5. Radiation Protection Flashcards
what are the 2 types of personal dosimeters badges and what must be done before the dose can be read
what kind of dose do they measure
thermolumiscent or film types
requires processing to reveal cumulative dose received
what are the 4 types of personal dosimeters
film badge
pocket ionizing chambers
thermoluminescent dosimeters
optically simulated luminescence
how do film badges work and what change do they undergo when its exposed to radiation
what is it measured with and what can be used to identify energy range
radiation darkens the developed x-ray film
amount of darkening increases with absorbed dose
measured with a densitometer
filters used to identify energy range
what is the crystal in thermiluminescent dosimeters
how does it work and what causes it to luminescence
amount of radiation dose is proportional to what
lithium fluoride crystal
traps and stores energy from ionising radiation
will luminescence if heated
measure intensity of light emitted and amount of light is proportional to radiation dose
what is the crystal in optically stimulated luminesce dosimeters
how does it work and what causes it to luminescence
amount of radiation dose is proportional to what
aluminum oxide crystal
traps and stores energy from ionising radiation
will luminescence if illuminated
measure intensity of light emitted and amount of light is proportional to radiation dose
what is the difference between what causes the luminescence for TLD and OSL dosimeters
TLD will luminescence if heated
OSL will luminescence if illuminated
how does the pocket ionisation chamber work as a dosimeter
what is the absorbed dose proportional to
is processing required
can it be reused and reset
radiation incident on chamber produces ionisation
voltage difference is produced as gas is ionised
voltage is directly proportional to the absorbed dose
dose is read directly from dosimeter, no processing required
yes can be reset and reused
what 2 types of radiation does a pocket ionisation chamber dosimeter measure
gamma
x-ray
what 3 types of radiation does a film badge dosimeter measure
beta
gamma
x-ray
what 3 types of radiation does a TLD measure
beta
gamma
x-ray
what 3 types of radiation does a OSLmeasure
beta
gamma
x-ray
what are 2 advantages to using a pocket ionisation chamber dosimeter
immediate reading
reasonably accurate
what are 4 advantages to using a film badge chamber dosimeter
permanent legal record
most common
cheap
can re-read
what are 2 advantages to using a TLD dosimeter
more accurate than film
durable, resistant to humidity
what are 3 advantages to using a OSL dosimeter
more accurate than film
durable resistant to heat and humidity
can be re-read
what are 5 disadvantages to using a pocket ionisation chamber dosimeter
no permanent legal record
reading can be lost
must be read each day
false readout if jarred/dropped
expensive
what are 3 disadvantages to using a film badge dosimeter
must be measured
affected by heat and humidity
accuracy limited
what are 4 disadvantages to using a TLD dosimeter
no permanent/legal record
must be measured
cant reread
more expensive than film
what are 3 disadvantages to using a OSL dosimeter
no permanent/legal record
must be measured
more expensive than film
the effective dose must be well below what limits over how long
well below 20mSv per year averaged over 5 consecutive years or a max of 50mSv in any single year
what kind of dose is especially a problem and why
cumulative dose is a problem as the more radiation exposed to overtime = more mutations likely to occur
what are the 3 components to ALARA
shielding
distance
time
what is the equation for X-ray attenuation
I = Io e^(-ux)
I = radiation intensity after shielding Io = radiation intensity before shielding u = linear attenuation coefficient x= thickness of shielding material (cm)
what is the linear attenuation coefficient
the constant that describes the fraction of x-ray photons that are absorbed or scattered per unit thickness of a material
which is more attenuating - soft tissue or bone?
soft tissue
what does it mean in terms of preventing penetration of x-ray beams if there is a High linear attenuation coefficient
High linear attenuation coefficient = more effective at removing x rays and stopping them from passing though materials
what is the HVL
the thickness of material required to reduce the intensity of a radiation beam by half
what is the equation for HVL
HVL = ln(2)/u = 0.693/u
what is the relationship between HVL and u
inverse
HVL changes with what?
Half value changes with energy
HVL increase as x ray energy goes up
what is the inverse square law
x-ray intensity is inversely proportional to the square of the distance from the source
I is proportional to 1/d^2
what is the equation used when comparing the x-ray intensity at 2 distances
I2/I1 = (d1)^2/(d2)^2
what is exposure control in terms of distance
small changes in distance and location can make a significant difference to cumulative dose recieved
what is the principle of justification
any decisions that alters the radiation exposure situation should do more good than harm
what is the principle of optimisation of protection
the likelihood of incurring exposure the number of people exposed and the magnitude of their individual doses should all be kept as low as reasonably achievable taking into account economic and societal factors
what is the principle of application of dose limits
total dose to any individual from regulated sources in planned exposure situations other than medical exposures of patients should not exceed the appropriate limits specified by the commission
what is the purpose of structural shielding of imaging facilities
limit radiation exposures of employees and members of the public to acceptable levels
what do the primary and secondary exposure of an individual in an adjacent area to be protected mainly depends on what 5 factors
the amount of radiation produced by the source
the distance between the patient and the radiation source
time spent in adjacent area
the amount of protective shielding between sources and individual
distance between source and the individual
what 3 factors are considered the structural shielding of imaging facilities
location of x-ray sources
orientation and location of x-ray beam for various acquisitions
adjacent areas with typical occupancy and shielding design goals
in terms of primary and secondary radiation, the barrier thickness is a function of which equation
N x T/(P x d^2)
T = how many people are there at one time P = goal of how small do you want to limit it to N = # of patients per week D = distance (meters) from radiation source
what are the DRLs and what are they
diagnostic reference levels
radiation dose levels for typical x-ray examinations for standard sized patients using standard equipment
