Topic 5 Flashcards
Characteristics of beta particles
Move quite fast
Quite small
Negative charge
Moderately ionising
Characteristics of alpha particles
Relatively big Heavy Slow moving Strong positive charge Strongly ionising Don't penetrate far into particles HELIUM nuclei
Characteristics of gamma
Weakly ionising
Penetrate a long way into materials
Chain reaction of Nuclear fission
- slow-moving neutron absorbed by nucleus
- nucleus becomes unstable and splits
- 2 daughter nuclei atoms produced
- 2 or 3 neutrons given out
- these neutrons hit other uranium atoms, causing them to split
- this is a chain reaction
How are chain reactions slowed in reactors?
Uranium fuel rods placed in a moderator to capture and slow down the fast moving neutrons
How to limit the rate of fission in a reactor
Control rods (often made of boron) lower the rate of fission by absorbing excess neutrons.
Are isotopes stable or unstable?
Some are stable (Carbon-12) but most are UNSTABLE (Carbon-14)
Unstable means it will give off radiation
What happens when a nucleus is unstable?
It emits radiation spontaneously and randomly to try and stabilise it. This process is called decay.
What are the three types of ionising radiation
Alpha -
Beta -
Gamma
Ionising radiation disadvantages
Mutations
Cell death
Cancer
Describe alpha
Most ionising
Has a short range
2 protons and 2 neutrons (helium nucleus)
Charge: +2
STOPPED BY: paper, skin
Describe beta
Medium ionising power
Medium range
Fast moving electron
Charge: -1
STOPPED BY: thin aluminium
Describe gamma
Low ionising power
Low range
Electromagnetic wave
Charge: none
STOPPED BY: lead, concrete
What is fission?
The process of splitting a large atom into two smaller bits whilst releasing lots of energy
What happens in fission
Neutron absorbed into parent nucleus
Parent nucleus becomes unstable and splits
Daughter nucleus’ given out as well as 2 or 3 neutrons
These neutrons can go and fission other nuclei, leading to a chain reaction
What keeps the reactor safe
Control rods
What is the job of a control rod. Why is it used
Controls the rate of FISSION
If too much fission is happening the reactor can overheat and melt
How do control rods work in a reactor
The control rods can be lowered to absorb neutrons. They are made of particular isotope or material (ie boron or silver) that can absorb neutrons without becoming radioactive themselves
How does a moderator work in a reactor?
It slows down the neutrons emitted from fission reactions
Why are moderators used to keep reactors safe
If the neutrons are moving to fast they won’t be absorbed by other nuclei to create fission
How do moderators work in reactors to keep them safe?
The fuel rods are generally placed in or surrounded by the moderator. Water is the most common moderator, although another example is graphite.
What three things keep the reactor safe during fission
Control rods (ie made of boron or silver)
Moderator (ie water/graphite)
Coolant
What is the job of the coolant in a reactor
Keeps down the temperature of the reaction
Why are coolants used?
Without something to take heat away, the heat generated by the reaction could cause a melt-down
How does a coolant keep a reactor safe?
- The coolant material (usually water) is pumped into the reactor where it heats up.
- It is then cooled by heating a separate supply of water (which is used to turn the turbine).
- It condenses and is pumped round again.
What is fussion?
The opposite of fission - joining together very small nuclei to make a larger one.
It released even more energy than fission (it’s how the Sun gets its power).
What conditions are needed for fusion to occur?
- Very high temperature (higher than sun)
- Very high pressure
Why is fusion difficult?
Because it needs such a high temperature and pressure due to electrostatic repulsion. We cannot wait (like the Sun can) for fusion to happen over thousands of years, so it needs to be hotter so that fusion occurs quicker
What two types of hydrogen jump start fusion
Deuterium (hydrogen with 1 neutron) and Tritium (2 neutrons)
This reactions makes energy, helium neutrons and protons and neutrons
Why do scientists have to use extremely strong magnets in fusion?
To accelerate and contain plasma which they use to ignite fusion
