Download Radioactivity - Mrs. Sjuts` Science Site

10/28/14 Nucleus and the Strong Force !   Protons and neutrons are packed tightly together !   Two positives normally repel each other, so why don’t the protons in the nucleus repel? !   Strong force = one of four basic forces that causes protons and neutrons to be attracted to each other Radioactivity and Nuclear Reactions !   100 times stronger than electric force !   Short-­‐range force, so it weakens with distance Ch 9.1-­‐9.2, 9.4 Small vs Large Nuclei Radioactivity !   Protons and neutrons are held together less tightly in large nuclei. Why? !   In many nuclei, the strong force keeps the nucleus together (STABLE) !   Small nuclei have few protons, so the repulsive force on a proton due to other protons is small !   When it can’t, the nucleus can decay and give off matter and energy in a process of radioactivity !   In a large nuclei, the attractive strong force is exerted only by the nearest neighbors. All the protons exert repulsive forces making the repulsive force large. !   Larger nuclei tend to be unstable – all nuclei containing more than 83 protons are radioactive Stable and Unstable Nuclei Nuclear Radiation !   Smaller elements neutron to proton ratio is 1:1 to be stable isotopes !   Heavier elements neutron to proton ratio is 3:2 to be stable isotopes !   Nuclei of any isotopes that differ much from these ratios are unstable, whether heavy or light !   All elements with more than 92 protons are synthetic and decay soon after they are created (UNSTABLE) !   When an unstable nucleus decays, particles and energy are emitted from the decaying nucleus !   Alpha Particles – (2 p and 2 n lost) massive, comparatively speaking; loses energy quickly; can’t pass through paper; changes the element (transmutation); mass changes; can damage the body !   Beta Particles – (n turns into p and emits e) e emitted from n; transmutation changes the element; mass doesn’t change; much faster and penetrating; damage body !   Gamma Rays – electromagnetic waves that carry energy; most penetrating form; cause less damage to biological molecules 1 10/28/14 At a glance… Radioactive Half-­‐Life !   Some radioisotopes decay in less than a second, while others take millions of years !   Half-­‐life: the amount of time it takes for half the nuclei in a sample of the isotope to decay Radioactive Half-­‐Life cont Ch 21.3: Absolute-­‐Age Dating of Rocks !   Relative-­‐age dating vs. Absolute-­‐Age Dating !   Relative-­‐age dating: compares past geologic events based on the observed order of strata in rock record !   Absolute-­‐age dating: determines actual age of a rock, fossil, or other object Radioactive Decay !   Radioisotopes are found in igneous and metamorphic rocks, some fossils, and organic remains !   Emission of radioactive particles and the resulting change into other elements over time is called radioactive decay ! I  love you Mrs. Sjuts! ☺ !   This decay stays constant regardless of the environment, pressure, temperature, or any other physical changes !   So, these atomic particles become accurate indicators of the absolute age of an object 2 10/28/14 Radioactive Dating Carbon Dating !   Fossils and rocks can be dating using radioactive isotopes !   The radioactive isotope C-­‐14 is often used to find the ages of once living objects !   Amounts of the radioisotope and its daughter nucleus are measured in a sample !   It is naturally found in most all living things !   Then, the number of half-­‐lives that need to pass to give the measured amounts of the isotope are calculated !   The number of half-­‐lives is the amount of time that has passed since the isotope began to decay AND usually is the same as the age of the object. !   An atom of C-­‐14 eventually will decay into N-­‐14 with a half-­‐life of 5,730 years !   By measuring the amount of C-­‐14 in a sample and comparing it to the amount of C-­‐12, scientists can determine the approx age of plants and animals that lived within the last 50,000 years Ch 9.4 Nuclear Reactions Uranium Dating !   Some rocks contain uranium, which has two radioactive isotopes with long half-­‐lives, both decaying into isotopes of lead !   By comparing the uranium isotope and the daughter nuclei the number of half-­‐lives since the rock was formed can be calculated !   U-­‐235 " 0.7 billion years !   Nuclear Fission – the process of splitting a nucleus into two nuclei with smaller masses !   Chain reaction – ongoing series of fission reactions !   Critical mass – the amount of fissionable material required so that each fission reaction produce approximately one more fission reaction !   U-­‐238 " 4.5 billion years !   Nuclear Fusion – two nuclei with low masses are combined to form one nucleus of larger mass Nuclear Fission !   Large elements need a TON of energy in order to hold their nucleus together. !   When the large nucleus is split into smaller nuclei, those smaller nuclei don’t require as much energy to stay together… !   So, that leftover energy is released! !   Atomic bomb – used in Hiroshima and Nagasaki Fission -­‐ Chain Reaction Nuclear Fission: Pros and Cons Nuclear Meltdown Cooper Nuclear Station near Brownville, NE Fort Calhoun Nuclear Generating System between Ft. Calhoun and Blair 3 10/28/14 Nuclear Fusion !   Need very high temperatures in order to overcome the repulsive forces. Sun's Fusion !   Scientists cannot control fusion reactions for the purpose of power. Nuclear Decay vs. Nuclear Reactions !   Decay happens spontaneously !   Reactions are controlled and self-­‐sustaining and release much more energy !   We can, however, use it to make nuclear weapons. Large ones. Hydorgen Bomb -­‐ Fusion Nuclear Reaction: Plutonium !   Pu-­‐239 Used to make nuclear weapons like the one dropped on Nagasaki in 1945 4