13. RADIATION HEALTH EFFECTS: DOSE LIMITS Flashcards
1
Q
- Fill in the empty spaces in the table.
A
- 20 mSv in a year averaged over 5 years
- 1 mSv in a year
- 20 mSv
(milliSilvert) - 500 mSv
- 500 mSv
- 50 mSv
2
Q
- What is meant by Occupational?
A
- people who work with radiation
- such as nurses, doctors and staff
3
Q
- In terms of Absorbed Energy, what can be said about Ionising Radiation?
A
- Ionising Radiation is much more harmful than chemical
or other physical agents
4
Q
- What happens when ionisation occurs?
A
- it results in a small cluster of ion pairs
- each of these clusters represent a very small amount
of energy - this energy is highly localised
- it has around 100 eV per cluster
5
Q
- What happens when small radiation exposures occur?
A
- these are known as Dental Exposures
- they will create millions of ion pairs in the exposed
tissue
6
Q
- What can be said about energy deposition at the Bimolecular Level?
A
- the energy deposition is highly localised
- it is non-uniform
7
Q
- Which parts of the organism receive no energy at all?
A
- relatively large volumes of each cell and the
macromolecules within it - they receive no energy at all
8
Q
- What happens in the regions where Ionisation occurs?
A
- the energy deposited is very high
9
Q
- How much energy does an ionising radiation event produce?
A
- it produces approximately 70 times more energy than
the energy required to break a hydrogen bond in DNA
NB:
- this means that even small doses of (mGY) of Ionising
Radiation will produce a large number of random sub-
molecular events in cells
10
Q
- What happens to the sensitive macromolecules when they are exposed to ionising radiation?
A
- they may be damaged
- this can happen without raising the temperature of the
cell outside of the normal range
NB:
- this unique form of Radio-sensitivity only happens with
ionising radiations
11
Q
- What percentage of Ionisation levels are potentially harmful?
A
- 1%
- this is because the energy absorption events rarely
occur close to important cellular macromolecules
12
Q
- What is the most abundant cellular molecule?
A
- water
- this means that radiation absorption mostly ionises
H2O molecules - this occurs within nanoseconds during exposure
13
Q
- What happens when the Radiolysis of water molecules occurs?
A
- transient free radicals (+OH°) (hydroxyls)
and +H° (Hydrogens)
and Hydrated Electrons are formed
14
Q
- What are Hydrated Electrons?
A
- these are extra electrons that are solvated in liquid
water
15
Q
- What can be said about the Transient free radicals, the +H° and the Hydrated electrons?
A
- they are highly reactive
- they usually recombine within milliseconds to re-form
water molecules
16
Q
- What happens if these radicals are formed within a few nanometers of larger biological macromolecules or cell membranes?
A
- they may interact with these cellular components
THIS INDIRECT ACTION MAY INITIATE:
- a chain of sub-cellular events
- these will produce temporary or permanent
microscopic and detectable changes in the cells
17
Q
- What can happen even if Free Radicals are made due to low radiation doses?
A
- the Free Radical effects may lead to delayed and
increased risks of cancer in the exposed individual - it may cause genetic changes in the future
18
Q
- What happens if the Free Radicals are made due to high radiation doses?
A
- the microscopic damage due to the Free Radical Attack
is more severe - it is more likely to kill the cells
- this would lead to the temporary or permanent
changes in normal tissue functions
19
Q
- Which is the most damaging of the Free Radicals?
A
- the Hydroxyls
- the +OH°
- it is believed to initiate about ⅔ of all the effects of the
external exposure of the body to X and Y Rays
20
Q
- In which two ways can radiation attack the DNA?
A
- Indirect Route
- Direct Route
21
Q
- What is meant by the Indirect Route?
A
- Radiation
- Water molecules are ionised by the radiation
- Free Radicals are formed
- These attack the DNA
- This causes damage
22
Q
- What is meant by the Direct Route?
A
- Radiation
- Damage
NB:
- this route is very high in energies
- it can attack the DNA directly due to this
23
Q
- What attacks the DNA through the Indirect Route?
A
- the Free Radicals that are surrounding the cellular DNA
attack it - this attack produces most of the known high or low
dose effects of Ionising Radiation
24
Q
- Other than the Free Radicals, what else can cause damage directly to the DNA?
A
- the relatively smaller free electrons
- these are negatively charged
- heavier and more densely ionising charged particles
are much more likely to cause direct DNA damage - EG: alpha particles
: such as Radionuclides
25
Q
- Does this diagram make sense?
A
- yes
26
Q
- What is Base Modification or Deletion?
A
- it is a type of radiation damage to the DNA
- it causes genetic defects
- it increases the mutation rates in the reproductive cells
27
Q
- What happens if the damaged DNA Bases are not repaired or eliminated?
A
- it increases the risk of malignant cell transformation
28
Q
- What is Bond Breakage?
A
- this facilitates the loss of a base
- it changes the molecular shape and structure
29
Q
- What is Single Strand Breakage?
A
- this can occur at random
- it happens in either strand along the DNA double helix
30
Q
- What are Double Strand Breaks?
A
- these are due to a single event
- they can also be caused by the random coincidence of
two single events that occur at the same time on the
complementary DNA strands
NB:
- this process becomes more probable the higher the X-
Ray dose and Dose rate are
31
Q
- What is Cross-Linkage?
A
- this potentially inhibits the replication of the DNA
