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