Chapter 21
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Transcript of Chapter 21
Particles
• α alpha particle 4He a helium nuclei
• β beta particle…an electron 0e
• -1
• γ gamma particle, no mass, no charge
2p + 2n & NO electrons!
• Subatomic Particles• Particle• Charge• Mass (g) • Nomenclature• alpha• 2+• 6.64e-24
• 42He 4
2α• beta• 1-• 6.64e-24
• 0-1e 0
-1β• gamma• 0• 0• 0
0γ• proton• 1+• 6.64e-24
• 11H 1
1p• neutron• 0• 6.64e-24
• 0n• elelctron• 1-• 9.11e-28
• 0-1e
• positron• 1+• 9.11e-28
• 0+1e
•
Radioactive decay leads to particle which lies in the Belt of stability.
Above Belt - β -emitters (High n:p)neutron-rich lowers ratio and move right towards belt of stability. Below Belt - electron capture or position emitters (Low n:p)proton-rich raise ratio and move left toward belt of stability.
Nuclei with Z > 83 tend to be α-emittersHeavy nuclei decrease both proton and neutron.
Pattern to Stability
• Other Considerations• Other Factors to Nuclear Stability
• Magic number Protons with - 2, 8, 20, 28, 50 or 82 Neutrons with - 2, 8, 20, 28, 50, 82 or 126
• Nuclei with even # of protons and neutrons more stable than with any odd number of protons and neutrons.
• • Magic number correspond to filled, closed-shell nucleon configuration.
• Pairs of protons and neutrons analogous to pair of electrons in the atom.
Nuclear Binding Force
• Mass defect - Difference between mass the nucleus and the masses of nucleon.Binding Energy - The energy required to separate a nucleus into its nucleons.E=mc2 → E(binding energy) = m(mass defect) c2
• Mass of nuclei < ∑mass nucleons Mass of helium nucleus = 4.00150 amuMass of ∑nucleons = 4.03190 amuMass defect = 0.03040 amu (Binding Energy)
• Average binding Energy per nucleon increases to a maximum at a mass of 50 to 60 and decreases slowly thereafter. Fusion (bring nuclei together) is exothermic for low mass number and fission (splitting of nuclei) is exothermic for high mass number.
Nuclear Fission
• Splitting of heavy nuclei is exothermic for large mass number
In a nuclear Fission Process:• Neutrons move slowly because it is absorb by the nucleus.
• 235U nucleus split into different daughter nuclei and 3.5•1011 J / nucleus
• Every 235U nucleus produced 2.4 neutrons.
• Each neutron produced can cause fission to another 235U
• Number of fission and energy increase rapidly.
• Eventually a chain reaction forms and without control an explosion.
Nuclear Equation: The process
• Radionuclides - spontaneously emit particles and radiation which can be expressed by a nuclear equationSpontaneous Emission: Mass and charge are conserved.
• Three quarks for Muster Mark!
• Sure he has not got much of a bark
• And sure any he has it's all beside the mark.• —James Joyce, Finnegans Wake.