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Assessment of Characteristics of Thermoluminescence Dosimetry (Tld) System Used In Centre For Energy Research And Training (Cert), Ahmadu Bello University, Zaria

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Assessment of Characteristics of Thermoluminescence Dosimetry (Tld) System Used In Centre For Energy Research And Training (Cert), Ahmadu Bello University, Zaria.

ABSTRACT

Thermoluminescence dosimetry (TLD) system has been used to estimate the personal dose for external occupationally exposed workers in CERT.

The reliability and precision of dose measurements and the accuracy of dose evaluation are important factors for the improvement and achievement of individual monitoring objectives.

In this piece of work, evaluation of characteristics of TLD system was investigated at the Centre for Energy Research and Training, Ahmadu Bello University Zaria.

Dose sensitivity, dose linearity, residual signal, fading, batch homogeneity, stability of Calibration factor, re-usability over 10 cycles, sensitivity to ambient light, and the influence of environmental conditions were evaluated.

Not all investigated properties were found to be within the limits defined by IEC standard. These results are discussed in order to demonstrate the degree of accuracy achieved and the need for its improvement where necessary.

TABLE OF CONTENTS

Content………………………………………………………………Page No
Title page……………………………………………………………. i
Declaration………………………………………………………….. ii
Certification…………………………………………………………. iii
Dedication…………………………………………………………… iv
Acknowledgement…………………………………………………… v
Abstract………………………………………………………………. vi
Table of contents……………………………………………………… vii
List of tables………………………………………………………….. x
List of figures…………………………………………………………. xi
CHAPTER ONE

INTRODUCTION
1.1 Thermoluminescence detectors in dosimetry………………….. 1
1.2 Statement of research problem…………………………………. 3
1.3 Aim and objectives………………………………………………. 5
1.4 Justification………………………………………………………. 5
CHAPTER TWO

LITERATURE REVIEW
2.1 Thermoluminescence (TL)……………………………………… 7
2.2 Role of lattice imperfection in luminescence……………………. 8
2.3 Principles of thermoluminescence……………………………….. 9
2.4 Thermoluminescent dosimetric (TLD) system………………….. 14
2.4.1 TL detectors……………………………………………………… 14
2.4.2 TL reader………………………………………………………… 16
2.4.3 TL measurement cycle…………………………………………… 17
2.4.4 Mathematical evaluation of dose………………………………… 20
2.5 The main characteristics of the TLD system…………………….. 21
2.5.1 Batch homogeneity………………………………………………. 21
2.5.2 Dose linearity…………………………………………………….. 22
2.5.3 Energy response………………………………………………….. 23
2.5.4 Reproducibility…………………………………………………… 25
2.5.5 Dose sensitivity…………………………………………………… 26
2.5.6 Residual signal…………………………………………………… 27
2.5.7 Fading……………………………………………………………. 28
2.5.8 Sensitivity to ambient light………………………………………. 30
2.5.9 Sensitivity to other environmental conditions……………………. 31
CHAPTER THREE

EXPERIMENTAL MEASUREMENT
3.10 Introduction……………………………………………………… 33
3.20 Materials…………………………………………………………. 33
3.2.1 Four detector cards……………………………………………….. 33
3.2.2 TLD reader………………………………………………………. 34
3.2.3 Irradiation facility……………………………………………….. 34
3.30 Methods………………………………………………………….. 36
3.3.1 Batch homogeneity………………………………………………. 36
3.3.2 Reproducibility test……………………………………………… 36
3.3.3 Sensitivity factor (individual correction factor)………………….. 37
3.3.4 Calibration factor………………………………………………… 38
3.3.5 Stability of calibration factor…………………………………….. 38
3.3.6 Dose linearity……………………………………………………. 39
3.3.7 Residual signal…………………………………………………… 39
3.3.8 Sensitivity to ambient light………………………………………. 40
3.3.9 Sensitivity to other environmental conditions……………………. 40
3.3.10 Thermal fading…………………………………………………… 40
CHAPTER FOUR

RESULTS AND DISCUSSION
4.1 Batch homogeneity………………………………………………. 42
4.2 Reproducibility test………………………………………………. 44
4.3 Dose sensitivity (individual correction factor)…………………… 45
4.4 Calibration factor and stability of calibration factor…………….. 47
4.5 Dose linearity…………………………………………………… 48
4.6 Effect of residual signal………………………………………… 49
4.7 Effect of ambient light…………………………………………… 52
4.8 Sensitivity to other environmental conditions…………………… 52
4.9 Time effect of fading……………………………………………… 53
CHAPTER FIVE

SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
5.1 Summary of characteristics of TLD system used in CERT……… 55
5.2 Conclusion……………………………………………………….. 58
5.3 Constraint…………………………………………………………. 58
5.4 Recommendation………………………………………………… 58
References…………………………………………………………… 60
Appendix I (55101 series response over 10 cycles of reading)………… 62
Appendix 2 (6400 series response over 10 cycles of reading)………… 62
Appendix 3 (55101 series response over 10 cycles of reading)……….. 63

REFERENCES

Bilski, P. and Budzanowski, M. (2005). Dosimetric properties of TLD European Cards with high sensitive MCP-7   PCuMgLif .,:7 thermoluminescence detectors for personal dosimetry. In: Annual Report No. 1964/D, Institute of Nuclear Physics, Polish Academy of Science, Krakow.

Daniels, F., Boyd, C.A. and Saunders, D.F. (1953). Thermoluminescence as a Research Tool, Journal of Science, 117: 343-349.

Danilkin, M., Kerikmäe, M., Kirillov, A., Lust, A., Ratas, A., Paama, L. and Seeman, V. (2006). Thermoluminescent dosimeter: Li2B4O7:Mn,Si – a false-dose problem. Proc. Estonian Acad. Sci. Chem., 55(3): 123–131

Duggan, L., Budzanowski, M., Przegietka, K., Reitsema, N., Wong, J. and Kron, T. (2000). The light sensitivity of Thermoluminescent materials:LiF:Mg,Cu,P, LiF:Mg,Ti and Al2O3:C. Radiation. Measurement, 32: 335-342

El-Faramawy, N. A., El-Kameesy, S. U., El-Agramy, A. and Metwally, G. (2000). The Dosimetric Properties of In-House Prepared Copper Doped Lithium Borate Examined Using the TL-Technique. Radiat. Phys. Chem. 58: 9-13

Furetta, C. and Weng, P.S. (1998). Operational Thermoluminescence Dosimetry, World Scientific Publishing, Singapore. pp. 1-247

Haug, A. (1972). Theoritical Solid State Physics, Vol II. Technical University Berlin. pp. 142-143

Herman, C. (1992). Introduction to Health Physics. McGraw-Hill, Inc. pp. 246-248

Izewska, J. and Rajan, G. (2004): Radiation Dosimeters. IAEA Publication, (ISBN 92-0107304-6).

Karikmae, M. (2004). Some Luminescent Materials for Dosimetric Application and Physical Research. Ph.D Dissertation. Chemistry Department, University of Tartu, Estonia. Tartu University Press.

Miljanic, S., Ranogajec-Komor, M., Knezevic, Z. and Vekic, B. (2002). Main Dosimetric Characteristics of Some Tissue-Equivalent TL Detectors. Radiation Protection Dosimeter, 100: 437-442.

CSN Team.

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