““DOSIMETRY”DOSIMETRY”

Measuring Radiation Measuring Radiation

National 5National 5

Why should we Why should we measure radiation? 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

ActivityActivityof a sourceof a source

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 Dose

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.”

Equivalent DoseEquivalent Dose

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

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