Introduction and Radiation Review Flashcards
Angiography
- The radiographic visualisation of blood vessels after injection of a radio opaque contrast
- Help people who have blockages to the heart by inserting a permanent stent to hold the blood vessel open
May be
- Diagnostic
- Interventional
Radiation Protection (ICRP)
- Legislation and regulations are guided by recommendations from the International Commission on Radiological Protection
- Give the ‘official’ scientific view of the effects of radiation on people and so laws are written around their content
Radiation Protection (ARPANSA)
- Australian Radiation Protection and Nuclear Safety Authority
- Most of the QLD regulations are based on the ARPANSA regulations and codes
Deterministic Effect
- Most organs/tissues are unaffected by the loss of even a large number of cells
- When the number lost becomes large enough there is observable damage or loss of function
- Probability of causing observable damage or loss of function will be zero at small doses but rise rapidly (to 100%) above threshold dose
- Above the threshold, the severity of the damage will also increase with dose
Stochastic (Random) Effects
- As a result of exposure to IR, a cell is modified but still left viable and able to divide
There is a period in which:
- The probability that the effect will occur increases with dose
- The severity is not affected by the magnitude of the dose
- Examples include the induction of cancer and genetic effects
Recommendations for limiting exposure to IR are designed to:
- Prevent deterministic effects
- Keep the probability of stochastic effects from exceeding an acceptable level
Isotope
Nuclides with the same Z but different A
Same number of Protons but different number of Neutrons
Alpha Decay
Emission of a He particle from the nucleus
Beta Decay
Emission of an anti-neutrino and the conversion of a neutron to a proton
Positron Decay
Emission of a neutrino and the conversion of a proton to a neutron
Gamma Rays
- Emitted following nuclear decays due to changes in nucleon configuration
- A nucleus in an unstable, high energy state can decay to a lower energy state
- Excess energy is emitted
X-Rays
- Emitted following a change in the state of the atom (e.g., in particular the electron structure)
- Usually following ionisation, when an outer electron may fill the vacancy, the excess energy is emitted as an X-ray
Photon Interactions with Matter
- Photoelectric Effect
- Compton Scattering
- Pair Production
- Coherent Scattering
- Photonuclear Disintegration
Energy Loss Processes - Photons
- Photons penetrating matter will be attenuated via the 3 interaction processes
Intensity - Mew
- Is difficult to calculate so known features are obtained from experimental measurements
- Increases rapidly with atomic number
- Decreases rapidly with photon energy
Energy Loss Processes - Electrons/Positrons
Some expected properties of electron interactions:
- Large angular deflection due to similar masses (range is defined as the linear distance penetrated into material)
- Large kinetic energy transfer in collisions
- Large changes in direction and magnitude in velocity
Types of Ionising Radiation
Particulate
- Alpha and beta particles
Electromagnetic
- X rays and gamma rays
LET
Linear Energy Transfer refers to the amount of energy locally transferred to the material per unit path length of the IR
LET Radiations
Low LET Radiation
- x ray, gamma ray, electrons, beta particles
Medium to High LET Radiations
- Protons, neutrons and alpha particles
Interaction of Medium/High LET radiations with Matter: Neutrons
- Neutron are unchanged so they cannot interact via coulomb forces
- They deposit most of their energy in biological tissue by knocking on protons from water molecules
- These ‘knock on protons’ being moving charged particles then cause ionisation and gradually slow down in the material
- Hence the biological effect of neutrons and of protons is similar (for the same amount of energy deposited in tissue)
Interaction of Medium/High LET radiations with Matter: Alpha Particles and Protons
- Interact mainly with the atomic electrons and gradually slow down in the material
- They have a short range and high LET
Interaction of Low LET radiations with Matter: Electrons and Beta Particles
- These are electrically charged, so they interact by coulomb forces primarily with atomic electrons but occassionally with a nucleus
- When they interact with an atomic electron they lose energy and slow down
- Generally they move on to produce further ionisations
- The net effect is that each incident electron or beta-particle produces many
ionisations, losing energy (slowing) on each occasion until it stops in the
material
Interaction of Low LET radiations with Matter: Photons
Interact with matter primarily by:
- The photoelectric effect
- Compton scattering
- Pair Production
- These moving electrons behave as do incident electrons interacting with matter via the coloumb forces
- These coulomb interactions cause ionisation and excitation of the material and the moving electrons gradually slow down and stop
Dose
- When IR transfers energy to matter the energy transferred is quantified as Dose
- There is a quantity ‘exposure’ which is also sometimes incorrectly called dose
Exposure
- Applies to x rays and gamma rays only and is a measure of the flux (number) of photons
- It is ‘that quantity of x or gamma radiation that produces in air, ions carrying 1 coulomb of charge per kg of air
Absorbed Dose
- This is the fundamental dose unit in radiation protection
- Expresses the energy absorbed per unit mass as a result of exposure to IR
- ‘The energy imparted by the IR per unit mass of matter’
Equivalent Dose
- For the same absorbed dose, the biological effects of IR depend on the type and energy
- The equivalent dose is a weighted dose
- With the weighting factor determined by the type and energy of the radiation to which the organ or tissue is exposed
Effective Dose
- A variation of the response of different tissues to radiation
- Need to apply a tissue weighting factor to the equivalent dose
Tissue Weighting Factor
- Represents the relative contribution of that organ or tissue to the total detriment due to effects resulting from uniform irradiation of the whole body
- Vary with the population of exposed individuals
Equivalent and Effective Doses
- Desirable that a uniform equivalent dose over the whole body should numerically be the same as the effective dose
- Achieved by setting the tissue weighting factors
- Factors are chosen to be independent of the type and energy of radiation
- It is desirbale that a uniform equivalent dose over the whole body should give an effective dose equal to that uniform equivalent dose
- Hence, an effective dose of 1mSv has the same risk whether the equivalent dose was delivered to the thyroid or to the the lung or to the total body
Committed Effective Dose
- External Radiation Exposure
- Internal Radiation Exposure
External Radiation Exposure
- Ceases when the source is turned off or when a person moves away from the source
Internal Radiation Exposure
- An intake of a radionuclide commits the person to receiving a dose for a period of time which depends on the effective half-life of the radionuclide
Committed Equivalent Dose
The equivalent dose which an organ or tissue is committed to receive from the intake of radioactive material
Committed Effective Dose
The effective Dose which a person is committed to receive from the intake of radioactive material
Justification
- the justification of a practice
- no practice shall be adopted unless it produces sufficient benefit to the exposed individuals or to society offset the radiation detriment it causes
Optimisation
Three considerations
- The magnitude of doses
- The number of people exposed
- The liklihood that potential exposures will be kept ALARA
Limitation
- Places limits on the risk to individuals so that risks do no exceed a value which is considered unacceptable for everyday, long term exposure
