TL Phosphor Research Articles

SrAl2O4: Ce: Synthesis and dosimetric characteristics of a new highly sensitive TL phosphor for dosimetry

Strontium aluminate (SrAl2O4) doped with different Ce concentrations was synthesized by the solid-state reaction method to find the best thermoluminescent response. The crystal structure of the material has been analyzed by Rietveld refinement of X-ray diffraction (XRD) results. The effects of different dopant concentrations and thermal annealing regimes on TL sensitivity and the optimum conditions for producing dosimeters with superior sensitivity to commercial dosimeters were investigated. It has been shown that the maximum TL sensitivity is obtained at a concentration of 0.3 mol% Ce and a heat treatment at 1000 °C for 2 h. The TL glow curve of Ce-doped strontium aluminate (SrAl2O4) pellets shows three TL peaks at 90, 150, and 250 °C. The dosimetric characteristics of the new material examined in this work are linear response in the dose range with applications in personal and environmental dosimetry; TL sensitivity; minimum detection dose; reproducibility; energy dependence; and TL signal fading. Based on the results obtained, the synthesized material is a dosimeter with a sensitivity 2.44 times higher than the commercial dosimeter TLD-100 (LiF:Ti,Mg).

Defect Induced MgO: Li, Sm nanophosphor as a new highly sensitive material for thermoluminescence dosimetry

MgO is drawing considerable attention owing mainly due to its tissue equivalency (Zeff = 10.8) and excellent luminescence response. In this work, we report the synthesis and investigation of a highly sensitive MgO: Li, Sm phosphor in nanocrystalline form for TL dosimetry application. The structural and morphological study has been done using X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). TL intensity of gamma irradiated MgO nanophosphor increases with doping of Li and further improves by co-doping with Sm. The MgO: Li, Sm nanophosphor exhibit TL glow curve structure having isolated single peak at 169 °C and linearity in the low dose (13 mGy-5 Gy) as well as high dose range (10–1000 Gy). The TL structure and peak position remains stable at all doses. The phosphor shows excellent stability (low fading rate) and repeatability. TL intensity of MgO: Li, Sm is 12 times higher than that of commercially available LiF: Mg, Ti (TLD 100) and almost equivalent to LiF: Mg, Cu, P (TLD-700 H). This may be attributed to the formation of greater number of density of traps and suitable trapping levels with optimum dopant selection in MgO nanophosphor. The incorporation of the Sm3+ has improved the TL intensity manifold with appearance of desired isolated single peak. The photoluminescence (PL) spectra confirm the Sm3+ emission at 566, 603, 651 and 708 nm with an excitation wavelength of 315 nm. Further the role of dopants has been discussed on the basis of charge transfer mechanism and corelated with associated kinetic parameters for better understanding of TL process. The newly explored MgO: Li, Sm nanophosphor has shown attractive TL dosimetry properties owing to its high sensitivity, stable glow curve structure, dose linearity, low fading and repeatability which meet all the requirement to establish this as a next generation TL phosphor for medical and personal dosimetry application.

Development of LiMgBO3:Tb3+ as a new generation material for thermoluminescence based personnel neutron dosimetry

LiMgBO3:Tb3+ TL phosphor was systematically developed having better personnel neutron dosimetry properties as compared with the standard LiF:Mg,Ti dosimeter. Neutron irradiated PL and EPR studies delineated the underlying defect induced TL mechanism.

Study on Occupational Radiation Exposure at Different Hospitals in Nepal using ThermoluminescenceDosimetry

The clinical efficacy of using ionizing radiation in diagnosis and treatment of diseases has been revolu­tionized, benefitting humankind and, at the same time, imposing deleterious health effects, if not han­dled carefully. Personnel dosimetry has emerged as an essential tool to monitor occupational radiation exposure. The present study intends to reveal and describe the scenario of occupationally exposed staff by assessing an individual’s dose in radiological facilities at different hospitals in Nepal. Thermo luminescent Dosimetry (TLD) has been used for assessing individual doses. Altogether eight hospitals were chosen from different locations of Nepal. TLD badges were worn by the radiation workers on their chest level while working with the radiological equipment for about three to ten months during their routine work. Later the badges were read out in the TLD badge reader system available at Nepal Academy of Science and Technology (NAST) to obtain the exposed doses. CaSO4: Dy was used as TL phosphor. Exposed doses for health personnel during their routine work were founding the range of (2.21 to 16.17) 0.01 mSv per year, which was low compared to the permissible dose limit of 20 mSv per year set up by International Commission on Radiological Protection(ICRP). Although the exposed dose rates in the monitored hospitals are below the recommended dose limits, it should be made as low as possible based on the ALARA principle.

Gamma dose rate effects in luminescence signals of various artificial, well established dosimetric phosphors

The present work attempts to study tentative gamma dose rate effects for the stable TL and OSL signals of specific, well established artficial luminescence dosimeters. Two different dose rates of gamma radiation (2 and 31 Gy/h) were used. The study has been performed to the stable TL peaks of 5 different TL phosphors (LiB4O7:Cu,In; MgB4O7:Dy,Na; LiF:Mg,Ti; CaF2:Dy; BeO) as well as to both OSL components of BeO. Tentative dose rate effects were studied for both dosimetric dose response features as well as kinetic parameters after deconvolution for both signals. Two different groups of materials were revealed. The first one includes materials such as LiF: Mg,Ti, BeO and MgB4O7: Dy,Na; for these, both TL dose response features and TL kinetic parameters are independent on the dose rate. This is also the case for both OSL components of BeO besides the linearity index of the dose response of the fast OSL component; the latter seems to mildly depend on the dose rate. At the same time, experimental arguments based on both dosimetric as well as deconvolution features suggest the presence of tentative dose rate effects for the cases of LiB4O7:Cu, In and CaF2:Dy. Moreover, the effective use of these aforementioned features as probes for identification of dose rate effects is also discussed. The results of the present study suggest that the basic postulate of most phenomenological TL models that traps pre-exist and they are simply filled during irradiation has to be reconsidered.

Impact of C5+ ion beam on Dy activated Sr2B5O9Cl TL phosphor

Sr2B5O9Cl: Dy phosphor was synthesized by modified solid state diffusion method and the impact of C5+ ion-beam on its TL behavior was studied in detail. Phosphor was annealed at 1000 °C for obtaining single phase host. XRD technique was used to confirm the formation of the material and was matched with JCPDS-27-08835. The synthesized phosphor was characterized for photoluminescent spectra. Characteristic emission at 484 nm (4F9/2→6H15/2) and 575 nm (4F9/2→6H13/2) confirms the presence of Dy3+ ions in the Sr2B5O9Cl host matrix. Further TL properties of the synthesized material were studied for fluence range 1.5 × 1011–30 × 1011 ion/cm2 (i.e. 40.14–802.9 kGy dose) of C5+ ion-beam (75 MeV) and were found to show the non linear behavior between a dose range 40.14–802.9 kGy. TL glow curve for Sr2B5O9Cl:Dy irradiated with C5+ ion-beam (75 MeV) was compared with that of γ-ray irradiated phosphor. TRIM/SRIM calculations were performed to correlate the changes in TL properties of Sr2B5O9Cl:Dy phosphor.

Optically stimulated luminescence in doped K3Na(SO4)2 phosphors

Optically stimulated luminescence (OSL) in Cu and Eu doped K3Na(SO4)2 is reported for the first time. The Cu-doped sample shows OSL sensitivity which gets enhanced by co-doping with Mg2+ ions. The Cu-doped and quenched sample shows better sensitivity which is almost double than that of the slowly cooled sample, whereas the sensitivity of Mg co-doped sample remains nearly same irrespective of the thermal treatment. The Cu-doped sample shows TL peak around 200 °C and moderate OSL sensitivity. Doping of Mg shifts the TL peak to around 160 °C and is correlated with good OSL sensitivity. Eu-doped sample does not show OSL sensitivity. However, relatively good OSL sensitivity is observed in Aluminium co-doped and slowly cooled sample, which is about 15% of the commercial Al2O3:C(Landuer Inc.). A near fully optically sensitive TL peak around 155 °C is observed. The dose response is linear and practically no OSL fading is observed in first five days of storage in slowly cooled sample. This study on conventional sulphate-based TL phosphors will be useful in developing OSL phosphors for radiation dosimetry.

Present status and future trends in the development of thermoluminescent materials

There is a continuous growing interest in developing materials for TL radiation dosimetry, especially in the fields of medical, environmental and personal applications. Although several phosphors are being used in these fields today, many efforts are being made in order to develop new TL materials, having better tissue equivalence, and increased sensitivity to gamma radiation, high energy photons, electrons, neutrons and heavy ions. Different preparation methods and properties of several TL materials have been studied so far and it is found that many of these materials constitute a class of TL phosphors with good performances, especially when they are doped with suitable activators.Most widely used and extensively studied materials for TL dosimetry (TLD) are fluorides, sulfates, borates and sulfides of alkali and alkaline earth elements. Besides these, have been developed other phosphors based on metal oxides and mixtures of metal oxides, halo sulfates and different kinds of glasses and perovskites. In this paper, a review of the status and future trends in the development of TL materials is presented.

Micro-Angiographic Fluoroscope: Comparison for Different Input Phosphors

Although flat panel detectors are preferred for image-guided interventional endo-vascular treatments of stroke, they still have limitations in spatial resolution and excess additive noise, which restricts their low-dose performance. The Micro-Angiographic Fluoroscope (MAF), a CCD-based region-of-interest indirect X-ray imager recently developed, can meet the needs for high-resolution, high-sensitivity, real-time image guidance. Although the prototype MAF has better resolution (MTF) and detective quantum efficiency (DQE) than a standard flat panel detector, its performance could be improved by a change in the phosphor. The spatial resolution of such X-ray-to-light converting phosphors is limited by stochastic blurring and k-fluorescent X-ray reabsorption. Thinner phosphors generally improve resolution at the cost of lowering quantum detection efficiency (QDE) and increasing Swank noise, while thicker phosphors provide better absorption at the expense of spatial resolution. Two other Hamamatsu CsI(Tl) phosphors, 300- μm-thick HR, and 500- μm-thick HR, both without front reflective surface, were compared with the current 300- μm HL phosphor with front reflective surface. The phosphors were evaluated by comparing the MTF, NNPS, and DQE of the MAF detector used with each phosphor. All detector configurations showed linearity and quantum noise limited operation for a large range of exposures appropriate for both fluoroscopy and angiography. While the 300- μm HR type prototype demonstrated better resolution than the 500- μm HR type, the latter demonstrated better overall DQE and improved resolution compared to the original 300- μm HL, suggesting it would be the better choice for the MAF design.

Advances in synthesis and characterization of LiMgBO3:Dy3+

The low Z polycrystalline LiMgBO3:Dy3+ material has been successfully synthesized by novel solution combustion synthesis and studied for its luminescence characteristics. LiMgBO3:Dy3+ material has shown promising TL sensitivity with a broad dosimetric glow peak at 154°C. Near the tissue equivalent TL phosphor with Dy dopant has half of the TL sensitivity as compared to commercial TLD-100. The kinetic parameters i.e. trap depth or activation energy and frequency factor from the glow curve derived by using peak shape method. The main dosimetric characteristics such as dose response and fading effect are investigated. The state of dopant confirmed using photoluminescence spectra.

Evaluation of base materials of TL slab dosimeter for heavy-ion radiotherapy

In order to measure a three-dimensional dose distribution in X-ray radiotherapy, we developed TL slab dosimeter with new TL phosphor Li3B7O12(Cu), which has Zeff = 7.42 and a density of 1.01 g/cm3 and synthetic resin as binder [ 1]. We can measure a three-dimensional dose distribution easily and reliably using this detector. This detector showed a promising tool for QA/QC in advanced X-ray radiotherapies such as IMRT, etc. In heavy-ion radiotherapies which shape precipitous dose distributions, it is also necessary to measure three-dimensional dose distribution easily. To use TL slab dosimeter in heavy-ion dosimetry, it is essential to measure its LET dependence sufficiently. And it is necessary to evaluate the dosimetric water equivalence of this dosimeter for heavy ions. Previous studies showed that the relative TL efficiency of this TL phosphor decreased to ∼20% at the Bragg-peak of carbon 290 MeV/u beams and the stopping-power ratio of this dosimeter to water for carbon ions was 0.87 [ 2]. These results were not good for application in heavy-ion radiotherapy. It was often reported that there is a relationship between the glow curve shape of general TLDs (such as LiF and BeO) and LET. Using this relationship of glow curve and LET, the relative TL efficiency can be corrected and we could apply TLDs to dose measurement in heavy-ion radiotherapies.In this study, in order to develop better TL slab dosimeter for heavy-ion radiotherapy using TL phosphors with the above characteristics, we evaluated the dosimetric water equivalence of several base materials for TL slab dosimeter. We chose several kinds of ceramics with heating resistance as the base material; ISOPLATON E3, P1, M2, A98 S1 and Machinable Ceramics, TBS N64, N66, N1, N3 (ISOLITE Co., Ltd). We focused attention on stopping power, scattering power and nuclear cross-section of these materials for heavy ions. We calculated these interactions using the Bethe formula, the Gottschalk formula and the Sihver formula. Figure 1 shows the result of theoretical calculation of the water-equivalence ratio, stopping power ratio S/Sw, scattering power ratio T/Tw and nuclear cross-section ratio σ/σw for carbon-ion beam. In these ceramics, ISOPLANTON S1 was the best of base material for TL slab dosimeter for carbon-ion beam. On the basis of this evaluation, we will develop the TL slab dosimeter for heavy-ion radiotherapy. Fig. 1.Water-equivalence ratio of the base materials for TL slab dosimeter.

Basic characteristics of tissue-equivalent phantom thermoluminescence slab dosimeter using new TL phosphor Li3B7012:Cu

Here we investigate the basic characteristics of the tissue-equivalent phantom thermoluminescence slab dosimeter with synthetic resin type 1 (TEP-TLSD/SR1), a two-dimensional TLD based on TL phosphor Li3B7012:Cu developed by the Urushiyama Research Group. Li3B7O12:Cu has a single glow peak at 120 °C at a heating rate of 0.317 °C s−1. The dose response is linear between 0.1 and 10 Gy. The phosphor, when combined with a synthetic resin, can be molded into 200 mm × 200 mm × 2.5 mm slabs. The system has a Charge Coupled Device (CCD) dependent spatial resolution (pixel pitch) of 640 μm and a pixel response standard deviation of 1.33%. Using simple pixel-based noise compensation, we were able to improve the signal-to-noise ratio (SNR) in the final image. In tests as a TEP, this system gives off axis ratio and percentage dose depth results highly correlated with those of an ion chamber suspended in a water phantom. The TEP-TLSD/SR1 produces similar images to Gafchromic film for X-ray imaging. This TEP-TLSD/SR1 is not only larger than the prototype, but also has a better SNR and improved usability. With further improvements in tissue equivalence, we foresee a system where a TEP and dosimeter are combined into a three-dimensional dosimeter.

Synthesis and study on the luminescence properties of cadmium borate phosphors

Cadmium borate compound prepared through wet chemical reaction from the starting chemicals followed by high temperature solid state synthesis below the melting point to get the final TL phosphor powder. Phase purity and bond details of cadmium borate crystals are characterized using X-ray diffraction technique and infrared spectroscopy. Feasibility of these materials for radiation dosimetry applications was studied after gamma and neutron irradiation. Gamma irradiation of undoped phosphors show a single peak around 185°C whereas doping with gadolinium and silver, new more intense peak observed at 290°C. Irradiation to thermal neutrons revealed single peak around 170°C for all the phosphors. TL emission spectra and photoluminescence (PL) studies were also carried out on the phosphors. These borate materials are found to be highly sensitive to neutrons and hence can be used for neutron detection. Neutron sensitivity of the material is about ten times that of TLD-600.

Response of a plate-type thermoluminescence dosimeter to a therapeutic carbon beam

In order to measure the three-dimensional dose distribution in X-ray radiotherapy, we developed a plate-type thermoluminescence dosimeter (TLD) using the TL phosphor Li3B7O12:Cu, which has Zeff = 7.42 and a density of 1.01 gcm−3. This detector was expected on useful application in advanced X-ray radiotherapies such as intensity-modulated ratiation therapy (IMRT) etc., because it can obtain 3D dose measurements simply and quickly with a single exposure. In this paper, we report the response of this plate-type TLD to a therapeutic carbon beam at the Heavy Ion Medical Accelerator in Chiba (HIMAC). Using a plate heater and charge coupled device (CCD) camera, we captured thermoluminescence images of plate-type TLDs irradiated by a therapeutic carbon beam. The TL intensity was measured at each water equivalent depth and compared with output of the ionization chamber. The relative TL efficiency of this TLD as 60Co gamma-ray equivalent decreased gradually with increasing dose-averaged linear-energy-transfer (LET), reaching about 20% at the Bragg peak of 290 MeV/u carbon ions.

The effect of pre-irradiation annealing on the thermoluminescence of LiF:Mg, Cu, P phosphor grown by EFG technique

LiF crystal doped with magnesium (Mg), copper (Cu) and phosphorous (P) was grown in the form of multicrystalline sheet using Edge-defined film-fed growth (EFG) technique for dosimetry application. These crystals were grown in argon gas atmosphere using graphite crucible and stainless steel die. Dosimetry peak was observed at 210 °C for as-grown crystal. As reported earlier LiF:Mg, Cu, P is a highly sensitive material but losses its sensitivity if annealed at temperature above 240 °C. In this paper, the effect of annealing temperature on thermoluminescence glow-curve structure, maximum peak temperature, peak height and integrated area of the glow peak of EFG grown samples was investigated in detail. Annealing temperature range from 220 °C to 500 °C was considered for the study. Experimental results of the obtained glow curve show that with increase in annealing temperature, glow peak shift towards higher temperature region with substantial increase in TL intensity. Annealing at 500 °C for 10 min gave maximum TL intensity with main dosimetry peak positioned at 233 °C. Change in the defect structure with different pre-annealing temperature was analysed using trapping parameters. ► LiF:Mg, Cu, P phosphor in crystal form has been prepared using EFG technique. ► TL intensity increases with increasing annealing temperature from 220 °C to 500 °C ► Highest TL intensity is observed at annealing temperature of 500 °C ► Advantage of EFG technique for developing TL phosphor is discussed.

Design, Characterization, and Modeling for a Modular High-Resolution Solid-State X-Ray Image Intensifier (SSXII)

A high resolution x-ray imaging system designated the solid state x-ray image intensifier (SSXII) is being developed as a potential replacement of conventional lower-resolution x-ray detectors for neurovascular interventions. The SSXII consists of a CsI(Tl) phosphor to convert x-rays to light, a fiber optic taper to extend the field-of-view and to couple the phosphor to an Electron-Multiplying CCD (EMCCD) which has a built-in gain to boost the signal above the read-out noise floor. A parallel cascade linear-system model is explored and applied to quantitatively analyze the signal and noise transfer at each stage, and optimize the detector performance. The modulation transfer function (MTF), detective quantum efficiency (DQE) and frequency dependent instrumentation noise equivalent exposure (INEE) can be obtained from the theoretical model and experimental measurement. Agreement of these results validates the effectiveness of the model. Finally, compared with the traditional flat-panel detector (FPD), the SSXII exhibits better performance with higher spatial resolution, higher DQE and lower INEE.

Measurement of gamma attenuation for ANR end shield model using CaSO4:Dy phosphor

In the present study, gamma attenuation factors were measured for End shield model of Advanced Nuclear Reactor (ANR). The model is of the size 700×700×1250mm3 and made of steel ball and water mixture with 2×2 lattice locations at the centre of the model. The measurements were carried out using CaSO4:Dy TL phosphor. The streaming of gamma rays (includes core gamma, fission product gamma, activation gamma and capture gamma) was found to be attenuated by a factor of about 1500–4000 at a distance of 1125mm from the incident face of the model, when it is filled with the mixture of water and steel ball. The corresponding exposure rate of streaming gamma rays was found to be about 1.2–2R/h. The attenuation factors derived from the study was used for the designing of actual End shield for ANR.

SU-E-I-99: An Ultra-High Resolution Small Field-Of-View Solid State X-Ray Imaging Detector Based on an Electron Multiplying CCD.

To demonstrate the ultra-high resolution capability of a small field-of-view (FOV) solid state x-ray imaging detector based on an EMCCD sensor. A micro-solid state x-ray image intensifier (micro-SSXII) was developed to serve as an ultra-high resolution region-of-interest (ROI) imaging detector. It is based on an 8 micron, 1004 by 1002 pixel electron multiplying CCD (EMCCD) optically coupled to a 100 micron thick CsI(Tl) phosphor through a fiber optic window resulting in a FOV of 8 mm. The modulation transfer function (MTF) of the micro-SSXII was measured by the slanted edge method. A cast of a rat kidney (made by mixing resin and iodine for contrast) and a mammography line pair test object were imaged at 50 kVp to demonstrate the detector's ultra-high resolution capability visually. The MTF was determined and was 5% at 20 cycles/mm. This is consistent with the clear visualization of the maximum 20 lp/mm group in the image of the mammography test object. Also, iodine bubbles with diameters as small as 25 microns, which are formed by the non-uniform mixing of the iodine in the resin cast, can be clearly identified in the rat kidney vessels. The ultra-high resolution capability (>20 lp/mm) but small FOV (8 mm) of the micro-SSXII in combination with a low-energy x-ray source may have application for investigations of vascular specimen details and other fine structures where optical or other surface imagers would be unsuited for evaluating features below the surface. Contact radiography with this imager combined with a large higher-load focal spot x-ray tube may be a promising substitute for magnification radiography which is limited by the use of specialized low output microfocus x-ray tubes and geometric un-sharpness for large magnifications. Supported in part by: NIH Grants R01-EB008425, R01-EB002873 and an equipment grant from Toshiba Medical Systems Corp.

SU-E-I-112: Pre-Clinical Imaging with an Ultra-High Resolution X-Ray Detector.

To explore the possible applications for a newly developed ultra-high resolution, small field-of-view (FOV) micro-solid state x-ray image intensifier (micro-SSXII) detector. The micro-SSXII is based on an 8 micron, 1004 by 1002 electron-multiplying CCD (EMCCD) optically coupled to a 100-micron thick CsI(Tl) phosphor through a fiber optic window resulting in a FOV of 8 mm with a resolution limit of more than 20 lp/mm. The system has the capability of providing real-time images at low exposures because of the high variable gain of the EMCCD. Several phantoms were prepared by filling catheter tubes of 470 micron internal diameter with separate mixtures of a casting resin with different ratios of three different contrast agents (Omnipaque 350, barium sulphate, tantalum powder). These were imaged with the micro-SSXII at 50 kVp to help select the best mixture for use in making a cast of a rat kidney whose vasculature would then be made radiopaque and visualized. The images of all phantoms showed clumping of these contrast agents within the resin resulting in a non-uniform mix. The image of the phantom filled with Omnipaque and resin in a 1:4 ratio showed the best mixture although large bubble formation of the iodine was observed. This combination was used to make a cast of a rat kidney vasculature and imaged with the micro-SSXII. Small iodine bubbles with diameters as small as 25 microns were clearly delineated in the rat kidney vessels confirming the sharp detail capability of the micro-SSXII. The micro-SSXII in combination with a soft x-ray spectrum can provide excellent images of small animal casts prepared with an appropriate radiopaque resin to study finer details of the vasculature. This new imager has the potential to be used for region-of-interest x-ray image guidance for interventional studies in small animals. Supported in part by: NIH Grants R01-EB008425, R01-EB002873 and an equipment grant from Toshiba Medical Systems Corp.

Synthesis and luminescence in some fluoro-silicates for the possible applications in OSL dosimetry

Various fluoro-silicates, viz. M 2SiF 6 (M=Li, Na, K) were synthesized by reacting the mixture of corresponding salt and silicic acid with Hydrofluoric acid. The thermal analysis of these materials was performed. These materials were doped with ions Ce 3+, Cu +, Ag + and photoluminescence, TL, OSL properties were studied. Intense TL and OSL was observed from these materials. Due to decomposition during heating, these materials may not be suitable as TL Phosphors, but will be good phosphors for radiation dosimetry using OSL.