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Nuclear Chemistry Unit. Textbook: Ch. 19 and 20. Part 1: Radioactivity and Radiation. What is Radioactivity?. Textbook Definition The process by which certain elements emit (give off) forms of radiation 3 Common Types of Radiation Alpha Particles Beta Particles Gamma Radiation. - PowerPoint PPT Presentation
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Nuclear Chemistry UnitTextbook: Ch. 19 and 20
Part 1: Radioactivity and Radiation
What is Radioactivity?
• Textbook Definition– The process by which certain
elements emit (give off) forms of radiation
• 3 Common Types of Radiation– Alpha Particles– Beta Particles– Gamma Radiation
All About the Alphas (-particle)
• -particles – Fast-flying– Positive Charge
(++ or +2)– Essentially a
Helium nucleus
• particles are large, and don’t move through solid material easily
• Their size gives them the most kinetic energy of the particles, so they can do significant damage
• Their positive charge holds them back– particles interact with electrons in the air
and very quickly turn into harmless Helium
All About the Alphas (-particle)
The Team (Beta Particles)
• particles – Fast-flying– Negative Charge– Tiny mass
• particles are electrons that have been ejected (kicked out) by an atomic nucleus
• Smaller than alpha particles, and usually faster
• Able to penetrate light materials such as paper and clothing
• They can penetrate human skin, and can kill cells
• Once stopped, become part of the material they are in, like any other electron
The Team (Beta Particles)
Gamma () Radiation
• Extremely energetic form of electromagnetic radiation– No Mass– No charge– Much more energy
than alpha and beta radiation
• No Mass, No Charge – Pure Energy• Can penetrate most materials• Gamma rays destroy cellular
molecules• Most dangerous type of radiation to
humans• May be used to help fresh produce
have a longer shelf life
Gamma () Radiation
Review of Radiation Penetration
How Radioactivity OccursNuclear Chemistry—Lecture 2
Textbook Sections 19.2 and 19.3
Radioactivity is a Natural Phenomenon
• Radioactivity has been around longer than people
• Denver gets about twice as much radiation as New Orleans. Why?
Biological Response to Radiation
• How do cells respond to radiation?– Usually, it’s not a big
deal– 90+% of your DNA isn’t
important– If the DNA damage is
really bad, the cell will kill itself (apoptosis—taking one for the “team”)
• If the DNA damage can’t be fixed, one of two things can happen
• Apoptosis—cell kills itself• Cell Divides
– If the cell divides, it produces an identical cell with the same mutation
– May lead to cancer– #mutagenproblems #ohnomelanoma
#aintnobodygottimeforthat
What Happens if it can’t be fixed?
• Leading source of naturally occurring radiation
• Heavier than air—accumulates in basements
• Varies based on geology– Some areas of West
Virginia and Pennsylvania are highly affected
• Over 7000 cases of lung cancer annually due to Radon exposure
Radon-222
• How do protons (all + charge) hang out in the nucleus when like repels like?
• Strong Nuclear Force—an attractive force between nucleons over short distances
• Repulsive forces are able to act over longer distances and are also very strong forces
Strong Nuclear Force
Why do large atoms have much more neutrons than smaller atoms?
• Strong nuclear force acts over very short distances
• The bigger the atom, the smaller strong nuclear force
• Large atoms require more neutrons to act as a “cement” to keep the protons from repelling one another
Strong Nuclear Force
• Neutrons aren’t stable by themselves– Can transform into a proton or electron
• Lots of protons around keeps this from happening. • When there are too many neutrons, the protons can’t
keep the neutrons in check (like a prison with too few guards)
• When neutrons become protons, it causes the atom to eject it
Limitations of Neutrons
• By Strong Nuclear Force, protons are only attracted to surrounding protons and repelled by all other protons– Like a clique
• As more protons are added to the nucleus, atoms become more unstable– More than 83 protons: radioactive
Limitations of Strong Nuclear Force
• Carbon-14, an isotope, is radioactive– 8 Neutrons, 6 Protons
• Not enough protons to keep the neutrons occupied, resulting in instability
Small Atoms Can Be Radioactive
TransmutationNuclear Chemistry Lecture 3
Textbook Section 19.4
Transmutation
• When a radioactive nucleus emits an alpha or beta particle, the atomic nucleus changes
• If the atomic number changes, the element changes– Transmutation is the
changing of one element into another
Release of Energy
• Energy is released from a transmutation reaction– Energy from
gamma radiation– Kinetic Energy from
alpha particle
- Most of the energy released is due to the kinetic energy of the alpha particle
Decay
• decay is when an element breaks down and releases an particle
• The atomic number will decrease by 2• Atomic mass will decrease by 4
Decay
• As a neutron transforms to a proton, it kicks out an electron ( particle)
• The atomic number will increase by 1
• The atomic mass will NOT change
Nuclear FissionNuclear Chemistry Lecture 4
Textbook Sections 20.1 and 20.2
What is Nuclear Fission?
• Nuclear fission is the splitting of an atomic nucleus
• When a neutron is added to U-235 it splits into…– Krypton– Barium– 3 Neutrons
Nuclear Chain Reactions
• A nuclear chain reaction occurs when neutrons attack other radioactive atoms in succession
• Nuclear chain reactions don’t occur that often in nature– U-235 is a rare isotope
(1/139) of U-238, and U-235 is much more fissionable than U-238
• Remember that unstable atoms will be undergoing fission, not the stable ones which are more commonly found in nature
Frequency of Nuclear Chain Reactions
Critical Mass
• Not all pieces of U-235 will result in an atomic bomb– If it’s too small, the neutrons
will escape and not cause additional fission events
• Critical Mass is the required size and weight of a radioactive material for a chain reaction to occur
Applications of Fission
• Atomic Bomb• Nuclear Reactors: Nuclear Energy Electrical
Energy– 20% of the energy in the US is nuclear energy
• Nuclear reactors work by boiling water to produce stream that runs a turbine– 1 kg of Uranium is more powerful than 30 freight
car loads of coal
Nuclear Reactors
• 3 Required Components– Nuclear Fuel (mostly U-238, 3% U-235) Why?– Water– Heat Transfer into a turbine
• Fission plans do NOT release radioactive waste to the environment– Coal does!
• Limitation: what do to the with radioactive waste products
Nuclear Fusionfinal Nuclear Chemistry Lecture
Nuclear Fusion
• Definition: When small nuclei “fuse” or come together– Opposite of nuclear fission
• Mass per nucleon decreases as we move from Hydrogen to Iron– Mass Lost is converted into Energy
• Nuclei must be travelling at high speeds in order for fusion to occur to overcome repulsion
The Sun uses Nuclear Fusion
• 657 million tons of Hydrogen is fused with 653 million tons of Helium every second– Loss of 4 million tons
is converted into energy
The Thermonuclear Bomb
• Temperature inside of an atomic bomb is 4-5 times greater than the sun
• Hydrogen bombs, or thermonuclear bombs, are typically 1000 times more destructive than the atomic bomb dropped on Hiroshima
• How?– Critical mass limits the size of a fission bomb– No such limit exists in fusion bombs
Fission vs. Fusion Bombs