Main Dosimetry Peak Research Articles

Thermoluminescence characteristics of gamma-irradiated nano-alumina

The focus of this study lies in exploring the properties of thermoluminescence (TL) in nano-alumina, including the correlation between TL intensity and absorbed dose, identification of individual luminescence peaks, and investigation of trap parameters for potential dosimetry applications. The samples were irradiated by 60Co with doses ranging from 530 to 2646 Gy. Micro-sized α-Al2O3 had a prominent dosimetry peak at maximum temperature Tm = 435 K. Nano-α-Al2O3 samples with 40 and 50 nm particle sizes exhibited a TL luminescence glow curve, with the main dosimetry peak in the low-temperature region and a complex structure at higher temperatures (above 500 K). The observed maximum of the main dosimetry peak depended on the nanoparticle size and was 460 K for the sample with particle size of 40 nm and 467 K for 50 nm. The main dosimetry peak was described by the superposition of the two peaks.A computerized glow curve deconvolution method was applied to determine the parameters of the traps responsible for TL using the Microsoft Windows-operated GlowFit program, assuming first-order kinetics. The found values of the activation energies were 0.97 ± 0.01 eV for the trapping center responsible for the peak with Tm = 458 ± 3 K and, accordingly, 1.05 eV for the peak with Tm = 473 ± 3 K. The estimated values of the frequency factor were s ≈ 1.01 × 1010 and 1.3 × 1010 s−1 for the peak with Tm = 458 ± 3 K, and 2.06 × 1011 s−1 for the peak with Tm = 473 ± 3K, respectively. The lifetime for the traps in nano-α-Al2O3 was estimated as 43–56 days for the first trap and approximately 65 days for the second trap. It is assumed that these traps are responsible for TL emission at the low-temperature part of the glow curve.

Thermoluminescence properties of nano-alumina with two different particle sizes

This research aims to examine the thermoluminescence (TL) properties of nano-sized alumina, including the relationship between TL intensity and absorbed dose, the identification of individual luminescence peaks, and determining trap parameters for use as a possible dosimeter. The samples were exposed to 530 to 2646 Gy doses from 60Co irradiation. The results show that micro-sized α-Al2O3 had a main dosimetry peak at Tm = 435 K, while nano-α-Al2O3 samples with particle sizes of 40 and 50 nm displayed a TL luminescence glow curve, with the primary dosimetry peak located in the low-temperature range and a complex structure at higher temperatures (above 500 K). The primary dosimetry peak was influenced by nanoparticle size, with a maximum of 460 K for the 40 nm sample and 467 K for the 50 nm sample. The main dosimetry peak was described by the superposition of two peaks

Thermoluminescence, OSL and defect centers in Tb doped magnesium orthosilicate phosphor

Mg2SiO4:Tb phosphor exhibits four thermoluminescence (TL) peaks at 124, 244, 300 and 370°C for a heating rate of 2°C/s, 244°C peak being the main dosimetry peak. The irradiated phosphor exhibits CW-OSL response on stimulation with blue (470nm) light. Thermal decay of OSL shows that all the TL traps contribute to CW-OSL signal. Its TL and OSL sensitivities are 0.21 and 0.038, respectively, than that of Al2O3:C (Landauer Inc.). Its CW-OSL response increases linearly up to 30Gy, thereafter increase was supralinear up to the studied dose of 1000Gy. Electron Spin Resonance (ESR) studies were carried out to study the defect centers induced in the phosphor by gamma irradiation and also to identify the centers responsible for the TL process. Room temperature ESR spectrum of irradiated phosphor appears to be a superposition of at least three distinct centers. One of the centers (center I) with an isotropic g-factor 2.0122 is attributable to an intrinsic O- radical and this correlates with the main TL peak at 244°C. Center II with an isotropic g-factor 2.0012 is assigned to an F+-center (singly ionized oxygen vacancy) and is the likely recombination center for all the TL peaks. Both the centers grow with radiation dose at least up to 1 kGy. Center III with an axial symmetric g-tensor with principal g-values g||=2.0049 and g⊥=2.0029 is identified as an F+-center and is not related to the observed TL peaks in the phosphor.

Investigations of thermoluminescence properties of multicrystalline LiF: Mg, Cu, Si phosphor prepared by edge defined film fed growth technique

Thermoluminescence (TL) properties of LiF: Mg, Cu, Si phosphor prepared in multicrystalline form using edge defined film fed growth (EFG) technique has been investigated. The effect of preparation route on TL properties and thermal stability has been studied. To improve the TL dosimetry properties, phosphor is subjected to different annealing temperatures ranging from 250 °C to 450 °C. The shape of the glow curve structure and peak temperature remains similar at different annealing temperatures, however peak intensities vary. The consistency in the glow curve structure with annealing temperature elucidate that TL trapping states are stable in nature. Thermal annealing at 300 °C for 10 min gives maximum TL intensity with main dosimetry peak at 209 °C. The TL intensity of the main dosimetry peak is increased by a factor of five as compared to as-grown crystal. The thermal stability of LiF: Mg, Cu, Si is found to be better than LiF: Mg, Cu, P. Trapping parameters are calculated to have an insight study of defect states. A simple glow curve structure, tissue equivalency, thermal stability, low residual signal, linear response and reusability makes LiF: Mg, Cu, Si a suitable phosphor for radiation therapy, radio diagnostics and personnel dosimetry applications.

Kinetic analysis of high temperature secondary thermoluminescence glow peaks in α-Al2O3:C

The kinetic analysis of secondary glow peaks in carbon-doped aluminium oxide is reported. A glow curve measured at 0.4 °C s−1 after beta irradiation to 3 Gy revealed at least five peaks as a result of various techniques of glow curve resolution; the dominant peak at 156 °C (peak II) and two weaker-intensity secondary peaks one at 36 °C (peak I) and the other at 264 °C (peak III). Peaks IIA and IV at 170 and 422 °C respectively only became apparent after removal of preceding more prominent peaks. The secondary peaks are particularly weak in intensity and are as usual dominated by the main dosimetry peak. The analysis in this report focusses on peak III, usually seen adjacent to the main dosimetry peak but whose presence is masked by the extreme sensitivity of the latter. Complementary analyses of the weaker intensity peaks I, IIA and IV are included. Peaks I, IIA and III are subject to first-order kinetics while for peaks II and IV the issue is less conclusive. The activation energy increases from 0.72 eV for peak I to about 1.3 eV for peak IV with values for peak II and IIA similar at ∼1 eV. In general, the frequency factor corresponding to the lower temperature peaks (I, II, and IIA) have values (1010–1012 s−1) that are an order of magnitude or so greater than for peaks III and IV (109–1011 s−1). Except for peak I, peak II and all other secondary peaks are affected by thermal quenching whose activation energy was determined as ΔE = 0.95 ± 0.04 eV using peak IIA and as ΔE = 1.48 ± 0.10 eV using peak III. The overall conclusion is that all peaks correspond to electron traps and are associated with the same recombination centre.

Silicon solar cells as a gamma ray dosimeter

Monocrystalline silicon solar cell of the construction n+pp++ Passivated Emitter Solar Cell (PESC) irradiated by 60Co gamma ray dose was studied. Thermoluminescence detectors (TLD) main dosimetry peak was investigated. The results showed that it is possible to determine gamma dose more accurate from TL main dosimetry peak for monocrystalline silicon solar cell in comparison with TLD (100). Also the various sources of uncertainty were analyzed. The expanded uncertainty at 95% confidence level should be added to the value of measurements to obtain accurate dose.

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.

Improving dosimetric properties of tellurite glasses

Abstract Thermoluminscence (TL) properties of quaternary tellurite glass in the form 80(TeO2)–5(TiO2)–(15−x)(WO3)–(x)AnOm where AnOm=Nb2O5, Nd2O3, Er2O3 and x mol% have been measured. TL main dosimetry peak for each produced glass sample were investigated for 60Co gamma rays. Dosimetric properties of the quaternary tellurite glasses have been measured as a function of different compositions of the glass system in different rare earth oxides concentration by using thermoluminescence (TL) detection technique.

TL and PTTL of TLD-100 and TLD-700 after irradiation with Pu–Be neutrons

Phototransfered thermoluminescence (PTTL) found its use in radiation dosimetry for dose reassessment. After the dose has first been evaluated by a common thermoluminescence (TL) measurement, the same dosimeter is subjected to the PTTL dose reassessment with the intention of obtaining a new estimation by a completely independent measurement procedure. Recently, some experimental data indicated that PTTL could be used as a tool for dose discrimination in a mixed field using single TL detector. In this work TL (main dosimetry peak and high temperature peak) and PTTL characteristics for TLD-100 and TLD-700 detectors were investigated for Pu–Be neutrons. The results show that it is possible to determine separately gamma and neutron dose components with a single detector due to different sensitivities of TL and subsequent PTTL to neutrons in comparison to gamma rays. The main disadvantage, the low sensitivity of both TL and PTTL, to neutrons restricts the use only for the case of radiation accident.

TL and PTTL of TLD-100 and TLD-700 after irradiation with 14.5 MeV neutrons

In radiation dosimetry, phototransfered thermoluminescence (PTTL) found its use for dose reassessment. After the dose has first been evaluated by a normal thermoluminescence (TL) measurement, the same dosimeter is subjected to the PTTL dose reassessment procedure with the intention of obtaining a new estimation by a completely independent measurement procedure. Recently, some experimental data indicated that PTTL could be used as a tool for dose discrimination in a mixed field using single TL detector. In this work, the short overview of the use of LiF-based TL detectors in mixed field dosimetry is presented. In the experimental part, TL (main dosimetry peak and high-temperature peak (HTP)) and PTTL characteristics for TLD-100 and TLD-700 detectors were investigated for 137Cs gamma rays and neutrons of 14.5 MeV. The results show that it is possible to determine separately gamma and neutron dose components with a single detector due to different sensitivities of TL and subsequent PTTL to neutrons in comparison to gamma rays.

ESR study of phosphorus-related defects in irradiated LiF:Mg,Cu,P and related phosphors

ESR results on the irradiated LiF:Mg,Cu,P are reported. A new defect centre was found. A comparative study of centres formed in various lithium phosphates allowed us to identify the defect centre in LiF:Mg,Cu,P as ( PO 4 ) 2 - radical. The ( PO 4 ) 2 - centres decay in the same temperature range as the main dosimetry peak of LiF:Mg,Cu,P. These findings are very important for understanding the mechanism of TL in LiF:Mg,Cu,P phosphor.

Thermoluminescence Properties of LiF(Mg,Cu,P) with Different Cu Concentrations

TL emission characteristics have been studied from LiF(Mg,Cu,P) samples prepared at the Institute of Nuclear Physics in Krakow, Poland in which the Cu concentration has been varied from 0.002 mol% to 0.5 mol% while the Mg content (0.2 mol%) and P content (1.25 mol%) were kept constant. Thermoluminescence has been recorded both as function of temperature and wavelength and absorption spectra were derived from diffuse reflectance measurements. The TL response of main dosimetry peak 4 increases with increasing Cu concentration up to 0.02 mol% and decreases for higher Cu content. With increasing Cu concentration the high temperature TL decreases. The emission spectra can be described with two overlapping emission bands peaking at 352 nm and 387 nm. The ratio of the intensities of both emission bands alters with temperature and Cu concentration. The high temperature thermoluminescence shows more 352 nm emission. No unique role of copper as trapping or as luminescent centre could be derived. Copper appears to play an indirect role in the trapping of charge carriers, possibly reducing the occurrence of higher order Mg defects and/or the improvement of the efficiency of the luminescent centre.

Elimination of the High Temperature Glow Peak in LiF:Cu,Mg,P

Abstract Previous studies have reported a significant residual signal in LiF:Cu,Mg,P (GR-200) which arises from a peak at 270 oC with an intensity of 7-50% relative to the main dosimetry peak. A method has been found to prepare LiF:Cu,Mg,P in two forms; one with a TL sensitivity 30-40 times greater than TLD-100 but with a residual signal of only 2-3% following 240 oC for 10 s readout, the other, even more optimised material (SSD-NR), with a sensitivity 15-20 times that of TLD-100 but with the 270 oC peak almost totally eliminated, leading to a residual signal of 0.25-0.5%.

Elimination of the High Temperature Glow Peak in LiF:Cu,Mg,P

Previous studies have reported a significant residual signal in LiF:Cu,Mg,P (GR-200) which arises from a peak at 270 oC with an intensity of 7-50% relative to the main dosimetry peak. A method has been found to prepare LiF:Cu,Mg,P in two forms; one with a TL sensitivity 30-40 times greater than TLD-100 but with a residual signal of only 2-3% following 240 oC for 10 s readout, the other, even more optimised material (SSD-NR), with a sensitivity 15-20 times that of TLD-100 but with the 270 oC peak almost totally eliminated, leading to a residual signal of 0.25-0.5%.

Elimination of the Residual Signal in LiF:Cu,Mg,P

The relative intensity of the residual signal (ratio of the second readout to first readout) is an important parameter in the application of 'unannealed' TL materials in personnel and environmental dosimetry. Previous studies have indicated a significant residual in LiF:Cu,Mg,P (GR-200, Beijing); 2-3% following 240 oC for 10 s readout and 3% following even 270 oC readout. These residual signals arise from a high temperature peak at approximately 270 oC in GR-200 with an intensity of approximately 7-25% relative to the main dosimetry peak. We have continued our multiparameter investigation of the LiF:Cu,Mg,P preparation technique with a view to minimising the residual signal. Conventional preparation techniques lead to a material with a TL sensitivity 35±4 (1 SD) greater than that of LiF:Mg,Ti(TLD-100, Harshaw), with a residual signal of 4-5% following 240 oC for 10s readout. Incorporation of oxygen in the melt suppresses the high temperature TL and leads to a residual signal of 2-3% with no loss of sensitivity in the main dosimetric peak. It is also possible to prepare a material (SSD-NR) with a sensitivity 17±2 (1 SD) times greater than that of TLD-100 but with a residual signal of only 0.25-0.5% following 240 oC for 10 s readout. This negligible residual is achieved via almost total elimination of the high temperature peak and renders the material usable in unannealed form. The chemical configuration of the incorporated phosphorous has an important influence on both the TL sensitivity and the residual signal. The number of OH groups attached to the phosphorus atom seems also to have a direct influence on the main peak sensitivity indicating that these ions play a role in the TL mechanism.

Studies of PTTL and OSL in TLD-400

Abstract We present data on the mechanisms of phototransferred thermoluminescence (PTTL) and optically stimulated luminescence (OSL) in single crystal CaF2:Mn (3%) and in TLD-400 chips. The TL peak under study is the main dosimetry peak near 275 oC. From measurements of the excitation spectra for PTTL it is found that the maximum transfer rate occurs when the wavelength of the illuminating light is 280 nm. This corresponds to the wavelength of an absorption peak which remains in the sample following initial irradiation and heating to 400 oC. This wavelength also corresponds to a complex peak which is seen in the OSL excitation spectra of irradiated samples. Possible models based on optical stimulation of electrons and diffusion of excited F centres are discussed.

The effect of ultra-violet and visible radiation on CaSO4:Dy in Teflon discs used for personnel gamma-radiation monitoring.

The influence of ultra-violet and visible radiation (UV/VIS) on the read-out obtained from the main dosimetry peak of CaSO4:Dy in Teflon discs exposed to the gamma-radiation levels measured by a personnel-monitoring service has been studied as a function of wavelength, irradiance and radiant exposure. The results have been explained by the net effect of three separate factors, namely (i) an inherent response, (ii) a phototransfer and (iii) an optical bleaching. The response obtained from unirradiated discs illuminated with fluorescent room lighting became saturated after 16 hrs at a value corresponding to 0.33 microC kg-1 whilst gamma-irradiated discs faded to 90% of their initial exposure for the same illumination period.

Isothermal read-out for thermoluminescence dosimetry with CaSO4:Dy (TLD-900)

Experiments on the isothermal decay of the therraoluminescence associated with the main dosimetry peak of CaS04:Dy (TLD-900) dosemeters are described in this paper. The results on the kinetics parameters s (the frequency factor) and b (the order of the kinetics) and a new time dependence study on accidental high dose occurrence are also reported.