Biological effects of radiation Flashcards
Name three interactions of electrons with matter.
- Ionization
- Excitation
- Heat production
How are electrons produced from incident radiation and how many interactions will a 100KeV electron undergo before stopping?
- e-s produced from photoelectric, Compton scatter and pair production.
- e-s lose approx 34eV for each ionisation
- 100KeV photon will make 100000/32 ~3000 interactions.
Describe how an incident electron can cause excitation.
- Incident e- raises orbital e- to high energy orbit.
- chemical reactivity may change.
- e- returns to original state with emission of low energy photon (UV or visible).
Describe how an incident electron can cause heat production.
- Incident e- can transfer energy to whole atom.
- increase in K.E of atom can produce heat.
List the physical and chemical effects of radiation.
- Ionization.
- Heating effects: 45mGy give 1/100000 degree rise.
- Light production: fluorescence, phosphorescence and thermoluminescence.
- Physio-chemical effects i.e. photographic film.
- Chemical changes i.e. Fe++ - Fe+++.
List the Biochemical and Biological effects of radiation.
- Biochemical: enzyme inactivation.
- Biological: killing of cells and bacteria, damage to DNA.
What effect does cell division rate have on radio-sensitivity and give examples of radio-sensitive cells?
- More rapid cell division, greater the radio-sensitivity.
- e.g. Lymphoma cells, haemopoetic stem cells, intestinal crypt cells, spermatagonia.
Describe how free radicals are created.
- Radiation ionises water molecules.
- H2O + radiation -> H2O+ + e-.
- H2O+ -> H+ + OH*.
- e- + H2O -> H2O-.
- H2O- -> H* + OH-.
- Hydroxyl radical is highly reactive.
- OH* + OH* ->H2O2 hydrogen peroxide: toxic.
Explain how free radicals cause damage to DNA.
- OH radical involved in producing DNA single strand breaks, chromosome aberration, bacterial and mammalian cell killing.
- Indirect action causing single or double strand breaks.
What are the two types of action on DNA when exposed to ionising radiation?
- Direct action: arising from initial x-ray interaction.
- Indirect action: arising via free-radical interactions.
List two ways that DNA can break and give the number of breaks that a 1Gy x-ray will cause for each one.
- Signle strand break: 1Gy -> 1000 SSBs.
- Double strand break: 1Gy -> 50-100 DSBs.
Describe how radiation can damage chromosomes.
- 2 different pre-replication chromosomes.
- 1 break in each chromosome.
- Illegitimate union
- Replication
What is Linear energy transfer (LET)?
- LET is a measure of the rate at which energy is transferred to the medium (i.e. ionization density along the track of the particle).
- More penetrating beam has lower LET.
Rank the following from highest to lowest LET:
100KVp x-rays, 5MeV neutrons, 20KeV beta particles, 1MeV gamma rays, 5MeV alpha particles
- 5Mev alpha particles: 50 KeVμm^-1.
- 5MeV neutrons: 20 KeVμm^-1.
- 20KeV beta particles: 10 KeVμm^-1.
- 100KvP x-rays: 6 KeVμm^-1.
- 1MeV gamma rays: 0.5 KeVμm^-1.
State the linear quadratic equation.
- S = exp-(αD + β^2).
- S is the surviving fraction.
- D is the dose.
- α and β are coefficients.
