Chemistry - Nuclear

Unstable nucleus

Undergoes spontaneous decay to make the nucleus more stable

- All nuclides after 83 are unstable and radioactive

Radioactivity

The process by which an unstable nucleus becomes stable -> energy emitted (much more than chemical)

Ionizing Radiation

Particles with enough energy to knock away electrons from atoms and molecules (turn them into ions)

- Includes alpha, beta, and gamma

Effects of ionizing radiation

DNA damage -> tissue damage and/or cancer

When are alpha particles hazardous?

If they are inhaled (bc stopped by skin)

Uranium History

Originally considered worthless (waste product of silver)

Henri Becquerel

Experiment -> Wrapped photographic film in black paper, and put a piece of uranium on top (and it was exposed and developed), concluding that energy must come from uranium)

Uranium-238

Unstable Nucleus: 92 protons and 146 neutrons

So unstable it releases radiation (helium nucleus/alpha)

Changes to Throium-234 (90 p+)

Decay Series

A series of radioactive nuclides produced by successive decays until a stable nuclide is produced

Alpha Decay

4/2 He

Helium nucleus -> 2 p+, 2 n0

Nuclei is too big, so shoots particles out to minimize repulsive forces between protons and neutrons

Alpha Particle Characteristics

Emitted by heavy nuclei

Heaviest, largest

Travels the least

Least penetrating power -> skin

The biggest contributor to an individual's background radiation dose

Alpha

Beta Decay

0/-1 B

Neutron turns into a proton, and an electron -> electron is emitted (beta particle)

Beta Particle Characteristics

Negatively charged

Fast moving

Lightest, smallest

Travels farther than alpha

More penetrating than alpha -> aluminum

Gamma Emmission

- high-energy waves emitted from nucleus as it changes from an excited to ground energy state

- Usually occurs immediately following other types of decay as the alpha or beta particles leave the nuclues in an excited, unstable condition

Gamma Characteristics

Travels farthest

Most penetrating

Stopped by lead/thick concrete

Can pass through body -> creating thousands of ions throughout the body

Band of Stability

Ratio of nuetrons to protons that produces the most stable nucleus

Low atomic #s -> 1:1 ratio

Higher atomic #s -> 1.5:1 ratio

Fission Reaction

Forcing the nuclei to break apart (purposely adding neutrons to make it unstable)

- A large nucleus splits into 2+ stable daughter nuclei

- Releases energy

Mass deficit

A little bit of missing mass is converted to a lot of energy

E = mc^2

c = (300,000,000 m/s)

Nuclear Chain Reaction

The material that starts the reaction is also one of the products and can start another reaction

Manhattan project

Secret project to build an atomic (uranium-based) bomb

Most common type of uranium

Most from mining is U-238; not U-235

- Need U-235 isotope to keep chain reaction going

Critical Mass

The amount needed to sustain a runaway chain reaction

Bombs

Little Boy -> hiroshima (uranium-235)

Fat Man -> nagasaki (Plutonium-239)

Fusion

Smaller nuclei combine to produce a nucleus with a greater mass

- In the sun, hydrogen nuclei fuse to make helium nuclei

- More change in mass -> releases more Energy than fission reactions

- Requires high temperatures

Atomic Bomb

Fission only

Hydrogen Bomb

Fission bomb used to start a fusion reaction of hydrogen

Much more energy released

Process of Nuclear Power to get electricity

1) Heat produced from fission

2) Water boils

3) Steam produced

4) Steam turns turbine

5) Turbine generates electricity

How do the atoms split/how is heat produced in nuclear power plants?

In reactor:

- Fire neutron at unstable element

- Element absorbs neutron, and splits into 2 smaller elements

- Mass lost is converted to energy

What is fission controlled by

1) Using water to absorb and remove heat producted during the reaction

2) Using control rods in the fuel assembly to absorb excess neutrons

Control rods

Absorb excess neutrons to reduce the number of neutrons that collide with nuclei

- IF malfunction -> reactor core overheats -> meltdown

Fuel Rods

Made from fissionable material (U-235, or Plutonium-239)

Spent rods

High level waste

- Stored in holding tanks with water

Purpose of water in tanks for spent rods

Water absorbs heat and acts as radiation shield

Dry Cask

Spent rods moved into canisters on land after spending years in the water

Process of Nuclear Waste

As the reaction progresses, the amount of fissionable material decreases

Nuclear rods considered spent -> removed/replaced -> stored bc contain radioactive material

Geiger Counter

Measures nuclear radiation

- In rem or microsierverts

- In rem or microsierverts

A measure of the health effect of radiation on the human body

Film Badges

Personal device worn that contains photographic film to measure and record radiation exposure

3 factors in Risk of Exposure to radiation

1) Type of radiation

2) Dose

3) Dose rate (time)

Background Radiation

Average ~ .2 microsevierts/hour

- In air, food, soil and space

Acute Radiation Syndrome

High dose of radiation in a short period of time

- Several health effects including DNA damage

Half life

Time required for half of the radioactive atoms to undergo decay

- Unique to a particular isotope

Half life of Cesium-137

30 years

Half-life of U-238

4.5 billion years

Carbon Dating

Use half life of C-14 to determine how old something is

- Scientists measure amount of C-14 left and compare it to the amount of C-12 still in sample and to the amot of C-14 in living organisms

About Carbon Dating

C-12 and C-14 are absorbed by plants in same ratio present in atmosphere

C-14 is rare

C-12 and C-14 taken in by animals as they consume plants

C-14 decays but the living organism is constantly taking in new C-14 (photosynthesis or eating) so level of C-14 remains constant while organism is alive

Plants and animals stop taking in carbon when they die

C-14 Decays into N-14 at a regular rate (half-life=5730)

C-12 doesn't change because it is stable

Ratio between C-14 and C-12 changes as C-14 decays

Space Exploration

Voyager Z: Powered by nuclear radiation

Radiactive Tracers

Radioactive atoms that are incorporated into substances so that their movement can be followed by radiation detectors

- Tc-99 detects cancer -> gathers at site of fast-growing tumors (half life: 6 hours)

What is radioactive in marie curie's lab?

The door knob to her lab

What radioactive element did marie Curie discover?

Radium

What is enriched uranium

Uranium with a much higher concentration of U-235

What makes isotopes of elements stable or not stable

The amount of neutrons

How does radiotherapy help patients with cancerous tumors?

the radiation affects the DNA of cancer cells and stops them from replicating

What is the source of the heat in a nuclear power plant?

the fission of large uranium nuclei into smaller nuclei

When technicians at a nuclear power plant decide that they need to produce LESS heat or they need to shut a reactor down completely they should:

insert control rods into the fuel assembly

Why did Alexander Litvinenko die?

Alpha radiation levels in Litvinenko's body were too high.

Alexander Litvinenko

- ex-KGB agent

- poisioned with rare polonium-210. (releases alpha); and Beryllium goes through fission reaction

2 most commonly used smoke alarms

- photoelectric

- ionization

Photoelectric Smoke Alarm

Used a beam of light sent from a LED that is detected by a photocell

- When smoke enters, light is scattered by particles, and rays get sent to photocell

- Photocell generates an electrical current that triggers the alarm

Smoke Detectors - Ionization

1) A radioactive substance releases alpha particles

2) the alpha particles collide/interact with air in the chamber

3) ions are produced (bc when collide with alpha particles, the air splits into electrons and charged ions)

4) positively charged plate attracts neg ions; neg plate attracts pos ions -> creates small electric current

5) When smoke enters chamber -> particles attach to charged ions; making them neutral; and disrupting electrical current

6) Alarm is triggered

3Ts and

gold

Tungsten, Tantalum, Tin and Gold

war profiteering

the mining of valuable minerals is funding armed militant groups in the area at the expense of civilians

- the mining is managed by armed militias and other armed forces

Process of selling conflict materials

Mines -> Trading Houses (Not licensed) -> Exporters -> Refiners (raw minerals into purified metals) -> electronics company

Why are these exported minerals considered "conflict" minerals?

the minerals are sold by armed groups and support continued violence in the area

When is it impossible to distinguish the origin of 3TS?

Once refined into purified metals

Chernobyl disaster

During a scheduled safety test, there was a uncontrollable power spike blowing the reactor

Fukushima

Earthquake -> Tsunami -> knocked out emergency diesel generators -> loss of cooling; reactors overheated

Radon in homes

- Radon (radioactive) is a daughter nuclei of uranium

- Can seep out of ground, into house, and be ingested

- Dangerous if high level

Fission v Fusion

Fission: Larger nucleus splits into smaller

Fusion: 2+ smaller are combined into larger