Chapter 18 Flashcards
Radioactive decay is a…
Random process
Why are ionising radiations beneficial?
- Ionising radiations are easily detected
- When absorbed, the energy from the radiation warms things up
- Energy carried by radiations means they can damage living matter (put to good use when sterilising medical equipment)
Radiation can help kill cancerous cells, but…
It must not damage any surrounding healthy tissue
Ionising an atom =
To knock an electron out of the atom (requires energy)
Difference between x-rays and gamma rays
X-rays = photons produced by accelerated electrons Gamma-rays = photons emitted by nuclei
Ionising radiations loose energy when…
They pass through matter
The more readily the radiation ionises atoms =
The less thickness of shield is required (less penetrating the radiation is)
How are labs etc. designed to prevent radiation risks
- Lead-lined canisters are used
- Thick steel + concrete walls shield nuclear reactors
The thickness of the shield increase as…
The energy of the radiation increases
Intensity of radiation decreases…
Exponentially with thickness
Graph of intensity I, against thickness, x
Exponential relationship
y decreases as x increases
Equation for the intensity I
I = I0 x e ^(-μx)
where I0 is the initial intensity of the beam, μ is the absorption coefficient of the material and x is its thickness.
What is the unit of the absorption coefficient?
The unit of μ is m–1.
What is ‘half-thickness’
The thickness needed to half the number of photons getting through.
Equation for half-thickness
X1/2 = ln(2)/ μ
Ways that photons are absorbed?
- Ionise atom or put atom in higher energy level
- Scattering from electrons
- Electron-position pair production
What factors are taken into account when considering how harmful the radiation will be?
-Energy of radiation
-Ionisation damage to cells
Depends on type of radiation and type of tissue
Absorbed does =
Number of joules absorbed per kilogram of tissue measured in Grays (Gy)
Activity in Becquerel’s =
disintegrations per second
Absorbed dose in grays =
Energy per kg
Does equivalent in Sievert =
Does in gray x quality factor
Probability of developing cancer =
From radiation = 5% per Sievert
Equation for risk =
Probability of event x consequence
Methods of transfer (types of radiation):
- Alpha
- Beta
- Gamma
- X-rays
- Photons
- Neutrons
- Cosmic rays