Chapter 7 nuclear physics
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Chapter 7 nuclear physics

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Chapter 7 nuclear physics Chapter 7 nuclear physics Presentation Transcript

  • Chapter 7: NUCLEAR PHYSICS
  • 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
  • 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
  • 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.
  • STRUCTURE & STRUCTURE & PROPERTIES OF PROPERTIES OF NUCLEUS NUCLEUS
  • STRUCTURE & STRUCTURE & PROPERTIES OF PROPERTIES OF NUCLEUS NUCLEUS
  • 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
  • DISCOVERY OF DISCOVERY OF NEUTRONS NEUTRONS James Chadwick (1891-1974) James Chadwick (1891-1974)
  • 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.
  • DISCOVERY OF DISCOVERY OF NEUTRONS EXPERIMENT OF NEUTRON NEUTRONS
  • 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.
  • 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.
  • 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).
  • 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.
  • NUCLEAR FORCES NUCLEAR FORCES
  • 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.
  • MASS NUMBER, A MASS NUMBER, A DEFINITION DEFINITION Total number of protons and neutrons (nucleons) in the nucleus Neutron number : N = A - Z
  • 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
  • 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.
  • 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
  • ATOMIC MASS UNIT ATOMIC MASS UNIT
  • 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.
  • 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).
  • 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.
  • BINDING ENERGY PER BINDING ENERGY PER NUCLEON NUCLEON Binding energy = ( Mass defect ) c 2 = ( ∆m ) c 2
  • BINDING ENERGY PER BINDING ENERGY PER NUCLEON NUCLEON BINDING ENERGY PER NUCLEON The total binding energy of a nucleus divided by The total binding energy of a nucleus divided by mass number, A mass number, A
  • BINDING ENERGY PER BINDING ENERGY PER NUCLEON NUCLEON
  • BINDING ENERGY PER BINDING ENERGY PER NUCLEON NUCLEON Example: Binding energy for iron. Calculate the total binding energy and the binding energy per nucleon for , the most common stable isotope of iron. Solution: Calculate the mass of the iron nucleus, the mass of 26 protons, and the mass of 30 neutrons. The total binding energy is the difference, 492 MeV, and the binding energy per nucleon is 8.79 MeV.
  • MASS-ENERGY MASS-ENERGY EQUATION EQUATION The energy change in a nuclear reaction is considerably greater than that of a normal chemical reaction. This change can be calculated using Einstein's equation: ΔE = Δmc22 ΔE = Δmc where ΔE is the change in energy, Δm is the change in mass, c is the speed of light (3.00 x 108 m/s).
  • ISOTOPES OF ISOTOPES OF ELEMENT ELEMENT DEFINITION DEFINITION Nuclei that contain the same number of protons but different numbers of neutrons
  • ISOTOPES OF ISOTOPES OF ELEMENT ELEMENT
  • ISOTOPES OF ISOTOPES OF ELEMENT ELEMENT Every nuclide is an isotope of some other nuclide. Most elements have several isotopes. In most cases some of the isotopes of a given element are stable (not radioactive), and some are radioactive. For example, iodine has 23 known isotopes with mass numbers ranging from 117 to 139. Two of these, I-127 and I-131, are shown below.
  • ISOTOPES OF ISOTOPES OF ELEMENT ELEMENT
  • ISOTOPES OF ISOTOPES OF ELEMENT ELEMENT The relationship between the two nuclides is that they are isotopes. I-131 is an isotope of I-127, and I-127 is also an isotope of I-131. For most elements the most common or most abundant form is the stable isotope. The radioactive forms are therefore isotopes of the more common forms, explaining the strong association isotopes have developed with radioactivity.
  • MASS MASS SPECTROMETER SPECTROMETER
  • MASS MASS SPECTROMETER SPECTROMETER DEFINITION DEFINITION An instrument which can measure the masses and An instrument which can measure the masses and relative concentrations of atoms and molecules. It relative concentrations of atoms and molecules. It makes use of the basic magnetic force on a moving makes use of the basic magnetic force on a moving charged particle. charged particle.
  • MASS MASS SPECTROMETER SPECTROMETER
  • DETECTION OF DETECTION OF PRESENCE OF PRESENCE OF EXAMPLE ISOTOPES ISOTOPES Two radioactive isotopes of sodium—sodium-22 and sodium-24—are used Two radioactive isotopes of sodium—sodium-22 and sodium-24—are used in medicine and other applications. They can be used as tracers to follow in medicine and other applications. They can be used as tracers to follow sodium in aaperson's body. A tracer is aaradioactive isotope whose presence sodium in person's body. A tracer is radioactive isotope whose presence in aasystem can easily be detected. The isotope is injected into the system at in system can easily be detected. The isotope is injected into the system at some point. Inside the system, the isotope gives off radiation. That radiation some point. Inside the system, the isotope gives off radiation. That radiation can be followed by means of detectors placed around the system. can be followed by means of detectors placed around the system.
  • DETECTION OF DETECTION OF PRESENCE OF PRESENCE OF ISOTOPES ISOTOPES Sodium-24 also has non-medical applications. For example, it is used to test Sodium-24 also has non-medical applications. For example, it is used to test for leaks in oil pipe lines. These pipe lines are usually buried underground. for leaks in oil pipe lines. These pipe lines are usually buried underground. It may be difficult to tell when aa pipe begins to leak. One way to locate aa It may be difficult to tell when pipe begins to leak. One way to locate leak is to add some sodium-24 to the oil. If oil leaks out of the pipe, so does leak is to add some sodium-24 to the oil. If oil leaks out of the pipe, so does the sodium-24. The leaking oil may not be visible, but the leaking sodiumthe sodium-24. The leaking oil may not be visible, but the leaking sodium24 is easily detected. It is located by instruments that are designed to detect 24 is easily detected. It is located by instruments that are designed to detect radiation. radiation.
  • ~~ THE END ~~ “ Write it on ur heart that every day is the best day in the year” ~Ralph Wardo Emerson~