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Nuclear ChemistryNuclear Chemistry
Chapter 25
Nuclear RadiationNuclear Radiation
Section 25.1
Nuclear ReactionsNuclear Reactions
1. Occur when nuclei emit particles and/or rays.
2. Atoms are often converted into atoms of another element.
3. May involve protons, neutrons, and electrons
4. Associated with large energy changes.5. Reaction rate is not normally affected
by temperature, pressure, or catalysts.
Wilhelm RoentgenWilhelm Roentgen
• 1845-1923
1895: When electrons
bombarded surface of certain materials, invisible rays were emitted
Henri BecquerelHenri Becquerel
• 1852-1908
studied minerals that when exposed to sunlight, emit light
phosphorescence discovered uranium salts
(pitchblende)
Marie CurieMarie Curie
• 1867-1934
Marie & Pierre Curie isolated components
emitting rays identifed Po & Ra
MORE HISTORYMORE HISTORY
Rutherford (1871-1937) identified alpha,
beta, and gamma radiation
PROPERTIES OF RADIATIONPROPERTIES OF RADIATION
1. Alpha () 4
2He, helium nuclei Blocked by paper; 6.64 x 10-24 kg Slow moving due to mass and charge!
2. Beta () 0
-1 or 0-1e, electrons
Blocked by metal foil; 9.11 x 10-28 kg Fast moving Emitted from a neutron of an unstable nucleus Insignificant mass compared with mass of nucleus Greater penetrating power than alpha particles
3. Gamma () 0
0 , photons Not completely blocked by lead or concrete; 0 kg High energy electromagnetic radiation Almost always accompanies alpha and beta radiation
Radioactive DecayRadioactive Decay
Section 25.2
NUCLEAR STABILITYNUCLEAR STABILITY
• Correlated with atom’s neutron-to-proton ratio.
• < 20 atomic number most stable
BETA DECAYBETA DECAY
• Instability of isotope due to too many neutrons relative to its number of protons.
ALPHA DECAYALPHA DECAY
• All nuclei with more than 83 protons decay spontaneously
POSITRON EMISSIONPOSITRON EMISSION
• Positron is a particle with the same mass as an electron but the opposite charge
• 01 or 0
1e
• During emission, a proton in the nucleus is converted to a neutron and a positron• 1
1p --> 10n + 0
1
ELECTRON CAPTUREELECTRON CAPTURE
• Nucleus of an atom draws in a surrounding electron (from lowest energy level)
• Captured electron combines with a proton to form a neutron• 1
1p + 0-1e --> 1
0n
PROBLEMPROBLEM
What particle is formed when
polonium-210 undergoes alpha decay?
PROBLEMPROBLEM
What particle is formed when
polonium-210 undergoes alpha decay?
21084Po --> mass
atomic #Po
PROBLEMPROBLEM
What particle is formed when
polonium-210 undergoes alpha decay?
21084Po --> 4
2He +
PROBLEMPROBLEM
What particle is formed when
polonium-210 undergoes alpha decay?
21084Po --> 4
2He + 20682 ?
How did I get 20682 ?
PROBLEMPROBLEM
What particle is formed when
polonium-210 undergoes alpha decay?
21084Po --> 4
2He + 20682 ?
How did I get 20682 ? The numbers must
add up the same on both sides of the equation (top #’s =, and bottom #’s =)
PROBLEMPROBLEM
What particle is formed when
polonium-210 undergoes alpha decay?
21084Po --> 4
2He + 20682 ?
How do you determine the element?
By atomic number!
PROBLEMPROBLEM
What particle is formed when
polonium-210 undergoes alpha decay?
21084Po --> 4
2He + 20682 Pb
How do you determine the element?
By atomic number!
PROBLEMPROBLEM
What would the decay process of iodine-131 into xenon-131 look like?
PROBLEMPROBLEM
What would the decay process of iodine-131 into xenon-131 look like?
13153I --> 131
54Xe + ?
PROBLEMPROBLEM
What would the decay process of iodine-131 into xenon-131 look like?
13153I --> 131
54Xe + 0-1?
What type of radiation: 0-1?
PROBLEMPROBLEM
What would the decay process of iodine-131 into xenon-131 look like?
13153I --> 131
54Xe + 0-1
What type of radiation: 0-1? Beta!
RADIOACTIVE SERIESRADIOACTIVE SERIES
• A series of nuclear reactions that begins with an unstable nucleus and results in the formation of a stable nucleus.
TRANSMUTATIONTRANSMUTATION
Section 25.3
TRANSMUTATIONTRANSMUTATION
• Conversion of an atom of one element to an atom of another element
• In all but gamma emission nuclear reactions
INDUCED TRANSMUTATIONINDUCED TRANSMUTATION
• Striking nuclei with high-velocity charged particles
• Must be moving at high speeds to overcome electrostatic repulsion of target atom’s nucleus
• Use particle accelerators (“atom smashers”
TRANSURANIUM ELEMENTSTRANSURANIUM ELEMENTS
• Elements immediately following uranium in the periodic table
• Atomic number of 93 or greater
• Developed in the laboratory by induced transmutation
• Radioactive
PROBLEMPROBLEM
Write a balanced nuclear equation for the induced transmutation of
aluminum-27 into phosphorus-30 by alpha particle bombardment. A neutron is emitted from the aluminum atom in the reaction.
PROBLEMPROBLEM
Write a balanced nuclear equation for the induced transmutation of aluminum-27 into phosphorus-30 by alpha particle bombardment. A neutron is emitted from the aluminum atom in the reaction.
Write all symbols on proper sides of the equation. Make certain numbers add up!
PROBLEMPROBLEM
Write a balanced nuclear equation for the induced transmutation of aluminum-27 into phosphorus-30 by alpha particle bombardment. A neutron is emitted from the aluminum atom in the reaction.
Write all symbols on proper sides of the equation. Make certain numbers add up!
2713Al + 4
2He ---> 10n + 30
15P
PROBLEMPROBLEM
Write a balanced nuclear equation for the induced transmutation of aluminum-27 into phosphorus-30 by alpha particle bombardment. A neutron is emitted from the aluminum atom in the reaction.
2713Al + 4
2He ---> 10n + 30
15P
How did I know the symbol for a neutron?A neutron has mass but no nuclear charge!
HALF-LIFEHALF-LIFE
• Time required for one-half of a radioisotope’s nuclei to decay into its products.
• Exponential decay!
• Strontium-90 has a half-life of 29 years.
• So, if you had 10 g of this, in 29 years you would have 5 grams left.
HALF-LIFEHALF-LIFE
Amount remaining = (initial amount)(1/2)n
n is equal to the number of half lives that has passed
OR
Amount remaining = (initial amount)(1/2)T/t 1/2
T is equal to the elapsed time and t 1/2 is the duration of the half-life
PROBLEMPROBLEM
Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days?
PROBLEMPROBLEM
Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days?
Amount remaining = (initial amount)(1/2)n
X = 2.000 (1/2)133.5/44.5
PROBLEMPROBLEM
Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2,000 mg sample will remain after 133.5 days?
Amount remaining = (initial amount)(1/2)n
X = 2.000 (1/2)133.5/44.5
Amount remaining = 0.2500 mg
RADIOCHEMICAL DATINGRADIOCHEMICAL DATING
• Process of determining an age of an object by measuring the amount of a certain radioisotope remaining in that object
• Uranium• Half-life of 4.5 c 109 years• Meteorites; have estimated age of solar system at 4.6 x
109 years
• Carbon dating• 14
6C ---> 147N + 0
-1• Half-life of 5730 years• Limited to accurately dating objects up to 24,000
years of age
Fission and Fusion of Atomic Nuclei
Fission and Fusion of Atomic Nuclei
Section 25.4
∆E = ∆ mc2∆E = ∆ mc2
• I lied! (kind of…) • For most practical situations, mass is
conserved, but…• Energy and mass can be converted into each
other!• It has been determined that the mass of the
nucleus is always less than the sum of the masses of the individual protons and neutrons that comprise it. (CALLED MASS DEFECT)
• The missing mass provides tremendous energy required to bind the nucleus together.
NUCLEAR FISSIONNUCLEAR FISSION
• Heavier atoms (mass # > 60) tend to fragment into smaller atoms to increase their stability
• This is accompanied by a very large release of energy
NUCLEAR POWER PLANTSNUCLEAR POWER PLANTS
• Use fission to generate power• UO2 encased in corrosion-resistant fuel rods• Enriched to contain 3% uranium-235 (meets critical
mass to sustain the chain reaction)• Control rods of cadmium or boron absorb neutrons
released during the reaction, controlling the fission process
• Water circulates throughout the core to carry off the heat generated
• This is used to power stream driven turbines which produce electrical power
• Dense concrete structure encloses the reactor
NUCLEAR POWER PLANTSNUCLEAR POWER PLANTS
• Drawbacks• Hazardous radioactive fuels and fission products• Limited supply of uranium-235• Where to store spent fuel rods?• Require 20 half-lives to decay to safe levels
Amount of spent fuel for a lifetime/person would equal the size of a basketball
NUCLEAR FUSIONNUCLEAR FUSION
• Binding together two light (mass # < 60) and less stable nuclei
• Capable of releasing very large amounts of energy
• The sun!• Requires temperatures of 40,000,000 K!• Can achieve this by atomic explosion (not safe!)• Don’t have materials capable of withstanding
these high temperatures
ATOMIC BOMBATOMIC BOMB
• Utilizes principles of fission (uncontrolled!)
• Equal to effect of 20,000 tons of TNT
HYDROGEN BOMBHYDROGEN BOMB
• Never used in warfare
• Explosive force 1000 X greater than atomic bomb
Fission reaction triggers a fusion reaction of hydrogen isotopes (deuterium and tritium)
Equal to 15 million tons of TNT
IONIZING RADIATIONIONIZING RADIATION
• Radiation energetic enough to ionize matter with which it collides
• Detected by:• Geiger counter• Metal tube filled with a gas; gets ionized; creates
an electrical current
• Scintillation counter• Radiation energizes a phosphorcoated surface
that releases bright flashes
USES OF RADIATIONUSES OF RADIATION
• Neutron activation analysis• Determine quality of silicon wafers used in
computers
• Radiotracers• Trace biological pathways
• PET• Imagery used in medical diagnoses
• Radiation to kill cancer cells• Irradiation of meats, fruits…