Page 1 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Ch. 30: Nuclear Physics Nucleus –Nucleons (A) = Protons (Z) + Neutrons (N) –Mass and Atomic Numbers –Number of protons & neutrons in nucleus is limited. Radioactivity is the decay of nuclei to more stable element via emission of “radiation” (α or β particles,  rays, etc.). Half-Life (2 n exponential decay) Isotopes known nuclei, but only 266 stable ones! Radioactive Processes – α, β, and γ-rays –Natural radioactivity > At. No. 83 –Fusion (Joining) v. Fission (Splitting) of Atoms – both release energy.

Page 2 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Nucleus: Particle Composition Z protons + N neutrons = A nucleons (1 – 10 fm diam.). 1920: Ernest Rutherford –Bombarded Au foil with Alpha particles –Most of atom is empty space with massive + charged nucleus. 1932: James Chadwick discovered neutron (bombarded Be with α). Isotope: same Z (# protons), different N (# neutrons). – 15 O and 16 O … or … 12 C and 14 C … or … 238 U and 235 U …

Page 3 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) The Atom: Particle Properties ParticleCharge amu kg Proton+1.6x x Neutron ~1.67x Electron–1.6x × x Recall the 4 Models: 1.Single Indivisible Particle 2.Plum-Pudding 3.Planetary 4.Planetary-Quantum (Bohr Model)

Page 4 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Nuclear mass is slightly less than mass of constituent protons and neutrons due to nuclear binding energy. Mass is converted to energy when a nucleus is formed, E = mc 2. Nucleus: Binding Energy Binding energy per nucleon peaks at A = 56 (~8 MeV/nucleon) and slowly decreases. Energy is released when a heavy nucleus (A~200) fissions into lighter nuclei near A~60. Nucleon Number A Binding Energy / Nucleon ( MeV) Peaks at Fe (A = 56) Fission (A ~ 200)

Page 5 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Radioactivity: Historical Overview 1896: Becquerel accidentally discovered that a mysterious rock emitted invisible radiation onto a photographic plate. 1898: Marie and Pierre Curie discovered polonium (Z=84) and radium (Z = 88), two new radioactive elements. 1903: Becquerel and the Curie’s received the Nobel prize in physics for radioactive studies. 1911: Marie Curie received a 2 nd Nobel prize (in chemistry) for discovery of polonium and radium. 1938: Hahn (1944 Nobel prize) and Strassmann discovered nuclear fission - Lisa Meitner played a key role! 1938: Enrico Fermi received the Nobel prize in physics for producing new radioactive elements via neutron irradiation, and work with nuclear reactions.

Page 6 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Antoine Henri Becquerel 1/2 of the prize (France) The Nobel Prize in Physics 1903 "in recognition of the extraordinary services he has rendered by his discovery of spontaneous radioactivity" "in recognition of the extraordinary services they have rendered by their joint researches on the radiation phenomena discovered by Professor Henri Becquerel" Pierre Curie France 1/4 of the prize Marie Curie France 1/4 of the prize Contributors to the Study of Nuclear Physics

Page 7 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Recall: Nuclear Physics.

Page 8 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Radioactive Decay Examples = +

Page 9 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Types of Nuclear Radiation  ALPHA (  ) PARTICLE is identical to helium nucleus. It has 2 protons and 2 neutrons, mass number of 4 and atomic number of 2.  BETA (  ) PARTICLE is a high-energy Electron. It has a negative charge and mass number of 0.  GAMMA (  ) RAYS are high-energy radiation, like X-rays. They contain no mass or charge, only energy. λ = to m

Page 10 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Alpha Emitters Note: An Alpha particle has the same structure as a Helium nucleus.

Page 11 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Alpha Emitters:  226 Ra  ? He  First, let’s figure out the identity of the new nucleus. How? Determine the atomic number: 88 – 2 = 86. The new element is Rn.  Next, figure out the mass number of the new nucleus: 226 – 4 = 222.  Ra  Rn He 88

Page 12 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Beta Emitters Note: During Beta Decay, a Neutron spontaneously changes to a Proton.

Page 13 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Beta Emitters 14 6 C  X e To find the new mass # we take 14-0 = 14 To find the new atomic # we take 6+1 = 7 The element with atomic number 7 is Nitrogen 14 6 C  14 7 N e

Page 14 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Producing Radioactive Isotopes:  TRANSMUTATION is the process of changing one element into another (can be via bombardment OR emission of radiation).  This can be natural or artificial.  A stable atom can be bombarded with fast- moving  particles, protons, or neutrons.  A radioactive isotope is called a RADIOISOTOPE.

Page 15 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) A stable atom can be bombarded with fast-moving  particles.

Page 16 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Radiation Exposure:  BACKGROUND RADIATION is the radiation that is in the environment.  Background radiation can come from food, building materials, cosmic rays, etc.  The air molecules in the atmosphere block out some cosmic rays.

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Page 18 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Radiation Exposure:  Radiation sickness from too much radiation. Nausea, vertigo, and fatigue (side effects of chemotherapy). More exposure can lead to death.  Exposure is measured by LD 50 or lethal dose that is expected to cause death in 50% of the people receiving that dose.  To minimize problems, workers often wear badges to monitor the maximum permissible dose.

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Page 20 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Note: Chart displays average values of doses for common isotopes. a basements of buildings

Page 21 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Radioactivity

Page 22 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Half-Life:  The HALF-LIFE of a radioisotope is the amount of time it takes for half of the sample to decay.  A DECAY CURVE is a graph of the decay of a radioisotope (amount vs. time).  Some radioisotopes have long half-lives. For other radioisotopes, the half-life can be short.

Page 23 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Note: Chart displays average values of half-life for common isotopes. A( T ) = A o 2 -T/t T/t = n, number of half-lives

Page 24 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Note: Chart displays average values of half-life for common isotopes.

Page 25 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Chart based on individual isotopes, with average half-life estimates. Radio-Isotopes Used in Medicine

Page 26 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Fission and Fusion:  FISSION is splitting a big atom into two smaller atoms by bombarding with neutrons.  Energy is released according to Einstein’s equation: E = mc 2. E is energy, m is mass, c is speed of light.  The fission process can continue until all of the available “big atoms” are gone. This is a CHAIN REACTION.

Page 27 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) A Nuclear Fission Reaction MeV Unstable More Unstable

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Page 29 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Chain Reaction: A Chain Reaction Uranium 235, struck with a neutron, and split into Krypton and Barium

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Page 31 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Fission and Fusion:  FUSION is the combining of two small atoms into one bigger atom with release of energy.  More energy is released than fission.  Occurs continuously in the sun and stars  Requires temperature of 100,000,000  C  Problem to reach and maintain this temp  Good source of future energy – lots of H in ocean  Waste products decay much faster than fission

Page 32 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) NUCLEAR FUSION : Joining atoms. 1 H H 3 2 He n MeV

Page 33 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Nuclear Power:  This is a fission reaction. Mass of uranium is kept small and CONTROL RODS absorb neutrons to prevent chain reaction.  Problems are: Public perception Security Hazardous radioactive waste that has half-life of thousands of years * storage 2150 ft underground in NM  10% of power in US from nuclear power

Page 34 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) ( A Nuclear Reactor Used to Boil Water for a Steam Turbine

Page 35 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) A Nuclear Reactor Used to Generate Electricity

Page 36 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) What Happened at Chernobl. 1. Steam Explosion. 3. Containment held. 2. Partial Meltdown.

Page 37 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Radioactivity: Overview of Units Activity:Becquerel (Bq) = 1 decay / s 1 curie (Ci) = 3.7×10 10 decays / s (or Bq) (disintegration rate of 1g of radium) Ion Dose: Ionizing behavior of radiation is most damaging to us! Roentgen = 2.6×10 –4 C/ kg air (or J/kg) Energy Dose:rad = 0.01 J/kg Energy Dose for Human Health Considerations: rem = # rads × quality factor (  = 10 and  = 1) Dosages: 0.5 rem / yr = natural background 5 rem / yr = limit for nuclear power plant workers 500 rem = LD 50 (50% die within a month) 750 rem = fatal dose (5000 rem = fatal within 1 week)

Page 38 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Particle detectors: 1. Photographic Film. 2. Scintillation Screen. 3. Gieger-Muller Tube. 4. Cloud Chamber. 5. Bubble Chamber.

Page 39 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) The Nobel Prize in Physics 1939 Awarded to E.O. Lawrence, Univ. of California, Berkeley "for the invention and development of the Cyclotron and for results obtained with it, especially with regard to artificial radioactive elements"

Page 40 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) The Linear Accelerator was invented by John Cockcroft and E. T. S. Walton at the Cavendish Laboratory, Cambridge, England, in the late 1920s

Page 41 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Known Elementary Particles ParticleSymbolChargeMass (amu) Protonp, 1 H Neutronn Electron -1 e 0, β - 0 Alpha 2 He 4, α Positron +1 e 0, β Neutrinoυ00 Quark,+2/3, -1/30 u d

Page 42 1/4/2016 5:42 PMPhys Hon Nuclear Physics (Ch.30) Note: The neutron differs from a proton only by “d”  “u” quark replacement! The Discovery of Quarks! u Charge Q Mass +2/3-1/3 ~5 [MeV/c 2 ]~10 [MeV/c 2 ] Quarkupdown d u u d Proton Q = +1 M=938 MeV/c 2 d u d Neutron Q = 0 M=940 MeV/c 2 The Building Blocks of Protons and Neutrons.