A material is ___________ if it spontaneously emits energy to become more stable ________ is the energy or particles emitted from a nucleus by a radioactive atom _________ refers to the particles contained in the nucleus: protons and neutrons. So, the Mass Number is equal to the nucleon number. A ____________ is the radioactive atom of an element Natural Radioactivity The symbols are still the same… Mass number (protons and neutrons) Element Atomic number (protons) I 135 53
Types of Radiation • Alpha () an alpha particle contains 2 protons and 2 neutrons • mass number = 4 • atomic number = 2 • or 2He Alpha particle • Beta () a beta particle is a high-energy electron. It has a charge = -1. Because the mass of an electron compared to a proton is so small, is given a mass number of 0. It is produced by a neutron transforming into a proton and a (high energy) electron. • mass number = 0 • atomic number = -1 • Beta particleor -1e 4 0 Gamma () a gamma ray is high-energy radiation. It is released as an unstable nucleus, which rearranges to a more stable, lower energy nucleus. There is no mass or charge or symbol associated with this type of radiation. Energy only! Gamma Ray
Radiation Protection ______________ is a device used to measure radiation. It consists of a metal tube filled with a gas (Ar). In the presence of radiation, the gas produces an electrical current. This current is amplified to give a “click” and hence a readout on a meter.
Nuclear Equations… alpha emitters Radioactive decay is the process of a nucleus spontaneously breaking down by emitting radiation We can represent this event with a nuclear equation Radioactive nucleus new nucleus + radiation (,,,+)
Nuclear Equations Guide to completing a nuclear equation…. Turn it into a simple math problem! 1. Account for all the mass: 238 = 234 + 4 2. Account for the atomic number: 92 = 90 + 2 Example… 88Ra ? + 2He 1. Account for all the mass: 2. Account for the atomic number: Therefore… 4 226
Sample Problem Complete the following nuclear equation for the decay of americium-241: 95 Am ? +2He 4 241 Answer Determine the missing mass number… Determine the missing atomic number… Determine the symbol of the nucleus… Complete the nuclear equation…
Nuclear Equations… beta emitters Radioactive nucleus new nucleus + radiation (,,,+) Turn it into a simple math problem! 1. Account for all the mass: 14 = 14 + 0 2. Account for the atomic number: 6 = 7 + -1
Sample Problem Cobalt-60 decays by emitting a beta particle. Write the nuclear equation for its decay. Answer Write the incomplete nuclear equation… Determine the missing mass number… Determine the missing atomic number… Determine the symbol of the nucleus… Complete the nuclear equation…
Half-Life The half-life of a radioisotope is the amount of time it takes for one-half of a sample to decay 20 g 131I 1 half-life 10 g 131I 2 half-lives 5 g 131I
Half-Life A decay curve is a diagram of the decay of a radioactive isotope
Sample Problem Phosphorus-32, a radioisotope used in the treatment of leukemia, has a half-life of 14 days. If a sample contains 8.0 g of phosphorus-32, how many grams of phosphorus-32 remain after 42 days? Answer How many half-lives if 42 days? 1. Write the equality: 2. Treat the problem like any other with a conversion-factor! 3. Determine how much sample decays and how much remains….
Nuclear Fission Fission is…. The process in which large nuclei are split into smaller pieces, releasing large amounts of energy 0n + 92U 36Kr + 56Ba + 3 0n + E Where E = mc2 E = Energy Released m = mass lost c = speed of light = 3 x 108 m/s Chain Reaction is a fission reaction that will continue once it has been initiated by a high E neutron bombarding a heavy nucleus such as U-235 235 91 142 1 1
Nuclear Fusion Fusion is … a reaction in which large amounts of energy are released when small nuclei combine to form larger nuclei This process occurs continuously in the sun and other stars, providing us heat and light Requires high Ts (1 x 109 ºC) to overcome H-H nuclei repulsion Great promise for fusion!!! Advantageous because… H2(g) is plentiful as a natural resource The waste products of fusion have shorter half-lives compared with fission Less waste generated by fusion than fission Issues to work out…
Nuclear Power Plants • Uranium-235 is used • Held below critical mass quantities (therefore no chain reaction) • Energy production selectively maintained with control rods, which absorb some of the fast-moving neutrons • Heat from fission produces steam • Steam drives the generator, leading to energy production! Causes for concern… http://www.chernobyl.co.uk/ Safely storing radioactive waste Safely transferring radioactive waste to storage sights
Percentages of electric power generation in the U.S. in 2003 from various sources. Electricity Energy Supplied in the United States
The U.S. uses much less nuclear energy than many developed nations do. Nuclear Energy Nuclear power plants produce minimal air pollution. However, many elaborate and expensive safety precautions must be employed. Also, fission products (nuclear waste) must be dealt with.