7 - Radiation Flashcards
What can unstable nuclei emit?
Radiation to become more stable
How do unstable nuclei decay?
By emitting high energy particles or waves
Why type of process is radioactive decay?
Random
What charge do alpha particles have?
+2
What can alpha particles be affected by?
An electric field
When are beta particles produced in nuclei?
When a neutron changes into a proton and an electron
What charge do beta particles have ?
-1
Which type of electromagnetic wave has the highest energy?
Gamma rays
What is the charge on gamma rays ?
No charge
What is alpha stopped by?
Paper
What is beta stopped by?
A few millimetres of aluminium
What can gamma rays be partially stopped by?
Thick lead
What can gamma pass through?
Paper + aluminium
What does ionising do to an atom?
Gives it a non-zero charge
What is the most ionising form of radiation?
Alpha
What is the least ionising form of radiation?
Gamma
What happens when a nucleus emits a neutron ?
- total number of particles in nucleus decreases by 1
- the mass number decreases by 1
What can radiation be measured and detected by?
A Geiger-Muller tube
What is activity ?
The rate at which the unstable nuclei from a source of radiation decays
What happens to the activity of a source with time?
It decreases
What is half life?
The time taken for the activity of a sample to fall to half its original level
Gives examples of uses of radioactivity?
- smoke detectors
- sterilising medical equipment
- cancer treatment
What can beta particles be used for?
To measure the thickness of thin materials eg paper, cardboard
What can gamma particles be used for?
Radiotherapy + sterilising food
When does contamination occur?
When a radioactive isotope gets onto a material where it should not be
What is irradiation ?
The process of exposing a material to alpha, beta or gamma radiation
What does contamination cause the material to become?
Radioactive
What does irradiation cause the material to become?
NOT radioactive, however can kill living cells
How can you protect against radiation?
- protective clothing
- shielded container
What is fusion?
When 2 small nuclei join together to produce a larger nucleus
What is fission?
One large nucleus splits into 2 smaller nuclei
What is nuclear fission?
The splitting of a large unstable nucleus into 2 smaller nuclei
Which isotopes undergo fission and are used in nuclear power stations?
Uranium + plutonium
What is spontaneous fission?
When a nuclei undergoes fission without additional energy being put into the nucleus
How does fission normally occur?
The unstable nucleus must first absorb a neutron
What happens during the induced fission of uranium-235?
A neutron is absorbed by the uranium-235 nucleus to make uranium-236
What are the products of fission?
- gamma rays
- 2 daughter nuclei
- 2 or 3 neutrons
Describe a chain reaction
when a neutron splits a nucleus, releasing more neutrons, which go on to split even more nuclei
What are control rods used for + made of ?
Boron- To absorb neutrons
What does lowering the control rods do?
Decreases rate of fission - more neutrons absorbed
What does raising the control rods do?
Increases rate of fission - fewer neutrons absorbed
What is a moderator made of + used for ?
Graphite - To slow down neutrons
What is the nuclear reactor surrounded with?
Shielding materials
What is the purpose of shielding ?
To absorb hazardous radiation
What keeps a nuclear reactor running ?
A chain reaction
What 2 factors must be controlled when a rector is producing energy at the correct rate?
- number of free neutrons in reactor
- energy of the free neutrons
What is nuclear fusion?
When 2 light nuclei join to form a heavier nucleus
What are the conditions for fusion?
- very high temperature of fuel
- very high kinetic energy
- very high density/pressure
Why can fusion not take place at a low temperature/low pressure
Positively charged nuclei need to be close to fuse, therefore need to be moving very fast to overcome the strong force due to electrostatic repulsion.
