2-Radiation Safety for Student

8/3/2019 2-Radiation Safety for Student

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BASIC TYPE of RADIATIONs


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ACCIDENT#1

February 1, 2000 The radiation source of a teletherapy unit was stolenfrom a parking lot in Samut Prakarn, Thailand and

dismantled in a junkyard for scrap metal.Workers completely removed the 60Co source from thelead shielding, and became ill shortly thereafter.The radioactive nature of the metal and the resultingcontamination was not discovered until 18 days later.

Eight injuries and two deaths were a result of thisincident.

Teletherapy - Radiation treatment administered by using a source that isat a distance from the body, usually employing gamma-ray beams fromradioisotope sources.


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Where is Samut Prakarn?


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ACCIDENT#2

December 2000 Three woodcutters in the nation of Georgia spent thenight beside several "warm" canisters they found deep inthe woods and were subsequently hospitalized withsevere radiation burns. The canisters were found to containconcentrated 90Sr. The disposal team consisted of25 men who were restricted to 40 seconds' worth ofexposure each while transferring the canisters tolead-lined drums.The canisters are believed to have been intended foruse as generators for remote lighthouses andnavigational beacons, part of a Soviet plan datingback to 1983.


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Where is Georgia?


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ACCIDENT #3

March 11, 2006 at Fleurus, Belgium, an operator working for the company Sterigenics, at amedical equipment sterilization site, entered the irradiation room and

remained there for 20 seconds. The room contained a source of 60Co whichwas not in the pool of water. Three weeks later, the worker suffered ofsymptoms typical of an irradiation (vomit, loss of hair, fatigue). One estimatethat he was exposed to a dose of between 4.4 and 4.8 Gy due to a malfunctionof the control-command hydraulic system maintaining the radioactive source inthe pool. The operator spent over one month in a specialized hospital beforegoing back home. Today he still shows after-effects (fatigue) that should

attenuate in several months. To protect workers, the federal nuclear controlagency AFCN and private auditors from AVN recommended Sterigenics toinstall a redundant system of security. It is an accident of level 4 on the INESscale.


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Recent Accident

Alexander Litvinenko, Russian KGB

Litvinenko died on 23 November, and on 24

November his death was linked to a "major dose" ofradioactive polonium-210. Polonium-210 is an alphaemitter with a half-life of 138 days and is a fairlyvolatile metal; the ingested maximum permissiblebody burden is 0.03 microcuries, or about 7

nanograms. Reportedly Litvinenko's symptoms andtime from exposure to death are consistent with theingestion of about 5 microcuries of polonium-210(about 1 microgram, equivalent to a sphere 0.6millimeters in diameter).


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Be Aware!


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SCOPE of LECTURE

External Radiation

radiation source is outside the body,

Only for X-ray and Gamma-ray


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Overview

Basic Discussion on X-Ray tube

Brief discussion on Biological Effect ofRadiation

SI Unit for radiation Dose,

Radiation Dose Limit

Measurement of Radiation Dose

Method to control radiation dose


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X-Ray Generation


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X-Ray Generation


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X-RAY TUBE


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BASIC PARAMETERS

POTENTIAL DIFFERENCE

normally stated in kV (1 kV = 1000 V),

determine maximum energy of the x-ray,

controlling the penetrating power of the x-ray

FILAMENT CURRENT

determine the intensity of the beam

determine the dose rate


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ESSENTIAL RADIATION UNIT

Radioactivity

Curie (Ci)

Bacquerel

Xray Intensity (Roentgen, R) Absorbed Dose

rad

Gray (Gy)

Equivalent Dos

rem

sievert

IMPORTANT NOTE:FOR X-RAY1 rad = 1 rem1 Gy = 1 Sv

IMPORTANT NOTE:FOR X-RAY1 Gy = 100 rad1 Sv = 100 rem


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Possible Effects with Dose Level

5 to 20 Possible latent effects (cancer), possible chromosomalabberations

25 to 100 Blood changes

More than 50 Temporary sterility in males

100 Double the normal incidents of genetic defects

100 to 200 Vomiting, diarrhea, reduction in infection resistance,possible bone growth retardation in children

200 to 300

More than 300

300 to 400

400 to 1000

Serious radiation sickness, nausea

Permanent sterility in females

Bone marrow and intestine destruction

Acute illness and early death (usually within days)


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BIOLOGICAL EFFECT OFRADIATION


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Characteristics

One characteristic of ionizing radiation on human body is that the energy

absorbed is low but the biological effects are serious. For example after

receiving a lethal dose of 10 Gy (for x ray=10 Sv ), the body temperature will only

increase by 0.02 oC but the dose may lead to death of all the exposed entities.

The second characteristic is the latent biological effects of radiation. Acute

biological effects can occur within several hours to several days while the long

term effects usually appear several years after the exposure.


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Maximum Permissible Dose

Radiation Worker:

50 mSv/year

about 25 microSv/hour (base on 50 wks/yr

and 40 hrs/week working time). General Public:

5 mSv/yr


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ANNUAL DOSE LIMIT

Recommendations of the International Commission on RadiologicalProtection (ICRP Publication No. 60)


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Hourly Rate

Assuming 50 working weeks/year and 40hrs/week

1mSv

yr

1yr

50week

1week

40hr=0.0005

mSv

hr=0.5

Sv

hr


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RADIATION MONITORINGDEVICES


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Why do we need them?

Radiation threats are unique in that youcan't see, smell, taste, hear or feelthem, until it's already done its damage

and you are suffering the effects.


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FOUR COMMON DOSIMETER

SURVEY METER,

PEN DOSIMETER,

FILM BADGE,

TLD


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SURVEY METER


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STYLISH SURVEY METER


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Notes on Survey Meter

Regular Calibration

One low range and if possible (highrange)

low range to ensure safe level,

high range for accurate large dose rate.

Must have instrument for any radiation

related work (a portable one)


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PEN DOSIMETER


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How to read?


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FILM BADGE


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Inside View

Thermoluminescence


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ThermoluminescenceDosimeter


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Thermoluminescence


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ThermoluminescenceDosimeter


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RADIATION CONTROL


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CONTROLLING THE EXPOSURE

TIME


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TIME

Determine the dose rate using SurveyMeter

Calculate the allowable time

Equivalent Dose=Dose RateTime

Time=Equivalent Dose

Dose Rate

C St d


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Case Study

In a day, you are allowed to receive 4Sv. Thus, if you have to be in a

region with the dose rate of 100 Sv/hour, then you can only spend a

maximum of:

T=Permitted Dose

Dose Rate

=4Sv

100Sv hr1=0.04 hr=2.4 minutes

CONTROLLING BY DISTANCE


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CONTROLLING BY DISTANCE

Inverse Square LawThe dose is inversely proportional to the

square of the distance from the radiationsource,

Example

If the dose rate at 1 meter from the source is 100microSievert/hr, than the dose at 10 meter fromthe source is 1 microSievert/hr

I S L


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Inverse Square Law

I t t F l


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Important Formula

D2

D1

= x1x2

2

Dose rate at Point 1

Dose rate at Point 2

Distance between Point 1 and Source

Distance between Point 2 and Source

D1

D2

x1

x2

Example


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Example

D1=100Sv/hr

D2=?

x1=1meter

x2=10

D2=

x

1

x2

2

D1

D2= 0.510

2

100Sv

=1

100100Sv

=1Sv

CASE STUDY:


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CASE STUDY:

The radiation dose rate from an X Ray machine at 1 meter

away is 100 Sv/hr. Calculate the safe distance?

Solution:

We will define safe distance as the distance where the radiationdose rate is 0.5 Sv/hr.

X2=X1

D

1

D2

=1

100

0.5=14.14meter

SHIELDING


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SHIELDING

Rule of thumb: Hiding behindsomething is better than directlyexposed yourself to radiation.

What is the best material? How thick the material should be?

What is the best material?


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What is the best material?

Dense material: plumbum (most common)

Other common material:

Concrete

Steel Plate

SHIELDING


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SHIELDING

Thickness Calculation


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Thickness Calculation

x=1

M

ln D

0

D is the mass attenuation coefficient at given energy,

is the density of the material used,

is the dose rate without shielding,

is the permissible dose rate0.5Sv

hour

M

D0

D

Requirement


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Requirement

Get the data on mass attenuationcoefficient of the chosen materials

For this workshop: lead and concrete

Get the kV value Get the density of the material

Get the dose rate of machine, from the

manufacture or measurement usingsurvey meter.


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from:http://physics.nist.gov/PhysRefData/XrayMassCoef/tab3.html


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CASE STUDY #1


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CASE STUDY #1

Calculate the thickness of lead required to reduce the dose rate of

a 400 kV x-ray machine from 100 Sv/hr to a safe level?Given:Density of Lead = 11.35 g/cm3,Mass attenuation coefficient = 0.2323 cm2/g

x=1

M

ln D

0

D x=

1

0.232311.35 ln 100

0.5 =2.0cm

CASE STUDY #2


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CASE STUDY #2Calculate the thickness of ordinary concrete required to reduce the dose

rate of a 400 kV x-ray machine from 100 Sv/hr to a safe level?Given:Density of Lead = 2.3 g/cm3,Mass attenuation coefficient = 0.0978 cm2/g

x=1

M

ln D

0

D x=

1

0.09782.3 ln 100

0.5 =23.6 cm

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