The Age of the Solar System

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Physics, Engineering Physics and Astronomy
ASTR 101

The Age of the Solar System • Natural Radioactive Decay: Elements are naturally radioactive meaning they break down into other elements over time (Emit gamma, alpha and beta rays in the process)  Example: Uranium decays into the daughter product, Lead at a specific rate over time  Acts as a precise clock known as a chronometer  Fundamental process of geochronology  Analogy: A farmer moves cows to a new field every few weeks and forgets when he should next move them  If the field has lots of manure, it indicates the cows have been there for awhile  Must understand process that eliminate manure from the field (rain) to make a correct calculation of how long the cows have been there Atoms: • Atoms contain a massive central nucleus (like the Sun in the Solar System), composed of protons (+) and neutrons (neutral charge)  Electrons orbit the nucleus and are less massive (like Planets) and there are usually as many electrons as protons to balance the charge  Electrons are negatively charged and 2000 times smaller than protons • Atomic Number: number of protons in the nucleus which determines the type of element  Hydrogen = 1, Helium = 2 • Atomic Mass: number of protons and neutrons in the nucleus Isotopes: • Given elements can exist in many different forms known as isotopes  The number of protons must always stay the same (otherwise the element changes since # of protons = atomic number), however the number of neutrons changes  Isotopes cause a change in the mass of an atom  Example: Hydrogen exists with one proton and no neutrons, however there is an isotope with 1 proton and 1 neutron, which doubles the mass  Known as heavy hydrogen or deuterium  Hydrogen isotopes with 1 proton and 2 neutrons are radioactive and are used in atomic weapons • Heavy Water: When deuterium replaces the hydrogen in water molecules, heavy water is formed  Nuclear interaction with heavy water is very different than normal water, which is why heavy water is a principle component of regulating nuclear reactors (controls reaction rates)  Heavy water is also useful at detecting neutrinos • Limitations to Isotopes: Lighter elements typically have as many protons as neutrons whereas heavy elements have more protons than neutrons  Elements are restricted to a small amount of isotopic forms as there are a limited amount of variations that produce stable atoms Radioactivity: • Radioactivity is the process under which the nucleus can change spontaneously from one element to another by losing an electron from the nucleus  Neutrons in the nucleus become protons and therefore must lose an electron (ejects a β particle) OR it ejects 2 protons and 2 neutrons (ejects an α-particle)  Electrons that are lost are known as β-particles  α-particles are more massive than β-particles and travel slower (α- particles are composed of 2 protons and 2 neutrons, which form helium gas when trapped as they are helium nuclei)  Most helium found on Earth was a result of radioactive decay  Causes the nucleus to transmute into another element  Radioactive decay sometimes also emits neutrinos: lightweight particles with no charge • α-Particles can only travel a few centimeters in air  Often "smash into other atoms" and cause ionization, thus releasing gamma  Damages DNA if inhaled or ingested (α cannot pass through our skin) • β-Particles can penetrate much farther and are used in medicine • γ-Waves are also emitted and are extremely energetic and can pass right through our body  Radioactive substances produce heat and can therefore produce power  Can be used in radioactive therapy to kill cancer OR can be bad and cause cancer Decay I
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