Flashcards in P4 Deck (27):
How does nuclear fusion work?
Two small hydrogen nuclei(isotopes) fuse together to form a larger, heavier helium nuclei
It releases large amounts of energy as heat
Why is it hard to sustain nuclear fusion on Earth?
The positively charges nuclei(because of protons) repel each other so they must be travelling at very high speeds to get close to each other to smash and fuse
This requires extremely high temperatures and pressure that is too dangerous to do on Earth
What is a typical nuclear fusion reaction equation?
H 1, 1 + H2, 1 -------> He3, 2
How does a hydrogen bomb work?
Nuclear fission of Plutonium 239 and Uranium 235 cause it to explode and there is an explosion releasing lots of heat energy which starts a chain reaction
This causes hydrogen nuclei to fuse releasing even more energy
How much of our energy comes from nuclear power?
What are the benefits of nuclear fusion?
- No C02 emissions
- No radioactive waste
- Large amounts of energy generated
What happens in nuclear fission?
Uranium 235 and Plutonium 239 absorb an extra neutron- making their nucleus unstable and spin and then split into two smaller nuclei which make up radioactive waste
This releases lots of energy and also 2 or three more neutrons which go on to split more atoms creating a chain reaction
Lots of splitting is needed to create enough electricity
How is a chain reaction controlled?
By having control rods placed in to absorb extra neutron released because otherwise the number of chain fissions increase rapidly as more and more neutrons are released from each atom
They are placed at correct positions and lowered at right times to make sure there is enough neutrons to keep going:
one fission leads to one more fission- constant
How are medical radioisotopes made and why are they made?
Materials are placed inside nuclear reactor and they absorb neutrons. The extra neutrons make them unstable and emit gamma rays
They are created because atoms emitting gamma are decaying all the time
How does a gamma knife work?
It emits a wife beam of low intensity gamma rays into the body focused on the tumour
It moves around the body to reduce exposure of healthy tissue but tumour receives large dose to kill
What must ingested radioactive sources do?
- They must have a short half life so it doesn't stay in for as long and harm patient or their family
- They must be very penetrative to be able to leave the body and be detected by equipment
How are X- rays used?
Most X-rays pass through the body because of high frequency but some are absorbed by denser tissue- bones
This causes a variation in the X- rays received on the photographic film and thus created an image of your skeleton
How are X- rays produced?
Electrons are fired at high speeds (using high voltages)
at an angled metal plate. When it moves at high enough speed, X- rays are emitted
The larger the voltage, the smaller the wavelength and more penetrating it is
Why are X- rays easier to control than gamma rays?
Because you can stop the emission of X- rays by turning off the voltage but you can't stop a nuclei emitting gamma
How does radioactive dating work?
ORGANIC MATERIALs absorb carbon 14 throughout its life through gaseous exchange but stops once it dies and when it decays it loses number of carbon 14 atoms
The amount of carbon 14 atoms in the sample is measured
The amount is compared to amount found in living things and the fewer it has the older it is
How do you determine the age of rocks?
As rocks age, the Uranium in it decays into lead so the number of uranium atoms decrease and lead increases
The smaller the uranium to lead ratio, the older the rock is
Where does background radiation come from?
- Cosmic rays
- Power plants
- Nuclear weapons testing
- Radon gas from rocks breaking down
Why are alpha and beta very ionising? Why is alpha more ionising?
They both have a charge so when they pass close to an atom, they attract or repel electrons away from it, ionising them.
Alpha particles have a greater mass and charge so they are more ionising
What is radioactivity?
The number of radioactive decays per second- the amount of times the nucleus breaks down
How is ultrasound used to make pregnancy scans?
Ultrasound waves(with high frequencies) are sent from transmitter into body
They are reflected by the different layers of tissue and come back at different times depending on the depth
Computer processes reflected waves and creates image of baby
What are the advantages of ultrasound over X- ray?
X- rays are too penetrative so soft tissue is hard to see so ultrasound creates clearer image
X- rays are highly ionising and damages human cells but ultrasound doesn't so is safer for baby
What are the features of a longitudinal wave?
There is a series of oscillations or vibrations which travel in a parallel direction to the wave movement
There are compressions where the air is bunched together- a region of higher pressure (eg. when speaker cone moves out)
There are rarefactions where air is spread out- low pressure
The particles move side to side rather than up and down
What is the wavelength and frequency of a longitudinal wave?
The distance from one compression to the next
The number of compressions passing through a point in a second
What happens to a longitudinal wave if the frequency increases?
The particles of the wave vibrate more rapidly
If the sound is louder,
the particles vibrate with a higher amplitude and the max distance it travels from central position increases
What is ultrasound?
It is a sound wave with a frequency above the range of human hearing- 20000Hz