Nuclear Chemistry

Definitions Nuclear radiation: radiation emitted from a nucleus during nuclear decay alpha particle (a): a helium nucleus, He2+; contains two protons and two neutrons, has mass of 4 amu, and atomic number 2 beta particle (b): an electron; has a charge of -1, and a mass of 0.00055 amu positron (b+): has the mass of an electron but a charge of +1 gamma ray (g): high-energy electromagnetic radiation

Electromagnetic Radiation All electromagnetic radiation consists of waves the wavelength, l is the distance between each crest. frequency, n: the number of crests that pass a given point in a second

Electromagnetic Radiation The electromagnetic spectrum

Nuclear Radiation Table 9.1 summarizes the types of nuclear radiation we deal with in this chapter

Nuclear Radiation There are more than 300 naturally occurring isotopes of these 264 are stable, they do not give off radiation among the lighter elements, stable isotopes have approximately the same number of protons and neutrons; this is the case of 126C, 168O, and 2010Ne among the heavier elements,stability requires more neutrons than protons More than 1000 artificial isotopes have been made in the laboratory; all are radioactive

Beta Emission beta emission: a type of nuclear decay in which a neutron is converted to a proton and an electron, and the electron is emitted from the nucleus emission of a beta particle transforms the element into a new element with the same mass number but an atomic number one unit greater phosphorus-32, for example, is a beta emitter note in this nuclear decay equation that the sum of both the mass numbers and atomic numbers are the same on each side of the equation

Beta Emission Problem: carbon-14 is a beta emitter. When it undergoes beta emission, into what element is it converted?

Beta Emission Problem: carbon-14 is a beta emitter. When it undergoes beta emission, into what element is it converted? Solution: it is converted into nitrogen-14

Alpha Emission alpha emission: a type of nuclear decay in which a helium nucleus is emitted from the nucleus in alpha emission, the new element formed has an atomic number two units lower and a mass number four units lower

Positron Emission positron emission: a type of nuclear decay in which a positive electron is emitted from the nucleus in positron emission, the new element formed has an atomic number one unit lower but the same mass number

Gamma Emission In pure gamma emission, there is no change in either the atomic number or the mass number of the element a nucleus in a higher-energy state emits gamma radiation as it returns to its ground state (its most stable energy state) in this example, the notation “11m” indicates that the nucleus of boron-11 is in a higher-energy (excited) state

Half-Life half-life of a radioisotope, t1/2: the time it takes one half of a sample of a radioisotope to decay iodine-131 decays by beta, gamma emission

Characteristics of Radiation Intensity to measure intensity, we take advantage of the ionizing property of radiation instruments such as a Geiger-Müller or proportional counter contain a gas such as helium or argon when a radioactive nucleus emits beta particles, these particles ionize the gas in the instrument; it registers the ionization by indicating that an electric current has passed between two electrodes another measuring device, called a scintillation counter, has a phosphor that emits a unit of light when a beta particle or gamma ray strikes it intensity is recorded in counts/min or counts/s

Characteristics of Radiation Energy and penetrating power

Radiation Dosimetry average exposure to radiation from common sources

Nuclear Medicine Radioisotopes have two main uses in medicine; diagnosis and therapy

Nuclear Medicine

Nuclear Fusion The transmutation of two hydrogen nuclei into a helium nucleus liberates energy in the form of photons this process is called nuclear fusion all transuranium elements (elements with atomic number greater than 92) are artificial and have been prepared by nuclear fusion to prepare them, heavy nuclei are bombarded with lighter ones

Nuclear Fusion examples are the preparation of Bk, Cf, and Lr these transuranium elements are unstable and have very short half-lives; that of lawrencium-257, for example, is only 0.65 second

Nuclear Fission Nuclear fission: the fragmentation of larger nuclei into smaller ones when uranium-235 is bombarded with neutrons, it is broken into two smaller elements more importantly, energy is released because the products have less mass than the starting materials the mass decrease in fission is converted into energy this form of energy is called atomic energy

Nuclear Fission Nuclear fission is a chain reaction

Nuclear Fission today more than 15% of the electrical energy in the United States is supplied by nuclear power plants disposal of spent but still radioactive fuel materials is a major long-term problem spent fuel contains high-level fission products together with recoverable uranium and plutonium in addition, there are radioactive wastes from nuclear weapons programs, research reactors, and so forth recently the government gave its final approval to store nuclear wastes at a site deep under Yucca Mountain in Nevada