nuclear reactions vs. normal chemical changes nuclear reactions involve the nucleus nuclear...

Download Nuclear Reactions vs. Normal Chemical Changes Nuclear reactions involve the nucleus Nuclear reactions involve the nucleus The nucleus opens, and protons

If you can't read please download the document

Post on 26-Dec-2015

212 views

Category:

Documents

0 download

Embed Size (px)

TRANSCRIPT

  • Slide 1
  • Nuclear Reactions vs. Normal Chemical Changes Nuclear reactions involve the nucleus Nuclear reactions involve the nucleus The nucleus opens, and protons and neutrons are rearranged The nucleus opens, and protons and neutrons are rearranged The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together called binding energy The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together called binding energy Normal Chemical Reactions involve electrons, not protons and neutrons Normal Chemical Reactions involve electrons, not protons and neutrons
  • Slide 2
  • The Nucleus Remember that the nucleus is comprised of the two nucleons, protons and neutrons. The number of protons is the atomic number. The number of protons and neutrons together is effectively the mass of the atom.
  • Slide 3
  • Isotopes Not all atoms of the same element have the same mass due to different numbers of neutrons in those atoms. There are three naturally occurring isotopes of uranium: Uranium-234 Uranium-235* Uranium-238
  • Slide 4
  • Nuclide Symbols
  • Slide 5
  • Slide 6
  • Slide 7
  • Isotopes Two Categories Unstable isotopes that continuously and spontaneously break down/decay in other lower atomic weight isotopes Unstable isotopes that continuously and spontaneously break down/decay in other lower atomic weight isotopes Stable isotopes that do not naturally decay but can exist in natural materials in differing proportions Stable isotopes that do not naturally decay but can exist in natural materials in differing proportions
  • Slide 8
  • Radioactivity It is not uncommon for some isotopes of an element to be unstable, or radioactive. We refer to these as radioisotopes. There are several ways radioisotopes can decay and give off energy known as radiation.
  • Slide 9
  • Slide 10
  • Slide 11
  • Types of Radioactive Decay Alpha Decay Loss of an -particle (a helium nucleus) He 4242 U 238 92 Th 234 90 He 4242 +
  • Slide 12
  • Types of Radioactive Decay Beta Decay Loss of a -particle (a high energy electron) 0101 e 0101 or I 131 53 Xe 131 54 + e 0101
  • Slide 13
  • Types of Radioactive Decay Gamma Emission Loss of a -ray (high-energy radiation that almost always accompanies the loss of a nuclear particle) 0000
  • Slide 14
  • Types of Radiation Alpha () a positively charged helium isotope - we usually ignore the charge because it involves electrons, not protons and neutrons Alpha () a positively charged helium isotope - we usually ignore the charge because it involves electrons, not protons and neutrons Beta () an electronBeta () an electron Gamma () pure energy; called a ray rather than a particleGamma () pure energy; called a ray rather than a particle
  • Slide 15
  • Penetrating Ability
  • Slide 16
  • Slide 17
  • Slide 18
  • Slide 19
  • Slide 20
  • Slide 21
  • Geologic Time Radioactive Isotopes used in Geologic Dating Radioactive Isotopes used in Geologic Dating ParentDaughterhalf-life (y) ParentDaughterhalf-life (y) U-238Lead-2064.5 billion U-238Lead-2064.5 billion U-235Lead-207713 million U-235Lead-207713 million Thorium 232Lead 20814.1 Billion Thorium 232Lead 20814.1 Billion K-40Argon-401.3 billion K-40Argon-401.3 billion R-87Sr-8747 billion R-87Sr-8747 billion C-14N-145730 C-14N-145730 Half-life = time it takes for 1/2 of the parent mass to decay into the daughter mass Half-life = time it takes for 1/2 of the parent mass to decay into the daughter mass
  • Slide 22
  • Slide 23
  • Geologic Time 14 Carbon Dating Dating is accomplished by determining the ratio of 14 C to non-radioactive 12 C which is constant in living organisms but changes after the organism dies Dating is accomplished by determining the ratio of 14 C to non-radioactive 12 C which is constant in living organisms but changes after the organism dies When the organism dies it stops taking in 14 C which disappears as it decays to 14 N When the organism dies it stops taking in 14 C which disappears as it decays to 14 N
  • Slide 24
  • Slide 25
  • Slide 26
  • Slide 27
  • Forensic 14 Carbon Cases Dead Sea Scrolls 5-150 AD Stonehenge 3100 BC Hezekiahs Tunnel - 700 BC
  • Slide 28
  • Forensic 14 Carbon Cases King Arthurs Table in Winchester Castle, England 14 C dated to 13 th century AD King Arthurs Table in Winchester Castle, England 14 C dated to 13 th century AD Cave painting at Lascaux, France 14 C dated to 14,000 BC Rhind Papyrus on Egyptian math 14 C dated to 1850 BC
  • Slide 29
  • Forensic 14 Carbon Cases The Shroud of Turin was 14 C dated 1260-1390 AD which suggests that it is a fake However, recent evaluation shows that the sample measured was from a medieval patch and/or that it was seriously contaminated with molds, waxes, etc New estimates date the shroud from 1300-3000 ybp bases on vanillin retention
  • Slide 30
  • Forensic 14 Carbon Cases Nuclear testing during 1955-63 put large amounts of 14 C into the atmosphere which was incorporated into the enamel of human teeth. Because such testing stopped the 14 C input ended and the 14 C in the teeth decayed at a fixed rate allowing dating of the teeth
  • Slide 31
  • Nuclear Reactions Alpha emission Alpha emission Note that mass number goes down by 4 and atomic number goes down by 2. Nucleons (nuclear particles protons and neutrons) are rearranged but conserved
  • Slide 32
  • Nuclear Reactions Beta emission Beta emission Note that mass number is unchanged and atomic number goes up by 1.
  • Slide 33
  • Write Nuclear Equations! Write the nuclear equation for the alpha decay of radon-222 222 Rn 218 Po + 4 He Write the nuclear equation for the beta emitter Co-60. 60 Co 60 Ni + 0 e 84862 2728
  • Slide 34
  • Bellringer Fill in Chart Radioactive ParticleNuclear SymbolPertinent Information alpha beta gamma positron 4 He 2 0 e 0 0 e +1 helium atom without any electrons high energy electron, no mass with a negative charge high energy ray with no mass and no atomic number mass of an electron but a positive charge
  • Slide 35
  • Neutron-Proton Ratios Any element with more than one proton (i.e., anything but hydrogen) will have repulsions between the protons in the nucleus. A strong nuclear force helps keep the nucleus from flying apart. Neutrons play a key role stabilizing the nucleus. Therefore, the ratio of neutrons to protons is an important factor.
  • Slide 36
  • Stable Nuclei The shaded region in the figure shows what nuclides would be stable, the so-called belt of stability.
  • Slide 37
  • Neutron-Proton Ratios For smaller nuclei (Z 20) stable nuclei have a neutron- to-proton ratio close to 1:1
  • Slide 38
  • Neutron-Proton Ratios As nuclei get larger, it takes a greater number of neutrons to stabilize the nucleus.
  • Slide 39
  • Stable Nuclei Nuclei above this belt have too many neutrons. They tend to decay by emitting beta particles.
  • Slide 40
  • Stable Nuclei Nuclei below the belt have too many protons. They tend to become more stable by positron emission or electron capture. Positron = 0 e +1
  • Slide 41
  • Stable Nuclei There are no stable nuclei with an atomic number greater than 83. These nuclei tend to decay by alpha emission.
  • Slide 42
  • Radioactive Series Large radioactive nuclei cannot stabilize by undergoing only one nuclear transformation. They undergo a series of decays until they form a stable nuclide (often a nuclide of lead).
  • Slide 43
  • Nuclear Transformations Nuclear transformations can be induced by accelerating a particle and colliding it with the nuclide. These particle accelerators are enormous, having circular tracks with radii that are miles long.
  • Slide 44
  • Measuring Radioactivity One can use a device like this Geiger counter to measure the amount of activity present in a radioactive sample. The ionizing radiation creates ions, which conduct a current that is detected by the instrument.
  • Slide 45
  • Energy in Nuclear Reactions There is a tremendous amount of energy stored in nuclei. Einsteins famous equation, E = mc 2, relates directly to the calculation of this energy. In chemical reactions the amount of mass converted to energy is minimal. However, these energies are many thousands of times greater in nuclear reactions.
  • Slide 46
  • Nuclear Fission How does one tap all that energy? Nuclear fission is the type of reaction carried out in nuclear reactors.
  • Slide 47
  • Nuclear Fission Bombardment of the radioactive nuclide with a neutron starts the process. Neutrons released in the transmutation strike other nuclei, causing their decay and the production of more neutrons. This process continues in what we call a nuclear chain reaction.
  • Slide 48
  • This work is licensed under a Creative Commons Attribution-Noncommercial-S

Recommended

View more >