What are Thermoluminescence Dosimeters (TLDs)?
Thermoluminescence dosimeters (TLDs) are instruments that can store radiation energy for a certain amount of time before reading it after being heated up. TLD's operation relies on light being emitted. It is a tool used to measure radiation doses in the disciplines of clinical radiation doses, industrial quality control, irradiated food, environmental monitoring and radiotherapy. Due to its dependability, simplicity, and mobility, TLD continues to be the most effective way to detect radiation doses.
Recent Studies on Dosimeters
The thermoluminescence (TL) process depends on crystal flaws and impurities that increase the materials' ability to retain radiation energy. Since most dosimeters exhibit nonlinear responses across a large range of doses, several investigations have been conducted in recent years to build unique high-performance TLDs that display a linear response over a wide range of doses.
Most studies concentrate on block shape dosimeters such as discs, chips, and pellets. Contrarily, a few researchers have made limited attempts to study nanocomposites that creatively incorporate 2D thin films to function as TL materials. It is crucial to consider the dosimeter's size to make sure that they are suitable for a variety of applications and radiation measurement.
Zinc Oxide (ZnO)
Due to its broad bandgap of 3.37 eV, high transparency of 90% in the visible range, and exciton binding energy of 60 MeV, zinc oxide (ZnO) is advantageous to enhancing effective TL phosphor customized to be utilized in dosimetry applications.
Based on ZnO's characterization, the surface area to volume ratio rises as grain sizes in the nano-range drop, changing optical characteristics such as transmittance.
ZnO naturally contains structures with various morphologies, including nanorods, nanowires and nanoparticles.
ZnO also has drawbacks, such as a high rate of electron-hole recombination. Doping semiconductor nanocrystals with foreign atoms is essential for changing their properties and suggested applications to overcome this drawback. Hence, ZnO can be improved, and its optical and luminescent characteristics can be controlled by adding selective elements such as Ag, Cu, and Au.
Although several researchers created ZnO-based dosimeters, no published study comprehensively examines all aspects. Therefore, the dosimeter properties of hydrothermally produced Ag-doped ZnO thin films were thoroughly examined in this study.
Ag-Doped ZnO Thin Films were Prepared
Ag-doped ZnO thin film growth on the glass was produced using the hydrothermal technique.
In 100 mL of ionized water, 0.1 mol of hexamethylenetetramine and 0.1 mol of zinc acetate dihydrate were combined to create the solution. Introducing AgNO3 into the produced solution and continually stirring formed a homogenous mixture, to which NH3 was then added. The glass substrate was immersed in the solution, and the 150 mL Teflon autoclave was then firmly closed and heated at 180 oC in the furnace before being cooled to room temperature.
The sample was then purified by annealing it in the furnace for one hour at 400 oC. Multiple repeats of this method were carried out for various Ag concentrations.
How the Measurements were Performed
The structure of pure ZnO and Ag-doped ZnO thin films was analyzed using X-ray diffraction (XRD). A scanning electron microscope (SEM) was used to study the morphology of the thin layers.
Energy-dispersive X-ray (EDX) analysis was used to visualize the thin films' nanocomposite. A 0.18 mW laser was used to explore photoluminescence (PL) and ultraviolet-visible (UV-vis) spectrophotometry for transmittance measurement.
Significant Findings of The Study
The hydrothermal (autoclave) approach was used to effectively create the suggested dosimeter thin films, and optical and structural characteristics were examined. The near bandgap edge emission (3.26 eV) and a high-intensity defect in the visible region with a broad range were apparent as two peaks in the PL spectra (2.25 to 1.55 eV).
For linear response doses of 4 Gy, the TL optimal intensity was discovered at 0.5 mol% of Ag, and the glow curve displayed a single peak at 270 C. The TL sensitivity was discovered to be two times greater than that of the TLD 100 chips when it was adjusted to the mass of the thin films. Ag-doped ZnO thin films showed high repeatability, and the percentage depth doses (PDD) findings also supported a match with the TLD 100.
However, one of this study's drawbacks is that the thin films' synthesizing conditions significantly impact the location and form of the glow curve as well as optical fading. The effects of sunshine on these thin coatings were significant. The results showed that the synthetic sample had TL characteristics, making it a good candidate for radiation monitoring.
Reference
Hammam Abdurabu Thabit , Norlaili A. Kabir, Abd Khamim Ismail, Shoroog Alraddadi, Abdullah Bafaqeer and Muneer Aziz Saleh (2022) Development of Ag-Doped ZnO Thin Films and Thermoluminescence (TLD) Characteristics for Radiation Technology. Nanomaterials. https://www.mdpi.com/2079-4991/12/17/3068
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