atomic structure Flashcards
What are the four types of ionising radiation?
Alpha, beta, gamma, neutron
What is a radioactive substance?
A substance that contains unstable nuclei that becomes stable by emitting radiation
What is radioactive decay?
An unstable nucleus emitting radiation
What did the alpha particle scattering experiment show?
- Most alpha particles passed through gold foil
- A number of particles were deflected
`this showed:
* Most of the atom is empty space
* There is a small positive nucleus
* The nucleus is where most of the atom’s mass is located
What is an isotope?
Atoms of the same element with different numbers of neutrons
What is an alpha particle made up of?
2 protons and 2 neutrons
What is an alpha particle’s relative mass?
4
What is an alpha particle’s relative charge?
+2
What is beta radiation?
When a nucleus has too many neutrons, one of them changes into a proton, and an electron is emitted
What is a beta particle?
An electron
What is the relative mass of a beta particle?
Zero
What is the relative charge of a beta particle?
-1
What is gamma radiation?
Electromagnetic radiation from an atom’s nucleus
What is the relative mass of gamma radiation?
Zero
What is the relative charge of gamma radiation?
Zero
When does neutron radiation take place?
When alpha particles collide with unstable nuclei in a radioactive substance
What is neutron radiation?
An emitted neutron
What can’t alpha radiation penetrate?
Paper
What can’t beta radiation penetrate?
Aluminium foil
What can’t gamma radiation penetrate?
Thick lead
Rank the types of radiation by greatest ionising power to least.
Alpha, beta, gamma
What is alpha radiation’s range?
5 cm
What is beta radiation’s range?
1 m
What is gamma radiation’s range?
Unlimited
What is ionisation?
When atoms become charged because they lose electrons
What does irradiated mean?
When an object is exposed to ionising radiation, but does not become radioactive
What is radioactive contamination?
The unwanted presence of materials containing radioactive atoms on other materials
Why is ionisation potentially dangerous?
Ionisation of living cells can damage or kill those cells. If genes in a cell are damaged, the damage may be passed on, which could result in cancer
What are safety procedures to reduce radiation exposure?
- Using tools with long handles to keep as far away from sources of radiation when handling them
- Wearing thick gloves
- Spending as little time as possible in at-risk areas
- Shielding by staying behind concrete/lead barriers
What is peer review?
When scientists’ findings are published and shared with other scientists so that they can be checked and verified
What is the activity of a radioactive source?
The number of unstable atoms that decay per second, measured in becquerels (Bq)
What is half-life?
The average time taken for the count rate to fall by half
What are radioactive tracers?
They are used to trace the flow of a substance through an organ. They contain an isotope that emits gamma radiation so it can be detected outside the patient’s body.
What is the use of gamma radiation in cancer treatment?
Gamma radiation in a narrow beam is used to destroy cancerous tumours because it can penetrate deep into the body
What are radioactive implants used for?
To destroy cancer cells. Beta or gamma-emitting isotopes are used which have long enough half-lives to irradiate the tumour, but which are also short enough so that most of the unstable nuclei will have decayed soon after.
What are sources of background radiation?
- Air
- X-rays
- Food and drink (e.g., bananas)
- Nuclear weapons
- Nuclear reactors
What is nuclear fission?
The splitting of a large and unstable nucleus
What occurs during nuclear fission?
- A neutron is fired at an already unstable nucleus (like uranium-235) to make it more unstable
- The nucleus splits into 2 smaller daughter nuclei (of roughly equal size)
- 2 or 3 neutrons are also released from the nucleus, as is energy in the form of gamma radiation
What happens during a chain reaction?
Nuclear fission releases several neutrons which can cause other unstable nuclei to undergo fission and the process repeats, causing a chain reaction
What does a reactor core contain?
- Fuel rods
- Control rods
- Water at high pressure
Why does a nuclear reactor contain water?
It acts as a moderator, slowing down fission neutrons so as to not start an uncontrolled chain reaction
What do control rods in a nuclear reactor do?
They absorb surplus neutrons to keep chain reactions under control
What is nuclear fusion?
The joining of 2 light nuclei to form a heavier nucleus
What happens to some of the mass during nuclear fusion?
It is converted to energy, which is transferred as nuclear radiation
What issues are there with making fusion a useful energy source?
It requires very high temperatures and pressures for the nuclei to overcome the force of repulsion between them and fuse
Why could fusion be a useful energy source?
- Fuel would be easily available as hydrogen is naturally present in sea water
- Helium (the product) is not radioactive, so is harmless
- Releases more energy than fission, which could be used to generate electricity
What is the average atom’s radius?
1 × 10^-10 m
What is the size of the nucleus compared to the radius of an atom?
The radius of a nucleus is less than 1/10 000 of the radius of an atom
What happens when atoms absorb/emit electromagnetic radiation?
Electrons become excited and move to a higher energy level when electromagnetic radiation is absorbed or to a lower energy level when it is emitted
