Topic 7&8: Radioactivity & Astrophysics Flashcards
Why does gravitational field strength differ in different planets?
It depends on the mass of the planet
What type of forces causes stuff to orbit around something?
Gravitational force
What are the differences in the orbits of comets, moons and planets
- Comets orbit elliptically
- Moons orbit circularly
- Planets orbit in a slightly squashed circle (ellipses)
How do you calculate for the orbital speed?
2πr
Orbital speed = ———
T
Rank the colours of the star by their temperatures
Hottest ————————————————————> Coldest
Blue, Blue White, Yellow, Orange, Red
What is a nebula?
- A large cloud of dusts and gas particles drawn by gravitational force
- As particles get closer, the temperature and pressure becomes so large that it forms a star (nuclear fusion)
What is a star (main sequence)?
- Caused by nuclear fusion
- A main sequence star is when particles are balanced and doesn’t pull inwards.
- Remains for millions of years
What is a red giant?
- When a star runs out of hydrogen fuel, the gravitational force will push particles,especially inwards again
- Helium fusion will then happen and it expands into a bigger star
- As surface area is now larger, the temperature will be cooler
What is a white dwarf?
- As helium fuel runs out again, the red giant will collapse inwards
- It heats ups so much that it turns white and becomes really small and dense as no fusion occurs
How can a star evolute to have a bigger mass than the sun?
- A giant star forms into a red supergiant
- When it runs out of fuel, the it collapses and it explodes to form a Supernova
What is an absolute magnitude?
A measure of how bright the star would be if it were seen from a standard distance
What is a HR (Hertzsprung-Russel) diagram?
It shows the relationship between the luminosity and temperature of a star
What were the scientists’ belief in the evolution of the Universe
- The universe was originally a tiny and dense place
- It then exploded and it has been expanding till now.
- The red-shift proves the expansion and the CMBR proves the energy of explosion
Provide some evidence for the Big Bang Theory
Red-Shift:
- It is the stretching of a wave.
- Since the wave is stretching, that means that light is moving further away from us
- Which means that the universe is expanding
CMBR:
- The microwave radiation is something that would’ve been produced during the explosion
- Microwaves are stretched remains of high energy gamma radiations.
- They are stretched because the universe is expanding
What are the relationship between change in wavelength, reference wavelength, velocity of a galaxy and speed of light?
Change in wavelength Velocity of a galaxy
——————————— = ————————————
Reference wavelength Speed of light
Describe the red-shift in light received from galaxies at different distances away from the Earth
The further away a galaxy, the greater the red-shift will be.
What are the three types of ionising radiation
- Alpha (α)
- Beta (β)
- Gamma (γ)
Which ionising radiation is the strongest and which one is the weakest?
Strongest: Gamma
Beta
Weakest: Alpha
How can you investigate the penetration powers of different types of radiation
- Use a Geiger Muller tube
- Test the radiations with paper, aluminium and lead
- The count will significantly decrease if radiation is stopped
What are the mass and atomic numbers for the three ionising radiation
4 0 0
α β γ
2 -1 0
What is a photographic film for
The photographic film darkens the radiation to be able to detect for it
What is the definition of half-life
The time taken for a radioactivity source to half its original value
Describe how radioactivity is used in the medical industry
- Gamma radiography
- Medical tracer (MRI)
- Radiotherapy (Cancer treatments)
- Sterilisation
What is the difference between contamination and irradiation
- Contamination is when radioactive atoms deposits on it
- Irradiation is when it is exposed to radiations
What are the dangers of ionising radiations?
- They can cause mutations as it is very ionising
- They can damage cells and tissue
- Disposal of radioactive waste can cause harms
What is nuclear fusion?
When two daughter nuclei join to form a bigger nucleus
What is nuclear fission?
When a nucleus splits into two daughter nuclei and releasing three neutrons
Describe the process of nuclear fission of Uranium 235?
- Uranium 235 absorbs a neutron to initiate fission
- As it turns into 236, it becomes unstable
- It then splits into 2 daughter nuclei and releasing three neutrons
Describe the process of Uranium 235 fission
- Uranium 235 absorbs a neutron to initiate the fission
- As it is now 236, it turns unstable
- It then splits into 2 daughter nuclei and releases 3 neutrons
What is chain reaction and how does it happen with Uranium 235
- A series of event that is caused by the previous one
- When Uranium 235 absorbs neutron to split into 2 daughter nuclei, it releases 3 neutrons
- These 3 neutrons go on and react with other Uranium causing unlimited fission to occur
What does a moderator do in a nuclear reactor
It absorbs energy to slow down neutrons moving
What does control rods do in a nuclear reactor
It absorbs neutrons to completely stop chain reaction going on
What does a shielding do in a nuclear reactor
A really thick concrete and a steel reactor vessel that prevents radiation escaping
