4 - Biological effects of ionising radiation Flashcards
Describe an alpha particle.
- 2 protons, 2 neutrons
- large particle, travels a few inches
Describe a beta particle.
- electron
- small, travels a few feet
Describe a gamma ray.
- EM radiation
- high energy, travels long distances
Describe x-rays.
- high or low energy
- travel long distances
What is ionising radiation?
Radiation that has enough energy to knock an electron out of an atoms electron shell, making it an ion
How much energy is deposited into matter when it is ionised?
35 eV
How much energy is involved in atomic bonds?
4 eV
Define direct damage to DNA.
Radiation interacts with atoms of the DNA molecule or another important part of the cell
Define indirect damage to DNA.
Radiation interacts with the water in the cell, producing hydroxyl free radicals which damage the DNA
What type of radiation typically causes double strand damage?
Alpha
What effect does double strand damage have to DNA?
- harder to repair than single damage
- strands sometimes rejoin incorrectly and this can cause mutations
What is dose rate?
- the rate at which damage is caused, compared to the amount of radiation received
- if the dose rate is lower, the cell can repair damaged DNA before more damage occurs
What factors affect tissue radiosensitivity?
- the type of cells that make up the tissue
- whether the cells are actively dividing
Describe the radiosensitivity of stem cells.
Divide frequently therefore are very radiosensitive
Describe the radiosensitivity of differentiated cells.
No mitotic behaviour, therefore less radiosensitive
Which tissues would be considered highly radiosensitive?
- bone marrow
- lymphoid tissue
- GI
- gonads
- embryonic tissues
Which tissues would be considered moderately radiosensitive?
- skin
- vascular endothelium
- lungs
- lens of eye
Which tissues would be considered least radiosensitive?
- CNS
- bone and cartilage
- connective tissue
What are the three responses of a cell to mutation?
Repaired = viable cell
Death = nonviable cell
Survives but remains mutated = cancer
Define dose.
The measure of energy deposited in the subject by radiation, measured in Gy
Define equivalent dose.
Absorbed dose multiplied by the weighting factor of the radiation, measured in Sv
Define effective dose.
Equivalent dose multiplied by the tissue weighting factor, measured in Sv
Which radiations have a weighting factor of 1?
X-rays, beta, gamma rays
Which types of radiations have a weighting factor of 20?
Alpha
