12.CHAPTER 2 Literiture Review

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CHAPTER 2LITERATURE REVIEW

This chapter talks about the principal of TLD (Thermoluminescent dosimeter)

and the role of the Magnesium, cuprum and phosphorus as the other entities of

TLD.

2.1 Thermoluminescent principal

All buried materials are exposed to a constant flux of ionising radiation. This radiation

originates from naturally occurring radioactivity, which is present in all deposits, and from

cosmic radiation. When crystalline materials are exposed to ionising radiation, a

redistribution of electrical charge takes place within the crystal. Much of the displaced

charge finds its way back to its original state within a short space of time, but a small

fraction of it can become trapped for long periods in higher energy states. In this way the

crystal can be said to retain a memory of the ionising radiation to which it has been

exposed.

The extra energy that the crystal contains as a result of the radiation exposure can be

released by heating the material. When heat is applied, some of the released energy appears

in the form of light, causing the material to luminesce. If the crystal is then cooled and re-

heated it does not re-emit light, because the energy excess which produced the first

emission has now been released from the crystal. This effect is known as

thermoluminescence (TL). It appears only while irradiated crystals undergo a progressive

temperature increase, and should not be confused with incandescence, which is the light

radiated continuously by hot bodies.

The graph which traces the variation of the TL intensity with increasing temperature is

known as the glow curveof the sample. In general, the glow curve exhibits one or more


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peaks, which occur whenever the increasing thermal energy of the crystal becomes

sufficient to release electrical charge from the various traps in which it is held. Figure 1

shows a set of glow curves exhibiting the sharp peak at 275C which is characteristic of

stalagmitic calcite. Several portions of the same sample were measured to obtain this series

of glow curves. Some of the portions were given artificial radiation doses before theirmeasurement, while others were left unirradiated. The glow curves illustrate how the

intensity of the TL peak grows as the radiation exposure increases. The TL emission

produced by the unirradiated portions is known as the natural TL, since it results from the

radiation dose accumulated by the sample in the natural environment over geological time.

TL measurements such as those shown in figure 1 provide a means of determining the

amount of this radiation dose, which is termed thepalaeodose.

Figure 1. Characteristic glow curves of stalagmitic calcite, showing the growth in the

intensity of TL emission produced by exposing the material to increasing amounts of

ionising radiation. Measurements such as these enable the radiation dose received by the

sample over archaeological or geological time scales to be determined.


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Theory of project

Place and time of experiment

The experiment is being done at block 32, Standard Secunder Dosimetry Laboratory

(SSDL), Malaysia Nuclear Agency.

Irradiation bunker

During experiment, bunker 3 that contains OB-85 machine will be used for irradiation of

Co-60. This bunker is already equipped with angle marker, table, laser, floor ruler and

telescope.

TLD laboratory

TLD cards that had been irradiated will be sent to the laboratory. The laboratory acts as the

supplier of the TLD cards to the user around Malaysia while processing dose report from

users. Overall, there are three type of TLD reader that can read the TLD from card, chip

and powder but in this experiment, only Harshaw 6600 machine will be used to read the

TLD.

TLD card 100H

Gamma irradiation OB-85 machine

This machine was invented by the Steuerungstechnik and Stranlenschutz GmbH from

German for the use of dosimetry laboratory. Besides that, the purpose of this machine is to

maximizing the cover from irradiation, maximum safety and comfort ability by using long

distance control system. Moreover, this machine is keeping radionuclide which is the

source for gamma irradiation of Cesium-137 and Co-60. Furthermore, two seconds is

needed for the radioactive radiation to reach at the irradiation place. The shape of this

machine is cylinder and made of steel. The weight of this machine is around 700kg.

Water phantom


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Title of project: Angular dose response for TLD 100H using cobalt-60

Objectives: 1) To find the measured dose by different angle using TLD

2) To show ratio measured value over standard values are within ICRP

trumpet acceptance limit curve

Instruments

10 pieces of TLD film including one control parameter

Water phantom

Gamma radiation instrument OB-85

Angle marker

TLD Harshaw 6600 and WinREMs

Experimental methods

Overall, there are four main process which are annealing, irradiation, processing and data

analysis.

Annealing

The annealing process is performed before the first TLD cards flashed on the desired

source. This step is done using a Harshaw 6600 machine at a temperature of 400 degrees

Celsius. The annealing process is done to eliminate the remnants of the previous reading

and so that phosphorus returns to its original condition. This process of emptying traps

found in material and stabilizes the electron traps that are almost the same glowing arch

recovered for subsequent readings.

Irradiation


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Data analysis

After the report was released dose, dose reporting for both 2 and 3 element TLD cards of

Hp (10) will be transferred to excel

Charge value and actual dose report

When the reading of the TLD card is done by using Harshaw 6600 machine, the report dose

is obtained but the value obtained must be minus with control dose. The equations are:

Cas laporan bersih = Cas laporancas kawalan

Dos laporan bersih = Dos laporandos kawalan

Trumpet curve graph

Trumpet graph constructed to determine the dose at the right range of -33% to +50%. This

graph formed by plotting the ratio between the actual dose with a dose report (Re) against

the actual dose using the formula below

Dose ratio graph versus angle

This graph is made to differentiate the value of clean dose report be affected at different

angle.


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Results

Standard Dose DD-Control/2 SD-Control/2

2 0.992 0.623

2 1.022 0.6705

2 1.039 1.376

2 1.015 0.692

2 1.003 0.6655

2 1.104 0.7475

2 1.071 0.7435

2 1.052 0.655

2 0.914 0.746

Note :

DD = Deep dose

SD = Shalow dose

Data analysis

a) Trumpet curve

Figure : Dosimeter reading of TLD distribution of gamma Co-60

0

0.5

1

1.5

2

2.5

0.01 0.1 1 10 100 1000 10000

Middle

LimitLower

LimitUpper

Limit

Standar dose (mSv)Measureddose/Standarddose(mSv)


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According to this graph, the points are still in the between of the range from -33% and

+50%. This show that manipulated variable, angle is not having a big impact to the

irradiation dose measured. So, the TLD cards can be supply to the customer.

Discussion

After the experiment is done, the results show that the TLD 100H can be supplied to the

customer for their usage at radiation places. This is because all the value obtained for each

angle is quite the same. All the value obtained is within ICRP trumpet acceptance limit

curve which is between -33% and +50%.

Conclusion

Based on the experiment that had been done, the different angle used had no big effect

towards to the irradiation dose. This is because all the value obtained is within the ICRP

trumpet acceptance limit curve which is between -33% and +50%.

http://www.users.globalnet.co.uk/~qtls/tlnotes.htm
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12.CHAPTER 2 Literiture Review

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