Atomic structure II
Nucelar Fission
Splitting of a large and unstable nucleus into a smaller one
Two or more neutrons are also released aswell as energy
If the neutrons are absorbed by another nucleus, it can cause more fisison
Chain reaction
Process used to generate power in a power plant
Alot of energy is released
Risks
Effect on living cells
Radiation can enter cells and collide with molecules
Collisions cause ionisation, which damages or destroys cells
Lead to mutated cells that divided uncontrollably
Can lead to cancer
High doses kill alot of cells and can cause radiaiton sickness if alot of cells are killed at once
Uses
Gamma rays
medical tracers
Used to see why internal organs aren't working properly
Radioactive isotopes can be injected into people and then traced in the body
Radiotherapy
Treatment of cancer
High doses of radiation kill cancer cells and human cells
Sterilise surgical equipment
Preserve food - food irradiated with gamma-rays will last longer as microbes are killed by higher energy gamma-rays
Alpha particles - Smoke alarms
Beta Particles - controlling paper thickness
Precautions
Limiting exposure time - keep the time a person needs to be in contact with the ionising radiation as low as possible
Wearing protective clothing - wearing a lead apron will absorb much of the ionising radiation
Increasing the distance from the person to the radioactive source, the further a person is from ionising radiation, the less damage
Background radiation
The higher the radiation dose, the more likely to develop cancer
Sources
Radioactivty of naturally occuring unstable isotopes all around us
Radiation from space, cosmic rays come mostly from the sun
Radiation due to man made sources
We are always exposed to ionising radiation
Radon gas, produced when uranium rock decays
Ionising radiation emitted by the tracer can be detected and the biological process monitored
Destroying unwated tissue
Internally
Radioactive implants are used to destroy cancer cells in some tumors
Radioisotopes used have half lives long enough to irradiate the tumor over a given time, but short enough to limit the dose
Patient eats something containing the radioisotope
Externally
Several beams of gamma-rays are fired from different positions towards the cancer
Each beam damages the tumor
Gamma rays are used becasue the penetrate deeper into the body
Controlled chains
Two of the neutrons are absorbed by other materials
Only one netron from each dission can cause other fission
Neutrons released may be absorbed by other nuclei
Each of these nuclei undergo fission, and prodce even more neutrons
If a reaction is not controlled there will be a nuclear explosion
Nuclear reactors make use of controlled chain reactions
Nuclear Fusion
Fusion in stars
Very high temperatures and pressures are required
Some of the mass is converted into energy
Hydrogen nuclei can fuse to produce a helium nucleus
Two light nuclei collide at high speed and join to create a larger, heavier nucleus
Cast quantities of hydrogen nuclei are converted to helium nuclei
Over time heavier elements are formed and the star eventually dies
Mass of the product is slightly less than the reacts, the mass difference is released as thermal energy
Difficulties of fusion
Nuclei need to get very close to eachother before fusion can happen
Under normal conditions, the positive charged on nuclei repel eachother, electrostatic repulsion
Only at very high temperatures and pressures are the nucleu moving fast enough for them to overcome this electrostatic repulsion
Very high temperatures are difficult to produce in a fusion power station
Measurement of radioactive dose in Sieverts
To occur, and unstable nucleus must absorb a neutron