nuclear chemistry. mass defect difference between the mass of an atom and the mass of its individual...
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Nuclear
Chemistry
Nuclear
Chemistry
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Mass Defect
• Difference between the mass of an atom and the mass of its individual particles.
4.00260 amu 4.03298 amu
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Nuclear Binding Energy
• Energy released when a nucleus is formed from nucleons.
• High binding energy = stable nucleus.
E = mc2E: energy (J)m: mass defect (kg)c: speed of light
(3.00×108 m/s)
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Nuclear Binding Energy
Unstable nuclides are radioactive and undergo radioactive decay.
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He42
Radioactive DecayRadioactive DecayTypes of Radiation
• Alpha particle ()– helium nucleus paper2+
• Beta particle (-)– electron e0
-11-
lead• Positron (+)
– positron e01
1+
• Gamma ()– high-energy photon 0
concrete
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Nuclear Decay
• Alpha Emission
He Th U 42
23490
23892
parentnuclide
daughternuclide
alphaparticle
Numbers must balance!!
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Nuclear Decay
• Beta Emission
e Xe I 0-1
13154
13153
electron• Positron Emission
e Ar K 01
3818
3819
positron
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Nuclear Decay
• Electron Capture
Pd e Ag 10646
0-1
10647
electron• Gamma Emission
– Usually follows other types of decay.
• Transmutation – One element becomes another.
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Nuclear Decay
• Why nuclides decay…– need stable ratio of neutrons to protons
He Th U 42
23490
23892
e Xe I 0-1
13154
13153
e Ar K 01
3818
3819
Pd e Ag 10646
0-1
10647
DECAY SERIES TRANSPARENCY
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Half-life
• Half-life (t½)– Time required for half the atoms of a
radioactive nuclide to decay.– Shorter half-life = less stable.
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Half-life
nif mm )( 2
1
mf: final massmi: initial massn: # of half-lives
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Half-life• Fluorine-21 has a half-life of 5.0 seconds. If you
start with 25 g of fluorine-21, how many grams would remain after 60.0 s?
GIVEN:
t½ = 5.0 s
mi = 25 g
mf = ?
total time = 60.0 s
n = 60.0s ÷ 5.0s =12
WORK:
mf = mi (½)n
mf = (25 g)(0.5)12
mf = 0.0061 g
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F ission
• splitting a nucleus into two or more smaller nuclei
• 1 g of 235U = 3 tons of coal
U23592
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F ission• chain reaction - self-propagating reaction• critical mass -
mass required to sustain a chain reaction
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Fusion
• combining of two nuclei to form one nucleus of larger mass• thermonuclear reaction – requires temp of 40,000,000 K to sustain• 1 g of fusion fuel =
20 tons of coal• occurs naturally in
stars
HH 31
21
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Fission vs. Fusion
• 235U is limited• danger of meltdown• toxic waste• thermal pollution
• fuel is abundant• no danger of meltdown• no toxic waste• not yet sustainable
FISSION
FUSION
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Nuclear Power
• Fission Reactors Cooling Tower
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Nuclear Power
• Fission Reactors
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Nuclear Power
• Fusion Reactors (not yet sustainable)
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Nuclear Power
• Fusion Reactors (not yet sustainable)
Tokamak Fusion Test Reactor
Princeton University
National Spherical Torus Experiment
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Synthetic Elements
• Transuranium Elements– elements with atomic #s above 92– synthetically produced in nuclear reactors and accelerators– most decay very rapidly
Pu He U 24294
42
23892
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Radioactive Dating
• half-life measurements of radioactive elements are used to determine the age of an object
• decay rate indicates amount of radioactive material
• EX: 14C - up to 40,000 years238U and 40K - over 300,000 years
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Nuclear Medicine
• Radioisotope Tracers– absorbed by specific organs and used to
diagnose diseases
• Radiation Treatment– larger doses are used
to kill cancerous cells in targeted organs
– internal or external radiation source
Radiation treatment using
-rays from cobalt-60.
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Nuclear Weapons
• Atomic Bomb– chemical explosion is used to form a
critical mass of 235U or 239Pu– fission develops into an uncontrolled chain
reaction
• Hydrogen Bomb– chemical explosion fission fusion– fusion increases the fission rate– more powerful than the atomic bomb
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Others
• Food Irradiation radiation is used to kill bacteria
• Radioactive Tracers– explore chemical pathways– trace water flow– study plant growth, photosynthesis
• Consumer Products– ionizing smoke detectors - 241Am