Chapter 5 The Atomic Nucleus Lecture Presentation Chapter 5 The Atomic Nucleus Bradley Sieve Northern Kentucky University Highland Heights, KY

5.1 Radioactivity Results from Unstable Nuclei Due to the ratio of protons to neutrons Unstable Nuclei Contains an “off-balance” ratio of protons and neutrons Transforms the nucleus to a more stable composition

5.1 Radioactivity Results from Unstable Nuclei Radioactive Materials Material containing unstable nuclei Radioactivity Emitted high-energy particles and radiation from unstable nuclei Radioactive Decay Process of emitting radioactivity

5.1 Radioactivity Results from Unstable Nuclei Three types of radiation are emitted Alpha (α) Alpha particles carry a positive electric charge Beta (β) Beta particles carry a negative electric charge Gamma (γ) Gamma particles carry no electric charge

5.1 Radioactivity Results from Unstable Nuclei

5.1 Radioactivity Results from Unstable Nuclei Alpha Radiation Releases a stream of alpha particles Alpha Particle Contains two protons and two neutrons The same as a helium nuclei Low penetrating power due to large mass (2 a.m.u.) and double positive charge (+2)

5.1 Radioactivity Results from Unstable Nuclei Beta Radiation Releases a stream of beta particles Beta Particle Is simply an electron ejected Medium-range penetrating power with small mass and a single negative charge

5.1 Radioactivity Results from Unstable Nuclei Gamma Radiation High-frequency electromagnetic radiation Gamma Particle Is pure energy Highest penetrating power as there is no mass or charge with the particle

5.1 Radioactivity Results from Unstable Nuclei

5.1 Radioactivity Results from Unstable Nuclei

5.2 Radioactivity Is a Natural Phenomenon Radioactivity has always been present Contained in soil, air, the earth’s core Most radiation is natural background radiation 81% natural sources 15% medical and diagnostic sources 4% consumer products

5.2 Radioactivity Is a Natural Phenomenon

5.2 Radioactivity Is a Natural Phenomenon Radon-222 Is a common source of radiation Arises from uranium rocks Can collect in basements to unsafe levels

5.2 Radioactivity Is a Natural Phenomenon Mutations Alterations in genetic information contained in our cells Normally harmless but may cause conditions such as many types of cancer May be passed on to offspring if damage is in a person’s reproductive cells

5.2 Radioactivity Is a Natural Phenomenon Rems are units of radiation Units measure the ability of radiation to cause harm Lethal doses of radiation begin at 500 rems Often measured as millirems

5.2 Radioactivity Is a Natural Phenomenon Radioactive Tracers Allow molecules to be traced due to radiation Generally act the same as nonradioactive molecules

5.2 Radioactivity Is a Natural Phenomenon Medical Imaging Isotopes used for the diagnosis of internal disorders Tracer path not influenced by radioactive properties

5.2 Radioactivity Is a Natural Phenomenon

5.3 Radioactivity Results from an Imbalance of Forces Strong nuclear force Very strong force between nucleons Only effects very short distances Repulsive electric forces effect over relatively long-ranges

5.3 Radioactivity Results from an Imbalance of Forces Protons far apart may experience stronger repulsive force than the attractive strong nuclear force

5.3 Radioactivity Results from an Imbalance of Forces

Concept Check Two protons in the atomic nucleus repel each other, but they are also attracted to each other. Why?

Concept Check While two protons repel each other by the electric force, they also attract each other by the strong nuclear force. These forces act simultaneously.

5.3 Radioactivity Results from an Imbalance of Forces Neutrons act as the “nuclear cement” Neutrons feel attraction but not repulsion because they do not have a charge

5.3 Radioactivity Results from an Imbalance of Forces Neutrons can decay to a proton and an electron This will destabilize the nucleus by increasing the number of protons

5.4 Radioactive Elements Transmute to Different Elements Transmutation Changing of one element to another uranium transmuting into thorium

5.4 Radioactive Elements Transmute to Different Elements Nuclear Equation Mass numbers at the top balance Atomic numbers at the bottom also balance

5.4 Radioactive Elements Transmute to Different Elements Radioactive particle notations

5.4 Radioactive Elements Transmute to Different Elements Changes in atomic number by each type of particle release Alpha: decrease by two Beta: increase by one

5.4 Radioactive Elements Transmute to Different Elements U-238 decays to Pb-206 through a series of alpha and beta decays

5.5 The Shorter the Half-Life, the Greater the Radioactivity Radioactive isotopes decay at different rates Decay rate is measured as an element’s half-life Half-life is defined as the time required for half of the radioactive atoms to decay

5.5 The Shorter the Half-Life, the Greater the Radioactivity

5.6 Isotopic Dating Measures the Ages of Materials N-14 is converted to C-14 in the atmosphere C-14 is incorporated into plant life through photosynthesis Animals also ingest C-14 by eating plants

5.6 Isotopic Dating Measures the Ages of Materials C-14 decays back to C-12 over time Plants replenish C-14 while growing to maintain a constant amount Once plant dies, amount of C-14 decreases

5.6 Isotopic Dating Measures the Ages of Materials Carbon-14 Dating Used to calculate the age of carbon-containing artifacts Half of the C-14 decays in about 5730 years Exhibits roughly a 15% error rate

5.7 Nuclear Fission—The Splitting of Atomic Nuclei Splitting a large nucleus into smaller halves Releases enormous amounts of energy

5.7 Nuclear Fission—The Splitting of Atomic Nuclei Chain Reaction When a product of one reaction begins the next reaction Neutrons propagate the chain reaction for U-235

5.7 Nuclear Fission—The Splitting of Atomic Nuclei Nuclear Fission Reactors Produces electrical energy from nuclear reactions 1 kg of U yields more energy than 30 freight-car loads of coal

5.7 Nuclear Fission—The Splitting of Atomic Nuclei Major components of a fission reactor Nuclear fuel U-238 mostly with about 3% U-235 Control rods Neutron-absorbing material Moderator Slows the velocity of the neutrons Liquid Transfers the heat from the reactor

5.7 Nuclear Fission—The Splitting of Atomic Nuclei Radioactive Waste By-products of nuclear reactions Half-lives range from short to thousands of years Disposal of waste is problematic

5.8 The Mass-Energy Relationship. E=mc2 Albert Einstein Postulated that mass and energy are two sides of the same coin E=mc2 E = energy m = mass c = speed of light

5.8 The Mass-Energy Relationship. E=mc2 Variation of average mass based on the nucleus that contains it Nucleons lose mass in their transition from uranium to a smaller fragment

5.9 Nuclear Fusion—The Combining of Atomic Nuclei Combining two light nuclei to form a larger nucleus Mass is lost during the fusion process Lost mass is released as energy

5.9 Nuclear Fusion—The Combining of Atomic Nuclei Thermonuclear Fusion Fusion brought about by high temperatures Can be initiated by a fission reaction

5.9 Nuclear Fusion—The Combining of Atomic Nuclei Controlling fusion can be done using plasmas Magnetic straitjacket for hot ionized gases Currently no commercial fusion power plants in use