Page 1 12/25/2015 SCE 4350: Nuclear Science Nuclear Science Major Points of the Lesson: The Nucleus –Nucleons (A) = Protons (Z) + Neutrons (N) –Number of protons & neutrons in nucleus is limited. Radioactivity is the result of nuclear decay via emission of “radiation” (α or β particles,  rays, etc.) producing a more stable element. Half-Life (2 n exponential decay) Isotopes known nuclei, but only 266 stable ones! – medical applications Natural radioactivity > At. No. 83 Fusion (Joining) v. Fission (Splitting) of Atoms – both release energy.

Page 2 12/25/2015 SCE 4350: Nuclear Science Nucleus: Particle Composition Z protons + N neutrons = A nucleons With a 1 →10 fm diam., f = “femto” = : Ernest Rutherford –Bombarded gold (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 12/25/2015 SCE 4350: Nuclear Science Today, we know Particle Charge Mass (amu) Proton Neutron Electron –  Alpha (α) particle is identical to helium nucleus. It has 2 protons and 2 neutrons, mass number of 4 and atomic number of 2.  Beta (β) particle is a high-energy electron. It has a negative charge and mass number of 0.  Gamma (γ) rays are high-energy radiation, like X-rays. They contain no mass or charge, only energy. Wavelength, λ = to m.

Page 4 12/25/2015 SCE 4350: Nuclear Science Nuclear Shielding: 1.Thick paper stops Alpha. 2.A sheet of Aluminum can stop Beta. 3.A slab of Lead stops Gamma.

Page 5 12/25/2015 SCE 4350: Nuclear Science 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 6 12/25/2015 SCE 4350: Nuclear Science Radioactive Decay Examples = +

Page 7 12/25/2015 SCE 4350: Nuclear Science Alpha Emitters Note: An Alpha particle has the same structure as a Helium nucleus.

Page 8 12/25/2015 SCE 4350: Nuclear Science Beta Emitters Note: During Beta Decay, a Neutron spontaneously changes to a Proton.

Page 9 12/25/2015 SCE 4350: Nuclear Science 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 10 12/25/2015 SCE 4350: Nuclear Science A stable atom can be bombarded with fast-moving  particles.

Page 11 12/25/2015 SCE 4350: Nuclear Science 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.

Page 12 12/25/2015 SCE 4350: Nuclear Science Note: Chart displays average values of doses from common sources. a basements of buildings

Page 13 12/25/2015 SCE 4350: Nuclear Science Radioactivity Exposure

Page 14 12/25/2015 SCE 4350: Nuclear Science 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 15 12/25/2015 SCE 4350: Nuclear Science Note: Chart displays average values of half-life for an isotope. A = A o 2 -n A o = original amount A = final amount n = number of half-lives

Page 16 12/25/2015 SCE 4350: Nuclear Science Chart based on individual isotopes, with average half-life estimates. Radio-Isotopes Used in Medicine

Page 17 12/25/2015 SCE 4350: Nuclear Science 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 18 12/25/2015 SCE 4350: Nuclear Science

Page 19 12/25/2015 SCE 4350: Nuclear Science A Nuclear Fission Reaction MeV Unstable More Unstable

Page 20 12/25/2015 SCE 4350: Nuclear Science

Page 21 12/25/2015 SCE 4350: Nuclear Science Chain Reaction: A Chain Reaction Uranium 235, struck with a neutron, and split into Krypton and Barium

Page 22 12/25/2015 SCE 4350: Nuclear Science  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 23 12/25/2015 SCE 4350: Nuclear Science NUCLEAR FUSION : Joining atoms. 1 H H 3 2 He n MeV

Page 24 12/25/2015 SCE 4350: Nuclear Science 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 25 12/25/2015 SCE 4350: Nuclear Science ( A Nuclear Reactor Used to Boil Water for a Steam Turbine

Page 26 12/25/2015 SCE 4350: Nuclear Science A Nuclear Reactor Used to Generate Electricity

Page 27 12/25/2015 SCE 4350: Nuclear Science Nuclear Accident: Chernobl. 1. Steam Explosion. 3. Containment held. 2. Partial Meltdown.

Page 28 12/25/2015 SCE 4350: Nuclear Science Particle detectors: 1. Photographic Film. 2. Scintillation Screen. 3. Gieger-Muller Tube. 4. Cloud Chamber. 5. Bubble Chamber.

Page 29 12/25/2015 SCE 4350: Nuclear Science Thank you for your attention. Any questions/comments? Take a Quiz.