Physics Week 3 Flashcards
(28 cards)
How does ionising radiation damage tissue?
It ionises atoms, breaking chemical bonds in DNA, potentially leading to mutations, cell death, or cancer.
What factors affect the severity of radiation damage?
Type of radiation, dose, dose rate, and type of tissue exposed.
What are the two main timing categories of radiation effects?
Early (minutes–days) and late (months–years) effects.
What is a deterministic effect?
Severity increases with dose and usually has a threshold (e.g., burns, organ failure). The probability of a stochiatric effect also increases.
What is a stochastic effect?
Probability increases with dose, no threshold (e.g., cancer, genetic mutations).
What is the difference in time delay for deterministic vs stochastic effects?
Deterministic: prompt (hours–months); Stochastic: latent (5–30 years).
What is an acute effect of radiation?
High, brief exposure causing symptoms/death within days to months (e.g., >10 Sv causes death in weeks).
What are degenerative effects?
Long-term tissue/organ damage from doses of hundreds of mSv (e.g., skin erythema).
What are teratogenic effects?
Fetal abnormalities due to in utero exposure (e.g., malformations from tens of mSv).
What are stochastic effects?
Cancer or heritable mutations from low doses (~10 mSv), with delayed onset.
What is the Linear No-Threshold (LNT) model?
Assumes every dose carries risk with no safe threshold.
What is the linear threshold model?
Suggests there is a minimum dose below which no harm occurs.
What is the hormesis model?
Suggests low doses may stimulate protective biological responses.
What does ALARA stand for?
As Low As Reasonably Achievable.
What are the three principles of radiation protection?
Time, Distance, Shielding.
How does distance reduce radiation dose?
According to the inverse square law: intensity ∝ 1/d². Because radiation travels in an outward radial direction.
How does time reduce dose?
- less chance of being affected by the ionsing radiation.
How does shielding limit dose?
- Ionising radiation has attentuation interactions to reduce the intensity of radiation given as the dose.
What is attenuation in radiation protection?
Reduction in radiation intensity due to absorption or scattering.
What equation describes attenuation?
I(x)=I(0)e^−μx
What is the linear attenuation coefficient (μ)?
A measure of how easily a material attenuates radiation; depends on energy, density, and atomic number.
What is the mass attenuation coefficient (μ/ρ)?
Attenuation per unit mass; independent of density.
What is the half-value layer (HVL)?
The thickness of material that reduces radiation intensity by 50%;
HVL= 0.693/μ
HVL increases when the linear attenuation factor is lower because more material is required to reduce the radiation intensity by 50%.
HVL decreases when the linear attentuation factor is high because the material is more attenuating therefore less of it is required to reduce the intensity by 50%.
Describe the photoelectric effect.
- an incoming photon that has enough energy to be absorbed by an electron to remove it from its inner orbital shell. As the electron is removed, one jumps down an orbital releasing energy known as the secondary characteristic x-ray. This contains energy that is the difference between the inital and final energy of the orbital shell.
- the probability of this interaction occuring is directly proportion to the atomic numbe,r but inversly proportional to the energy of the photon.
- therefore, an x-ray with higher energy will have less attenuation interactions and therefore be transmitted through the material more easily, whereas a low intensity x-ray will have greater attenuation interactions.
