Section 3 - Radiation and Astronomy Flashcards
What happens when an electron gains energy?
It moves to a higher energy level
What happens when an electron loses energy?
The electron moves to a lower energy level
What is an alpha particle?
A helium nucleus
What is a beta particle?
An electron or positron
What is gamma radiation?
Gamma rays
What is the least penetrating type of radiation?
Alpha
What is the most penetrating type of radiation?
Gamma
What is the most ionising type of radiation?
Alpha
What is the least ionising type of radiation?
Gamma
How far does an alpha particle travel in air?
A few centimetres
How far does a beta particle travel in air?
About two metres
How far does gamma radiation travel in air?
A long distance. Thanks CGP guide very useful!
What are alpha particles stopped by?
Paper
What are beta particles stopped by?
A sheet of aluminium
What are gamma rays stopped by?
Lead or a few metres of concrete
What is annihilation?
When an electron and positron collide destroying them both and releasing gamma rays.
What is the half life of a radioactive source?
The average time taken for the number of radioactive nuclei in an isotope to halve
List some uses of radiation
Fire alarms
Sterilising food and medical equipment
Medical tracers
Thickness gauges
How is radiation used in fire alarms?
A radioactive source in the smoke detector releases alpha particles between two electrodes. This causes ionisation snd allows a current to flow. If smoke enters the detector, it will absorb the alpha particles, breaking the circuit.
How is radiation used in sterilisation?
Gamma rays are fired at the object, killing any microbes on the object.
How is radiation used in tracers?
A tracer is injected into the patient. The radiation released is picked up by a detector as the tracer moves around the body.
Why can’t alpha radiation be used for medical tracers?
Because the alpha radiation is not penetrating enough to make it out of the body.
How is radiation used to gauge thickness?
Fire beta radiation at the material. If too much radiation is going through, the material is too thin. If not enough radiation is passing through, the material is too thick.
Which isotope is most commonly used in nuclear fission?
Uranium-235
What happens during nuclear fission?
A neutron is absorbed by an unstable nucleus, making it more unstable. This causes it to split, creating two smaller nuclei, releasing energy and two or three neutrons.
What is the purpose of the fuel rods in a nuclear reactor?
They contain the uranium
What is the job of the moderator in a nuclear reactor?
To slow down the neutrons so they can be absorbed by the uranium nuclei.
What is the job of the control rods in a nuclear reactor?
To control the rate of the chain reaction be absorbing so e of the neutrons.
How does a chain reaction start in a nuclear reactor?
A neutron is fired at an uranium nuclei, causing it to split and release two or three neutrons. Those neutrons then go on to be absorbed by other uranium nuclei.
Why do the neutrons need be slowed down in a nuclear reactor?
If the neutrons are going too fast they will pass straight through the nuclei and not be absorbed.
How is electricity generated by a nuclear reactor?
The energy released by the uranium heats water, which evaporates, rises and turn a turbine.
Where are stars formed from?
A nebula
How is a protostar formed?
Gravity pulls the dust and gas from a nebula together
How is a main sequence star formed?
As a protostar gets denser, more particles collide with each other. This causes the temperature to rise. When the temperature gets high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei.
What is a main sequence star?
A star that is stable due to the energy produced from nuclear fusion of hydrogen. At this point the pressure from inside the star is in equilibrium to gravity.
What keeps a main sequence star stable?
The force of gravity pulling in and the force if pressure pushing out are in equilibrium
What determines the life span of a star?
Its mass
When the mass of a star gets larger what decreases?
Its lifespan
How is a red giant/red supergiant formed?
When the hydrogen in a main sequence star runs out of hydrogen, it can no longer do nuclear fusion of hydrogen. Gravity is larger than the internal pressure of the star, causing it to compress until it is dense and hot enough that the pressure inside the star makes the outer layers of the star expand.
How is a white dwarf star formed?
When a small or medium sized red giant ejects its outer layer of dust and gas. Leaving the hot, dense solid core.
What has stopped inside a white dwarf?
Nuclear fusion
What is the heaviest element that can be fused inside a star?
Iron
What happens before a supernova?
Elements heavier than iron are produced through nuclear fusion. The star expands and contracts several times before it explodes in a supernova.
What two things can form after a supernova?
Neutron star or a black hole
What is a neutron star?
The remaining, very dense core of a large star
What is the name of the stage in a star’s life when it’s in equilibrium?
Main sequence
What is fhe main material that makes a star?
Hydrogen
What determines the colour of a star?
Its temperature
What causes redshift?
If a galaxy is moving away from earth, the wavelength of light is shifted to longer wavelengths, moving the light towards the red end of the spectrum.
What does redshift tell us about the universe?
It is expanding
The other galaxies are moving away from us
Why do space telescopes have a clearer view than telescopes on Earth?
The Earth’s atmosphere absorbs a lot of light.
Light pollution makes it harder to pick out dim objects
