BASIC TYPE of RADIATIONs

ACCIDENT#1

February 1, 2000 – The radiation source of a teletherapy unit was stolen from a parking lot in Samut Prakarn, Thailand and dismantled in a junkyard for scrap metal. Workers completely removed the 60Co source from the lead shielding, and became ill shortly thereafter. The radioactive nature of the metal and the resulting contamination was not discovered until 18 days later. Eight injuries and two deaths were a result of this incident.

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

Where is Samut Prakarn?

ACCIDENT#2

December 2000 – Three woodcutters in the nation of Georgia spent the night beside several "warm" canisters they found deep in the woods and were subsequently hospitalized with severe radiation burns. The canisters were found to contain concentrated 90Sr. The disposal team consisted of 25 men who were restricted to 40 seconds' worth of exposure each while transferring the canisters to lead-lined drums. The canisters are believed to have been intended for use as generators for remote lighthouses and navigational beacons, part of a Soviet plan dating back to 1983.

Where is Georgia?

ACCIDENT #3

March 11, 2006 – at Fleurus, Belgium, an operator working for the company Sterigenics, at a medical equipment sterilization site, entered the irradiation room and remained there for 20 seconds. The room contained a source of 60Co which was not in the pool of water. Three weeks later, the worker suffered of symptoms typical of an irradiation (vomit, loss of hair, fatigue). One estimate that he was exposed to a dose of between 4.4 and 4.8 Gy due to a malfunction of the control-command hydraulic system maintaining the radioactive source in the pool. The operator spent over one month in a specialized hospital before going back home. Today he still shows after-effects (fatigue) that should attenuate in several months. To protect workers, the federal nuclear control agency AFCN and private auditors from AVN recommended Sterigenics to install a redundant system of security. It is an accident of level 4 on the INES scale.

Recent Accident

Alexander Litvinenko, Russian KGB

Litvinenko died on 23 November, and on 24 November his death was linked to a "major dose" of radioactive polonium-210. Polonium-210 is an alpha emitter with a half-life of 138 days and is a fairly volatile metal; the ingested maximum permissible body burden is 0.03 microcuries, or about 7 nanograms. Reportedly Litvinenko's symptoms and time from exposure to death are consistent with the ingestion of about 5 microcuries of polonium-210 (about 1 microgram, equivalent to a sphere 0.6 millimeters in diameter).

Be Aware!

SCOPE of LECTURE

● External Radiation– radiation source is outside the body,

● Only for X-ray and Gamma-ray–

Overview

● Basic Discussion on X-Ray tube● Brief discussion on Biological Effect of

Radiation● SI Unit for radiation Dose,● Radiation Dose Limit● Measurement of Radiation Dose● Method to control radiation dose

X-Ray Generation

X-Ray Generation

X-RAY TUBE

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

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

Possible Effects with Dose Level

5 to 20 Possible latent effects (cancer), possible chromosomal abberations

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)

BIOLOGICAL EFFECT OF RADIATION

CharacteristicsOne 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 x­ray=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.

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

ANNUAL DOSE LIMIT

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

Hourly Rate

● Assuming 50 working weeks/year and 40 hrs/week

1 mSvyr

×1 yr

50 week×

1 week40 hr

=0.0005 mSvhr

=0.5 Svhr

RADIATION MONITORING DEVICES

Why do we need them?

● Radiation threats are unique in that you can't see, smell, taste, hear or feel them, until it's already done its damage and you are suffering the effects.

FOUR COMMON DOSIMETER

● SURVEY METER,● PEN DOSIMETER,● FILM BADGE,● TLD

SURVEY METER

STYLISH SURVEY METER

Notes on Survey Meter

● Regular Calibration● One low range and if possible (high

range)– low range to ensure safe level,– high range for accurate large dose rate.

● Must have instrument for any radiation related work (a portable one)

PEN DOSIMETER

How to read?

FILM BADGE

Inside View

Thermoluminescence Dosimeter

Thermoluminescence Dosimeter

RADIATION CONTROL

CONTROLLING THE EXPOSURE

TIME

● Determine the dose rate using Survey Meter

● Calculate the allowable time

Equivalent Dose=Dose Rate×Time

Time=Equivalent DoseDose Rate

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 DoseDose Rate

=4Sv

100Sv hr−1=0.04 hr=2.4 minutes

CONTROLLING BY DISTANCE

● Inverse Square Law– The dose is inversely proportional to the

square of the distance from the radiation source,

– Example● If the dose rate at 1 meter from the source is 100

microSievert/hr, than the dose at 10 meter from the source is 1 microSievert/hr

Inverse Square Law

Important Formula

D2

D1

= x1

x22

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

x 2

Example

D1=100 Sv /hr

D2=?

x1=1meter

x 2=10D2=

x1

x22

×D1

D2= 0.510

2

×100Sv

=1

100×100Sv

=1 Sv

CASE STUDY:

The radiation dose rate from an X­Ray machine at 1 meter away is 100 Sv/hr. Calculate the safe distance?

Solution:We will define safe distance as the distance where the radiation dose rate is 0.5 Sv/hr.

X 2=X 1D1

D2

=11000.5

=14.14 meter

SHIELDING

● Rule of thumb: Hiding behind something is better than directly exposed yourself to radiation.

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

What is the best material?

● Dense material:– plumbum (most common)

● Other common material:– Concrete– Steel Plate

SHIELDING

Thickness Calculation

x= 1M⋅

ln D0

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 rate0.5 Sv

hour

M

D0

D

Requirement

● Get the data on mass attenuation coefficient 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 using survey meter.

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

CASE STUDY #1Calculate 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= 1M⋅

ln D0

D

x= 10.2323⋅11.35

ln 1000.5 =2.0 cm

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= 1M⋅

ln D0

D

x= 10.0978⋅2.3

ln 1000.5 =23.6 cm