Electric-field behavior and charge-density distribution in semi-insulating gallium arsenide Schottky diodes

The behavior of the electric field and the charge-density distribution in semi-insulating gallium arsenide Schottky diodes have been analyzed by optical-beam-induced current and surface potential;measurements. The electric field exhibits three different regions across the detector, the characteristics of which depend on the reverse applied voltage. Furthermore, a positive box-shaped space charge region exists, separated from the Schottky barrier by a neutral space-charge region, and widens and moves towards the Ohmic contact at increasing the reverse bias voltage. This study adds substantial information to the knowledge of the space-charge distribution in semi-insulating Schottky diodes, discriminates between the existing models on the electric field, and provides essential information to understand nuclear detector performance

Analysis of the output signal waveform and performances of semi-insulating GaAs particle detectors

This paper presents an extensive analysis of the signals at the output of a charge sensitive amplifier delivered by a semi-insulating liquid-encapsulated Czochralski grown GaAs particle detector, irradiated with 5.48 MeV alpha particles. When the detector is operated below full depletion the shape of the output signal can be explained by the equivalent circuit of the detector itself, while above full depletion it is affected only by trapping-detrapping processes and it is well interpreted in terms of trapping and detrapping times of deep level traps present in the materials. Spectral lines of alpha particles from an Am-241 source have shown a resolution of 1.1% at room temperature

Photon radiation damage in high purity silicon and LEC Si gallium arsenide detectors

Observations have been made of the behaviour of high resistivity silicon and semi-insulating gallium arsenide ionizing radiation detectors after exposure of up to 30 Mrad Co-60 photons. Results are presented on leakage current and deep level defects of the substrate material of photon damage devices. These findings have been related to the charge collection efficiency of the detectors

Defects induced by protons and gamma-rays in semi-insulating GaAs detectors

Semi-insulating gallium arsenide has been irradiated by protons and by gamma-rays with different doses. The irradiation-induced deep level defects have been investigated by current transient spectroscopy to find their energy, capture cross sections and generation rate.Two electron traps at Ec+0.14eV(E13) and Ec-0.70eV(E4) and a hole trap at Ec-0.14eV(H2) in addition to the levels existing before the irradiation have been detected in the irradiated samples. These findings have been related to the performance of gallium arsenide charge particle detectors

Bitter taste receptors as targets for tocolytics in preterm labor therapy

Preterm birth (PTB) is the leading cause of neonatal mortality and morbidity, with few prevention and treatment options. Uterine contraction is a central feature of PTB, so gaining new insights into the mechanisms of this contraction and consequently identifying novel targets for tocolytics are essential for more successful management of PTB. Here we report that myometrial cells from human and mouse express bitter taste receptors (TAS2Rs) and their canonical signaling components (i.e., G-protein gustducin and phospholipase C beta2). Bitter tastants can completely relax myometrium precontracted by different uterotonics. In isolated single mouse myometrial cells, a phenotypical bitter tastant (chloroquine, ChQ) reverses the rise in intracellular Ca2+ concentration ([Ca2+]i) and cell shortening induced by uterotonics, and this reversal effect is inhibited by pertussis toxin and by genetic deletion of alpha-gustducin. In human myometrial cells, knockdown of TAS2R14 but not TAS2R10 inhibits ChQ\u27s reversal effect on an oxytocin-induced rise in [Ca2+]i Finally, ChQ prevents mouse PTBs induced by bacterial endotoxin LPS or progesterone receptor antagonist mifepristone more often than current commonly used tocolytics, and this prevention is largely lost in alpha-gustducin knockout mice. Collectively, our results reveal that activation of the canonical TAS2R signaling system in myometrial cells produces profound relaxation of myometrium precontracted by a broad spectrum of contractile agonists, and that targeting TAS2Rs is an attractive approach to developing effective tocolytics for PTB management

Association of fetal hormone levels with stem cell potential: evidence for early life roots of human cancer

Intrauterine and perinatal factors have been linked to risk of childhood leukemia, testicular cancer, and breast cancer in the offspring. The pool of stem cells in target tissue has been suggested as a critical factor linking early life exposures to cancer. We examined the relation between intrauterine hormone levels and measurements of stem cell potential in umbilical cord blood. Cord blood donors were 40 women, ages \u3e/=18 years, who delivered, from August 2002 to June 2003, a singleton birth after a gestation of at least 37 weeks. We assayed plasma concentrations of estradiol, unconjugated estriol, testosterone, progesterone, prolactin, sex hormone binding globulin, insulin-like growth factor-I (IGF-I), and IGF binding protein-3. For stem cell potential, we measured concentrations of CD34(+) and CD34(+)CD38(-) cells and granulocyte-macrophage colony-forming unit (CFU-GM). We applied linear regression analysis and controlled for maternal and neonatal characteristics. We found strong positive associations between IGF-I and stem cell measures, 1 SD increase in IGF-I being associated with a 41% increase in CD34(+) (P = 0.008), a 109% increase in CD34(+)CD38(-) (P = 0.005), and a 94% increase in CFU-GM (P = 0.01). Similar associations were observed for IGF binding protein-3. Among steroid hormones, estriol and testosterone were significantly positively associated with CD34(+) and CFU-GM. These findings indicate that levels of growth factors and hormones are strongly associated with stem cell potential in human umbilical cord blood and point to a potential mechanism that may mediate the relationship between in utero exposure to hormones and cancer risk in the offspring

Gallium arsenide pixel detectors for medical imaging

Gallium arsenide pixel detectors processed on a 200 mu m Semi-Insulating (SI) Hitachi substrate were bump-bended to the Omega3 electronics developed at CERN for high energy physics [1]. The pixel dimensions are 50 mu m x 500 mu m for a total of 2048 cells and an active area of similar to 0.5 cm(2). Our aim is to use this system for medical imaging. We report the results obtained after irradiation of the detector with different X-ray sources on phantoms with different contrasts. The system showed good sensitivity to X-rays from Am-241 (60 keV) and Cd-109 (22.1 keV). It is also sensitive to p-particles from Sr-90 as well as from P-32 which is used as a tracer for autoradiography applications. The inherent high absorption efficiency of GaAs associated with the self-triggering capabilities of the pixel readout system reduced considerably the acquisition time compared with traditional systems based on silicon or emulsions. The present configuration is not optimised for X-ray imaging. The reduction of the pixel dimensions to 200 mu m x 200 mu m together with the integration of a counter in the pixel electronics would make the detector competitive for applications like mammography or dental radiology. For certain applications in biochemistry, such as DNA sequencing, where good spatial resolution is required only in one direction, the present setup should allow the best spatial resolution available up to now with respect to other digital autoradiographic systems. DNA sequencing tests are now under way

Gallium arsenide pixel detectors for medical imaging

Gallium arsenide pixel detectors processed on a 200 mu m Semi-Insulating (SI) Hitachi substrate were bump-bended to the Omega3 electronics developed at CERN for high energy physics [1]. The pixel dimensions are 50 mu m x 500 mu m for a total of 2048 cells and an active area of similar to 0.5 cm(2). Our aim is to use this system for medical imaging. We report the results obtained after irradiation of the detector with different X-ray sources on phantoms with different contrasts. The system showed good sensitivity to X-rays from Am-241 (60 keV) and Cd-109 (22.1 keV). It is also sensitive to p-particles from Sr-90 as well as from P-32 which is used as a tracer for autoradiography applications. The inherent high absorption efficiency of GaAs associated with the self-triggering capabilities of the pixel readout system reduced considerably the acquisition time compared with traditional systems based on silicon or emulsions. The present configuration is not optimised for X-ray imaging. The reduction of the pixel dimensions to 200 mu m x 200 mu m together with the integration of a counter in the pixel electronics would make the detector competitive for applications like mammography or dental radiology. For certain applications in biochemistry, such as DNA sequencing, where good spatial resolution is required only in one direction, the present setup should allow the best spatial resolution available up to now with respect to other digital autoradiographic systems. DNA sequencing tests are now under way