Nuclear Reactions & Decay

Nuclear Reactions & Decay CPS Chemistry Ch.22

Nuclear Binding Energy A nucleus is stable if it has a certain ratio of neutrons to protons. It becomes unstable if the ratio is below 1 proton to 1 neutron, or is higher than 1.5 neutrons to 1 proton Remember, the protons are positive charges, that left alone would repel each other. The neutrons are the “rubber bands” that hold the nucleus together

Band of stability

Nuclear Reactions • Unstable nuclei undergo spontaneous changes that will alter the number of protons and/or neutrons – in doing so, this process gives off energy • Mass must be conserved and accounted for

212 Po 84 Nuclear Reactions cont. Atomic Mass PTE Abbreviation Atomic Number

212 Po 84 Nuclear Reaction cont. The total atomic mass on the right must equal the atomic mass on the left 4 He Pb + 2 The total atomic number on the right must equal the atomic number on the left

212 Po 84 Nuclear Reaction cont. The total atomic mass on the right must equal the atomic mass on the left 4 208 He Pb + 2 82 The total atomic number on the right must equal the atomic number on the left

234 U 92 Nuclear Reaction cont. The total atomic mass on the right must equal the atomic mass on the left 4 He + 2 The total atomic number on the right must equal the atomic number on the left

234 U 92 Nuclear Reaction cont. The total atomic mass on the right must equal the atomic mass on the left 4 230 Th He + 2 90 The total atomic number on the right must equal the atomic number on the left

212 Po 84 Radioactive Decay • Alpha Particle (α) is two protons and two neutrons bound together and is emitted from the nucleus during some kinds of radioactive decay • Alpha emission is limited to very heavy nuclei 4 208 He Pb + 2 82

14 14 0 C N β + 6 7 -1 Radioactive Decay • Beta emission occurs when there are too many neutrons in a nucleus. The neutron can be split into a proton and an electron, or beta particle, (β)

38 38 0 K Ar β + 19 18 +1 Radioactive Decay • Positron emission – when there are too many protons, protons can be converted into a neutron by emitting a positron • Positrons are particles with the same mass as an electron, but have a positive charge

106 Ag 47 0 106 e Pd + -1 48 Radioactive Decay • Electron Capture – If a nucleus “captures” a electron from one of its inner orbitals, it combines with a proton to form a neutron

Radioactive Decay • Gamma Emission – different from the other types of radioactive decay because it is NOT an emission of particles, but an emission of high energy electromagnetic waves

Half-Life Since radioactive decay happens over time, we use half-life as a measure for the time it takes ½ of the original sample to decay into new particles

Half-Life Example March Madness (Basketball) If you count only the days games are played, than every 2 days the number of teams is cut in half 64 teams32168421 6 half lives

Half Life

Half-Life • How long will it take for there to be 7.8 grams of a sample of radioactive iodine, needed for medical testing, if the half-life is 14 days and the original sample is 1 kilogram? Hint: first start by converting to grams…

Half-life

Nuclear Fission • Heavy nuclei split into more stable, lighter nuclei and neutrons while releasing energy.

Nuclear Fusion • The process where lighter nuclei combine to form heavier nuclei

Nuclear power plants • Run on uranium fuel. • In the reactor, uranium atoms are split through a process known as fission. • When atoms are spilt, they produce a large amount of energy that is then converted to heat. • The heat boils water, creating steam that is used to turn turbines, which spins the shaft of a generator.

Schematic of a Nuclear Power Plant

Inside the generator • coils of wire spin in a magnetic field and electricity is produced. • Nuclear power plants in the United States use two types of reactors to achieve this process: boiling water reactors and pressurized water reactors.

How a Nuclear Power Plant Works • http://www.youtube.com/watch?v=cnjGYHOePu0

Nuclear Reactions & Decay