NUCLEAR DECAY REACTIONS & EQUATIONS NUCLEAR REACTIONS…
•Chemical reactions – gain/loss/share of electrons •Nuclear reactions – change of nuclei •Changes in protons and neutrons CHEMICAL, NUCLEAR OR PHYSICAL? • 2 HCl + CaCO 3 CaCl 2 + H 2O + CO 2 Chemical • H2O (g) H2O (l) Physical • ͦͧͩ ͦͧͥ ͨ ͭͦ U ͭͤ Th + ͦα Nuclear •C (graphite) C (diamond) Physical • HNO 3 + Zn ZnNO 3 + H 2 Chemical • ͥͨ ͤ ͥͨ ͪ C ͯͥβ + ͫ N Nuclear TRANSMUTATION •Transmutation – the conversion of an atom of one element to the atom of another element •Induced transmutation – striking nuclei with high velocity particles •Can occur from: • Radioactive decay • Particles bombarding the nucleus of an atom TRANSMUTATION TRANSURANIUM •All elements above atomic number 82 are radioactive
• Transuranium elements - The elements in the periodic table with atomic numbers above 92, the atomic number of uranium • All transuranium elements undergo transmutation. • None of the transuranium elements occur in nature, and all are radioactive. NUCLEI AND DECAY
• More than 1,500 different nuclei are known. • 264 are stable and do not decay or change with time. • In a region called the band of stability. WHY DECAY?? •The neutron to proton ratio determines the decay that will occur.
•Too many neutrons to protons – beta emission • Increases protons
•Too many neutrons and protons – alpha emission • Decreases protons and neutrons BETA DECAY • Above the band of stability • Too many neutrons to protons • INCREASES NUMBER OF PROTONS!! • Beta particle = fast moving electron that is emitted when a neutron converts into a proton • n p + β ͤ • - β or e = ͯͥ • ALPHA DECAY • Very heavy nuclei • Too many neutrons and protons • DECREASES PROTONS AND NEUTRONS! • Alpha Particle = Helium Nuclei • ͨ α = ͦ He
• GAMMA EMISSION
• The emission of gamma radiation from a nucleus does not involve any change in the atomic (proton) number or mass number. • When a 'new' nucleus is formed it tends to have excess energy making it potentially unstable. • To become more 'nuclear stable' the nucleus loses some energy as a burst of gamma radiation but the proton and neutron numbers do not change. SUMMARY OF DECAY PROCESSES RADIOACTIVE DECAY SERIES
• Radioactive decay series – series of nuclear reactions that begins with an unstable nucleus and results in the formation of a stable nucleus NUCLEAR EQUATIONS
•Nuclear reactions (alpha decay, beta decay, positron emission, and electron capture) are all expressed by balanced nuclear equations.
•Mass numbers and charges are conserved!! NUCLEAR EQUATIONS
• Plutonium-238 undergoes alpha decay and forms an unknown product. ͦͧͬ ͨ ͭͨ Pu X + ͦ He • What is the unknown product? (X) • Find the mass: 238 = A + 4 A = 234 • Find the atomic number: 94 = Z + 2 Z = 92 • ͦͧͨ Unknown product: ͭͦ U NUCLEAR EQUATIONS
• Write a balanced nuclear equation for the reaction in which oxygen-15 undergoes positron emission. • ͥͩ ͤ ͥͩ ͬ O ͥ β + ͫ N
• What type of decay occurs when thorium-229 decays to form radium-225? • Alpha Decay
• ͦͦͭ ͦͦͩ ͨ ͭͤ Th ͬͬ Ra + ͦ He