Phototransferred Thermoluminescence Research Articles

Thermoluminescence studies of LiF : Mg, Ti between 100 and 300 K

Thermoluminescence and phototransfer thermoluminescence glow curves, and the corresponding emission spectra of LiF (TLD-100) crystals were studied over the temperature range 100 to 300 K after pre-irradiation heat treatment at 373, 423 and 673 K for 1 h. The TL glow curve displays six glow peaks over this temperature range. The intensity and peak temperatures of glow peaks above 200 K are highly affected by the pre-irradiation heat treatment while the glow peaks below 200 K are not affected by this treatment. The various emission spectra include ‘ultraviolet’ bands at 5.42, 4.42 and 3.57 eV and ‘visible’ bands at 3.07, 2.65 and 2.22 eV. The first glow peak, seen at 138 K, emits in both the ultraviolet and visible with similar intensity. The next glow peak, seen at 156 K with reduced intensity, also emits in both regions but with relatively more in the ultraviolet than the visible. The peak intensity and energy of the individual visible emission bands are strongly affected by pre-irradiation heat treatment, while the ultraviolet bands are weakly affected. The data are explained with a band-gap model that extends Mayhugh–Christy's model for thermoluminescence above room temperature.

Phototransferred thermoluminescence of PWO and PWO:Y single crystals

The phototransferred thermoluminescence (PTTL) of PWO and PWO:Y crystalswas studied in the range of 30–300̂C. From the experiments, one can concludethat in PWO crystals there are abundant traps and that some traps must be verydeep. Visible light (blue, green and red) illumination can change the distributionof the trapped charges—namely, some charges trapped by deep traps can betransferred to shallow traps. These traps above room temperature are in practicedetrimental to the light yield and its stability. Doping with Y3+ is a good way toreduce the number of these traps, as can be concluded from the γ-irradiation-inducedthermoluminescence and PTTL curves. This paper provides us with some cluesas regards how to enhance the stability of the light yield, which is animportant requirement for PWO in high-energy physics detection applications.

Studies of UV induced phototransferred thermoluminescence in CaSO4:Dy pellets.

The ultraviolet (UV) radiation response of the CaSO4:Dy pellets produced at IPEN/SP was studied using phototransferred thermoluminescence (PTTL). The PTTL characteristics of three different types of CaSO4:Dy pellets were investigated. The main parameters studied were: thermal treatments, post UV exposure storage time, PTTL response as a function of gamma dose, exposure time, radiant energy response and lower detection limits.

Study of the phototransferred thermoluminescence in KCl:Eu2+ phosphors.

The phototransferred thermoluminescence (PITL) processes play an important role in the optical stimulated luminescence (OSL) and thermoluminescence (TL) dosimetric properties in KCl:Eu2+ crystals. In the present work, experimental evidence is presented about the participation of F and Fz centres in the associated recombination luminescence mechanisms involved with all three phenomena. An analysis of the TL glow curve of KCl:Eu2+ exposed to X ray ionising radiation shows three main thermoluminescence peaks around 370, 390 and 470 K. The 470 K highest intensity peak, considered the dosimetric peak due to its low fading and linear dose behaviour, is strongly correlated to the F and Fz centres. Through optical absorption spectra measurements of an optically bleached specimen, it was found that a minimum occurs at 560 nm, coinciding with the F centre band in KCl:Eu2+. Moreover, the diminishing of the integrated TL 470 K peak intensity is also seen to have a minimum at 560 nm (F centres); it also happens simultaneously with an increase of the integrated TL peak associated to the Fz band. This supports the close relation of the F and Fz centres in the PTTL process in KCl:Eu2+.

High-level gamma dosimetry using phototransferred thermoluminescence in quartz

Phototransferred thermoluminescence (PTTL) in natural quartz, separated from sand, has been studied for its application in high-level gamma dosimetry. The paper reports dose-vs.-PTTL response of 110°C and 180°C peaks in the dose range of 10 Gy to 6 kGy. Using this method, the dose rate delivered to the sewage sludge during irradiation at SHRI facility, Vadodara, India, was estimated to be 0.35±0.02 kGy/h.

Study of the Thermoluminescence and Optical Stimulated Luminescence properties of quartz crystal

Thermoluminescence (TL) and Optical Stimulated Luminescence (OSL) of natural quartz crystals from sediments have been studied in order to obtain the ages of the sediments' deposition. The sediments were collected from an archaeological site, located in State of Mato Grosso do Sul, Brazil. In the present work the phototransfer TL process was observed in the 394°C TL peak, which increased 10–20% in its intensity when the sample was exposed to sunlight. As the samples did not provide a residual TL, a new methodology to evaluate the paleodose (P) was devised. Annual doses were evaluated based on uranium, thorium and potassium contents determined by neutron activation analysis. Preliminary ages were compared to those obtained by OSL and ages between (11–35) 103 BP were obtained.

Luminescence of LiKYF5:Pr3+ crystals

Abstract X-luminescence (XL), photoluminescence (PL), optically stimulated luminescence (OSL), thermoluminescence (TL), phototransferred thermoluminescence (PTTL) as well as optical absorption have been studied in pure and Pr3+ doped LiKYF5 crystals. Dependencies of the luminescence efficiency on the Pr3+ concentration and on the radiation dose have been measured and possible applications of the novel TL phosphor based on LiKYF5 : Pr3+ for solid state dosimetry have been investigated. There are main emission bands at 340 and 385 nm in the XL and the PL spectra of pure crystals and both these PL emission bands have an excitation maximum at 215 nm. Additional narrow emission bands at 230, 270, 479, 530 and 605 nm are observed from the LiKYF5:Pr3+ crystals. In the doped crystals, the 215 nm light mainly excites the 230 and the 270 nm emission, and there are additional excitation maxima at 442, 459, 468 and 480 nm. During heating of X- or β-irradiated crystals, TL peaks have been recorded and thermal activation energies have been evaluated by various methods. TL from the LiKYF5: Pr3+ crystals shows emission bands at 229, 262, 340, 486, 527, 610, 640 and 705 nm whereas there are only a main 340 nm band and weaker bands at 486 and 450 nm on the TL spectra of the pure crystals. Samples exposed to prolonged X- or β -irradiation at RT and then illuminated with the 295 or 442 nm light at LNT show strong PTTL during heating from LNT to RT. The dose dependence of the TL intensities in LiKYF5: Pr3+ has been found to be linear for radiation doses up to 2 kGy.

The Reassessment of High Doses for Different LET Irradiations

One of the main shortcomings of the TLD method is the exposure information deletion during readout. There are two ways of reassessment of high doses: performing a second reading and by the phototransferred thermoluminescence (PTTL). In the PTTL method, charge carriers, usually created by irradiation with ionising radiation, are transferred from deep traps to shallow traps, giving rise to lower temperature peaks. In the present work, LiF:Mg,Ti (TLD-100) cards were irradiated to several doses of gamma rays and thermal neutrons. The residual dose and the PTTL were evaluated for both radiations. It was found that both the residual dose and the PTTL are higher for the thermal neutrons than for the gamma rays. The residual dose after the first reading is about 2% for neutrons and about 0.2% for gamma rays, and the PTTL is about 9% for neutrons and about 2% for gamma rays. Neutron and gamma ray doses can be re-estimated by a second reading or by PTTL, but the factors are LET dependent.

PTTL Dose Re-estimation Applied to Quality Control in TLD-100 Based Personal Dosimetry

A new method for quality control of dose performance in Personal Dosimetry using TLD-100 is presented. This method consists of the application of dose reassessment techniques based on phototransferred thermoluminescence (PTTL). Reassessment is achieved through a second TL readout of the dosemeters worn by the controlled workers, after a reproducible UV exposure. Recent refinements in the PTTL technique developed in our laboratory allow reassessing doses as low as 0.2 mSv, thus extending the reassessment capability to the entire dose range that must be monitored in personal dosimetry. After a one month exposure, even purely environmental doses can be reassessed. This method can be applied for either re-estimation of single doses or of the total dose accumulated after a number of exposures and dose measurements. Several tests to reconfirm low doses in normal working conditions for personal dosimetry have been performed. Each test consisted of several cycles of exposure and TL evaluations and a final PTTL re-estimation of the total accumulated dose in those cycles. The results obtained always showed very good agreement between the sum of the partial doses and the total reassessed dose. The simplicity of the method and the possibility of re-evaluating the doses assessed to the workers employing their own dosemeters are advantageous features to be considered in designing systems for the determination of real performance in personal dosimetry.

Comparative Studies on the Thermoluminescent Properties of Sintered Pellets of Natural and Synthetic CaF2 for UV Dosimetry

The phototransferred thermoluminescence (PTTL) of sintered pellets of natural CaF 2 from Brazil is compared with that of CaF 2 doped with Ce 3+ and/or Dy 3+ . It is shown that the excitation spectrum provides a convenient way to find an optimum condition of pre-heat treatment of sintered CaF 2 after UV irradiation. The sintered CaF 2 containing a small amount of Ce 3+ (0.2 mol%) shows a strong glow peak around 90°C after UV irradiation. On co-doping with Dy 3+ in CaF 2 :Ce 3+ , the prominent glow peak shifts to 270°C. The peak intensity shows a linear response to the UV irradiation dose. The recombination process of these main glow peaks is discussed on the basis of the TL emission and the excitation peaks caused by the relevant impurities.

Bleaching and phototransfer of thermoluminescence in limestone

The thermoluminescence from a French limestone shows peaks in the glow curve at 142±11, 164±14, 194±11, 286±10 and 360±10°C measured at a heating rate of 5.2°C s −1. The bleaching and phototransfer properties of these peaks are presented for bleaching times in a solar simulator extending up to 2 weeks. The height of the principal peak in the glow curve at 286°C declines exponentially with bleaching time over the first 10 min and then over the following 2 weeks declines in proportion to t −0.34±(0.01), where t is the bleaching time. The peak at 360°C is bleached exponentially with time over a period of 60 min and thereafter shows no detectable change in intensity. The phototransferred thermoluminescence rises to a maximum at 4 min of exposure in the solar simulator and thereafter for 2 weeks falls proportionally to t −0.32±(0.02), where t is the exposure time. The wavelength dependence of the bleaching of the principal 286°C peak in the natural thermoluminescence glow curve was investigated over the wavelength range 340–750 nm, obtained using optical filters and the solar simulator. The 340–400 nm region was found to be of most importance for bleaching, while wavelengths longer than 500 nm had little influence.

Phototransferred thermoluminescence from α-Al 2O 3:C using blue light emitting diodes

Phototransferred thermoluminescence (PTTL) from α-Al 2O 3:C single crystals was studied using a blue light emitting diode (LED) for phototransfer of charges from deep traps to the main dosimetry trap. The dose response was found to be linear in the region from ∼5 mGy to ∼5 Gy. It was observed that the corresponding deep traps were located near 500°C and heating to temperatures >600°C removes the PTTL effect induced by the light from the blue LED. The thermal activation energy of the source traps involved in the PTTL production was calculated as 3.23 eV.

The potential use of annealed high-albite (AlSi3O8Na) as an ultraviolet radiation dosimeter

The potential use of annealed high-albite (AlSi3O8Na) as an ultraviolet radiation dosimeter

Phototransferred thermoluminescence

We describe an analysis of phototransferred thermoluminescence (PTTL) using simple energy band models and considering the dynamics of charge transfer between localized trapping states during irradiation, illumination and heating. The various behaviours which are possible are highlighted and described. Particular attention is focused upon the dependences of the PTTL signal upon the illumination time and upon the wavelength of excitation. Some comparisons with experimental PTTL signals from crystalline quartz are discussed.

Radiation effects in pure and doped Al 2O 3 crystals

Effects of β-, X- and UV-radiation on optical properties of nominally pure as well as of variously doped α-Al 2O 3 crystals were studied. Optical absorption, thermoluminescence (TL) and photoluminescence (PL) were measured. The irradiation with wavelengths below 145 nm had essentially the same effects as X-irradiation, indicating that the same defects were formed in both cases. F and F + emission bands at 410 and 330 nm appeared in the TL and in the PL of all samples. In crystals doped with rare-earth ions the narrow bands, characteristic for these impurities, were dominant. In some of the nominally pure samples also a strong Cr 3+ band appeared at 698 nm. In the C-doped crystals the TL and PL emissions were relatively strong and dominated by the F and F + emission bands. These results support previous suggestions regarding a high anion vacancy concentration in the C-doped crystals. A weak emission band appeared near 500 nm with an excitation maximum near 300 nm and is attributed to interstitial Al i + ions. Prolonged UV- illumination with F-light caused a notable increase in the PL yield in the C-doped samples. Irradiation into the Al i + absorption band at 300 nm had a reverse effect and was also efficient for the optical bleaching of the phototransferred TL (PTTL).

Luminescence models

This paper reviews the main models which have been proposed to describe thermally and optically stimulated luminescence phenomena for materials of interest in dating applications. The review starts from the fundamental models established for the descriptions of the kinetics of thermoluminescence (TL) production and develops these as necessary to account for a variety of experimental phenomena. Among the experimental features discussed are anomalous fading, non-linear growth of thermoluminescence as a function of dose, sensitivity and sensitization, bleaching of TL glow curves with light, phototransferred TL (PTTL) and optically stimulated luminescence (OSL). The relevance of the models to some dating applications is highlighted and it is concluded that efforts to unify the disparate models for luminescence from these materials are now required.

An Integrating Ultraviolet-B Dosemeter Using Phototransferred Thermoluminescence in alpha-Al2O3:C

Until recently, atmospheric ozone has reflected all but approximately 1% of wavelengths below 320nm. Recent evidence of ozone depletion in the stratosphere has generated interest in the biological impact on plants and animals resulting from increased exposure to these wavelengths. This has created a need for ultraviolet dosimetry of wavelengths shorter than 320 nm, particularly at southern latitudes. This paper describes the design of a dosemeter which measures absorbed ultraviolet dose, for the wavelength band centred at 307 nm, based upon the phototransferred thermoluminescence properties of α-Al 2 O 3 :C. Thin-layer α-Al 2 O 3 :C detectors were used. The calibrated response of the detectors has an average standard deviation of 2.7%. This dosemeter can be used in air or in water. The dosemeter has a near-linear ultraviolet dose response with a dynamic range of at least 3 decades (from an energy fluence of 10 2 μJ.cm -2 to 10 5 μJ.cm -2 ) and very little temperature dependence in the region of biological interest (273-323 K). The inherent angular dependence of the interference filter used in the dosemeter is partially flattened due to the wavelength dependence of the phototransferred thermoluminescence efficiency in this wavelength region, the shift in the transmission wavelength of the filter as a function of incident angle and through the use of diffusers.

The relationship between quartz thermoluminescence, photo-transferred thermoluminescence, and optically stimulated luminescence

The effects of green light stimulation on the thermoluminescence (TL) of a sedimentary quartz from the Kimberley region of Western Australia are reported. The loss of TL at 310°C and the concomitant growth and decay of the photo-transferred TL (PTTL) at both 110 and 160°C are presented for optical stimulation of up to 200 s in a Risø TL/OSL reader. The optical decay lifetime for the 110°C peak was about 130 s, and we deduce that this decay probably arises from optical stimulation of electrons rather than loss of recombination centres. A linear correlation was found between the loss of TL from the rapidly bleaching peak at 310°C (following a natural (N) + 43 Gy dose) and the integrated optically stimulated luminescence (OSL), for stimulation at 125°C and for stimulation times between 0.1 and 100 s. For another N + 43 Gy sample, the OSL signal decreased by about 20% with increasing preheat temperature from 220 to 280°C, after correction for thermal activation of luminescence centres (monitored by an additional experiment). The TL signal associated with this OSL (i.e. the TL lost as a result of optical stimulation) decreased by about 30% with preheat temperature. For repeated 0.1 s stimulation at 25°C, there was a linear relationship between the OSL, and the PTTL at 110°C obtained after each stimulation. The effects of different doses and stimulation times on this relationship are reported, and the implications for dating protocols using the OSL signal are discussed.

The time and wavelength response of phototransferred thermoluminescence in natural and synthetic quartz

Phototransferred thermoluminescence (PTTL) properties from several types of crystalline quartz are presented. Several of the PTTL peaks display an increase, followed by a decrease, but not necessarily to zero. The data can be satisfactorily explained by a model which includes the recombination of electrons and holes during illumination, and two types of recombination center. Consideration of the rate equations describing the phototransfer of charge from deep traps to shallow traps, along with the wavelength dependence of the photoionization cross-section, leads to the realization that increasing the illumination intensity or decreasing the wavelength will have the same effect on the PTTL response. The wavelength dependence of the PTTL effect can be obtained by taking the initial slope of the PTTL-vs-illumination-time curve as a function of wavelength. Using this procedure reveals that only one source trap is emptying over the wavelength range of green light stimulation, but additional traps become active as the wavelength decreases. Over the whole wavelength range used three traps are active, with optical threshold energies of 2.37, 2.84 and 3.77 eV.

Solar bleaching of thermoluminescence of calcites

Original results of solar bleaching of thermoluminescence (TL) of twelve Greek calcitic (limestone, marble) stone profiles have been obtained. The residual TL signal due to sunlight exposures (zero to 130 h) differs in samples, but in general follows an exponential decay form consisting of one or two components. The first component bleaches fast within the first 30–70 h and the second component bleaches slowly; the latter, occasionally, formed a residual plateau. The first exponential term decays with different rates ranging between 1 – 6 (%/h) for the 280°C TL peak and slower, 0.1–0.3 (%/h) for the 350°C TL peak. Phototransferred TL (PTTL) of the 280 and 350°C TL peaks giving rise to a PTTL peak at around 180°C, was observed. The residual TL glow curve shape variation as a function of daylight exposure time is provisionally used to further develop the method of dating carved megalithic masonry [1]. The solar bleached TL signal of calcites provides bleached TL curves characterestics which inhere useful information regarding dating of calcitic stones derived from archaeological sites, and contribute to the complex luminescence phenomenon in calcites.