8.1 - Alpha, Beta and Gamma Decay Flashcards
What was the Rutherford scattering experiment?
The scattering of alpha particles on passage through thin metal foils in an angular distribution.
What does the Rutherford scattering experiment show?
It was proof of a new atomic model (nucleus and electron orbits)
as it indicated a concentration of positive charge at the atomic nucleus. (Since some alpha particles which were also positive got repelled and flung in different directions).
What are alpha particles?
High energy particles made up of 2 protons and 2 neutrons (helium nucleus).
When are alpha particles often emitted?
When a nucleus becomes too large.
What is the most ionising type of radiation? Why?
Alpha due to:
- highest charge +2e
- leads to greatest number of ion pairs per mm in air
- therefore can do more damage to cells
Which type of radiation is the least penetrating?
Alpha . It can only travel through a couple cm of air (can be stopped by paper).
What are beta minus particles?
High energy electrons that are emitted from the nucleus.
What are beta plus particles?
High energy positrons emitted from the nucleus. (antimatter)
When are beta minus particles emitted?
When a nucleus has too many neutrons.
When are beta plus particles emitted?
When a nucleus has too many protons.
How ionising is beta decay?
Moderately, due to it having +1e charge
(slight damage to cells).
How penetrating is beta decay?
Moderately, 20cm-3m in air.
Can be stopped by a few mm of aluminium foil.
What are gamma rays?
High energy electromagnetic waves.
When are gamma rays emitted?
When a nucleus must lose some energy.
What is ionisation?
The removal of electrons from atoms. If the type of radiation has enough energy, it can do this (mainly alpha).
What type of radiation is the most penetrating?
Gamma rays as they can travel the furthest distance in air before being absorbed. (infinite range - follows inverse square law)
Can be stopped by a few cm of lead.
What happens to the nucleons when a B minus particle is emitted?
A neutron turns into a proton
What happens to the nucleons when a B plus particle is emitted?
A proton turns into a neutron.
How do smoke detectors work?
They have Americium-241 stored in them (weak alpha source).
If smoke enters the alarm, it absorbs the alpha particles, hence reducing the current which causes the alarm to sound.
How do thickness controls work?
Beta radiation can determine the thickness of aluminium foil, paper plastic and steel.
Beta because -
alpha = absorbed by materials
gamma = pass straight through
Geiger counter on the other side of material to detect how many make it through.
What is the inverse square law?
When a quantity is inversely proportional to the square of the distance from the source because the surface area of a sphere increases with the square of the radius.
What is the inverse square law equation?
I = k/x²
I = intensity of the gamma radiation (wm⁻²)
k = constant of proportionality
x = the distance from the source (m)
What is the inverse square law equation for gamma radiation? (ratios)
I₁/I₂ = (x₁/x₂)²
I₁ = intensity of the gamma radiation at x₁
I₂ = intensity of the gamma radiation at x₂
x₁ = the initial distance from the source
x₂ = the subsequent distance from the source
What are the 2 categories of background radiation?
1 - natural sources
2 - man made sources
What are 4 examples of natural background radiation?
- Radon gas from rocks and soil (most of the background radiation)
- Cosmic rays from space
- Carbon-14 in biological material
- Radioactive material in food and drink
What are 4 examples of man made background radiation?
- Medical sources
- Nuclear waste
- Nuclear fallout from nuclear weapons
- Nuclear accidents
What is a corrected count rate?
Count rate found from source - background radiation = ccr
What are the best characteristics of a source (if you have to handle it)? (2)
- Short lived isotopes
- The smaller amount of radioactive material the better
What are 6 precautions to take when handling radioactive material?
- Lead lined box
- Protective clothing
- Keeping personal items far away
- Limited exposure (less time)
- Long tongs
- Monitoring the exposure of workers, (radiographers use detector badges for example)
What are the 2 precautions taken by the patient before radiation therapy?
- Patient must be protected with lead to cover parts of the body not to be exposed to radiation
- Exact dose, accurately directed at cancerous tissue
What are the 4 precautions taken by the radiography before radiation therapy?
- Handle source with tongs
- Protected by screen
- Far away from source while dose is given
- Source immediately stored in its lead case after dose is given.
