Synthetic spodumene polycrystals as a TL dosimetric material

Synthetic beta-spodumene polycrystals were produced by a devitrification method, undoped and doped with controlled concentration of the Ce3+ or Mn2+ impurities. The TL properties of these polycrystals and of a colourless natural spodumene were investigated. Some dosimetric properties of them were also discussed. The dopants do not affect the TL peak position with respect a pure beta-spodumene sample but the intensity of the TL peaks at 180 and 280 degrees C is improved in the Ce-doped one. The Ce3+ ions do not participate in the TL light emission; on the other hand, the presence of Mn2+ ions cause an emission band around 600-650 nm in the TL light emission spectrum. The emission around 400 nm appears in the TL emission spectrum of all the samples and it is believed to correspond to aluminium centre ([AlO4/hole](0)) recombination with an electron. The more sensitive samples to gamma-radiation are the colourless natural spodumene and the Ce-doped synthetic spodumene, respectively. The colourless natural spodumene crystal shows a TL peak at 180 degrees C suitable for dosimetry, while for Ce-doped beta-spodumene sample the TL peaks at 180 and 280 degrees C can be used. No fading of the TL emission was observed for Ce-doped beta-spodumene sample up to 80 days after irradiation. (C) 2007 Elsevier Ltd. All rights reserved.

Entrance surface dose measurements in pediatric radiological examinations

A survey of pediatric radiological examinations was carried out in a reference pediatric hospital of the city of Sao Paulo. in order to investigate the doses to children undergoing conventional X-ray examinations. The results showed that the majority of pediatric patients are below 4 years, and that about 80% of the examinations correspond to chest projections. Doses to typical radiological examinations were measured in vivo with thermoluminescent dosimeters (LiF: Mg, Ti and LiF: Mg, Cu, P) attached to the skin of the children to determine entrance surface dose (ESD). Also homogeneous phantoms were used to obtain ESD to younger children, because the technique uses a so small kVp that the dosimeters would produce an artifact image in the patient radiograph. Four kinds of pediatric examinations were investigated: three conventional examinations (chest, skull and abdomen) and a fluoroscopic procedure (barium swallow). Relevant information about kVp and mAs values used in the examinations was collected, and we discuss how these parameters can affect the ESD. The ESD values measured in this work are compared to reference levels published by the European Commission for pediatric patients. The results obtained (third-quartile of the ESD distribution) for chest AP examinations in three age groups were: 0.056 mGy (2-4 years old); 0,068 mGy (5-9 years old)-. 0.069 mGy (10-15 years old). All of them are below the European reference level (0.100mGy). ESD values measured to the older age group in skull and abdomen AP radiographs (mean values 3.44 and 1.20mGy, respectively) are above the European reference levels (1.5mGy to skull and 1.0 mGy to abdomen). ESD values measured in the barium swallow examination reached 10 mGy in skin regions corresponding to thyroid and esophagus. It was noticed during this survey that some technicians use, improperly, X-ray fluoroscopy in conventional examinations to help them in positioning the patient. The results presented here are a preliminary survey of doses in pediatric radiological examinations and they show that it is necessary to investigate the technical parameters to perform the radiographs. to introduce practices to control pediatric patient`s doses and to improve the personnel training to perform a pediatric examination. (c) 2007 Elsevier Ltd. All rights reserved.

Comparison between blue and green stimulated luminescence of Al(2)O(3):C

This paper presents a systematic comparison of OSL signals from Al(2)O(3):C when stimulated with blue and green light. Al(2)O(3):C detectors were irradiated with various doses and submitted to various bleaching regimes using yellow, green and blue light. Most of the investigations were carried out using Luxel (TM)-type detectors used in the commercial Luxet (TM) and InLight (TM) dosimetry systems (Landauer Inc.). Al(2)O(3):C single crystals and Al(2)O(3):C powder were also used to complement the investigations. The results show that, although blue stimulation provides faster readout times (OSL curves that decayed faster) and higher initial OSL intensity than green stimulation, blue stimulation introduced complicating factors. These include incomplete bleaching of the dosimetric trap when the Al(2)O(3):C detectors are bleached with yellow or green light and the OSL is recorded with blue light stimulation, and an increased residual level due to stimulation of charge carriers from deep traps. The results warrant caution when using blue stimulation to measure the OSL signal from Al(2)O(3):C detectors, particularly if the doses involved are low and the detectors have been previously exposed to high doses. (C) 2010 Elsevier Ltd. All rights reserved.

Thermoluminescence dating of Brazilian indigenous ceramics

Two indigenous ceramics fragments, one from Lagoa Queimada (LQ) and another from Barra dos Negros (BN), both sites located on Bahia state (Brazil), were dated by termoluminescence (TL) method. Each fragment was physically prepared and divided into two fractions, one was used for TL measurement and the other for annual dose determination. The TL fraction was chemically treated, divided in sub samples and irradiated with several doses. The plot extrapolation from TL intensities as function of radiation dose enabled the determination of the accumulated dose (D(ac)), 3.99 Gy and 1.88 Gy for LQ and BN, respectively. The annual dose was obtained through the uranium, thorium and potassium determination by ICP-MS. The annual doses (D(an)) obtained were 2.86 and 2.26 mGy/year. The estimated ages were similar to 1375 and 709 y for BN and LQ ceramics, respectively. The ages agreed with the archaeologists` estimation for the Aratu and Tupi tradition periods, respectively.

Diagnostic reference levels for the most frequent radiological examinations carried out in Brazil

Objectives. A large-scale survey of doses to patients undergoing the most frequent radiological examinations was carried out in health services in Sao Paulo (347 radiological examinations per 1 000 inhabitants), the most populous Brazilian state. Methods. A postal dosimetric kit with thermoluminescence dosimeters was used to evaluate the entrance surface dose (ESD) to patients. A stratified sampling technique applied to the national health database furnished important data on the distribution of equipment and the annual number of examinations. Chest, head (skull and sinus), and spine (cervical, thoracic, and lumbar) examinations were included in the trial. A total of 83 rooms and 868 patients were included, and 1 415 values of ESD were measured. Results. The data show large coefficients of variation in tube charge, giving rise to large variations in ESD values. Also, a series of high ESD values associated with unnecessary localizing fluoroscopy were detected. Diagnostic reference levels were determined, based on the 75th percentile (third quartile) of the ESD distributions. For adult patients, the diagnostic reference levels achieved are very similar to those obtained in international surveys. However, the situation is different for pediatric patients: the ESD values found in this survey are twice as large as the international recommendations for chest radiographs of children. Conclusions. Despite the reduced number of ESD values and rooms for the pediatric patient group, it is recommended that practices in chest examinations be revised and that specific national reference doses and image quality be established after a broader survey is carried out.

Dating archeological ceramics from the Valley of Vitor, Arequipa by the TL method

The age of some ancient pottery from the Valley of Vitor in the region of Arequipa, Peru, is determined by the thermoluminescence (TL) method. For dating, a 325 degrees C TL peak was used and irradiation with -dose from 5 to 50Gy was carried out for the additive method, and from 0.4 to 5Gy for the regeneration method. For these dose values, the TL intensity is observed to grow linearly, obtaining an accumulated dose of 1.62 +/- 0.09Gy and 1.36 +/- 0.03Gy for the additive and regeneration methods, respectively. The age (A) of the sample was calculated by the two methods, being A=867 +/- 195 years after Christ (AC) for the additive method and A=1050 +/- 157 years AC for the regeneration method. Both results are within 800-1200 years AC, which is the period of the Wari culture.

Extended analysis of the Kr V spectrum

The spectrum of four-times-ionized krypton (Kr V) has been observed in the 230-4900 angstrom wavelength range, resulting in 91 new classified lines. We were able to identify 21 new energy levels belonging to the 4s(2)4p5d, 4s(2)4p5s, 4s(2)4p6s, 4s(2)4p5p and 4s4p(2)4d configurations. Relativistic Hartree-Fock calculations were used to predict energy levels and transitions. (c) 2010 Elsevier Ltd. All rights reserved.

Extended analysis of the Al-like argon spectrum

A new analysis of the aluminium-like five times ionized argon (Ar VI) spectrum in the vacuum ultraviolet region is reported in this paper. Two adjusted and 14 new energy levels and 68 new classified lines between the configurations 3s(2)3p, 3p(3), 3s3p3d, 3s(2)4p and 3s3p(2), 3s(2)(3d + 4d + 5d), 3s(2)5s, 3p(2)3d, 3s3d(2) were obtained. Atomic calculation using the HFR program was also used in the analysis.

Can efficiency of the photosensitizer be predicted by its photostability in solution?

We have investigated a possible correlation between the photostability and photodynamic efficacy for different photosensitizers; hematoporphyrin derivatives and chlorines. To perform such analysis, we combined the depth of necrosis (d (nec)) measurement, expressed by the light threshold dose and a photodegradation parameter, measured from investigation of photosensitizer degradation in solution. The d (nec) analysis allows us to determine the light threshold dose and compare its value with the existent results in the literature. The use of simple models to understand basic features of Photodynamic Therapy (PDT) may contribute to the solid establishment of dosimetry in PDT, enhancing its use in the clinical management of cancers and others lesions. Using hematoporphyrin derivatives and chlorines photosensitizers we investigated their properties related to the photodegradation in solution and the light threshold dose (D (th)) in rat livers.

Influence of pH on the phototransformation process of PhotogemA (R)

PhotogemA (R) is a hematoporphyrin derivative that has been used as a photosensitizer in experimental and clinical Photodynamic Therapy (PDT) in Brazil. Photosensitizers are degraded under illumination. This process, usually called photobleaching, can be monitored by decreasing in fluorescence intensities and includes the following photoprocesses: photodegradation, phototransformation, and photorelocalization. Photobleaching of hematoporphyrin-type sensitizers during illumination in aqueous solution is related not only to photodegradation but is also followed by the formation of photoproducts with a new fluorescence band at around 640-650 nm and with increased light absorption in the red spectral region at 640 nm. In this study, the influence of pH on the phototransformation process was investigated. PhotogemA (R) solutions, 40 mu g/ml, were irradiated at 514 nm with intensity of 100 mW/cm(2) for 20 min with different pH environments. The controls were performed with the samples in the absence of light. The PhotogemA (R) photodegradation is dependent on the pH. The behavior of photodegradation and photoproducts formation (monitored at 640 nm) is distinct and depends on the photosensitizer concentration. The processes of degradation and photoproducts formation were monitored with Photogemin the concentration of 40 mu g/mL since that demonstrated the best visualization of both processes. While below pH 5 the photodegradation occurred, there was no detectable presence of photoproducts. The increase of pH led to increase of photoproducts formation rate with photodegradation reaching the highest value at pH 10. The increase of photoproducts formation and instability of PhotogemA (R) from pH 6 to pH 10 are in agreement with the desired properties of an ideal photosensitizer since there are significant differences in pH between normal (7.0 < pH < 8.6) and tumor (5.8 < pH < 7.9) tissues. It is important to know the effect of pH in the process of phototransformation (degradation and photoproduct formation) of the molecule since low pH values promotes increase in the proportion of aggregates species in solution and high pH values promotes increase in the proportion of monomeric species. There must be an ideal pH interval which favors the phototransformation process that is correlated with the singlet oxygen formation responsible by the photodynamic effect. These differences in pH between normal and tumor cells can explain the presence of photosensitizers in target tumor cells, making PDT a selective therapy.

Phototransformation of hematoporphyrin in aqueous solution: Anomalous behavior at low oxygen concentration

The photoactivation of a photosensitizer is the initial step in photodynamic therapy (PDT) where photochemical reactions result in the production of reactive oxygen species and eventually cell death. In addition to oxidizing biomolecules, some of these photochemical reactions lead to photosensitizer degradation at a rate dependent on the oxygen concentration among other factors. We investigated photodegradation of Photogem A (R) (28 mu M), a hematoporphyrin derivative, at different oxygen concentrations (9.4 to 625.0 mu M) in aqueous solution. The degradation was monitored by fluorescence spectroscopy. The degradation rate (M/s) increases as the oxygen concentration increases when the molar ratio of oxygen to PhotogemA (R) is greater than 1. At lower oxygen concentrations (< 25 mu M) an inversion of this behavior was observed. The data do not fit a simple kinetic model of first-order dependence on oxygen concentration. This inversion of the degradation rate at low oxygen concentration has not previously been demonstrated and highlights the relationship between photosensitizer and oxygen concentrations in determining the photobleaching mechanism(s). The findings demonstrate that current models for photobleaching are insufficient to explain completely the effects at low oxygen concentration.

Thermoluminescent and optical absorption properties of neodymium doped yttrium aluminoborate and yttrium calcium borate glasses

Neodymium doped yttrium aluminoborate and yttrium calcium borate glasses were prepared by the conventional melting-quenching technique with neodymium concentration varying from 0.10 to 1.0 mol%. The obtained glasses present a wide transparency in the UV-visible region (till 240 nm). The thermoluminescent (TL) emission of beta-irradiated samples was measured, showing a broad peak at similar to 240 degrees C with intensities related to the Nd(3+) content, for both glasses. Calcium borate glass samples are about one order of magnitude less luminescent than the aluminoborate glasses. Probably the presence of Ca(2+), instead of Al(3+) and Y(3+) in the matrix, inhibits the production of the intrinsic hole centers. connected to boron and oxygen, known in the literature to act as luminescent centers in TL emission of borate glasses. We suggest that Nd(3+) ions act as electron trapping centers in both glass matrices, as they modify the temperature of emission and the light intensity. Also, the Nd:YAIB glass can be used as a dosimeter in various applications, including radiotherapy. but the sensitivity of this material to neutron should be checked. (C) 2008 Elsevier B.V. All rights reserved.

Dosimetric properties of UV irradiated calcium co-doped borate glass-ceramic

The thermoluminescence (TL) response of Dy and Li doped 20CaB(4)O(7)-80CaB(2)O(4) (Wt%) glass-ceramic irradiated with ultraviolet (UV) radiation was studied. In order to act as TL activator ions, the Dy and Li ions were included in the matrix during the melting process to increase its TL efficiency. A single crystalline CaB2O4 phase was present in the glass-ceramic as determined by X-ray diffraction (XRD). The glass-ceramic 20CaB(4)O(7)-80CaB(2)O(4):Dy,Li wt% (named 20CBO7:Dy,Li) is a newly prepared TL material. Its thermoluminescent dosimetric characteristics have shown a linear response under UV radiation exposure and a good TL signal reproducibility, thus proving to be a promising material for using as an ultraviolet radiation dosimeter. (C) 2007 Elsevier B.V. All rights reserved.

Aggregation susceptibility on phototransformation of hematoporphyrin derivatives

Photosensitizers used in PDT suffer degradation by light. In this work, photobleaching of Photogem((R)) (PG), Photofrin((R)) (PF), and Photosan((R)) (PS), hematoporphyrin derivatives, were induced by light in the presence or absence of 1% Triton X-100. The degradation efficiency in the absence of 1% Triton X-100 follows the sequence: Pf > PF > Ps, which means that PF presented a greater degradation than PF and PS. Forever, in the presence of the surfactant the degradation efficiency is different: PF congruent to PS > PF. Besides aggregation susceptibility, studies in cell culture (tumor and non tumor cells) and in animals (depth of necrosis) were performed, trying to correlate the stability of these photosensitizers with their photodynamic effect. The results suggest that PF presents higher light induced photo-cytotoxicity than PF and PS for both types of cells. For the depth of necrosis studies, more aggregated photosensitizer showed a longer time to accumulate in liver (30 min for PG, 120 h for PF and 720 h for PS). The, to establish an ideal dosimetry in PDT, one must consider the intrinsic physical chemistry characteristics of the photosensitizer as well as their ability to undergo photobleaching.

Experimental evidence and model explanation for cell population characteristics modification when applying sequential photodynamic therapy

We present experimental evidence of the existence of cell variability in terms of threshold light dose for Hep G2 (liver cancer cells) cultured. Using a theoretical model to describe the effects caused by successive photodynamic therapy (PDT) sessions, and based on the consequences of a partial response we introduce the threshold dose distribution concept within a tumor. The experimental model consists in a stack of flasks, and simulates subsequent layers of a tissue exposed to PDT application. The result indicates that cells from the same culture could respond in different ways to similar PDT induced-damages. Moreover, the consequence is a partial killing of the cells submitted to PDT, and the death fraction decreased at each in vitro PDT session. To demonstrate the occurrence of cell population modification as a response to PDT, we constructed a simple theoretical model and assumed that the threshold dose distribution for a cell population of a tumor is represented by a modified Gaussian distribution.