chapter 7 nuclear physics

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  • 1. Chapter 7: NUCLEAR PHYSICS
  • 2. SCOPE OF STUDY SCOPE OF STUDY 11 main sub topics students should learn and understand in this chapter are : Structure and Properties of the Nucleus Discovery of Neutrons The Nuclear Forces Atomic Number and Mass Number Atomic Mass Unit
  • 3. SCOPE OF STUDY SCOPE OF STUDY Mass Defect Binding Energy per Nucleon Mass-Energy Equation Isotopes of an Element Mass Spectrometer Detection of Presence of Isotopes
  • 4. STRUCTURE & STRUCTURE & PROPERTIES OF PROPERTIES OF NUCLEUS NUCLEUS Nucleus consists of protons and neutrons. A proton is the nucleus of the simplest atom hydrogen. Proton has positive charge. Neutron carries no electric charge and has mass slightly larger than a proton. The number of neutrons in the nucleus is N.
  • 5. STRUCTURE & STRUCTURE & PROPERTIES OF PROPERTIES OF NUCLEUS NUCLEUS
  • 6. STRUCTURE & STRUCTURE & PROPERTIES OF PROPERTIES OF NUCLEUS NUCLEUS
  • 7. STRUCTURE & STRUCTURE & PROPERTIES OF PROPERTIES OF NUCLEUS NUCLEUS Neutrons and protons are collectively called nucleons. Although hydrogen nucleus consists of a single proton alone, the nuclei of all other elements consist of both neutrons and protons. Nuclei is a plural of nucleus. The different nuclei are often referred to as nuclides. The radius, r of nucleus depends on atomic mass number, A ( r 1.2 10 15 ) 13 mA
  • 8. DISCOVERY OF DISCOVERY OF NEUTRONS NEUTRONS James Chadwick (1891-1974) James Chadwick (1891-1974)
  • 9. DISCOVERY OF DISCOVERY OF NEUTRONS NEUTRONS In 1932, Chadwick proved the existence of neutrons - elementary particles devoid of any electrical charge. In contrast with the helium nuclei (alpha rays) which are charged, and therefore repelled by the considerable electrical forces present in the nuclei of heavy atoms, this new tool in atomic disintegration need not overcome any electric barrier and is capable of penetrating and splitting the nuclei of even the heaviest elements.
  • 10. DISCOVERY OF DISCOVERY OF NEUTRONS EXPERIMENT OF NEUTRON NEUTRONS
  • 11. DISCOVERY OF DISCOVERY OF NEUTRONS NEUTRONS Chadwick smashed alpha particles into beryllium, a rare metallic element, and allowed the radiation that was released to hit another target: paraffin wax. When the beryllium radiation hit hydrogen atoms in the wax, the atoms were sent into a detecting chamber. In physics it is known that only a particle having almost the same mass as a hydrogen atom could effect hydrogen in that manner. The experiment results showed a collision with beryllium atoms would release massive neutral particles, which Chadwick named neutrons.
  • 12. NUCLEAR FORCES NUCLEAR FORCES Two types : Strong nuclear forces and weak nuclear forces. Strong nuclear force is an attractive force that acts between all nucleons (protons and neutrons alike). Protons attract each other via strong nuclear force at the same time they repel each other via electric force. Strong nuclear force > electric force. Neutrons (electrically neutral) only attract other neutron or protons via strong nuclear force.
  • 13. NUCLEAR FORCES NUCLEAR FORCES Strong nuclear force is a short-range force. It acts only over a very short distance. It is very strong between 2 nucleons if they are < 10 -15 m apart. It is 0 if they are separated by a distance > 10 -15 m apart. Electric and gravitational forces are long-range forces. If the nuclide contains too fewer or too many neutrons relative to the number of protons, the binding of nucleons reduce (nuclide unstable).
  • 14. NUCLEAR FORCES NUCLEAR FORCES Nuclei stable have the same number of protons as neutrons (N=Z) up to about A = 30. Beyond this, stable nuclei contain more neutrons and protons. As Z increase, electric repulsion increase, greater number of neutrons require to maintain stability. For very large Z, no number of neutrons can overcome the greatly increased electric repulsion. (Above Z = 82, no completely stable nuclide). Weak nuclear force second type of nuclear force that is much weaker than strong nuclear force.
  • 15. NUCLEAR FORCES NUCLEAR FORCES
  • 16. ATOMIC NUMBER, Z ATOMIC NUMBER, Z DEFINITION DEFINITION Number of protons in the nucleus To establish the chemical identity of the atom. Each atomic number corresponds to a different chemical element. It symbols by Z.
  • 17. MASS NUMBER, A MASS NUMBER, A DEFINITION DEFINITION Total number of protons and neutrons (nucleons) in the nucleus Neutron number : N = A - Z
  • 18. MASS NUMBER, A MASS NUMBER, A It symbols by A. A and Z sufficient to specify a nuclide. Nuclide are symbolized by symbol : X is the chemical symbol for the element. It contains the same information of recognizable form. Z but in the more easily in the
  • 19. ATOMIC MASS UNIT ATOMIC MASS UNIT It is symbolized by amu or u. It is a unit to specify the nuclear masses because the very small size of protons it is not convenient to express the mass of nuclei and atomic particles in the conventional unit of kilograms. Masses of atoms are measured with reference to the carbon-12 atom, which is assigned a mass of exactly 12 u.
  • 20. ATOMIC MASS UNIT ATOMIC MASS UNIT The relationship between the atomic mass unit and kilogram is : where c : speed of light = 3.0 x 108 m/s
  • 21. ATOMIC MASS UNIT ATOMIC MASS UNIT
  • 22. MASS DEFECT, m MASS DEFECT, m DEFINITION DEFINITION The amount by which the sum of the individual masses The amount by which the sum of the individual masses of the protons and neutrons exceeds the mass of intact of the protons and neutrons exceeds the mass of intact nucleus nucleus It is also known as the difference in mass of the nucleus.
  • 23. BINDING ENERGY PER BINDING ENERGY PER NUCLEON NUCLEON BINDING ENERGY The energy needed to break the nucleus into its The energy needed to break the nucleus into its constituent protons and neutrons ((nucleons). constituent protons and neutrons nucleons).
  • 24. BINDING ENERGY PER BINDING ENERGY PER NUCLEON NUCLEON Because of the strong nuclear force, the nucleons in a stable nucleus are held tightly together. Thus, energy is required to separate a stable nucleus into its constituent nucleons. The more stable the nucleus is, the greater is the amount of energy needed to break it apart. Each of the separated nucleons is at rest and out of range of the forces of the other nucleons.
  • 25. BINDING ENERGY PER BINDI

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