Abstract
Purpose: The purpose of this study was to compare calibration factors for deep dose equivalent Hp (10) and shallow dose equivalent Hp (0.07) between Cesium (Cs)-137 and X-ray sources when they are exposed to same dose and to determine uncertainties with MTS-N (LiF: Mg, Ti) chips when they are exposed to low dose ≤ 2mGy. Material and Methods: Thermoluminescent (TL) chips were annealed at 400oC for one hour and allowed to cool and were subjected to a temperature of 100oC for another two hours using a TLD Furnace Type LAB-01/400. They were then taken to a Secondary Standard Dosimetry Laboratory (SSDL) for irradiation using a Cs-137 source at known doses (0.2-2mGy). A RadPro Cube 400 manual TLD Reader was used to determine corresponding TL signal. The above process was replicated but with a calibrated X-ray unit as the source for calibration. Results: The calibration factors (CF) from the line graph of dose (mGy) against TL signal (count) for Cs-137 source with Hp (10) and Hp (0.07) were 3.72 x 10-6 and 5.97x10-6 mGy/count respectively. Those with X-ray source for Hp (10) and Hp (0.07) were 3.44x10-6 and 4.05x10-6 mGy/count respectively with an overall coefficient of determination (R2) = 0.99. The adjusted maximum percentage deviation between the actual and calculated dose for both sources was -2.74%. The percent (%) deviation of the mean with both sources for Hp (10) and Hp (0.07) was 3.9% and 19% respectively. Conclusion: Adjusted percent deviation from both sources were within the recommended dose limit of ±30% by the Radiological Protection Institute of Ireland (RPII) and within the International Commission on Radiological Protection (ICRP) limit respectively. Better accuracy was seen for Hp (10) with both sources compared to Hp (0.07). Calibration of the MTS-N chips using both sources was successful and can be used for personal dosimetry.
Highlights
In the past half century, many books have been written on the characteristics, performance, and theory of thermoluminescence (TL) [1,2]
The slope is practically regarded as the calibration factor for the thermoluminescence dosimters (TLDs) chips
Our study compared the use of two different sources for MTS-N (LiF: Mg, Ti) calibration
Summary
In the past half century, many books have been written on the characteristics, performance, and theory of thermoluminescence (TL) [1,2]. The physical principle of operations of thermoluminescence can be described as a two-way process. The first stage is the change of the system from equilibrium to metastable state by absorption of energy from ultraviolet (UV) or ionizing radiation. The second stage is the relaxation of the system back to equilibrium by energy release such as light with the help of a thermal stimulation (TLD reader). TL is the thermally stimulated emission of light following the previous absorption of energy from radiation [3, 4]. The most commonly used thermoluminescence dosimters (TLDs) for medical applications are LiF: Mg, Ti, LiF: Mg, Cu, P and Li2B4O7: Mn because of their tissue equivalence. MTS-N (LiF: Mg, Ti) was used in our study
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