The Physical Universe, 11/e Konrad B. Krauskopf, Prof. Emeritus of Geochemistry, Stanford Univ. Arthur Beiser ISBN:  00724...
Chapter 7  <ul><li>The Nucleus   </li></ul>
The Nucleus: Main Ideas <ul><li>Atomic Structure </li></ul><ul><ul><li>Rutherford Model </li></ul></ul><ul><ul><li>Nuclear...
The Atom and its Nucleus <ul><li>The atom was accepted as the building block of matter </li></ul><ul><li>More experiments ...
Very little was known <ul><li>The nucleus of the atom was a mystery until Ernest Rutherford set out to investigate the ins...
Rutherford’s discovery <ul><li>The relatively heavy particles passed through the gold fold with very little deflection </l...
Quick look at simple Atomic Structure <ul><li>All atoms are composed of </li></ul><ul><ul><li>NEUTRONS </li></ul></ul><ul>...
Rutherford’s conclusion <ul><li>MOST of the volume of the atom is  </li></ul><ul><li>EMPTY SPACE </li></ul><ul><li>Nucleus...
Atom Identity <ul><li>Atoms are identified by  </li></ul><ul><li>the number of protons in the nucleus </li></ul><ul><li>At...
Isotopes <ul><li>Since an atom is identified by the number of protons, changes to the number of protons result in a comple...
NUCLIDE <ul><li>A nucleus with a particular composition </li></ul><ul><li>Noted by the symbol: </li></ul><ul><li>The ‘X’ s...
Radioactivity <ul><li>Becquerel discovered accidentally: </li></ul><ul><ul><li>Uranium produces penetrating radiation </li...
Radioactive elements <ul><li>Most elements do NOT have radioactive isotopes </li></ul><ul><ul><li>About 2000 nuclides have...
Radioactive atoms <ul><li>What is “radioactivity”?? </li></ul>Radioactivity  is the term given to the  spontaneous “fallin...
Why do nuclei decay? <ul><li>Reasons for nuclear decay: </li></ul><ul><ul><li>LARGE NUCLEUS </li></ul></ul><ul><ul><ul><li...
Radioactivity <ul><li>Types of decay: </li></ul><ul><ul><ul><ul><ul><li>Alpha (  ) emission </li></ul></ul></ul></ul></ul...
Five Decay Processes
What’s the difference?? <ul><li>Alpha emission  (lowest energy) </li></ul><ul><ul><li>stream of particles that are identic...
What’s the difference??  <ul><li>Beta Emission (medium energy) </li></ul><ul><ul><li>when a neutron becomes a proton by  e...
What’s the difference?? (cont.) <ul><li>Gamma Emission (highest energy) </li></ul><ul><ul><li>Gamma rays originate inside ...
Alpha Beta Gamma
After Decay <ul><li>When an atomic nucleus is unstable, decay brings the nucleus to a more stable state </li></ul><ul><li>...
WHEN DO ATOMS DECAY? <ul><li>Any unstable nucleus EVENTUALLY decays </li></ul><ul><li>For a collection of UNSTABLE nuclei,...
BUT, we can MEAUSURE <ul><li>We can measure the decay as it happens </li></ul><ul><li>THE PERCENTAGE OF NUCLEI THAT DECAY ...
Characterizing Radioactive Elements <ul><li>What is a “half-life”?? </li></ul><ul><li>The  half life  of a radioactive iso...
More about half life <ul><li>The “half-life” of a radioactive isotope is the  amount of time needed for 1/2 of the materia...
Here is how it goes <ul><li>Half life is really the AVERAGE TIME for a single atom to decay </li></ul><ul><li>Let’s say we...
Radiation Hazards <ul><li>All ionizing radiation is harmful to living tissue </li></ul><ul><li>The hazardous effects of ra...
Radiation Exposure: Sources
Measuring radiation exposure <ul><li>Exposure to radiation is defined in terms of DOSAGE </li></ul><ul><li>The unit for DO...
Typical Radiation doses <ul><li>Natural sources: 3mSv per year </li></ul><ul><li>Medical and Dental x-rays: 0.6 mSv per ye...
Dose Limits <ul><li>In many countries the recommended dose limit is  20 mSv  the </li></ul><ul><ul><li>Corresponds to esti...
Nuclear Energy <ul><li>Using the atomic nucleus as an energy source provides an alternative to fossil based fuel sources <...
The atomic mass unit <ul><li>The atomic mass is small when compared with everyday objects </li></ul><ul><li>A new unit is ...
The Electronvolt <ul><li>The most commonly used unit for atomic physics is the </li></ul><ul><li>Electronvolt (eV) </li></...
The MEGAelectronvolt <ul><li>Because the energies involved in nuclear decay are large, the electron volt is not useful to ...
What holds the nucleus together <ul><li>If you think about all those (+) protons being jammed into such a small space,  </...
When a nucleus decays <ul><li>Energy is given off as the strong nuclear forces work is done against strong nuclear forces ...
Energy Equivalent <ul><li>The energy equivalent of the missing mass of a nucleus is called the binding energy of the nucle...
Binding energy per nucleon <ul><li>The ratio of the total binding energy with the number of nucleons  </li></ul><ul><li>Gi...
Two remarkable conclusions <ul><li>If a heavy nucleus were to be divided into two smaller nuclei, the binding energy per n...
 
Fission/Fusion means CONfusion?!? <ul><li>Fission: (heavy elements) </li></ul><ul><li>separation of an atomic nucleus acco...
Binding energy to Nuclear Energy <ul><li>NUCLEAR ENERGY </li></ul><ul><ul><li>The binding energy per nucleon lead scientis...
Difficulties in harnessing nuclear energy <ul><li>The spontaneous chain reaction </li></ul><ul><ul><li>When a nucleus begi...
Chain reaction
The Chain Reaction <ul><li>Too few neutrons: chain reaction ceases quickly </li></ul><ul><li>Too many neutrons: chain reac...
Nuclear Fission Reactor <ul><li>First reactor built by Enrico Fermi at University of Chicago </li></ul><ul><ul><li>in a sq...
Historic anniversary <ul><li>December 2, 1942 </li></ul><ul><li>the first atomic reactor was brought to criticality by Dr....
KEY – 1 - : CRITICALITY <ul><li>Getting the chain reaction  </li></ul><ul><ul><li>means that neutrons emitted by one U235 ...
KEY –2-: MODERATION <ul><li>The reaction must be ‘slowed down’ in order to fully exploit all the possible available nuclei...
Modern Nuclear Power Plants <ul><li>Most power plants use Uranium as the radioactive source </li></ul><ul><ul><ul><li>Uran...
 
Nuclear fuel <ul><li>Super heated water (enclosed) </li></ul>LAST, and VERY IMPORTANT is the COOLING of the whole system. ...
What about nuclear FUSION? <ul><li>Fusion reactions can release more energy than fission reactions </li></ul><ul><ul><li>F...
Smaller pieces of matter <ul><li>Electrons Protons Neutrons </li></ul><ul><ul><li>Considered to be ‘elementary’ particles ...
A word on ANTIMATTER <ul><li>Any ANTIMATTER particle has the  </li></ul><ul><ul><li>Same mass as its ‘regular’ matter part...
Fundamental Interactions <ul><li>By study of the fundamental interactions of the building blocks of matter, scientists hav...
The Basic Four <ul><li>STRONG INTERACTION </li></ul><ul><ul><li>Holds nucleons together </li></ul></ul><ul><li>ELECTROMAGN...
Unification <ul><li>The work of particle physicists and other scientists is to try to understand how these four fundamenta...
Leptons and Hadrons <ul><li>Two broad categories for elementary particles </li></ul><ul><li>Affected by the strong interac...
Six kinds of quarks <ul><li>The internal structure for hadrons! </li></ul><ul><li>Six types </li></ul><ul><ul><li>Up </li>...
Let’s sum it up <ul><li>Hadrons are made from leptons </li></ul><ul><ul><li>ONLY 6 different leptons </li></ul></ul><ul><l...
In-Lecture Quiz Questions Chapter 7
In-Lecture QUIZ CHAPTER 7 <ul><li>Longer half life means ____________decay rate </li></ul><ul><li>A. faster </li></ul><ul>...
In-Lecture QUIZ CHAPTER 7 <ul><li>T/F Nuclear weapons are based on the idea of nuclear fusion. </li></ul>
In-Lecture QUIZ CHAPTER 7 <ul><li>Write down two types of nuclear reactors commonly used to produce electric energy. </li>...
In-Lecture QUIZ CHAPTER 7 <ul><li>What causes radioactivity? </li></ul><ul><ul><li>A. Some atomic nuclei spontaneously col...
In-Lecture QUIZ CHAPTER 7 <ul><li>What are the three types of radioactive emission? </li></ul><ul><ul><li>A. Alpha, Beta, ...
In-Lecture QUIZ CHAPTER 7 <ul><li>Which types of emission result in a daughter nucleus that is a different element than th...
In-Lecture QUIZ CHAPTER 7 <ul><li>The antimatter partner for every particle is identical except that it has opposite_____....
In-Lecture QUIZ CHAPTER 7 <ul><li>(short essay) Why is the binding energy per nucleon such an important result? </li></ul>
In-Lecture QUIZ CHAPTER 7 <ul><li>The most prevalent source of radiation in the average lifetime is due to: </li></ul><ul>...
In-Lecture QUIZ CHAPTER 7 <ul><li>The atomic mass unit is defined as being approximately equal to </li></ul><ul><ul><li>A....
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The Physical Universe: Nucleus

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The Physical Universe: Nucleus

  1. 1. The Physical Universe, 11/e Konrad B. Krauskopf, Prof. Emeritus of Geochemistry, Stanford Univ. Arthur Beiser ISBN: 0072418265 Copyright year: 2004
  2. 2. Chapter 7 <ul><li>The Nucleus </li></ul>
  3. 3. The Nucleus: Main Ideas <ul><li>Atomic Structure </li></ul><ul><ul><li>Rutherford Model </li></ul></ul><ul><ul><li>Nuclear Structure </li></ul></ul><ul><li>Radioactivity </li></ul><ul><ul><li>Radioactive decay </li></ul></ul><ul><ul><li>Half Life </li></ul></ul><ul><ul><li>Radiation Hazards </li></ul></ul><ul><li>Nuclear Energy </li></ul><ul><ul><li>Units </li></ul></ul><ul><ul><li>Binding Energy </li></ul></ul><ul><li>Fission and Fusion </li></ul><ul><li>Elementary Particles </li></ul>
  4. 4. The Atom and its Nucleus <ul><li>The atom was accepted as the building block of matter </li></ul><ul><li>More experiments were needed to better understand the details of atomic structure… </li></ul>
  5. 5. Very little was known <ul><li>The nucleus of the atom was a mystery until Ernest Rutherford set out to investigate the inside of the atom </li></ul><ul><li>In 1911, Rutherford performed a series of experiments in which he bombarded a gold foil with energetic particles </li></ul>
  6. 6. Rutherford’s discovery <ul><li>The relatively heavy particles passed through the gold fold with very little deflection </li></ul><ul><li>Rutherford concluded that the nucleus must be </li></ul><ul><ul><li>VERY SMALL </li></ul></ul><ul><ul><li>VERY MASSIVE (and thus DENSE) </li></ul></ul><ul><ul><li>OVERALL POSITIVELY CHARGED </li></ul></ul>
  7. 7. Quick look at simple Atomic Structure <ul><li>All atoms are composed of </li></ul><ul><ul><li>NEUTRONS </li></ul></ul><ul><ul><li>PROTONS </li></ul></ul><ul><ul><li>ELECTRONS </li></ul></ul><ul><li>All atoms have a nucleus </li></ul><ul><ul><li>contains NUCLEONS </li></ul></ul><ul><ul><li>That means PROTONS and NEUTRONS </li></ul></ul>These are “nucleons”
  8. 8. Rutherford’s conclusion <ul><li>MOST of the volume of the atom is </li></ul><ul><li>EMPTY SPACE </li></ul><ul><li>Nucleus occupies 1 trillionth of the volume </li></ul><ul><ul><li>this means the nucleus is very massive and </li></ul></ul><ul><li>The mass of the proton is about 2000 times that of an electron </li></ul>dense
  9. 9. Atom Identity <ul><li>Atoms are identified by </li></ul><ul><li>the number of protons in the nucleus </li></ul><ul><li>Atoms are arranged in the periodic table according to increasing number of protons </li></ul><ul><li>The number of protons in the nucleus is called the ATOMIC NUMBER </li></ul><ul><li>Simplest atom </li></ul><ul><ul><li>H (Hydrogen) 1 proton, 1 electron </li></ul></ul>
  10. 10. Isotopes <ul><li>Since an atom is identified by the number of protons, changes to the number of protons result in a completely different atom </li></ul><ul><li>However, changes in the number of NEUTRONS results only a change in mass </li></ul><ul><li>These variations in neutron number for a specific atom are called ISOTOPES </li></ul>
  11. 11. NUCLIDE <ul><li>A nucleus with a particular composition </li></ul><ul><li>Noted by the symbol: </li></ul><ul><li>The ‘X’ stands for the chemical symbol for an element </li></ul><ul><li>Z is the atomic number (# of protons) </li></ul><ul><li>A is the MASS NUMBER (# protons +#of neutrons) </li></ul>
  12. 12. Radioactivity <ul><li>Becquerel discovered accidentally: </li></ul><ul><ul><li>Uranium produces penetrating radiation </li></ul></ul><ul><li>Pierre and Marie Curie did further experimentation </li></ul><ul><ul><li>Discovered more materials that exhibited the same behavior </li></ul></ul>
  13. 13. Radioactive elements <ul><li>Most elements do NOT have radioactive isotopes </li></ul><ul><ul><li>About 2000 nuclides have been identified. Of these only 256 do not undergo radioactive decay. </li></ul></ul>
  14. 14. Radioactive atoms <ul><li>What is “radioactivity”?? </li></ul>Radioactivity is the term given to the spontaneous “falling apart” of an atomic nucleus When the nucleus falls apart, LARGE AMOUNTS OF ENERGY can be released…..
  15. 15. Why do nuclei decay? <ul><li>Reasons for nuclear decay: </li></ul><ul><ul><li>LARGE NUCLEUS </li></ul></ul><ul><ul><ul><li>The strong force that holds the nucleus together acts only over very short distances Large nucleus  large separation </li></ul></ul></ul><ul><ul><ul><li>The heaviest stable nucleus has 83 protons (Bismuth) </li></ul></ul></ul><ul><ul><li>RATION OF NEUTRONS TO PROTONS </li></ul></ul><ul><ul><ul><li>If the ration is too large, or too small, the nucleus is unstable </li></ul></ul></ul>
  16. 16. Radioactivity <ul><li>Types of decay: </li></ul><ul><ul><ul><ul><ul><li>Alpha (  ) emission </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Beta (  ) emission </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Gamma (  ) emission </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Electron Capture </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Positron Emission </li></ul></ul></ul></ul></ul><ul><li>When these processes occur, a different element may be formed </li></ul>The nucleus of an atom becomes UNSTABLE. As a radioactive nucleus begins to DECAY, these particles/rays are emitted
  17. 17. Five Decay Processes
  18. 18. What’s the difference?? <ul><li>Alpha emission (lowest energy) </li></ul><ul><ul><li>stream of particles that are identical to helium nuclei </li></ul></ul><ul><ul><ul><li>not from helium, but pieces of a larger nucleus of a “heavy” atom </li></ul></ul></ul><ul><ul><li>Alpha emission can be stopped by a thin layer of skin or paper </li></ul></ul><ul><ul><li>emission of an alpha particle means </li></ul></ul><ul><ul><li>the nucleus of the decaying atom is reduced by 2 protons and 2 neutrons </li></ul></ul>
  19. 19. What’s the difference?? <ul><li>Beta Emission (medium energy) </li></ul><ul><ul><li>when a neutron becomes a proton by emitting an electron </li></ul></ul><ul><ul><li>so, beta emission is actually a stream of energetic electrons </li></ul></ul><ul><ul><li>can be stopped by a thin sheet of aluminum or even thin layers of clothing </li></ul></ul><ul><li>THE NUCLEUS CHANGES WITH THE LOSS OF 1 NEUTRON, GAIN OF ONE PROTON </li></ul>
  20. 20. What’s the difference?? (cont.) <ul><li>Gamma Emission (highest energy) </li></ul><ul><ul><li>Gamma rays originate inside the nucleus of heavy atoms </li></ul></ul><ul><ul><li>energy HIGHER than x-rays </li></ul></ul><ul><ul><li>gamma rays will penetrate even into a thick sheet of lead </li></ul></ul><ul><ul><li>Gamma radiation is VERY DANGEROUS </li></ul></ul><ul><li>NUCLEAR MAKEUP IS UNCHANGED </li></ul>
  21. 21. Alpha Beta Gamma
  22. 22. After Decay <ul><li>When an atomic nucleus is unstable, decay brings the nucleus to a more stable state </li></ul><ul><li>The final product of nuclear decay is a stable element </li></ul><ul><li>This may require numerous decay steps </li></ul><ul><ul><li>Uranium 238 requires 8 alpha decays and 6 beta decays to eventually become Lead 206, a stable element </li></ul></ul>
  23. 23. WHEN DO ATOMS DECAY? <ul><li>Any unstable nucleus EVENTUALLY decays </li></ul><ul><li>For a collection of UNSTABLE nuclei, the occurrence of DECAY is </li></ul><ul><ul><li>SPONTANEOUS </li></ul></ul><ul><ul><li>RANDOM </li></ul></ul><ul><li>You can’t tell which one will decay first, second, etc. </li></ul><ul><li>Furthermore, we cannot PREDICT what a half life will be based on the fundamental properties of the atom! </li></ul>
  24. 24. BUT, we can MEAUSURE <ul><li>We can measure the decay as it happens </li></ul><ul><li>THE PERCENTAGE OF NUCLEI THAT DECAY EACH SECOND REMAINS CONSTANT </li></ul><ul><li>Decay means the emission of Alpha, Beta, or Gamma Radiation. </li></ul><ul><li>The “TIME” of the decay is characterized by a MATERIAL CONSTANT </li></ul>HALF-LIFE
  25. 25. Characterizing Radioactive Elements <ul><li>What is a “half-life”?? </li></ul><ul><li>The half life of a radioactive isotope is the </li></ul><ul><li>time necessary for </li></ul><ul><li>half of any given quantity </li></ul><ul><li>of the material to decay. </li></ul><ul><li>For example: If you had a collection of 100 radioactive atoms, and after 20 minutes, 50 of the atoms had undergone decay -we say the half life is 20 minutes </li></ul>
  26. 26. More about half life <ul><li>The “half-life” of a radioactive isotope is the amount of time needed for 1/2 of the material to DECAY </li></ul><ul><li>this time is the same for ANY AMOUNT </li></ul><ul><li>MOST half-life times are too long to sit and measure </li></ul><ul><ul><li>like Radium 226, half life = 1620 years! </li></ul></ul><ul><li>half-life is determined by measuring the RATE at which decay occurs, and then EXTRAPOLATING to find out the half life </li></ul>FAST rate -> SHORT half-life SLOW rate -> LONG half-life
  27. 27. Here is how it goes <ul><li>Half life is really the AVERAGE TIME for a single atom to decay </li></ul><ul><li>Let’s say we start with 100 atoms of X with a half life of 10 minutes </li></ul><ul><ul><li>After 10 minutes, we would have 50 X atoms </li></ul></ul><ul><ul><li>After 20 minutes, we would have 25 X atoms </li></ul></ul><ul><ul><li>After 30 minutes, we would have 12-13 X atoms </li></ul></ul><ul><ul><li>After 40 minutes, we would have 6.5 X atoms </li></ul></ul><ul><li>Each ‘time period’ of one half life, means half of the remaining atoms have PROBABLY undergone decay… </li></ul>
  28. 28. Radiation Hazards <ul><li>All ionizing radiation is harmful to living tissue </li></ul><ul><li>The hazardous effects of radiation exposure may not be immediate </li></ul><ul><li>The harmful effects of radiation may result in GENERATIONAL damage to living organisms </li></ul><ul><li>MOST radiation is “background” </li></ul><ul><ul><li>This is natural and generally unavoidable exposure </li></ul></ul>
  29. 29. Radiation Exposure: Sources
  30. 30. Measuring radiation exposure <ul><li>Exposure to radiation is defined in terms of DOSAGE </li></ul><ul><li>The unit for DOSAGE is </li></ul><ul><li>SIEVERTS (Sv) </li></ul><ul><ul><li>1 Sv is the amount of any radiation that has the same biological effects as those produced when 1kg of tissue absorbs 1 Joule of x-rays or gamma rays </li></ul></ul>
  31. 31. Typical Radiation doses <ul><li>Natural sources: 3mSv per year </li></ul><ul><li>Medical and Dental x-rays: 0.6 mSv per year </li></ul><ul><li>Typical mammogram: 4 mSv per year </li></ul><ul><li>Average per individual: </li></ul><ul><li>About 3.6mSv per year </li></ul>
  32. 32. Dose Limits <ul><li>In many countries the recommended dose limit is 20 mSv the </li></ul><ul><ul><li>Corresponds to estimated risk of cancer for 1 in 1000 </li></ul></ul><ul><li>In the U.S. the recommended dose limit is set at 20 mSv </li></ul><ul><li>The risk of radiation induced cancer is much smaller than other hazardous activities such as smoking! </li></ul>
  33. 33. Nuclear Energy <ul><li>Using the atomic nucleus as an energy source provides an alternative to fossil based fuel sources </li></ul><ul><li>Using nuclear energy for good has been contrasted by using nuclear energy for mass destruction </li></ul>
  34. 34. The atomic mass unit <ul><li>The atomic mass is small when compared with everyday objects </li></ul><ul><li>A new unit is required to describe the small mass of the atom </li></ul><ul><li>THE ATOMIC MASS UNIT </li></ul><ul><li>(u) </li></ul><ul><li>1 u = 1.66  10 -27 kg </li></ul><ul><li>Note: this is the approximate mass of a hydrogen atom </li></ul>
  35. 35. The Electronvolt <ul><li>The most commonly used unit for atomic physics is the </li></ul><ul><li>Electronvolt (eV) </li></ul><ul><li>1 eV = 1.60  10 -19 Joules </li></ul><ul><li>For example </li></ul><ul><ul><li>It takes 14.5 eV to remove an electron from a neutral Nitrogen atom </li></ul></ul>
  36. 36. The MEGAelectronvolt <ul><li>Because the energies involved in nuclear decay are large, the electron volt is not useful to describe nuclear energies </li></ul><ul><li>Instead the megaelectronvolt (MeV) is used </li></ul><ul><ul><li>1 million eV = 1MeV </li></ul></ul><ul><ul><li>1MeV = 1.60  10 -13 Joules </li></ul></ul>
  37. 37. What holds the nucleus together <ul><li>If you think about all those (+) protons being jammed into such a small space, </li></ul><ul><ul><li>It seems like, since they have SAME CHARGE, they would REPEL EACH OTHER!!! </li></ul></ul><ul><li>So, how is it that the DENSE, DENSE, DENSE NUCLEUS of an atom stays together?? </li></ul><ul><li>THERE MUST BE SOME ATTRACTIVE FORCE BETWEEN NUCEAR PARTICLES THAT OVERCOMES THE NATURAL ELECTROSTATIC REPULSION…. </li></ul><ul><ul><li>This is called the STRONG NUCLEAR FORCE </li></ul></ul>
  38. 38. When a nucleus decays <ul><li>Energy is given off as the strong nuclear forces work is done against strong nuclear forces </li></ul><ul><li>The energy is a result of the transformation of some of the mass in the nucleus to ENERGY </li></ul>
  39. 39. Energy Equivalent <ul><li>The energy equivalent of the missing mass of a nucleus is called the binding energy of the nucleus. </li></ul><ul><li>Nuclei with larger binding energies require more energy to break up the nucleus </li></ul><ul><li>Typical binding energies are large! </li></ul><ul><ul><li>For stable nuclei:  2.2 MeV to 1640 MeV </li></ul></ul>
  40. 40. Binding energy per nucleon <ul><li>The ratio of the total binding energy with the number of nucleons </li></ul><ul><li>Gives a way to characterize the stability of a particular nucleus </li></ul><ul><li>When the ratio is analyzed graphically, remarkable conclusions can be made </li></ul>
  41. 41. Two remarkable conclusions <ul><li>If a heavy nucleus were to be divided into two smaller nuclei, the binding energy per nucleon of the two smaller nuclei WILL BE LARGER! </li></ul><ul><li>If two lighter nuclei were to be joined together, the binding energy per nucleon of the heavier nucleus WILL BE LARGER </li></ul><ul><li>The ‘center’ point is the most stable element: Iron 56 </li></ul>
  42. 43. Fission/Fusion means CONfusion?!? <ul><li>Fission: (heavy elements) </li></ul><ul><li>separation of an atomic nucleus accompanied by a large release of ENERGY </li></ul><ul><li>Fusion: (light elements) </li></ul><ul><li>joining together of two small atomic nuclei accompanied by a large release of ENERGY </li></ul>
  43. 44. Binding energy to Nuclear Energy <ul><li>NUCLEAR ENERGY </li></ul><ul><ul><li>The binding energy per nucleon lead scientists to understand that changes in nuclear structure might be used to harness tremendous amounts of energy through </li></ul></ul><ul><ul><li>NUCLEAR FISSION </li></ul></ul><ul><ul><li>NUCLEAR FUSION </li></ul></ul>
  44. 45. Difficulties in harnessing nuclear energy <ul><li>The spontaneous chain reaction </li></ul><ul><ul><li>When a nucleus begins to decay, several neutrons may be released. </li></ul></ul><ul><ul><li>These neutrons can cause neighboring nuclei to begin decay </li></ul></ul><ul><li>This is GOOD, since it means that the decay reaction will continue </li></ul><ul><li>BUT, this causes difficulties due to the spontaneous nature—making the reaction difficult to control </li></ul>
  45. 46. Chain reaction
  46. 47. The Chain Reaction <ul><li>Too few neutrons: chain reaction ceases quickly </li></ul><ul><li>Too many neutrons: chain reaction is uncontrollable, the reaction becomes volatile </li></ul><ul><ul><li>Energy release causes an explosion </li></ul></ul><ul><ul><ul><li>This realization quickly led to the exploration of the use of nuclear energy for weapons </li></ul></ul></ul>
  47. 48. Nuclear Fission Reactor <ul><li>First reactor built by Enrico Fermi at University of Chicago </li></ul><ul><ul><li>in a squash court in the basement under an athletic field... </li></ul></ul><ul><li>Fermi discovered that the way to safely control the rate of the chain reaction was through the use of a MODERATOR element </li></ul><ul><ul><ul><li>carbon (graphite) rods </li></ul></ul></ul>
  48. 49. Historic anniversary <ul><li>December 2, 1942 </li></ul><ul><li>the first atomic reactor was brought to criticality by Dr. Enrico Fermi in Chicago Illinois. </li></ul>
  49. 50. KEY – 1 - : CRITICALITY <ul><li>Getting the chain reaction </li></ul><ul><ul><li>means that neutrons emitted by one U235 will cause another U235 atom to fission, and so on. </li></ul></ul><ul><li>A certain amount of mass is required in order for a CHAIN REACTION to occur </li></ul><ul><ul><li>CRITICAL MASS is the amount needed to sustain this reaction. </li></ul></ul>
  50. 51. KEY –2-: MODERATION <ul><li>The reaction must be ‘slowed down’ in order to fully exploit all the possible available nuclei </li></ul><ul><li>Slower neutrons increase the probability for the U atom fission. </li></ul><ul><li>There are several ways to moderate the chain reaction </li></ul><ul><ul><li>In Fermi’s reactor, graphite rods worked to SLOW DOWN the neutrons emitted. </li></ul></ul><ul><ul><li>In some modern reactors, water is used as the moderating medium </li></ul></ul>
  51. 52. Modern Nuclear Power Plants <ul><li>Most power plants use Uranium as the radioactive source </li></ul><ul><ul><ul><li>Uranium 238 atoms </li></ul></ul></ul><ul><li>The basic process uses the heat generated by the U decay to produce steam </li></ul><ul><ul><li>The steam is then used to turn turbines which produce electric energy </li></ul></ul>
  52. 54. Nuclear fuel <ul><li>Super heated water (enclosed) </li></ul>LAST, and VERY IMPORTANT is the COOLING of the whole system. This is the ONLY WATER THAT IS NOT COMPLETELY ENCLOSED. Usually comes from a nearby lake or river, recirculated back into the river… NUCLEAR DECAY PRODUCES HEAT ENCLOSED water circulates around fuel—gets HOTHOTHOT More ENCLOSED water is heated to boiling, producing steam, which turns a turbine—causing the coils of an ELECTRIC GENERATOR to rotate---remember Ampere’s law?
  53. 55. What about nuclear FUSION? <ul><li>Fusion reactions can release more energy than fission reactions </li></ul><ul><ul><li>For example: Our Sun! </li></ul></ul><ul><li>Three Issues </li></ul><ul><ul><li>HIGH temperature (>100 million  C) </li></ul></ul><ul><ul><li>High density of nuclei </li></ul></ul><ul><ul><li>Nuclei stability </li></ul></ul><ul><ul><ul><li>The nuclei must remain together long enough to make produce more energy than is required to fuse them </li></ul></ul></ul><ul><li>Achieving these three critical conditions is the quest of scientists around the world </li></ul>
  54. 56. Smaller pieces of matter <ul><li>Electrons Protons Neutrons </li></ul><ul><ul><li>Considered to be ‘elementary’ particles </li></ul></ul><ul><li>But, experiments have shown that nucleons can be divided into smaller particles called </li></ul><ul><li>QUARKS </li></ul><ul><li>In addition, scientists have discovered numerous other ‘pieces’ </li></ul><ul><ul><li>While these small bits of matter may not be relevant to the ordinary matter we deal with in our daily lives, they have led scientists to many discoveries about how nature works </li></ul></ul>
  55. 57. A word on ANTIMATTER <ul><li>Any ANTIMATTER particle has the </li></ul><ul><ul><li>Same mass as its ‘regular’ matter partner </li></ul></ul><ul><ul><li>OPPOSITE charge as its ‘regular’ matter partner </li></ul></ul><ul><li>For example: </li></ul><ul><ul><li>The antiparticle for the electron is called the positron </li></ul></ul><ul><ul><li>When an electron collides with a positron, gamma radiation is emitted WHILE THE MATTER UNDERGOES ANNIHILATION </li></ul></ul>
  56. 58. Fundamental Interactions <ul><li>By study of the fundamental interactions of the building blocks of matter, scientists have devel0ped a theory that describes the basic interactions of all matter </li></ul><ul><li>This theory is summarized in terms of four fundamental forces of nature </li></ul>
  57. 59. The Basic Four <ul><li>STRONG INTERACTION </li></ul><ul><ul><li>Holds nucleons together </li></ul></ul><ul><li>ELECTROMAGNETIC INTERACTION </li></ul><ul><ul><li>Produces electric and magnetic phenomenon </li></ul></ul><ul><li>WEAK INTERACTION </li></ul><ul><ul><li>Causes beta decay; helps determine nuclear composition </li></ul></ul><ul><li>GRAVITATIONAL INTERACTION </li></ul><ul><ul><li>Responsible for the attractive forces between all masses in the universe </li></ul></ul>
  58. 60. Unification <ul><li>The work of particle physicists and other scientists is to try to understand how these four fundamental forces might have, at one point in time, been unified into a single force of interaction for all matter in the universe. </li></ul>
  59. 61. Leptons and Hadrons <ul><li>Two broad categories for elementary particles </li></ul><ul><li>Affected by the strong interaction </li></ul><ul><li>Well defined sizes </li></ul><ul><li>Example: protons and neutrons </li></ul><ul><li>Not affected by strong interaction </li></ul><ul><li>Point particles </li></ul><ul><li>Example: electron, neutrino </li></ul>Hadrons Leptons
  60. 62. Six kinds of quarks <ul><li>The internal structure for hadrons! </li></ul><ul><li>Six types </li></ul><ul><ul><li>Up </li></ul></ul><ul><ul><li>Down </li></ul></ul><ul><ul><li>Top </li></ul></ul><ul><ul><li>Bottom </li></ul></ul><ul><ul><li>Charm </li></ul></ul><ul><ul><li>Spin </li></ul></ul><ul><li>Unlike any other particle, quarks can have a charge of less than e </li></ul><ul><ul><li>The charge of a quark is a fraction of e: 1/3e or 2/3e </li></ul></ul>
  61. 63. Let’s sum it up <ul><li>Hadrons are made from leptons </li></ul><ul><ul><li>ONLY 6 different leptons </li></ul></ul><ul><li>6 quarks, 6 leptons, SYMMETRY </li></ul><ul><ul><li>as expected VERY SIMPLE </li></ul></ul><ul><li>Each particle has an ANTIMATTER partner... </li></ul>
  62. 64. In-Lecture Quiz Questions Chapter 7
  63. 65. In-Lecture QUIZ CHAPTER 7 <ul><li>Longer half life means ____________decay rate </li></ul><ul><li>A. faster </li></ul><ul><li>B. slower </li></ul>
  64. 66. In-Lecture QUIZ CHAPTER 7 <ul><li>T/F Nuclear weapons are based on the idea of nuclear fusion. </li></ul>
  65. 67. In-Lecture QUIZ CHAPTER 7 <ul><li>Write down two types of nuclear reactors commonly used to produce electric energy. </li></ul>
  66. 68. In-Lecture QUIZ CHAPTER 7 <ul><li>What causes radioactivity? </li></ul><ul><ul><li>A. Some atomic nuclei spontaneously collide and cause an explosion, emitting high energy particles or rays </li></ul></ul><ul><ul><li>B. When atomic nuclei are large, they spontaneously decay, emitting high energy particles or rays </li></ul></ul><ul><ul><li>C. When atomic nuclei are small, they sometimes bump into each other, emitting high energy particles or rays </li></ul></ul>
  67. 69. In-Lecture QUIZ CHAPTER 7 <ul><li>What are the three types of radioactive emission? </li></ul><ul><ul><li>A. Alpha, Beta, Tau </li></ul></ul><ul><ul><li>B. Alpha, Beta, Gamma </li></ul></ul><ul><ul><li>C. Delta, Omega, Zeta </li></ul></ul>
  68. 70. In-Lecture QUIZ CHAPTER 7 <ul><li>Which types of emission result in a daughter nucleus that is a different element than the ‘parent’? </li></ul><ul><ul><li>A. Only Gamma </li></ul></ul><ul><ul><li>B. Only Alpha and Beta </li></ul></ul><ul><ul><li>C. All emissions (alpha, beta, and gamma) </li></ul></ul>
  69. 71. In-Lecture QUIZ CHAPTER 7 <ul><li>The antimatter partner for every particle is identical except that it has opposite_____. </li></ul><ul><li>A. weight </li></ul><ul><li>B. force </li></ul><ul><li>C. mass </li></ul><ul><li>D. charge </li></ul>
  70. 72. In-Lecture QUIZ CHAPTER 7 <ul><li>(short essay) Why is the binding energy per nucleon such an important result? </li></ul>
  71. 73. In-Lecture QUIZ CHAPTER 7 <ul><li>The most prevalent source of radiation in the average lifetime is due to: </li></ul><ul><li>A. dental x-rays </li></ul><ul><li>B. natural background radiation </li></ul><ul><li>C. flying at high altitudes </li></ul><ul><li>D. living next door to a nuclear power plant </li></ul>
  72. 74. In-Lecture QUIZ CHAPTER 7 <ul><li>The atomic mass unit is defined as being approximately equal to </li></ul><ul><ul><li>A. The mass of a helium atom </li></ul></ul><ul><ul><li>B. The mass of a carbon nucleus </li></ul></ul><ul><ul><li>C. The mass of a silicon atom </li></ul></ul><ul><ul><li>D. The mass of a hydrogen atom </li></ul></ul>
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