Synthesis, characterization and thermoluminescence properties of MgB4O7 phosphor co-doped with Tm and Dy.

The luminescent and dosimetric properties of the MgB4O7 phosphor co-doped with Tm and Dy ions (MgB4O7:Tm,Dy) obtained by the solution combustion technique were investigated. With the prepared material, sintered dosimeters in pellet form were made. The MgB4O7 dosimeters doped with Tm and Dy with 0.25 and 0.10 mol% respectively and sintered at 1223 K for 3 h showed a sensitivity almost 11 times greater than the sensitivity of the TLD-100 commercial dosimeter. The TL response as a function of the gamma dose showed linearity up to 50 Gy followed by a supralinearity region and, above 500 Gy, the saturation region of the electron traps is reached. The fading of the main TL peak was negligible in the first five days after irradiation reaching 13% after 60 days and the lower detection limit was 43 µGy. The kinetic parameters were determined using the deconvolution method revealing general and second order kinetics. The morphology, crystallography and photoluminescence of the prepared phosphor samples are also reported.

Effect of heating rate on MgB4O7:Tm,Dy glow curve and its kinetic parameters calculated with different methods.

This paper presents the results of a long experimental work carried out to study the influence of the heating rate (H.R.) on thermally stimulated light emission phenomenon, well known as thermoluminescence (TL) of MgB4O7 activated by Tm and Dy ions (MgB4O7:Tm.Dy) in pellet form. The kinetics parameters, i.e. the activation energy, E, the frequency factor, s, the kinetics order, b and the number of trapped electrons, n0, were determined using the algorithm of sequential quadratic programming glow curve deconvolution (SQPGCD). The results obtained for the kinetics parameters, were compared with those obtained by other methods like Initial Rise (IR), Chen General-Order Kinetics (PS-GOK) and variable heating rate (VHR). These results suggest that SQPGCD method gives more accurate kinetics parameters values for the experimental glow curves.

Luminescence and kinetics parameters of high sensitivity MgB4O7 phosphor co-doped with Tm and Dy.

This work reports the luminescence and kinetics parameters of high sensitivity MgB4O7 phosphor co-doped with Tm and Dy ions (MgB4O7:Tm,Dy) obtained by the solution combustion technique. With the obtained material, sintered dosimeters in form of discs were made and subjected to 1223 K for 3 h and exposed to gamma radiation from a60Co source. It was found that these dosimeters show a sensitivity approximately 10 times higher than that shown by the commercial dosimeter TLD-100 (LiF:Mg,Ti). The kinetic parameters from three samples with different concentration of dopants were determined using the initial rise, peak shape and deconvolution methods. Initial rise and peak shape methods showed lower values than those found by the deconvolution method for the main peak (Peak 1). MgB4O7:Tm, Dy shows a wide linearity interval of TL response with respect to gamma dose and low coefficient of variability (1.5%). These results suggest that this new high sensitivity phosphor could be a promising material to be used in clinical dosimetry.

Effect of sintering temperature on sensitivity of MgB4O7:Tm,Ag obtained by the solution combustion method.

Borates are appropriate TL materials for radiation dosimetry, because of their equivalence with tissue. Magnesium borate is a tissue equivalent material and its most important advantage over lithium borate, is that this material is insoluble in water. In this work the effect of sintering temperature on the sensitivity of magnesium borate obtained by the solution combustion technique is presented. The results showed that the material doped with Tm and Ag, subjected to 1223 K, for 3 h, had a sensitivity between two and four times higher than that of the commercial dosimeter TLD-100 making it highly appropriate for applications in clinical dosimetry.

Dosimetric properties of Li2B4O7:Cu,Ag,P solid detector.

This work presents results obtained following the preparation of lithium borate by the chemical reaction between lithium carbonate (Li2CO3) and boric acid (H3BO3), doping the host salt of lithium borate (Li2B4O7) with ions of copper, silver and phosphorus. With the obtained material dosimeters were produced in sintered pellet form which were exposed by gamma radiation that emitted from 60Co source. The highest sensitivity was found for the sample of Li2B4O7:Cu,Ag,P (in pellet form) with 0.45, 0.45 and 12 mol% of Cu, Ag and P, respectively, subjected to a thermal treatment at 1123 K during 2 h. The TL response shows linearity in the dose range from 0.005 to 100 Gy. The lower detection limit (LDL) was equal to 6.10 µGy. The fading was found to be 3% in the first ten days and 9% at the end of thirty days. The repeatability of TL measurements for twenty cycles, showed a variability coefficient equal to 4.15%. The glow curve shape of Li2B4O7:Cu,Ag,P sintered pellet shows two peaks with general-kinetics order. This new material could be appropriate for dosimetry in clinical radiation applications.

Dosimetric properties of KMgF3:Tb + PTFE.

This work presents the results obtained from the dosimetric properties of the new radiation detectors of KMgF3:Tb + PTFE. The thermoluminescent material was obtained by microwave technique. The polycrystalline powder obtained was mixed with polytetrafluoroethylene resin powder in the ratio 2:3 to make dosimeters in pellet form. The thermoluminescent response of these new detectors presented a linear behavior, in the dose range between 1 and 1000 Gy 60Co gamma radiation, the repeatability test in the measurements, during ten cycles of heat treatment, irradiation and readouts, showed ±â€¯3.7% DS, the stability test of thermoluminescent signal, during two months showed that the fading is practically null. For the results obtained, this new detector could be very useful for radiation dosimetry, in clinical applications.

Dosimetric properties of α-Al2O3: Tm+PTFE phosphor.

A new α-Al2O3 doped with Tm3+ ions was obtained by combustion method; doped α-Al2O3 in the powder form was mixed with polytetrafluoroethylene resin (PTFE) to obtain dosimeters in pellet form, in order to be used as radiation dosimeter. The glow curve, linearity, lower detection limit, repeatability and fading, were studied. The kinetic parameters were determined by deconvolution method. Morphological characteristics were studied by low vacuum scanning electron microscopy and X-ray diffraction. Results showed that α-Al2O3+PTFE obtained is a promising material to radiation dosimetry.

Kinetic parameters of thermally stimulated light emission phenomenon in CaF2 doped with Tm3+ ions.

The characterization of new materials thermoluminescent used in radiation dosimetry, require the determination of kinetic parameters, which are associated with the number and shape of the peaks which presents its glow curve, among the most important are: the activation energy, E, or depth of the traps, the frequency factor, s, and the kinetics order, b. These parameters are necessary to predict the stability of thermoluminescent information after irradiation of the material. In this work, we present the results obtained for the determination of kinetic parameters of Tm3+-doped CaF2, the methods used for the determination of kinetic parameters were; initial growth signal TL, General order Chen method, and Deconvolution of glow curve. The results showed that the glow curve of CaF2 presents three glow peaks, 492K main peak and two smaller peaks, one at 430K and another to 566K. The dosimetric glow peak fits to the general-order kinetics model.

Measurements of radiation exposure of dentistry students during their radiological training using thermoluminescent dosimetry.

Exposure among dentistry students has not been assessed or regulated in Mexico. This work assessed the average exposure of 35 dentistry students during their training with the aid of LiF:Mg,Cu,P+PTFE thermoluminescent dosimeters. For the students in the roles of dentist and observers, maximum accumulated equivalent dose obtained was 2.59±0.11 and 4.64±0.39 mSv, respectively. Students in the role as patients received a maximum accumulated effective dose of 28.41±0.31 mSv. If compared to occupational dose limits, this latter value is 56% of the recommended value of 50 mSv in any year. It was found that in all cases, values of equivalent dose to the women breasts were equal to the background dose. Results are discussed and compared to previous published work. Suggested recommendations were given to authorities in order to minimize exposure of the students in the role as patients.

Kinetics of the TL phenomenon in LiF:Mg irradiated to different dose of gamma radiation of 60Co using two different programs of deconvolution.

In this work, the results on determination of kinetic parameters using the method of deconvolution of glow curves obtained from the LiF doped with Mg(2+) ions, after having been irradiated to 5, 10 and 25 Gy of (60)Co gamma radiation, corresponding to the range of TL-vs-dose response linearity, are presented. The deconvolution is performed using two functions obtained by the method of asymptotic series and by the method based on the approximation of continued fractions. The glow curve of the studied material shows a dosimetric glow peak at 518 K and three peaks of very low intensity at 383, 423 and 463 K, all of a general-order kinetics. Kinetic parameters obtained with both methods showed that the values of kinetics, b, the energy of the traps, E, and the factor of frequency, s, do not differ significantly. However, the figure of merit, FOM, and the second derivative criteria indicate that the accuracy of the calculations with the second method improves considerably.

Determination of kinetics parameters of the main glow peaks for KMgF3:Lu and LiF:Mg phosphors after long-term high temperature storage.

The isothermal decay method is useful for determining the trap activation energy in thermoluminescent material for dosimetry purposes. Recently we proposed new modified expressions for isothermal decay method. As validation of the modified expressions, after long-term (4 h) high temperature storage, the activation energy of experimental TL glow peaks, KMgF3:Lu (0.17 and 0.34 mol%) and LiF:Mg (0.04 mol%), in the framework of the general-order kinetic was calculated. The results of the kinetics parameters were compared with those obtained by the other methods like Initial Rise (IR), Sequential Quadratic Programming Glow Curve Deconvolution (SQPGCD), deconvolution of the TL glow curves by assuming the General Order Kinetic (GOK), and Chen General-Order Kinetics method. It seems that both SQPGCD and GOK deconvolution methods give more accurate kinetics parameters values for the experimental glow curves.

Effect of thermal treatment on TL response of CaSO4:Dy obtained using a new preparation method.

We report the effect of thermal treatment on thermoluminescent (TL) sensitivity property of CaSO4:Dy obtained by a new preparation method at Instituto Nacional de Investigaciones Nucleares (ININ) of Mexico. Samples of phosphor powder were subjected to different thermal treatments respectively at 773, 873, 973 and 1,173K for 1h and then irradiated from 0.1 to 1,000 Gy gamma doses. Low energy dependence was analyzed too by irradiating with X-rays in the range of 16-145 keV. The results were normalized to the energy (1,252 keV) of (60)Co and they were compared with those obtained using the commercial dosimeters TLD-100. Also the kinetic parameters were determined by deconvolution of glow curve.

Heating rate effect on thermoluminescence glow curves of LiF:Mg,Cu,P+PTFE phosphor.

The influence of heating rate on the thermoluminescence (TL) property of LiF:Mg,Cu,P+PTFE was analyzed. The activation energy and the frequency factor as a function of the heating rate were determined. The kinetic parameters and their dependence on the heating rate were evaluated using the sequential quadratic programming glow curve deconvolution (SQPGCD). The results showed that as the heating rate increases, the peak intensity at the maximum (I(M)) decreases and shifts to higher temperature; similar behavior of the kinetics parameters was observed.

New modified expressions for isothermal decay of Teflon embedded LiF:Mg,Cu,P and BaSO4:Eu phosphors.

This paper gives a full mathematical description of the kinetics expressions used in thermoluminescent isothermal decay experiments. The corresponding equations have been slightly modified considering the peak intensity at the maximum (I(M)) instead of the peak area Φ as proportional to absorbed dose, given normally in isothermal decay equations. The isothermal decay method was applied to the principal glow peaks of two different phosphors: LiF:Mg,Cu,P+PTFE, using first- and second-order kinetics, and BaSO(4):Eu+PTFE, using second-order kinetics.

Comparison of the TL responses of two different preparations of LiF:Mg,Cu,P irradiated by photons of various energies.

The aim of this work is to present the results concerning the photon irradiation of a new phosphor, the LiF:Mg,Cu,P+PTFE, produced at the Instituto Nacional de Investigaciones Nucleares (ININ-Mexico). The photon irradiations were performed using X-rays of 16, 24, 34.5, 42, 100 and 145keV, and gamma rays from (137)Cs (662keV) and from (60)Co (1 252keV). The results obtained are normalized to the (60)Co response. The experimental data are then compared to those obtained using the commercial dosimeters TLD-100 and GR-200A.

Tuberculous brain abscess. Case report.

An abscess was removed from the left occipital region in a 73-year-old woman with no previous history of tuberculosis. The patient later died from aspiration bronchopneumonia. Autopsy revealed a basilar tuberculous meningitis and miliary tuberculosis in the peritracheal lymphatic glands, the liver, the spleen, and in isolated areas of the lungs. No chronic tuberculous foci were noted in any area. Including this case, only 18 instances of tuberculous abscess have been reported.