Radioactivity Flashcards
describe the plum pudding model (currant bun)
A sphere of positive charge with randomnly embedded negative electrons
nuclear model properties
- A small centrally situated positive nucleus
- electrons were found in energy levels (“shells”)
- It also contained neutrons discovered by James Chadwick
- Electrons occupy energy levels (2,8,8,2)
Describe the results and conclusions of Rutherford’s gold foil scattering experiment
- Most of the alpha particles (approximately 90%) passed straight through the gold foil
conclusion: the atom has space - A few particles (approximately 8%) approached the gold foil and deflected/ deviated at different angles
conclusion: The atom has charge (alpha is positive and the nucleus of an atom is positive- repulsion) - One or two of the alpha particles were reflected when striking the gold foil
conclusion: The mass of the atom is concentrated in the nucleus- change in momentum
RADioACtivity
The spontaneous/ random decay/ disintegration of an unstable nucleus by emitting alpha particles, beta particles and gamma radiation (and also neutrons).
When were neutrons discovered?
In 1930
When is an isotope highly reactive?
When the number of neutrons greatly exceeds the number of protons.
What makes a nucleus unstable?
When the number of protons is different from the number of neutrons. More protons than neutrons or fewer protons than neutrons.
Radioactivity is measured in
Becquerel (one decay/ disintegration per second)
How do you detect radioactivity?
Using a Geiger Muller tube/ counter and cloud chamber
Alp^2hea particle
- Helium nucleus (positively charged) - 2 protons and 2 neutrons
- Lowly penetrating (can be stopped by skin or thin sheet of paper)
- used in smoke alarms/ detectors
- highly ionising
- short range (approximately 5 cm)
- approximately 10% the speed of light
- alpha particles are charged: any charged particle can be deflected by a magnetic or electric field.
North pole
negative
South pole
positive
examples of radioactive materials
americinium, actinium
What radioactive material has a half life of 6 hours?
Technetium
Precautions when handling radioactive materials
1, A notice on the door to indicate radioactive use
2, Observe the Alara principle- keep exposure as low as reasonably achievable
3, Use tongs when handling
4, Safely store in lead containers
bET^2a
- a fast moving electrons (e-) can be deflected by an electric or magnetic field
- Beta particles are more penetrating than alpha but less ionising (charge of -1)
- stopped by very thin aluminium sheets, have a longer range than alpha
- approximately 90% the speed of light (2.7 x 10^8)
- Beta particles are used to measure the thickness of materials eg: paper, metals
- Beta particles can also be used as radioactive tracers (can be used to detect radioactivity) eg: health and detection of breakages in pipes.
GaMMA
- an electromagnetic wave/ radiation
- zero charge, zero mass
conclusion: cannot be deflected by an electric or magnetic field - most penetrating, least ionising (not charged)
- may be stopped by thick lead materials
- It travels at the speed of light (3x10^8 m/s)
- used in sterilisation of medical equipment
- can kill micro-organisms to preserve food and increase the shelf life (small dosage)
- It is used in radiography to kill cancerous cells due to its penetrating power.
Half life
The average time taken for the start value/ activity/ parent nuclei to decrease to half its’ value.
Uses of half lives
- medical purposes:
technetium- 99. Has a half life of 6 hours (does not expose the body to a significant degree of ionisation) - determination of the age of materials- carbon dating
- smoke detectors: materials must have relatively long half lives
- radioactive tracers- this can help to detect breakages in pipes and monitor the growth of plants
- MRI- magnetic resonance imaging
BaCkGRouND radiation
- RADON- approximately 50% of all background radiation
- Building and Rock
- medical supplies
- Cosmic radiation
- Geothermal (energy from hot rocks)
- fooD and Drinks
- Nuclear power stations/ Nuclear distasters
Age of sample =
actual half life x number of half lives
Vanderwaal’s forces
intermolecular forces
irradiation
exposing an object to nuclear radiation. The object/ body does not becomes radioatvie to contaminate other objects. eg: X-rays, gamma rays
contamination
unwanted presence of radioactive materials on other objects. The other objects become radioactive. This creates a hazardous situation which creates a health risk.
Nuclear disasters
Chernobyl (Ukraine) and Fukushima (Japan)
What is radiation does measured in?
Sieverts (Sv)
Describe the process of nuclear fission
The splitting of a large nucleus using neutron bombardment (collision) into two smaller nuclei and further neutrons are released. Kinetic energy is released. It takes place in a nuclear reactor (uranium or plutonium).
Nuclear fission definition
The splitting of a large nucleus using neutron bombardment (collision) into two smaller nuclei.
Nuclear fission definition
Nuclear fission is the joining together of two small nuclei to form a large nucleus and kinetic energy is released initially (Tokomak energy- super magnetcs to withstand these high temperatures).
nuclear fusion occurs in the formation of what?
stars
Chain reaction
After the first fission reaction, further neutrons are released which can collide/ bombard with other large nucle, sustaining the reaction. This is called a chain reaction.
Critical mass (uranium or plutonium)
The minimum mass that the nuclear fuel must have in order to cause a chain reaction.
What happens in a nuclear reactor?
The slow-moving neutron collides with the nuclear fuel.
What are the components of a nuclear reactor?
concrete/lead shell, coolant, control rod, nuclear fuel, moderator
What is the purpose of a concrete/lead shell?
to contain the high temperatures and to prevent any stray radiation from escaping
What is the purpose of a coolant in a nuclear reactor?
It cools down the temperature and acts as a heat exchanger (usually uses water)- transfers thermal energy from reactor to boiler).
control rod
They can be raised of lowered depending on the temperature. They ABSORB neutrons to regulate the fission reaction made from boron or cadmium.
purpose of nuclear fuel (uranium or plutonium) in nuclear reactors
They provide the radioactive source for the fission reaction.
moderator (water/ graphite)
It slows down neutrons to sustain the chain reaction.
