“DOSIMETRY” Measuring Radiation National 5. Why should we measure radiation?
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Transcript of “DOSIMETRY” Measuring Radiation National 5. Why should we measure radiation?
What can be measured?What can be measured?
We are concerned with 3 quantities of We are concerned with 3 quantities of measurement in radioactivitymeasurement in radioactivity
ActivityActivity
Absorbed DoseAbsorbed Dose
Equivalent DoseEquivalent Dose
Activity of a sourceActivity of a source
The The activityactivity (A) of a radioactive source is (A) of a radioactive source is the number of decays per second and is the number of decays per second and is measured in becquerelsmeasured in becquerels
One One becquerelbecquerel (1Bq) is one decay per (1Bq) is one decay per second.second.
ExampleExample
A radioactive source gives off 300 radioactive emissions in 2 minutes. What is the activity of the source in Becquerels?
Activity = Number of emissions time(s)
A = 300 / 120
Activity = 2.5 Bq
Absorbed DoseAbsorbed DoseNot all of the emissions from a radioactive Not all of the emissions from a radioactive
source will be absorbed by a body. source will be absorbed by a body. Much of the ‘activity’ from a radioactive Much of the ‘activity’ from a radioactive
source will miss the body. source will miss the body. Some will pass straight through without Some will pass straight through without
being absorbed. being absorbed.
Absorbed DoseAbsorbed Dose
The The absorbed doseabsorbed dose (D) is the energy (D) is the energy absorbed by each kg of the body.absorbed by each kg of the body.
The The graygray (Gy) is the unit of absorbed (Gy) is the unit of absorbed dose. dose.
One gray is one joule per kilogram. One gray is one joule per kilogram. (1 Gy = 1J/kg)(1 Gy = 1J/kg)
ExampleExample
“Exposure to a radiation dose of four Gray will typically kill about
half of all healthy adults.”
Biological effects of radiationBiological effects of radiation
The actual effect of the radiation on a body will The actual effect of the radiation on a body will depend on several factors;depend on several factors;
1.1. How much energy is absorbed (the How much energy is absorbed (the absorbed dose: D)absorbed dose: D)
2.2. What kind of tissue receives the radiation What kind of tissue receives the radiation (bone, muscle, brain, etc.)(bone, muscle, brain, etc.)
3.3. What type of radiation the tissue is exposed What type of radiation the tissue is exposed to (to (, neutron, proton), neutron, proton)
Equivalent doseEquivalent dose
The The equivalent doseequivalent dose (H) takes into (H) takes into account the type of radiation and the total account the type of radiation and the total energy absorbed.energy absorbed.
Equivalent dose is measured in Equivalent dose is measured in sievertssieverts (Sv).(Sv).
Typical levels of Equivalent DoseTypical levels of Equivalent Dose
Radiation DoseRadiation Dose EffectEffect
2 mSv/yr 2 mSv/yr
(millisieverts per (millisieverts per year)year)
Typical background radiation Typical background radiation experienced by everyone experienced by everyone
(average 1.5 mSv in Australia, 3 (average 1.5 mSv in Australia, 3 mSv in North America)mSv in North America)
9 mSv/yr9 mSv/yr Exposure by airline crew flying Exposure by airline crew flying New York-Tokyo polar routeNew York-Tokyo polar route
20 mSv/yr20 mSv/yr Current limit (averaged) for nuclear Current limit (averaged) for nuclear industry employeesindustry employees
Typical levels of Equivalent DoseTypical levels of Equivalent Dose
Radiation DoseRadiation Dose EffectEffect
50 mSv/yr50 mSv/yr
Former routine limit for nuclear Former routine limit for nuclear industry employees. It is also the industry employees. It is also the
dose rate which arises from natural dose rate which arises from natural background levels in several background levels in several
places in Iran, India and Europe places in Iran, India and Europe
100 mSv/yr100 mSv/yr Lowest level at which any increase Lowest level at which any increase in cancer is clearly evident.in cancer is clearly evident.
350 mSv/lifetime350 mSv/lifetime Criterion for relocating people after Criterion for relocating people after Chernobyl accidentChernobyl accident
Typical levels of Equivalent DoseTypical levels of Equivalent Dose
Radiation DoseRadiation Dose EffectEffect
1,000 mSv single dose1,000 mSv single dose
(1 Sievert)(1 Sievert)
Causes (temporary) Causes (temporary) radiation sickness such as radiation sickness such as
nausea and decreased white nausea and decreased white blood cell count, but not blood cell count, but not
death. Above this, severity of death. Above this, severity of illness increases with dose illness increases with dose
5,000 mSv single dose5,000 mSv single dose
(5 Sieverts)(5 Sieverts)Would kill about half those Would kill about half those receiving it within a monthreceiving it within a month
SummarySummary
QuantityQuantity UnitUnitUnit Unit
symbosymboll
DefinitioDefinitionn
Activity (A)Activity (A) BecquereBecquerell
BqBqNumber of Number of
disintegrations disintegrations per secondper second
Absorbed Absorbed dose (D)dose (D) GrayGray GyGy
Energy Energy absorbed per absorbed per
kgkg
Equivalent Equivalent dose (H)dose (H) SievertSievert SvSv
Measure of Measure of biological effect biological effect
of radiationof radiation
Equivalent Equivalent dose rate (H)dose rate (H)
Sievert Sievert per hourper hour SvhSvh-1-1 Biological effect Biological effect
per unit time.per unit time.
Comparison with rain!Comparison with rain!
QuantityQuantity DefinitionDefinitionIf it was rain If it was rain
it would it would be….be….
ActivityActivityNumber of Number of
disintegrations disintegrations per secondper second
How much How much rain is fallingrain is falling
Absorbed Absorbed dosedose
Energy Energy absorbed per kgabsorbed per kg
How much How much rain is hitting rain is hitting
youyou
Equivalent Equivalent dosedose
Measure of Measure of biological effect biological effect
of radiationof radiation
How wet you How wet you getget
Safety with RadioactivitySafety with Radioactivity
What are the What are the safety proceduressafety procedures necessary necessary when handling radioactive substances.when handling radioactive substances.
What are the 3 methods of What are the 3 methods of reducing the reducing the equivalent doseequivalent dose
Include the Include the radioactive hazard signradioactive hazard sign and and state where it should be displayedstate where it should be displayed