nuclear chemistry part 2. nuclear chemistry introduction in this section, we study some of the...

Download Nuclear Chemistry Part 2. Nuclear Chemistry Introduction In this section, we study some of the properties of the nucleus, its particles, and nuclear

Post on 25-Dec-2015

213 views

Category:

Documents

1 download

Embed Size (px)

TRANSCRIPT

  • Slide 1
  • Nuclear Chemistry Part 2
  • Slide 2
  • Nuclear Chemistry
  • Slide 3
  • Introduction In this section, we study some of the properties of the nucleus, its particles, and nuclear radiation Nuclear radiation: Nuclear radiation: radiation emitted from a nucleus during nuclear decay alpha particle ( ):alpha particle ( ): a helium nucleus, He 2+ ; contains two protons and two neutrons, has mass of 4 amu, and atomic number 2 beta particle ( ):beta particle ( ): an electron; has a charge of -1, and a mass of 0.00055 amu positron ( ): +1positron ( ): has the mass of an electron but a charge of +1 gamma ray ( ):gamma ray ( ): high-energy electromagnetic radiation
  • Slide 4
  • Electromagnetic Radiation All electromagnetic radiation consists of waves wavelength,the only difference between forms of electromagnetic radiation is the wavelength, frequency, :frequency, : the number of crests that pass a given point in a second the higher the frequency, the shorter the wavelength the higher the frequency, the higher the energy
  • Slide 5
  • Electromagnetic Radiation The electromagnetic spectrum
  • Slide 6
  • Nuclear Radiation Table 9.1 summarizes the types of nuclear radiation we deal with in this chapter
  • Slide 7
  • Nuclear Radiation There are more than 300 naturally occurring isotopes of these 264 are stable, meaning that the nuclei of these isotopes are not radioactive (they do not give off radiation); the remainder are radioactive among the lighter elements, stable isotopes have approximately the same number of protons and neutrons; this is the case of 12 6 C, 16 8 O, and 20 10 Ne among the heavier elements,stability requires more neutrons than protons; the most stable isotope of lead, for example, is lead-206, 124 82 Pb More than 1000 artificial isotopes have been made in the laboratory; all are radioactive
  • Slide 8
  • Beta Emission 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
  • Slide 9
  • Beta Emission Problem:Problem: carbon-14 is a beta emitter. When it undergoes beta emission, into what element is it converted?
  • Slide 10
  • Beta Emission Problem:Problem: carbon-14 is a beta emitter. When it undergoes beta emission, into what element is it converted? Solution:Solution: it is converted into nitrogen-14
  • Slide 11
  • Alpha Emission 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
  • Slide 12
  • Positron Emission 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
  • Slide 13
  • 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
  • Slide 14
  • Half-Life half-life of a radioisotope, t 1/2 : half-life of a radioisotope, t 1/2 : the time it takes one half of a sample of a radioisotope to decay iodine-131 decays by beta, gamma emission
  • Slide 15
  • Slide 16
  • Characteristics of Radiation Intensity to measure intensity, we take advantage of the ionizing property of radiation Geiger-Mllerproportional counterinstruments such as a Geiger-Mller 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 scintillation counteranother 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
  • Slide 17
  • Characteristics of Radiation Energy and penetrating power
  • Slide 18
  • Radiation Dosimetry although alpha particles cause more damage than x- rays or gamma radiation, they have very low penetrating power and cannot pass through skin consequently alpha particles are not harmful to humans or animals as long as they do not get into the body; if they do get into the body, they can be quite harmful beta particles are less damaging to tissue than alpha particles but penetrate farther and so are generally more harmful gamma rays, which can easily penetrate skin, are by far the most dangerous and harmful form of radiation
  • Slide 19
  • Radiation Dosimetry Terms and units Becquerel (Bq): one Bq is 1 disintegration/sBecquerel (Bq): one Bq is 1 disintegration/s Curie (Ci):Curie (Ci): one Ci = 3.7 x 10 10 Bq Roentgen (R):Roentgen (R): the amount of radiation that produces ions having 2.58 x 10 -4 coulomb/kg Radiation absorbed dose (Rad): gray (Gy)Radiation absorbed dose (Rad): an ionizing radiation unit; the SI unit is the gray (Gy) Gray (Gy):Gray (Gy): one Gy = 1 joule/kilogram (1 J/kg) Roentgen-equivalent-man (Rem): sievert (Sv)Roentgen-equivalent-man (Rem): a measure of the effect of the radiation when one roentgen is absorbed by a person; the SI unit is the sievert (Sv) where one Sv = 1 J/kg
  • Slide 20
  • Radiation Dosimetry the relationship between delivered dose in roentgens (R) and the absorbed dose in rads; exposure to 1 R of high energy photons yields 0.97 rad in water, 0.96 rad in muscle, and 0.93 rad in bone for lower-energy photons such as soft x-rays, 1 R yields 3 rads of absorbed radiation in bone; soft tissue lets radiation pass, but bone absorbs it, giving an X-ray
  • Slide 21
  • Radiation Dosimetry average exposure to radiation from common sources
  • Slide 22
  • Radiation Dosimetry a single whole-body irradiation of 25 rem is noticeable in blood count a single dose of 100 rem causes typical symptoms of radiation sickness a single dose of 400 rem causes death within one month in 50% of the exposed persons a single dose of 600 rem is almost invariably lethal within a month it is estimated that a single dose of 50,000 rem is needed to kill bacteria, and up to 10 6 rem is needed to inactivate viruses
  • Slide 23
  • Nuclear Medicine Radioisotopes have two main uses in medicine; diagnosis and therapy
  • Slide 24
  • Nuclear Medicine
  • Slide 25
  • Nuclear Fusion The transmutation of two hydrogen nuclei into a helium nucleus liberates energy in the form of photons nuclear fusionthis 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
  • Slide 26
  • 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
  • Slide 27
  • Nuclear Fission 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 atomic energythis form of energy is called atomic energy
  • Slide 28
  • Nuclear Fission Nuclear fission is a chain reaction
  • Slide 29
  • 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

Recommended

View more >