Mixed-Halide Perovskite Film-Based Neuromorphic Phototransistors for Mimicking Experience-History-Dependent Sensory Adaptation.

Sensory adaptation is an essential function for humans to live on the earth. Herein, a hybrid synaptic phototransistor based on the mixed-halide perovskite/organic semiconductor film is reported. This hybrid phototransistor achieves photosensitive performance including a high photoresponsivity over 4 × 103 A/W and an excellent specific detectivity of 2.8 × 1016 Jones. Due to the photoinduced halide-ion segregation of the mixed-halide perovskites and their slow recovery properties, the experience-history-dependent sensory adaptation behavior can be mimicked. Moreover, the light pulse width, intensity, light wavelength, and gate bias can be used to regulate the adaptation processes to improve its adaptability and perceptibility in different environments. The CsPbBrxI3-x/organic semiconductor hybrid films produced by spin coating are beneficial to large-scale fabrication. This study fabricates a novel solution-processable light-stimulated synapse based on inorganic perovskites for mimicking the human sensory adaptation that makes it possible to approach artificial neural sensory systems.

Recyclable metal nanoparticle-immobilized polymer dot on montmorillonite for alkaline phosphatase-based colorimetric sensor with photothermal ablation of Bacteria.

Development of simultaneous bacteria detection and eradication with simple, rapid, and reusable material is important in addressing bacterial contamination issues. In this study, we utilized the expression of alkaline phosphatase (ALP) from bacteria to design fluorescence ON/OFF system for bacteria detection, also using metal oxide nanoparticle for obtaining antibacterial activity and recyclability. The fluorescent-based biosensor with antibacterial activity was prepared by intercalating ALP-sensitive polymer dot (PD) containing ß-cyclodextrin (ß-CD) onto montmorillonite (MMT) as loading matrix via ionic exchange reaction, followed by immobilization of magnetic iron oxide (Fe3O4) and NIR-responsive cesium tungsten oxide (CsWO3). The PD-ßCD-MMT/Fe3O4-CsWO3 nanocomposite exhibited strong fluorescence intensity, which was quenched in the presence of bacterial ALP (0-1000 U/L) due to hydrolysis of p-nitrophenyl phosphate (NPP) into p-nitrophenol (NP) in the hydrophobic site of ß-CD. Furthermore, the nanocomposite could detect both gram-negative Escherichia coli and gram-positive Staphylococcus aureus in the range of 101-107 CFU/mL (LOD 5.09 and 4.62 CFU/mL, respectively), and showed high antibacterial activity against bacteria by generating photothermal heat under 5 min NIR irradiation, causing damage to bacterial cells. This material also demonstrated recyclability via magnetic field exposure due to the presence of Fe3O4. In addition, the fluorescence can be recovered following pH shock and re-conjugation of ß-CD molecules. After 4 cycles, nanocomposite still showed stable photothermal effects and fluorescence-based bacteria detection. Thus, this reusable material offers promising approach for simultaneous bacteria detection and killing, which is simple, rapid, and effective.

Hot Biexciton Effect on Optical Gain in CsPbI3 Perovskite Nanocrystals.

Combining the superior optical properties of their bulk counterparts with quantum confinement effects, lead halide perovskite nanocrystals are unique laser materials with low-threshold optical gain. In such nonlinear optical regimes, multiple excitons are generated in the nanocrystals and strongly affect the optical gain through many-body interactions. Here, we investigate the exciton-exciton interactions in CsPbI3 nanocrystals by femtosecond transient absorption spectroscopy. From the analysis of the induced absorption signal observed immediately after the pump excitation, we estimated the binding energy for the hot biexcitons that are composed of an exciton at the band edge and a hot exciton generated by the pump pulse. We found that the exciton-exciton interaction becomes stronger for hot excitons with greater excess energies and that the optical gain can be controlled by changing the excess energy of the hot excitons.

Enhanced emission of Mn2+ via Ce3+ → Mn2+ energy transfer in α-Sr2P2O7.

Mn(2+) doped and Ce(3+)-Mn(2+) co-doped α-Sr(2)P(2)O(7) phosphors were prepared by a traditional high-temperature solid-state reaction route. The UV-vis excitation and emission spectra for all samples were investigated. Luminescence of Mn(2+) is assigned to from two different sites, which is similar to that of Ce(3+). Energy transfer from Ce(3+) to Mn(2+) in co-doped phosphors α-Sr(2)P(2)O(7): 0.03Ce(3+), xMn(2+) and α-Sr(2)P(2)O(7): xCe(3+), 0.1Mn(2+) was investigated by the excitation and emission spectra as well as the luminescence decays. Both Ce(3+)(1) and Ce(3+)(2) can transfer energy to two types of Mn(2+) ions.

Synthesis and characterization of Ce2S3-ZnS-CuS nanoparticles and their photocatalytic activity.

ZnS-CuS nanoparticles were prepared by a controlled coprecipitation method and ZnS-CuS-Ce2S3 nanoparticles were prepared by ball milling. The photocatalysts were characterized by scanning electron microscopy, X-ray powder diffraction, transmission electron microscopy, and terephthalic acid photoluminescence probing technique. The photocatalytic activity of the photocatalysts was evaluated by photocatalytic reduction of Cr2O7(2-), nitrobenzene and photocatalytic oxidation of methyl orange. The results showed that the optimal preparation condition of ZnS-CuS is 200 degrees C for 7 h. The optimal doped amount of Ce2S3 for Ce2S3-ZnS-CuS photocatalyst is 1.0 wt%, and the optimal ball milling time is 16 h. For the ZnS-CuS photocatalyst, the photooxidation efficiency of methyl orange and the photoreduction efficiency of Cr2O7(2-) were 27.4% and 60.7%, respectively; and for Ce2S3-ZnS-CuS photocatalysts, they were 73.6% and 83.1%, respectively. The production efficiency of aniline for ZnS-CuS and Ce2S3-ZnS-CuS were 25.4% and 31.3%, respectively. The mechanisms of influence on the photocatalytic activity were also discussed.

CeO2 mediated photocatalytic degradation studies of C.I. acid orange 7.

CeO2 nanoparticles were prepared by a simple precipitation method, followed by calcination treatment. By selecting photocatalytic degradation of acid orange 7 (AO7) as a probe reaction, the influences of calcination temperature of catalyst, the concentration of AO7, initial pH value of AO7 solution and catalyst dosage on the photocatalytic activity of CeO2 were studied. It was found that CeO2 calcined at 550 degrees C shows the highest photocatalytic activity under visible light irradiation. It was revealed that under visible light irradiation the degradation of AO7 over CeO2 nanoparticles follows a dye self-sensitization mechanism. The degradation rate of AO7 increases with decrease in the initial pH value of the reaction solution, and degradation efficiency decreases with increase in the initial dye concentration. The optimal dosage of CeO2 in solution for AO7 degradation is 1 g/L.

Application of the Monte Carlo method for the efficiency calibration of CsI and NaI detectors for gamma-ray measurements from terrestrial samples.

Gamma-ray measurements in terrestrial/environmental samples require the use of high efficient detectors because of the low level of the radionuclide activity concentrations in the samples; thus scintillators are suitable for this purpose. Two scintillation detectors were studied in this work; CsI(Tl) and NaI(Tl) with identical size for measurement of terrestrial samples for performance study. This work describes a Monte Carlo method for making the full-energy efficiency calibration curves for both detectors using gamma-ray energies associated with the decay of naturally occurring radionuclides (137)Cs (661keV), (40)K (1460keV), (238)U ((214)Bi, 1764keV) and (232)Th ((208)Tl, 2614keV), which are found in terrestrial samples. The magnitude of the coincidence summing effect occurring for the 2614keV emission of (208)Tl is assessed by simulation. The method provides an efficient tool to make the full-energy efficiency calibration curve for scintillation detectors for any samples geometry and volume in order to determine accurate activity concentrations in terrestrial samples.

A fast, angle-dependent, analytical model of CsI detector response for optimization of 3D x-ray breast imaging systems.

PURPOSE: Accurate models of detector blur are crucial for performing meaningful optimizations of three-dimensional (3D) x-ray breast imaging systems as well as for developing reconstruction algorithms that faithfully reproduce the imaged object anatomy. So far, x-ray detector blur has either been ignored or modeled as a shift-invariant symmetric function for these applications. The recent development of a Monte Carlo simulation package called MANTIS has allowed detailed modeling of these detector blur functions and demonstrated the magnitude of the anisotropy for both tomosynthesis and breast CT imaging systems. Despite the detailed results that MANTIS produces, the long simulation times required make inclusion of these results impractical in rigorous optimization and reconstruction algorithms. As a result, there is a need for detector blur models that can be rapidly generated. METHODS: In this study, the authors have derived an analytical model for deterministic detector blur functions, referred to here as point response functions (PRFs), of columnar CsI phosphor screens. The analytical model is x-ray energy and incidence angle dependent and draws on results from MANTIS to indirectly include complicated interactions that are not explicitly included in the mathematical model. Once the mathematical expression is derived, values of the coefficients are determined by a two-dimensional (2D) fit to MANTIS-generated results based on a figure-of-merit (FOM) that measures the normalized differences between the MANTIS and analytical model results averaged over a region of interest. A smaller FOM indicates a better fit. This analysis was performed for a monochromatic x-ray energy of 25 keV, a CsI scintillator thickness of 150 microm, and four incidence angles (0 degrees, 15 degrees, 30 degrees, and 45 degrees). RESULTS: The FOMs comparing the analytical model to MANTIS for these parameters were 0.1951 +/- 0.0011, 0.1915 +/- 0.0014, 0.2266 +/- 0.0021, and 0.2416 +/- 0.0074 for 0 degrees, 15 degrees, 30 degrees, and 45 degrees, respectively. As a comparison, the same FOMs comparing MANTIS to 2D symmetric Gaussian fits to the zero-angle PRF were 0.6234 +/- 0.0020, 0.9058 +/- 0.0029, 1.491 +/- 0.012, and 2.757 +/- 0.039 for the same set of incidence angles. Therefore, the analytical model matches MANTIS results much better than a 2D symmetric Gaussian function. A comparison was also made against experimental data for a 170 microm thick CsI screen and an x-ray energy of 25.6 keV. The corresponding FOMs were 0.3457 +/- 0.0036, 0.3281 +/- 0.0057, 0.3422 +/- 0.0023, and 0.3677 +/- 0.0041 for 0 degrees, 15 degrees, 30 degrees, and 45 degrees, respectively. In a previous study, FOMs comparing the same experimental data to MANTIS PRFs were found to be 0.2944 +/- 0.0027, 0.2387 +/- 0.0039, 0.2816 +/- 0.0025, and 0.2665 +/- 0.0032 for the same set of incidence angles. CONCLUSIONS: The two sets of derived FOMs, comparing MANTIS-generated PRFs and experimental data to the analytical model, demonstrate that the analytical model is able to reproduce experimental data with a FOM of less than two times that comparing MANTIs and experimental data. This performance is achieved in less than one millionth the computation time required to generate a comparable PRF with MANTIS. Such small computation times will allow for the inclusion of detailed detector physics in rigorous optimization and reconstruction algorithms for 3D x-ray breast imaging systems.

A comprehensive study on the laser decontamination of surfaces contaminated with Cs(+) ion.

A Q-switched Nd:YAG laser with a 1064nm, 450mJ/pulse and 14ns pulse width was employed to study the decontamination characteristics of Type 304 stainless steel specimens contaminated with Cs(+) ions. The surrogate specimens were artificially contaminated with two kinds of premixed solutions. The laser was irradiated for 10, 20 and 100 shots. The results were investigated using a SEM, EPMA and XPS. For the surrogate specimen treated with the CsCl+KCl solution, more than 98% of the Cs(+) ions were removed during an irradiation of 100 shots. The specimen treated with the CsCl+KCl solution was easier to decontaminate. By comparing the ratio of the O(1s) intensity to the Fe(2p) intensity of the XPS spectra, it was found that the oxygen atoms that had evolved from the specimen treated with the CsNO(3)+KNO(3) solution had decreased the laser's decontamination performance.

Signal and noise transfer properties of CMOS based active pixel flat panel imager coupled to structured CsI:Tl.

Complementary metal-oxide-semiconductors (CMOS) active pixel sensors can be optically coupled to CsI:Tl phosphors forming a indirect active pixel flat panel imager (APFPI) for high performance medical imaging. The aim of this work is to determine the x-ray imaging capabilities of CMOS-based APFPI and study the signal and noise transfer properties of CsI:Tl phosphors. Three different CsI:Tl phosphors from two different vendors have been used to produce three system configurations. The performance of each system configuration has been studied in terms of the modulation transfer function (MTF), noise power spectra, and detective quantum efficiency (DQE) in the mammographic energy range. A simple method to determine quantum limited systems in this energy range is also presented. In addition, with aid of monochromatic synchrotron radiation, the effect of iodine characteristic x-rays of the CsI:Tl on the MTF has been determined. A Monte Carlo simulation of the signal transfer properties of the imager is also presented in order to study the stages that degrade the spatial resolution of our current system. The effect of using substrate patterning during the growth of CsI:Tl columnar structure was also studied, along with the effect of CsI:Tl fixed pattern noise due to local variations in the scintillation light. CsI:Tl fixed pattern noise appears to limit the performance of our current system configurations. All the system configurations are quantum limited at 0.23 microC/kg with two of them having DQE (0) equal to 0.57. Active pixel flat panel imagers are shown to be digital x-ray imagers with almost constant DQE throughout a significant part of their dynamic range and in particular at very low exposures.

Exfoliated nanosheet crystallite of cesium tungstate with 2D pyrochlore structure: synthesis, characterization, and photochromic properties.

Layered cesium tungstate, Cs(6+x)W(11)O(36), with two-dimensional (2D) pyrochlore structure was exfoliated into colloidal unilamellar sheets through a soft-chemical process. Interlayer Cs ions were replaced with protons by acid exchange, and quaternary ammonium ions were subsequently intercalated under optimized conditions. X-ray diffraction (XRD) measurements on gluelike sediment recovered from the colloidal suspension by centrifugation showed a broad pattern of a pronounced wavy profile, which closely matched the square of calculated structure factor for the single host layer. This indicates the total delamination of the layered tungstate into nanosheets of Cs(4)W(11)O(36)(2-). Microscopic observations by transmission electron microscopy and atomic force microscopy clearly revealed the formation of unilamellar crystallites with a very high 2D anisotropy, a thickness of only approximately 2 nm versus lateral size up to several micrometers. In-plane XRD analysis confirmed that the 2D pyrochlore structure was retained. The colloidal cesium tungstate nanosheet showed strong absorption of UV light with sharp onset, suggesting a semiconducting nature. Analysis of the absorption profile provided 3.6 eV as indirect band gap energy, which is 0.8 eV larger than that of the bulk layered precursor, probably due to size quantization. The nanosheet exhibited highly efficient photochromic properties, showing reversible color change upon UV irradiation.

Eu-doped CsBr phosphor as a new optically-stimulable phosphor material for medical X-ray imaging sensor.

CsBr phosphor ceramics doped with different luminescence centres such as In2O3, Eu2O3, EuCl3, SmCl3, TbCl3, GdCl3 or NdCl3 as the candidate for a new optically-stimulable phosphor for medical X-ray imaging sensor were prepared using a conventional ceramic fabrication process. It was found that X-ray-irradiated Eu-doped CsBr (CsBr:Eu) exhibited intense optically stimulated luminescence (OSL). The peak wavelength of the OSL emission and stimulation spectra of CsBr:Eu phosphor ceramic sample were 450 and 690 nm, respectively. The dependence of OSL properties on the conditions of preparation of phosphor ceramic samples, such as Eu concentration, sintering temperature and sintering time, were studied. The optimum preparation conditions were also studied. It was found that the OSL intensity of CsBr:Eu phosphor ceramics fabricated under optimum preparation conditions is higher than that of commercially available imaging plates using BaFBr:Eu.

Segmented crystalline scintillators: empirical and theoretical investigation of a high quantum efficiency EPID based on an initial engineering prototype CsI(TI) detector.

Modern-day radiotherapy relies on highly sophisticated forms of image guidance in order to implement increasingly conformal treatment plans and achieve precise dose delivery. One of the most important goals of such image guidance is to delineate the clinical target volume from surrounding normal tissue during patient setup and dose delivery, thereby avoiding dependence on surrogates such as bony landmarks. In order to achieve this goal, it is necessary to integrate highly efficient imaging technology, capable of resolving soft-tissue contrast at very low doses, within the treatment setup. In this paper we report on the development of one such modality, which comprises a nonoptimized, prototype electronic portal imaging device (EPID) based on a 40 mm thick, segmented crystalline CsI(Tl) detector incorporated into an indirect-detection active matrix flat panel imager (AMFPI). The segmented detector consists of a matrix of 160 x 160 optically isolated, crystalline CsI(Tl) elements spaced at 1016 microm pitch. The detector was coupled to an indirect detection-based active matrix array having a pixel pitch of 508 microm, with each detector element registered to 2 x 2 array pixels. The performance of the prototype imager was evaluated under very low-dose radiotherapy conditions and compared to that of a conventional megavoltage AMFPI based on a Lanex Fast-B phosphor screen. Detailed quantitative measurements were performed in order to determine the x-ray sensitivity, modulation transfer function, noise power spectrum, and detective quantum efficiency (DQE). In addition, images of a contrast-detail phantom and an anthropomorphic head phantom were also acquired. The prototype imager exhibited approximately 22 times higher zero-frequency DQE (approximately 22%) compared to that of the conventional AMFPI (approximately 1%). The measured zero-frequency DQE was found to be lower than theoretical upper limits (approximately 27%) calculated from Monte Carlo simulations, which were based solely on the x-ray energy absorbed in the detector-indicating the presence of optical Swank noise. Moreover, due to the nonoptimized nature of this prototype, the spatial resolution was observed to be significantly lower than theoretical expectations. Nevertheless, due to its high quantum efficiency (approximately 55%), the prototype imager exhibited significantly higher DQE than that of the conventional AMFPI across all spatial frequencies. In addition, the frequency-dependent DQE was observed to be relatively invariant with respect to the amount of incident radiation, indicating x-ray quantum limited behavior. Images of the contrast-detail phantom and the head phantom obtained using the prototype system exhibit good visualization of relatively large, low-contrast features, and appear significantly less noisy compared to similar images from a conventional AMFPI. Finally, Monte Carlo-based theoretical calculations indicate that, with proper optimization, further, significant improvements in the DQE performance of such imagers could be achieved. It is strongly anticipated that the realization of optimized versions of such very high-DQE EPIDs would enable megavoltage projection imaging at very low doses, and tomographic imaging from a "beam's eye view" at clinically acceptable doses.

X-ray imaging performance of structured cesium iodide scintillators.

Columnar structured cesium iodide (CsI) scintillators doped with Thallium (Tl) have been used extensively for indirect x-ray imaging detectors. The purpose of this paper is to develop a methodology for systematic investigation of the inherent imaging performance of CsI as a function of thickness and design type. The results will facilitate the optimization of CsI layer design for different x-ray imaging applications, and allow validation of physical models developed for the light channeling process in columnar CsI layers. CsI samples of different types and thicknesses were obtained from the same manufacturer. They were optimized either for light output (HL) or image resolution (HR), and the thickness ranged between 150 and 600 microns. During experimental measurements, the CsI samples were placed in direct contact with a high resolution CMOS optical sensor with a pixel pitch of 48 microns. The modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) of the detector with different CsI configurations were measured experimentally. The aperture function of the CMOS sensor was determined separately in order to estimate the MTF of CsI alone. We also measured the pulse height distribution of the light output from both the HL and HR CsI at different x-ray energies, from which the x-ray quantum efficiency, Swank factor and x-ray conversion gain were determined. Our results showed that the MTF at 5 cycles/mm for the HR type was 50% higher than for the HL. However, the HR layer produces approximately 36% less light output. The Swank factor below K-edge was 0.91 and 0.93 for the HR and HL types, respectively, thus their DQE(0) were essentially identical. The presampling MTF decreased as a function of thickness L. The universal MTF, i.e., MTF plotted as a function of the product of spatial frequency f and CsI thickness L, increased as a function of L. This indicates that the light channeling process in CsI improved the MTF of thicker layers more significantly than for the thinner ones.

Luminescence of CsGd2F7 crystals.

Optical and dosimetric properties of nominally pure CsGd2F7 crystals and of CsGd2F7 crystals doped with various concentrations of Pr3+ ions were investigated. Effects of X, beta and UV irradiation on these crystals were studied. Methods of optical absorption, X and UV excited luminescence, thermoluminescence (TL), phototransferred thermoluminescence and optically stimulated luminescence were used in these investigations. The dependence of the TL efficiency on the radiation dose was found to be linear up to 6 kGy for the 3 at.% Pr3+ doped samples. The crystals containing from 0.3 at.% to 1.0 at.% of Pr3+ ions were found to have the best TL sensitivity and the intensity of the main TL peak in these samples was more than two orders of magnitude higher than that of the pure crystals. The TL sensitivity of the CsGd,F7:Pr3+ crystals was also compared with that of other commonly used TLD materials.

Optimization of the scintillation detector in a combined 3D megavoltage CT scanner and portal imager.

A parametric study is described leading to the optimization of a custom-made scintillation detector with a relatively high quantum efficiency (QE) for megavoltage photons and light output toward a remote lens. This detector allows low-dose portal imaging and continuous cone-beam megavoltage CT acquisition. The EGS4 Monte Carlo code was used to simulate the x-ray and electron transport in the detector. A Monte Carlo model of optical photon transport in a detector element was devised and used as well as various irradiation experiments on scintillators. Different detector materials and configurations were compared in terms of the optical photon irradiance on the lens from on- and off-axis detector elements and the practical constraints regarding detector construction and weight. Effects of scintillator material, detector element size, crystal coating type, and reflectivity, combinations of different coatings on detector faces, scintillator doping level, and crystal transparency were studied. With scintillator thickness adjusted to give an 18% x-ray QE at 6 MV, the light output of CsI(Tl) was at least eight times higher than ZnWO4, BGO and NE118 plastic. Further, CsI(Tl) showed the smallest decrease in QE going from 6 to 24 MV. The off-axis reduction in emittance from the periphery of the detector was relatively small with a slight dependence on the type and reflectivity of the coating and the crystal thickness for a fixed detector element cross section. Light output was more strongly dependent on the reflectivity of lambertian coatings than specular ones. For a fixed detector element cross section, optimum coating type depended on crystal thickness. Typical CsI(Tl) crystals showed a relatively small variation in light output with changes in optical attenuation length. The optimum detector element was found to be CsI(Tl) coated on five faces with TiO2-loaded epoxy resin offering about a ten-fold improvement in light output per incident photon compared to typical metal/phosphor screens.

Repercussöes dermatológicas no acidente radioativo com o Césio 137 em Goiânia / Dermatological repercussions in the radioactive accident with Cesio 137 in Goiânia

O objetivo deste estudo foi analisar a ocorrência de dermatoses nos indivíduos expostos ao césio-137 no acidente radioativo ocorrido na cidade de Goiânia, em setembro de 1987, e evidenciar dermatoses precancerosas ou preditoras de baixa imunidade. Avaliaram-se grupos, conforme a intensidade de radiação, e um grupo-controle, composto por pessoas não expostas a radiação. Neste estudo a população exposta ao césio-137 corresponde a 109 pessoas, divididas em Grupos I e II, conforme normas da CNEN. No Grupo I incluiram-se 54 pessoas com exposição maior que ou igual 20 rads e/ou radiolesão, no Grupo II, 55 pessoas, sendo 42 pessoas com exposição menor que 20 rads e 13 filhos de pacientes do Grupo I. O estudo foi de coorte histórica, ou seja, retropectiva, por 9 anos, de setembro de 1987 a agosto de 1996. Pesquisou-se a presença da oncoproteina p-53 nas radiolesöes de 10 pacientes. Não se evidencia aumento na incidência das dermatoses nos grupos expostos, exceto as piodermites nos pacientes com radiolesão. As dermatoses mais frequentes foram as piodermites, a pitiriase vesicolor, a escabiose, as dermatofitoses e as dermatites seborreicas. Os resultados obtidos não apresentam significância estatística na avaliação das dermatoses precancerosas. A oncoproteína p-53, nos indivíduos com radiolesão, revela 80 (por cento) de positividade e um fator de risco estimado em oito vezes para o teste. Este teste mostra-se útil no sentido de acrescentar opçöes na avaliaço propedêutica e sugere uma atenção contínua para melhor controle evolutivo destes indivíduos

Incorporaçäo e eliminaçäo de césio-134 pelo caramujo Biomphalaria glabrata (Say, 1818) / Uptake and loss of cessium-134 by the snail Biomphalaria glabrata (Say, 1818)

A incorporaçiao e eliminaçäo de Cs-134, produzido no reator IEA-R1 do IPEN, foram observadas em caramujos adultos de água doce. Duas atividades de Cs-134 foram empregadas: 3.700 e 18.500 Bq/1. As contagens foram feitas em um analisador monocanal e foram registrados o número de desovas e de embriöes. O máximo de incorporaçäo do radioisótopo ocorreu por volta de 8§ dia e a meia-vida biológica foi de aproximadamente 6 dias. Apesar do número total de desovas e de embrioes terem sido menores na presença de Césio-134, isto näo pode ser afirmado em virtude da pequena amostragem utilizada

Recuperaçäo de fontes hospitalares seladas de 137 Cs / Recovery of lost medical 137 Cs sources

Existe uma grande probabilidade de perda de fontes de braquiterapia devido a falta de atençäo dos encarregados e/ou de um comportamento inesperado do paciente que a ela é submetido. Considerando os últimos acontecimentos envolvendo fontes de radiaçäo ionizante, achamos oportuno nos reportarmos ao trabalho por nós desenvolvido há alguns anos sobre a recuperaçäo de três fontes equivalentes a 10 mCi ou 37 x 10**7 Bq cada uma, extraviadas de um aplicador intrauterino do tipo Henscke por uma paciente com problema mental e jogadas no ralo do banheiro e no lixo. Um protocolo para fontes perdidas também é sugerido