Biological effects of ionising radiation Flashcards
What is ionising radiation?
radiation with enough energy to turn atoms into ions
What is the most significant effect of ionising radiation in living organisms?
Damage to DNA
How can radiation indirectly damage DNA?
- radiation interacts with water in the cell producing free radicals
- free radicals can cause damage
what are free radicals?
unstable, highly reactive molecules
How does radiation directly damage DNA?
By interacting with the atoms of a DNA molecule or another part of the cell
How does radiation directly damage DNA?
By interacting with the atoms of a DNA molecule or another part of the cell
briefly describe a double strand break
- usually result of alpha radiation
- if repair is faulty it can lead to mutations
What factors determine the biological effect of radiation?
- type of radiation
- amount of radiation/dose
- time over which dose is received/dose rate
- tissue or cell type irradiated
What 2 factors determine the radio sensitivity of tissues?
- the function of the cells that make up the tissues
- if the cells are actively dividing
Give examples of highly radiosensitive tissues
- bone marrow
- lymphoid tissue
- gastrointestinal
- gonads
- embryonic tissues
give examples of moderately radiosensitive tissues
- lens of eye
- skin
- lung
give examples of low radiosensitive tissues
- CNS
- bone and cartilage
- connective tissue
What is the absorbed dose, and what unit is it measured in?
- the energy deposited by radiation
- units of Gray (Gy)
What is the equivalent dose and what unit is it measured in?
- absorbed dose multiplied by weighting factor depending on type of radiation
- 1 for beta, gamma and x rays, 20 for alpha particles
- measures in Sieverts (Sv)
Briefly describe the Linear No Threshold (LNT) model
- estimates the long term biological damage from radiation
- assumes damage directly proportional to dose
- assumes radiation is always harmful e.g. several small exposures has same effect as one large exposure
what are the 2 types of radiation effects?
- Deterministic effects
- stochastic effects
Describe the deterministic effects of radiation
- tissue reactions
- only occur above a certain dose
- severity of effect is related to dose recieved
describe the stochastic effects of radiation
- the probability of occurrence is related to the dose recieved
- no known threshold
- likelihood of effect occurring increases as the dose increases
What 2 categories can stochastic effects be subdivided into?
- somatic - results in disease or disorder
- genetics - abnormalities in descendants
What is the estimated annual background radiation dose?
2.2mSv
Give sources of natural background radiation
- cosmic rays
- internal radionuclides from diet
- radionuclides in air e.g. radon gas
- external gamma radiation e.g. soil
- air travel
