Radiation Flashcards
Describe the arrangement of subatomic particles in a atom
A positively charged nucleus consisting of protons and neutrons surrounded by negatively charged electrons.
What is an ion?
An atom that has gained or lost electrons to become charged
Who proposed the plum pudding model?
J.J Thompson
Describe the plum pudding model
A positively charged sphere with negatively charged electrons embedded in it
Describe what happened in Rutherford’s alpha particle scattering experiment
- Alpha particles were fired at gold foil suspended in a vacuum
- Most alpha particles passed straight through the foil
- A small amount were deflected as they passed through the foil
- A very small amount came straight back off the foil
What did Rutherford discover from his alpha particle scattering experiment?
- Most of the atom is empty space
- There is a concentration of positive charge in the atom
- The positive charge and mass was concentrated in a tiny volume in the atom (the nucleus)
What did J.J Thompson discover?
Electrons
What did Niels Bohr change about Rutherford’s version of the nuclear model?
Electrons were only allowed to occupy particular orbits
What is an atom?
A positively charged nucleus of protons and neutrons surrounded by negatively charged electrons
Compare the size of the nucleus to the size of the whole atom
Nuclear radius is much smaller than the atom as a whole
Where is most of the mass stored in an atom?
The nucleus
What is an isotope?
An atom with the same atomic number but a different atomic mass to that of a typical atom of that element
Why does an isotope have a different atomic mass?
It has a different number of neutrons
Was charge does a nucleus have?
Positive
What is the charge of a proton?
+1
What is the charge of a neutron?
0
What is the charge of an electron?
-1
What is the relative atomic mass of a
proton?
1
What is the relative atomic mass of a neutron?
1
What is the relative atomic mass of an electron?
1
——-
1835
What is the relative atomic mass of a positron?
1
——-
1835
What is the charge of a positron?
+1
Electrons _____ around the nucleus
Orbit
What happens to electrons if EM radiation is absorbed or emitted?
It will change orbit
How are positive ions formed?
By an atom losing electrons
What are the different ionising radiation types?
- Alpha
- Beta minus (ß-)
- Positron (ß+)
- Gamma
Describe the structure of an alpha particle
The same as a helium nucleus: two protons, two neutrons
Which type of radiation is the most ionising?
Alpha
What type of radiation is stopped by paper?
Alpha radiation
What happens in beta minus decay (ß-)?
A neutron will turn into proton and emit an electron
What type of radiation is stopped by thin aluminium?
Beta minus (ß-)
What is radioactive activity measured in?
Becquerels (Bq)
What happens during positron decay?
A proton turns into a neutron and a positron is emitted from the nucleus
What is a positron?
A positively charged electron
What happens once a positron is emitted?
It is immediately annihilated
What is the most penetrating form of ionising radiation?
Gamma radiation
What is the most dangerous type of radiation if inside a human?
Alpha
What type of radiation is only stopped by thick lead?
Gamma radiation
What happens to the nucleus of an atom when it emits a gamma ray?
Nothing
Where is ionising radiation emitted from?
Unstable nuclei
What is neutron emission?
When a neutron is emitted from the nucleus of an atom
What is background radiation?
The amount of ionising radiation from natural and artificial sources
Name 4 sources of background radiation
- Radon gas
- Food & drink
- Medical uses
- Cosmic radiation
What piece of equipment can be used to measure the level of radiation?
Geiger-Müller tube (Geiger Counter)
What happens to the radioactivity of a source over time?
It decreases
What is half life?
The time taken for the activity from a radioisotope to decrease by half
OR
The time taken for the number of radioactive nuclei in a sample to decrease by half
What is nuclear fission?
The splitting of a large atomic nucleus into smaller nuclei
Describe what happens in a nuclear reactor
- A neutron is absorbed into a Uranium-235 nucleus causing it to become unstable
- It splits into 2 daughter nuclei and releases 2-3 neutrons
- This causes a chain reaction
What are the advantages of using nuclear power to generate electricity?
- No CO2 emissions
- Low fuel costs
- Power station has long lifetime
What are the disadvantages of using nuclear power to generate electricity?
- Negative public perception
- Radioactive waste disposal is difficult and expensive
- High cost to build and decommission
- Large scale accidents can be catastrophic
How is nuclear fission used to generate power?
Energy from neutrons is passed on to other components to heat water to turn turbines to generate electricity
How are nuclear chain reactions controlled?
With a moderator and control rods
What is nuclear fusion?
When two smaller nuclei join together to make one heavier nucleus, accompanied by a release of energy
What is the energy source for stars?
Nuclear fusion
Why can’t nuclear fusion happen at low temperatures or pressures?
Due to the electrostatic repulsion of the protons in the nuclei
Why isn’t nuclear fusion a viable source of energy on Earth currently?
Due to the high temperatures and pressures required, more energy is used to create the reaction than can be usefully harnessed
Name some uses of radioactivity
- In smoke alarms
- For irradiating food
- For sterilisation of equipment
- Cancer diagnosis and treatment
How does the irridation of food work using radiation?
- Food is exposed to a radoactive souce eg. Cobalt-60
- This will emmit gamma rays
- The gamma rays kill all bacteria present
- This will preserve the food for longer
What causes atoms to decay?
Them becoming unstable
When an atom becomes unstable, what happens?
It decays
How do smoke alarms work?
- Alpha particles are present that ionise the air
- These ions carry an electric charge
- Smoke will slow down the ions, reducing the current, setting off the alarm
How is radiation used to measure thickness?
- Radiation fired through material
- The amount of radioactive particles that go through determines the thickness
Which type of radiation is an antimatter particle?
Positron
What does a moderator do?
Slow down neutrons
What do control rods do?
Lower to absorb neutrons to slow down the reaction
