Space Physics and Radioactivity Flashcards
Explain the life cycle of a star:
- stars start life by forming from a cloud of dust and gas
- Force of gravity pulls together all the dust and gas to form a protostar, as it gets denser the temp rises, when it gets high enough it produces a hydrogen nuclei which undergoes nuclear fission to form a helium nuclei keeping the core hot
- The star enters a long stable period where the outward pressure is equal to the inward force of gravity, this is called a main sequence star
- Eventually the hydrogen will run out in the core and the radiation pressure will decrease making the core shrink. Due to the contracting core the temp will rise and cause the hydrogen on the outer layer to fuse and the helium can undergo nuclear fission. This expands the star due to high radiation pressure until it reaches a balance. Red giant if its a low mass star, supergiant if its a high mass star
- A red giant will stop fusing after helium and the star will shrink ejecting the outer layer and leaving behind a white dwarf
- However supergaints can undergo nuclear fusion much more meaning they expand and contract several times. through this they create heavier material. eventually they will explode and eject all the material (supernova), this creates new planets and stars from the material
- The exploding supernova throws the outer layer of dust and gas and gravity causes the core to shrink leaving a very dense core called a neutron star or if the mass is big enough it will become a black hole.
What is the name of the diagram that shows the different stages in a stars life?
Hertzsprung-russsel
How was the solar system created?
A big cloud of dust and gas was spewed from the supernova, the force of gravity brought the cloud closer and closer causing the matter to collapse and become dense further in the middle. areas of high density had a greater gravitational pull so they became denser. The region at the centre became so hot from the pressure it formed a star. further areas of density formed planets. rocks tented to gather closer to the sun forming terrestrial planets like mars and earth whereas more gaseous plantes gathered further away.
Describe an alpha particle:
Two neutrons and two protons- nucleon number of 4. charge of 2+. relatively big and heavy and slow moving
Describe a beta particle:
High energy electron with virtually no mass. charge of -1. fast and small. emitted when a neutron turns into a proton in the nucleus.
Describe a Gamma Ray:
After spitting out a alpha particle or beta, the nucleus may need to get rid of some extra energy and therefore will emit a gamma ray, they have no mass no charge and are just energy so they dont change the nucleus.
What measures radioactivity?
Geiger-Muller tube and counter
What is half life?
Time taken for the number of radioactivity nuclei to half
How are Nuclear reactions contained?
Nuclear fission reactors are often located in a containment buildings which have thick concrete and steel walls, they absorb gamma radiation, they also have a high internal pressure to prevent radioactive substances leaving if theres a leak. One way to contain a nuclear fusion reactor is with a magnetic field but these are expensive to set up and run.
What is nuclear fusion?
The opposite of nuclear fission, two light nuclei collide at a high speed and fuse to create a larger heavier nucleus. This creates energy. However, fusion only happens at really high pressure and temperature . Because the positively charged nuclei repel each other due to electrostatic repulsion, so they have to get very close which is done through the pressure.
What is nuclear Fission?
slow moving neutron is fired at a large unstable nucleus (uranium 235) this causes it to split. When it splits it creates two new lighter elements (daughter nuclei) and releases energy. each time it splits up it also releases two or three fast moving neutrons which can hit more uranium so make a sustainable chain reaction.
