Nuclear Physics Flashcards
What does the nucleus of an atom consist of? Mention charges
Protons +1 charge
Neutrons 0 charge
What orbits the nucleus of an atom?
Mention charge
Electrons -1 charge
What is the bottom number of an element? (Smaller number)
Atomic number, total protons/electrons
What is the top number of an element?
(Bigger number)
Mass number, total of protons and neutrons
What determines which element an atom is
The number of protons it has
What are isotopes?
Atoms with the same number of protons but different amounts of neutrons
(Different versions of the same element)
- Have the same atomic number
What is radioactive decay?
When unstable isotopes decay into other elements by emitting radiation
(Alpha, beta or gamma)
Or sometime they just emit neutrons
What makes an isotope unstable?
When it’s nucleus has a different amount of protons and neutrons
What does it mean when an electron becomes excited?
The electron gains enough energy to increase its energy level (jump to the next shell)
- the energy comes from electromagnetic radiation
How is electromagnetic radiation formed?
When an electron get excited and jumps up and energy level, it soon falls back down to the lower energy level and will re emit the energy as electromagnetic radiation
What is ionization?
Occasionally one of the outer most electrons can gain enough energy to leave the atom completely, giving the atom a positive charge
(It’s now a positive ion)
What is ionizing radiation?
Able to knock electrons off atoms turning them into ions
What does it mean when we say a material is radioactive?
It consists of unstable isotopes that can decay.
What are the 4 types of nuclear radiation?
Beta particles, alpha particles, gamma rays, neutrons
Describe alpha particles
- made up of 2 protons and 2 neutrons
(Like helium, He) - don’t have any electrons so have 2+ charge
- large so can’t penetrate very far into other materials
(Can travel few cm in air, absorbed by a single sheet of paper) - large size and charge makes them strongly ionising (able to knock off electrons on atoms they collide with)
Describe beta particles
- electrons
- no mass and -1 charge
- not emitted from an atom’s shell; one of the atom’s neutrons decays into a proton and an electron. The proton stays in the nucleus but the electron is emitted out at high speed
- tiny so are moderately ionising and penetrate moderately far into materials
( takes several meters of air or 5mm of aluminum to stop them)
Describe gamma rays
- waves of electromagnetic radiation
( often emitted after alpha or beta radiation as a way for the nucleus to remove any extra energy) - no mass or charge
- passes straight through materials so moderately ionising
- can penetrate far into materials before being stopped ( long distances through air, thick sheets of lead to stop it)
Describe the emission of neutron
If a nucleus contains too many neutrons it can emit one to increase stability
What is activity?
Overall rate of decay of all isotopes in a samples
- measured in Becquerels
( 1Bq = 1 decay per second)
- as time passes the activity decreases as there are less nuclei that need to decay
What is half life?
The time taken for the no of radioactive nuclei in a sample to halve
What is equipment is used to measure activity?
Geiger counter
(Records all the decays that reach them each second)
What is irradiation?
The process by which objects are exposed to radiation
What is contamination?
When radioactive particles get onto other objects
- contamination isn’t a problem but likely the particles will decay will lead to irradiation
(Increased risk of irradiation)
What determines how harmful radiation is?
Ionising = more dangerous as they can enter living cells, ionise our dna and cause mutations
Ionising radiation:
Alpha, beta, gamma, x ray
If source of radiation is outside the body:
- alpha isn’t harmful as it can’t penetrate through skin
- beta and gamma can penetrate the skin so are very dangerous
If source is on or inside the body:
- alpha radiation would be the most dangerous
Explain nuclear fission
The splitting of a large unstable nucleus and the release of energy
- there are 2 fissionable substances commonly used in nuclear reactors:
Uranium-235 and plutonium-239
1) we start of with large unstable nuclei (uranium 235) and fire a slow moving neutron at it
2) this addition of a neutron causes the nuclei to become even less stable, causing it to split apart into 2 smaller nuclei (daughter nuclei)
3) this process also releases 2 or 3 more neutrons and loads of energy in the form of gamma radiation
4) a neutron released is then fired onto another unstable nuclei for the same process to repeat ( chain reaction)
5) in a nuclear reactor, control rods absorb fission neutrons to ensure that on average only one neutron per fission goes on to produce further fission and energy transfer
Waste:
Nuclear reactions produce waste which may be dangerous due to its radioactive nature and can remain so for a long time depending on half life.
The disposal for such waste needs to be managed with care making it a factor influencing the use of nuclear power for electricity
Explain nuclear fusion
When 2 lighter (positive) nuclei fuse to form a single larger nuclei
- releases tons of energy
The reason fusion produces so much energy:
Some of the mass from the lighter nuclei is being converted into energy rather than transferred to the larger nuclei
- doesn’t produce any radioactive waste
- only happens at very high temperatures and pressures as the force of repulsion between the 2 positive nuclei must be overcome for them to fuse
- the process by which energy is released in stars
