Week 1 Flashcards
What are the two most important documents in regards to radiation protection?
ICRP60
ICRP103
What is the ARPANSA?
Australian Radiation Protection Nuclear Safety Authority
What is the difference between deterministic and stochastic effects?
Deterministic: the cell my be prevented from surviving or reproducing (cell dies)
Stochastic: a viable but modified cell may result (cell lives but is mutated and goes on to reproduce)
What are the two outcomes of ionsing radiation induced cellular damage?
deterministic and stochastic
What are the effects when the number of cells dying due to radiation become too large? (Deterministic)
hair loss, cataract formation
Observable damage or loss of function
What affect on the organ being treated is evident during the lead up to, and once the threshold dose is reached? (Deterministic)
The probability of causing observable damage/ loss of function will be zero at small doses
Once the threshold dose is reached the damage/ loss of function will rise rapidly (to 100%).
Above the threshold the severity of the damage will also increase with dose.
What are the Stochastic Effects? (general)
when a cell is mutated but still left viable and able to divide
When should you expect to see the effects of damage due to ionising radiation, in regards to stochastic effects?
There is a latency period when nothing happens (can be decades) before the damage is evident
What is the effect of stochastic effects as dose increases?
The probability that the effect will happen increases with dose,
HOWEVER, the severity is not affected by the magnitude of the dose
What are recommendation for limiting exposure to IR designed to do?
Prevent deterministic effects
keep the probability of stochastic effects from exceeding an acceptable level
Describe alpha decay?
emission of a He particle from the nucleus
Describe beta decay?
Neutron decays to proton
Describe positron (B+) decay?
Proton to neutron
What are the two broad classes of ionising radiation?
- Particulate (particles/mass), alpha and beta particles
2. Electromagnetic (no mass), x and gamma rays (photons)
What do interactions of IR with matter involve?
transfer of energy from the IR to either the atomic electrons or nuclei
What is LET?
Linear Energy Transfer
how much energy will be transferred to the material per unit path length of the IR
High LET= ?
loses energy in short distance
Does the LET vary for different types of IR?
yes- the LET depends upon the energy of the IR
What types of IR are considered as low LET radiations?
x-ray, gamma, electrons and beta particles
What types of IR are considered as medium to high LET radiations?
protons, neutrons and alpha particles
How much energy does it take to produce and ion pair (in most materials)
it takes about 34 eV of energy deposited to produce an ion pair.
( 1 MeV deposited produces about 30,000 ionising events)
For high LET are the ionisation events close or far away?
They are much closer together in comparison to low LET radiations (Remember each dot represents an energy deposit of 34eV)
How does LET relate to biological damage?
Due to High LET the ionisation events are much closer together- therefore, its more likely to break both strands of DNA. (One break in the strand can usually be repaired)
Why are Low LETS less likely to cause biological damage?
Because the ionisation events are further apart.
Therefore the probability of causing a double break in the DNA strands is decreased.
Can neutrons interact with coulomb forces?
No- because neutrons are uncharged
How do neutrons deposit most of their energy into biological tissue?
They deposit most of their energy by smacking into protons from water molecules (billiard ball collisions), these ‘knock on’ protons are charged and therefore cause Ionisation
Tell me about alpha particles and protons in regards to high LET interactions with matter?
- Interact mainly with the atomic electrons- gradually slow down in the material
- They have short range and have high LET and thus cause more damage
Tell me about electrons and beta particles in regards to Low LET interactions with matter? (5)
- Electrons and beta particles are lighter and therefore cause less damage.
- Both interact by coulomb forces with electrons and sometimes a nucleus (positive and negative interactions)
- When the electrons or beta particles interact with electrons they lose energy and slow down
- When they interact with electrons large changes in directions occur (erratic paths)
- May cause the atomic electron to be ejected from the atom (ionising the atom)
How do photons and gamma rays primarily interact with matter?
the photoelectric effect
Compton scatter
pair production
Which two interactions with photons and gamma rays are the most important?
Particularly Compton scatter is the most important in tissues at the energies used in MI or RT
In which two interactions do the photons transfer all of or part of their energy to atomic electrons?
PE
CS
What happens when electrons and beta particles interact with an atomic electron?
When the electrons or beta particles interact with electrons they lose energy and slow down
Since electrons and beta particles are electrically charged, which type of force occurs and with which atomic particles?
they interact with coulomb forces primarily with atomic electrons but occasionally with a nucleus
When electrons and beta particles interact with atomic electrons what happens to their course of direction?
they undergo large changes in direction and therefore follow quite erratic paths and they may cause the atomic electron to be ejected from the atom
What is the overall effect when electrons or beta particles interact with low LET radiations?
each electron/ beta particle produces many ionisations, loses energy (slowing) and eventually stops
What is dose?
when IR transfers energy to matter the energy transferred is quantified as dose
What are the three terms used to quantify dose?
absorbed, equivalent, effect dose
What is the definition for exposure?
how much electrical charge is produced
(measure of the flux of photons)
applies only to x-rays and gamma
Explain what exposure is
it is the amount of x- or gamma radiation that produces ions carrying 1 coulomb of charge per kg of air (in air)
what does the term ‘Absorbed Dose’ mean?
it is the energy (IR) absorbed (by matter) per unit mass
What is the equation for absorbed dose?
D = dE/dm
where dE is the energy being deposited (joules)
dm is the mass of the matter (kg)
D is the absorbed dose (Gray)
What is 1 Gray equal to?
1 Joule /kg
Why is equivalent dose relevant?
This quantity is introduced to take into account that for the same absorbed dose, the biological effects of different types of IR will be different.
What is the symbol used to represent equivalent dose ?
Ht (little t)
What is the weighting factor used for, in terms of equivalent dose?
the weighting factor is determined by the type and energy of the radiation to which the organ or tissue is exposed to
In the equation for equivalent dose what do each of the symbols represent? (Ht = (sum of E) Wr x Dtr)
Ht is the equivalent dose Wr: is the radiation weighting factor for the particular radiaotn Dtr: is the absorbed dose averaged over the organ/tissue Sum of (E): is over the various radiations incident upon the organ
What is equivalent and effective dose measured in?
Sv and like the Gy = 1 Joule/kg
What is effective dose used for?
This shows how different tissues types respond differently to radiation
e.g. gonads are much more sensitive than skin
What type of weighting factor is used for effective dose?
tissue weighting factor Wt
In the equation for effective dose what do each of the symbols represent? E = (sum of) Wt x Ht
E is effective dose
Wt is the tissue weighting factor
Ht is the equivalent dose
As the tissue weighting factor increases what does that say about the sensitivity of that organ?
the more sensitive the organ, the higher the tissue weighting factor e.g. gonads = 0.20, skin = 0.01
What are the two classes of IR exposure?
external radiation exposure
internal radiation exposure
