Search

In this work, the luminescence properties of undoped, Tm3+ doped, and Tb3+ plus Tm3+ double-doped crystals of the lithium magnesium phosphate (LiMgPO4, LMP) compound were investigated. The crystals under study were grown from melt using the micro-pulling-down method. The intrinsic and dopant-related luminescence of these crystals were studied using cathodo-, radio-, photo-, and thermoluminescence methods. Double doping with Tb3+ and Tm3+ ions was analyzed as these dopants are expected to exhibit an opposite trapping nature, namely to create the hole and electron-trapping sites, respectively. The spectra measured for the undoped samples revealed three prominent broad emission bands with maxima at around 3.50, 2.48, and 1.95 eV, which were associated with intrinsic structural defects within the studied compound. These were expected due to the anion vacancies forming F+-like centers while trapping the electrons. The spectra measured for Tb and Tm double-doped crystals showed characteristic peaks corresponding to the 4f–4f transitions of these dopants. A simplified model of a recombination mechanism was proposed to explain the temperature dependence of the measured thermally stimulated luminescence spectra. It seems that at low temperatures (below 300 °C), the charge carriers were released from 5D3-related Tb3+ trapping sites and recombination took place at Tm-related sites, giving rise to the characteristic emission of Tm3+ ions. At higher temperatures, above 300 °C, the electrons occupying the Tm3+-related trapping sites started to be released, and recombination took place at 5D4-related Tb3+ recombination centers, giving rise to the characteristic emission of Tb3+ ions. The model explains the temperature dependence observed for the luminescence emission from double-doped LiMgPO4 crystals and may be fully applicable for the consideration of emissions of other double-doped compounds.

Lithium magnesium phosphate (LiMgPO4, called LMP) crystals doped with different concentration of Tb, B and Tm were tested in regard to their radioluminescence emitted during irradiation. LMP crystals were grown with a micro-pulling down method as rods at IFJ PAN. The samples in the form of the thin slices were very sensitive to the ionizing radiation. Differently doped LMP samples were tested in a fiber optic measurement system (called PORTOS) which was constructed and adopted to the specific spectral properties of LMP. The LMP detector placed at the end of 15 m fiber connected to the PORTOS device was tested with gamma rays emitted from Co-60 Theratron 780E as well as with a Cs-137 source in a Laboratory for Calibration of Radiation Protection Instruments at IFJ PAN. RL signal was roughly proportional to the dose rates in the wide range of the dose rates. The highest RL signal was recorded for LMP crystals doped with 0.8 mol% of Tb as well as doped with 0.8 mol% Tm. The radioluminescence signal was discussed in regard to the thermoluminescence (TL) glow curves and optically stimulated luminescence (OSL) decay curves for 14 differently doped LMP crystals.

In this work the spectral properties of emission of differently doped lithium magnesium phosphate (LiMgPO4, LMP) compound were investigated by thermoluminescence (TL), optically stimulated luminescence (OSL) and radio-luminescence (RL) methods. The samples were prepared in the form of crystals, which were grown from the melt by micro-pulling-down technique. Different rare-earth (RE) dopants have been studied regarding the influence on luminescence properties. It was found that the presence of boron ions together with the RE dopant seems to have an impact mainly on the TL emission spectra of the studied LMP crystals. TL, OSL, RL and after-glow emission spectra are comparable for the LMP crystals of the same dopants concentrations. The OSL emission spectra were obtained over a whole available wavelength range by the measurements of the after-glow spectra after the sample stimulation has ended. The obtained results tend to suggest that the investigated RE-doped LMP crystals exhibit promising luminescent properties and could be considered as appropriate candidates for real-time detectors.

LiMgPO4 (LMP) doped with a combination of Tb, B, Eu, Er, Gd or Tm activators in form of the crystals grown by micro-pulling down process (MPD) was examined as optically stimulated luminescence detectors using continues wave and time-resolved modes (CW and TR-OSL) as well as radioluminescence (RL) under X-ray tube irradiation. The RL-OSL measurements were performed using a HELIOS-3 OSL reader with a 460 nm diode light stimulation and 240–400 nm emission wavelength range for signal recording and compared with CW-OSL measured by Risoe reader. In TR-OSL mode the most sensitive samples were the crystals doped with Tb, B and doped with Tb, B, Er, in CW-mode the highest signal was recorded for crystal doped with Tb, B, Gd. The linear dose response was observed in the range from 0.5 to 10 Gy. RL signals measured for the dose rates of 62 mGy/min of X-rays was very high for all investigated crystals, especially for the crystal doped with Tm and Tb, B. The highest RL signal was observed for the crystal doped with 1.2mol% of Tm.

Erasure of the thermoluminescence (TL) signal on detector readout is considered to be a disadvantage of TL dosimetry, as post-readout dose reassessment is then impossible in principle. A method of dose reassessment based on phototransferred thermoluminescence (PTTL) has been developed at the Institute of Nuclear Physics, Polish Academy of Sciences (IFJ PAN) and applied to MTS-N (LiF:Mg,Ti) detectors. We demonstrate the possibility of applying PTTL for dose reassessment in MTS-N TL detectors routinely applied in the dosimetric service at IFJ PAN. Readings of TL detectors exposed to relatively high doses by the customers of our dosimetry service can now be reassessed using our automatic readers. A major obstacle in applying the PTTL method at lower exposures is the presence of residual dose accumulated in LiF:Mg,Ti detectors after many field exposure and readout cycles. Since most of the TL detectors in our service have been already used for a long time (e.g. for over 10 years in the case of some detector batches), we find that our PTTL method of dose reassessment is possible only in detectors which had received doses exceeding 5 mSv.

The thermoluminescent (TLD) method is one of the most commonly used in dose measurements in radiation protection dosimetry. Due to its many advantages this method is widely spread. However, TLD has especially one disadvantage which is very inconvenient: the dose information in already read detectors is erased and in routine standard way the dose can not be reassessed. The positive is that this shortcoming can be eliminated by applying UV radiation. After first readout the same detector can be subjected to UV exposure and then read once again to reassess the dose. This method for reassessment of dose is based on phototransferred thermoluminescence (PTTL). In an irradiated TL detector deep traps are not emptied during the first readout. During exposure to UV, electrons are transferred from deep traps to shallower dosimetric traps. This TL signal emerging during the second readout following UV illumination is called phototransferred thermoluminescence. A method for reassessment of dose in a previously readout TLD is presented in this work. Experiments show that the method works well within region of doses between 5 and 50 mGy, but could be applied for higher doses as well. The efficiency of dose reassessment reaches about 17 percent of the first readout. The method could be a noticeable improvement in TLD dosimetry, giving more opportunities for better control and reliability of measurements.

Wide and common applications of ionising radiation require continuous improvement of radiation safety and dosimetry methods. The thermoluminescent (TL) method is well known and very popular. Apart from its advantages, it also carries certain disadvantages. The erasure of the TL signal on detector readout and the resulting impossibility of post-readout dose reassessment is one of them. At the Institute of Nuclear Physics, Polish Academy of Sciences (IFJ PAN), a method for dose reassessment based on phototransferred thermoluminescence (PTTL) has been developed. This method has been applied for dose reassessment to MTS-N (LiF:Mg, Ti) detectors used in individual whole-body dosemeters and adjusted to an automatic reader used in routine measurements. The next step was to extend and adapt this method for extremity dosemeters. With the use of the PTTL method, it is possible to reassess relatively high doses measured on individual whole-body and extremity dosemeters collected from our customers after routine use. The influence of PTTL background has greater impact in extremity dosemeters where it is only one and thinner MTS-N detector compared with four MTS-N detectors in whole-body dosemeters. The minimum dose was determined as 5 mSv for extremity dosimetry. Below 5 mSv, the impact of PTTL background is comparable to the signal, and the estimated uncertainty of reassessed dose is at the level of reassessed dose.

Stringent standards of hygiene must be applied in medical institutions, especially at operating blocks or during interventional radiology procedures. Medical equipment, including personal dosemeters that have to be worn by medical staff during such procedures, needs therefore to be sterilised. In this study, the effect of various sterilisation procedures has been tested on the dose response of extremity rings and of eye lens dosemeters in which thermoluminescent (TL) detectors (of types MTS-N and MCP-N, respectively) are used. The effects of medical sterilisation procedures were studied: by chemicals, by steam or by ultraviolet (UV), on the dose assessment by extremity rings and by eye lens dosemeters. Since it often happens that a dosemeter is accidentally machine-washed together with protective clothing, the effect of laundering on dose assessment by these dosemeters was also tested. The sterilisation by chemicals is mostly safe for TL detectors assuming that the dosemeters are waterproofed. Following sterilisation by water vapour, the response of these dosemeters diminished by some 30 %, irrespectively of the period of sterilisation; therefore, this method is not recommended. UV sterilisation can be applied to EYE-D™ eye lens dosemeters if their encapsulation is in black. The accidental dosemeter laundry in a washing machine has no impact on measured dose.

Based on the newly discovered feature of LiF:Mg,Cu,P (MCP) detectors’ glow-curves at high and ultra-high doses, a new method of thermoluminescent (TL) measurement of radiation doses ranging from micrograys up to a megagray, has been recently developed at the Institute of Nuclear Physics (IFJ). The occurrence of a new, well separated TL peak has been observed in their glow-curves resulting from many specific radiation qualities, among them gamma, electron and proton beams, for doses of about 50 kGy and higher. The occurrence of the peak B follows significant growth of previously observed high temperature peaks of the glow-curve following smaller doses. This allows MCPs to be used for dosimetry of specific radiation types in the ultra-high dose range. In order to verify the response of MCP detectors to very high doses of high-LET radiation, the glow-curve behaviour of different types of these detectors, resulting from high and ultra-high thermal neutron fluences, was studied in this work. TLDs were exposed to the neutron spectrum of the TRIGA Mark II reactor at the Reactor Research Centre at the Jožef Stefan Institute in Ljubljana. The occurrence of the high dose peak B in the MCP detectors’ glow-curve resulting from high-LET neutrons was confirmed. Results of this experiment are presented in this paper. Thus the method of ultra-high dose TL measurements was proved to be useful in interpreting the glow-curves following thermal and epithermal neutron irradiation.

Introduction Reassessment of doses in film and OSL dosimetry is well known and standard method in contrary to TL dosimetry. By using the phototransferred thermoluminescence (PTTL) method which consist of the first readout, UV exposure and second readout it is possible to reassess doses in TL dosimetry. Purpose The PTTL method was developed and applied to reassess doses in whole body and ring dosimetry at Laboratory of Individual and Environmental Laboratory at IFJ PAN. Materials and methods Standard MTS-N (LiF: Mg, Ti) sintered thermoluminescent detectors (4.5 mm diameter and 0.9 mm thickness for whole body dosimeters and 0.7 mm thickness for ring dosimeters) have been applied. Some of them were used in routine control since 12 years. The TL detectors were read in automatic RE200 (Rados Oy, Finland) readers. After readout the PTTL method was applied. Detectors were subjected to UV radiation (254 nm length) and read once again in a reader. Results The PTTL method was applied to dose reassessment in individual and ring dosimetry. The reassessed doses are observed to be linear over the dose range 5–100 mSv in whole body dosimetry and 5–1000 mSv in ring dosimetry. Conclusion Due to checking behavior of different batches and different dose history it is possible to observe influence of residual dose to the PTTL effect. By using the PTTL method it is possible to reassess doses in whole body and ring dosimetry.

Highly sensitive LiF:Mg,Cu,P (MCP) detectors enable measurements of radiation doses from tens of nanograys up to a few kilograys, where the saturation of the signal of the main dosimetric peak occurs. Thanks to the recently observed high-dose high-temperature emission of MCP detectors heated to temperatures up to 600 °C after exposures to radiation doses ranging from 1 kGy to 1 MGy, a new method of thermoluminescent measurement of radiation doses has been recently developed at the Institute of Nuclear Physics (IFJ). This method can measure doses ranging from micrograys up to a megagray. So far, high dose measurements were performed on fresh MCP samples and each detector was used only once, because as a result of these measurements, the detectors lose their sensitivity to a large extent. In this study, a specific thermal treatment intended to fully restore the loss of MCPs TL sensitivity was sought. We have investigated several annealing procedures, applying different temperatures (from 400 °C up to 700 °C) for different periods of time (10–30 min) in argon atmosphere. In this way we were able to recover MCP sensitivity fully, allowing for reuse of the samples after high-dose irradiation and high-temperature measurement.