Radiation Protection Flashcards
What is ionising radiation
Radiation with enough energy so that during an interaction with an atom, it can remove tightly bound electrons from their orbits, causing the atom to become charged
What does the type of radiation depend ion?
The source of radiation
X rays - type? Source? Application?
Electro magnetic
Energetic electrons
Diagnostic radiotherapy
Gamma rays - type? Source? Application?
Electro magnetic
Radioactive material
Isotope imaging therapy
Alpha particles - type? Source? Application?
Only travel 1-2cm of air
Do not penetrate body so cannot be used for imaging
Beta particles - type? Source? Application?
Radioactive material
Isotope imaging therapy
X ray production: Bremsstrahlung
As electrons bombard a target, they decelerate when passing near the positively charged nucleus
The electron is deviated and looses energy the lost energy is emitted in the form of radiation
99% of the energy is converted to heat and only 1% of the incoming energy converts to X-rays.
Characteristic radiation
The second interaction occurs by the incoming electron ejecting an inner electron
An electron from a higher energy level takes its pace emitting x rat energy in the process
This energy emission is a characteristic of the target material
Sources of radiation
In uk exposed to 2.7mSv - background exposure
Interactions with tissue - why is radiation damaging?
DNA strand breaks
1 strand break normally repaired
If the strand doesn’t repair leads to cell death
If it repairs incorrectly leads to cell mutation
Biological effects might not become apparent for hours, weeks, years depending on dose rate of radiation received.
Photoelectric effect
Process whereby photons falling knock electrons out of a surface
Photoelectric absorption is responsible for creating contrast in the image
Describe the photoelectric effect in terms of electrons
Incident x ray comes across an atom in body, it knocks electron out of orbit shell (its ejected as a photo electron) an electron from a higher energy shell drops down to fill the gap in a lower energy shell and in this process energy is lost as radiation
Compton scattering
Occurs when an X-ray encounters an electron from an outer shell with little binding energy
Describe the Compton scattering in terms of electrons
The electron is ejected and the remaining energy is remitted immediately in the form of an X-ray
The result is a X-ray of different direction and slightly less energy
Not constructive in image formation
Patient becomes a source of radiation themselves
Compton effect -> (Produces scattered X-ray which degrades the image and is not constructive in image formation)
Units of radiation - absorbed dose
Energy deposited per unit mass of a material
Measured in joules per kilogram (J Kg^-1)
Given the unit gray (Gy)
Not useful measure,ent - doesn’t take into account the type of radiation or the tissues exposed)
Units of radiation - equivalent dose
Absorbed dose to a tissue multiplied by a radiation weighting factor Wr
Usually represented by the symbol H:
H= S D, Wr
Unit is J Kg-1 given he name sievert (Sv)
Equivalent dose is the absorbed dose multiplied by a radiation weighting factor - its measured in joules / kg (sievert)
Radiation weighting factors
Radiation type and weighting factors
Photons 1
Electrons 1
Protons 5
Alpha 20
Neutrons 5-20
Heavy nuclei 20
Eg, for heavy nuclei, Equivalent dose is 20x absorbed dose
Effective dose - what is it and why is it useful
Equivalent dose doesn’t take into account the tissues being radiated but the effected dose does as well as the sensitivity of that tissue to radiation.
Define effective dose
Effective dose (E) is derived from the equivalent dose to a tissue by multiplying by a tissue weighting factor (Wt)
The effective dose has to be summed over all tissues)
E= S Ht Wt
Effective dose is measured in sieverts (Sv)
Somatic effects
Manifested in the person irradiated
Genetic effects
Manifested in the offspring of the person irradiated
Deterministic (certain, tissue reactions) Radiation effects
Depends on threshold being met
Probability: will occur if a certain quantity of radiation is received
Severity: depends on dose
Limits: limits app,for deterministic effects
Effects: erythema, sterility, radiation sickness, epilation, death
Stochastic (random) radiation effects
Probability: depends on total dose received
Severity: independent of the dose / dose rate
Limit: there is NO lower limit
Effects: cancer / genetic effects
