuclei that was a product of the fission reaction is again split into smaller nuclei. Fission Reactors In a nuclear reactor, fission chain reacion take place under controlled conditions. To maintain this controlled chain reactoi, fast moving neutrons must be slowed down by using an effective moderator like heavy water. An effective moderator must always absorb the kinetic energy of the neutron and not the neutron itself. Fusion Fusion is the nuclear reaction where two smaller nuclei form one larger nucleus. These reactions are important for some nuclear reactors. Fusion reactor A few grams of deuterium and radioactive tritium are fed into the reactor core; the fuel is heated to a temperature of at least 2X10^8 celsius. At this temperature, the atoms are converted into plasma gas. Superconducting magnests around a tire -shape vessel or a large toroidal confine the plasma from touching the walls and induce a current in the plasma that heats it to ignition. The ignition fuse the deuterium and tritium to produce fusion energy and the resulting heat is removed using a water cooling system. The energetic helium and tritium heats up the lithium which drives the steam generator and turns the turbine for generating electrical power. The major safety feature of the fusion process is that it is completely controlled. Feyman Diagrams Richard Feynman, an american physicist portrayed the exchange of virtual particles and bosons.
Time is the vertical axis and space is the horizontal axis. Problems There are a lot of problems when it comes to baryons Baryons are made up of three quarks and it is possible to have quark combinations like uuu, however, three quarks in the same configuration violates the Pauli exclusion principle. Charges of oppositely charged particles, like the proton and electron add up to zero and the photons doesn't affect their respective charges during electromagnetic interactions. In 1965, scientists Moo-Young Han and Yoichiro Nambu at Duke University suggested that quarks could be possessing colour changes. Weak Nuclear force Like heavy nuclei, that decay into smaller nuclei, large leptons and quarks decay into smaller leptons and quarks caused by weak nuclear interactions. When subatomic particles decay, they form two or more particles and during this process, the total energy and mass is conserved except a part of the original mass which gets converted into kinetic energy. When large quarks and leptons decay to smaller quarks and leptons, it's said to change flavour(type) A C B A C B + 1 + e + v 0 0 0 -1 _ During positron emission, the atomic number of the nucleus becomes one less A C B A C B - 1 + e + v 0 0 0 -1 A C B + e 0 -1 B - 1 A C + v 0 0 + photon The field particle (Bosons) The end? Boson Exchange Bosons are undetectable particles that are emitted and absorbed within a short time. When two particles interact, bosons carry momentum and energy between the two particles. When a boson from one particle travels to another particle, it is absorbed by the second particle. Colour charges are carried by gluons that bind quarks together in hadrons by way of the strong nuclear forces. Quarks change their colour charge as they exchange gluons with other quarks. Colour charge The electromagnetic and weak forces are combined into one unified force called the electromagnetic force. How does the quarks overcome the tendency of the positive protons to repel? This allows scientists to predict possible quark combinations of hadrons An elementary particle is a particle that cannot be further broken down into smaller matter.