Transcript 31-4
Nuclear Energy Effects and Uses of Radiation Chapter 31 Nuclear Reactions and the Transmutation of Elements Section 31-1 A nuclear reaction takes place when a nucleus is struck by another nucleus or particle. If the original nucleus is transformed into another, this is called transmutation. Ernest Rutherford was the first to report seeing a nuclear reaction Conceptual Example 31-1 A neutron is observed to strike an 168O nucleus, and a deuteron is given off. (A deuteron equals 21H) What is the nucleus that results? 1 n 0 + 16 O 8 ?+ 2 H 1 The total number of nucleons initially is 1 + 16 = 17, and the total charge is 0 + 8= 8. The same totals apply after the reaction. Hence the product nucleus must have 17 nucleons and a total charge of 8. When comparing to the periodic table one can see that Nitrogen has 15 nucleons and a charge of 7, the equation is therefore balanced and everything is conserved. In any nuclear reaction electric charge, nucleon number, energy and momentum must be conserved a+XY+b a = projectile particle produced X = Nucleus a strikes Y = Nucleus produced b = particle Passage of Radiation Through Matter; Radiation Damage Section 31-4 Radiation α, β, γ, and X-rays, protons, neutrons, other particles Radiation produces ionization and can therefore cause damage to materials and biological tissue Charged Particles α, β rays, protons When they pass through a material, they can attract or repel electrons strongly enough to remove them from the atoms of the material A single α or β particle can cause thousands of ionizations Neutral Particles X-ray and γ-ray photons Ionize atoms by knocking out electrons. A neutron can collide with a nucleus and break it apart Charged particles produced can go on to produce more ionizations Damage to Materials Metals become brittle Strength can be weakened if radiation is intense (Ex: Nuclear reactor power plant, cosmic radiation) Damage to Biological Tissue cont. Damage to molecules such as proteins is not serious unless the dose of radiation is large Damage to DNA is more serious Death of one cell is normally not a problem (Exception?) A cell could survive, but be defective Categories of Radiation Damage to Biological Tissue Somatic Damage: refers to any part of the body except the reproductive organs Genetic Damage: refers to damage to reproductive cells *The damage caused by radiation must be balanced by the medical benefits. Radiation Therapy: Applications of Radioactivity & Radiation to Human Beings Section 31-6 In the medical field of radiation therapy, there are 2 basic aspects: 1) Radiation therapy 2) The diagnosis of the disease Radiation Radiation can cause cancer, but can also be used to treat it. Cancer cells are susceptible to destruction by radiation, yet large doses needed to kill cancer inevitably kill normal cells also. Radiation sickness To minimize destruction of normal cells, a narrow beam of gamma or X-rays is used if a cancerous tumor is well localized. Radiation sources include radioactive substances, photons from a X-ray machine, or even protons, neutrons, & electrons from particle accelerators In some cases, a tiny radioactive source may be inserted directly into a tumor, which will eventually kill the majority of cells. I.e. Thyroid cancer Although radiation can increase the lifespan of many patients, it is not always completely effective. o Another application of radiation is for sterilizing bandages, surgical equipment, and even packaged foods, since bacteria and viruses can be killed or deactivated by large doses of radiation. Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) Section 31-9 Nuclear Magnetic Resonance Scientific method that exploits nuclear magnetic resonance to study molecules All nuclei that contain certain odd numbers of protons or neutrons have intrinsic magnetic moment and angular momentum NMR frequencies for a particular substance are directly proportional to the strength of the applied magnetic field NMR studies magnetic nuclei by aligning them with an applied constant magnetic field and perturbing the alignment with an alternating magnetic field. The resulting response gives a spectra which correlates to chemical shifts The spectra is compared to known frequencies to determine the identity of a compound. Proton NMR is most commonly used Magnetic Resonance Imaging Known to the general public as MRI Uses a magnetic field to align the magnetization of hydrogen atoms in the body. Radio waves are used to alter the alignment causing the hydrogen atoms to produce a rotating magnetic field detectable by the scanner. The formation of 2-D or 3-D images can be done using techniques similar to those for computed tomography Homework Section 31-1 Question #1b, 1c Section 31-4 Question #24 Section 31-6 Question #25