As you may recall, isotopes are atoms of the same element that have different numbers of neutrons. Isotopes of atoms with unstable nuclei are called radioisotopes
Stable Isotopes -Atoms that do not release protons or neutrons from the nucleus and ARE NOT RADIOACTIVE. Unstable Isotopes - Atoms that spontaneously release protons and neutrons from its nucleus. These isotopes ARE RADIOACTIVE. Radioactive Isotopes
Band of Stability The region on a graph which indicates all stable nuclei when the number of neutrons are compared to the number of protons for all stable nuclei
Nuclear Reactions Nuclear reactions are different from chemical reactions Chemical Reactions Mass is conserved (doesn’t change) Small energy changes No changes in the nuclei; involve ONLY valance electrons Nuclear Reactions Small changes in mass Huge energy changes protons, neutrons, electrons and gamma rays can be lost or gained
Mass Defect Some of the mass can be converted into energy Some of the mass can be converted into energy Shown by a very famous equation! Shown by a very famous equation! E=mc 2 EnergyMass Speed of light
Types of Radiation The effect of an electric field on three types of radiation is shown. Positively charged alpha particles are deflected toward the negatively charged plate.
As you can see from the symbol, both the subscript and superscript are zero. Gamma rays are high-energy (short wavelength) electromagnetic radiation. They are denoted by the symbol. particle emission Thus, the emission of gamma rays does not change the atomic number or mass number of a nucleus. Gamma rays almost always accompany alpha and beta radiation, as they account for most of the energy loss that occurs as a nucleus decays.
Induced Nuclear Reactions Scientists can also force ( = induce) nuclear reactions by smashing nuclei with alpha, beta and gamma radiation to make the nuclei unstable or
BALANCING NUCLEAR EQUATIONS 1.The sums of mass numbers (left superscripts) on each side must be equal. 2.The sums of atomic numbers or nuclear charges (left subscripts) on each side of the equation must be equal. Examples: 238 U 4 He + 234 Th 922 90 214 Pb 0 214 Bi 82-1 83
Balancing Nuclear Equations Complete the following nuclear equations: 1. 217 At 213 Bi + ? 2. 231 Th 0 + ? 3. 208 Tl 0 + ? 85 83 4 He 2 90 231 Pa 91 208 Pb 82 81
Nuclear Reactions Two types: – Fission = the splitting of nuclei – Fusion = the joining of nuclei (they fuse together) Both reactions involve extremely large amounts of energy Albert Einstein’s equation E = mc 2 illustrates the energy found in even small amounts of matter
Nuclear Fission: Is the splitting of one heavy nucleus into two or more smaller nuclei, as well as some sub-atomic particles and energy. A heavy nucleus is usually unstable, due to many positive protons pushing apart. When fission occurs: 1.Energy is produced. 2.More neutrons are given off.
Nuclear Fission Neutrons are used to make nuclei unstable – It is much easier to crash a neutral neutron than a positive proton into a nucleus to release energy.
Nuclear Fission Complete the following nuclear equations: (a) 238 U + 1 n 239 U + ? (b) 9 Be + 1 H 6 Li + ? (c) 9 Be + 4 He 12 C + ?
Nuclear Fusion joining of two light nuclei into one heavier nucleus. – In the core of the Sun, two hydrogen nuclei join under tremendous heat and pressure to form a helium nucleus. – When the helium atom is formed, huge amounts of energy are released. The fusion of hydroge n nuclei
Scientists cannot yet find a safe, and manageable method to harness the energy of nuclear fusion. – “cold fusion” would occur at temperatures and pressures that could be controlled (but we haven’t figured out how to get it to happen)
Complete the following nuclear equations, thought to be the source of the energy of some stars. (a) 1 H + 12 C? (b) 13 N 13 C + ? (c) 13 C + 1 H? (d) 1 H + 14 N? (e) 15 O 15 N + ? (f) 15 N + 1 H 12 C + ? Nuclear Fusion
Applications Medicine – Chemotherapy – Power pacemakers – Diagnostic tracers Agriculture – Irradiate food – Pesticide Energy – Fission – Fusion
Food Irradiation Food can be irradiated with rays from 60 Co or 137 Cs.Food can be irradiated with rays from 60 Co or 137 Cs. Irradiated milk has a shelf life of 3 mo. without refrigeration.Irradiated milk has a shelf life of 3 mo. without refrigeration. USDA has approved irradiation of meats and eggs.USDA has approved irradiation of meats and eggs.
Challenges of Nuclear Power Disposal of waste products
Hazardous wastes produced by nuclear reactions are problematic. – Some waste products, like fuel rods, can be re-used – Some products are very radioactive, and must be stored away from living things. Most of this waste is buried underground, or stored in concrete It takes 20 half-lives (thousands of years) before the material is safe. Challenges of Nuclear Power » Disposal of waste products