Increase In Light Output Research Articles

Survey of mammographic cassette light output.

The purpose of the present paper was to assess the variation in light output from clinical mammographic screens, particularly in relationship to age and radiographic usage. The light output from 156 mammographic cassettes from 17 clinical centres was measured on site using a novel light detector. Survey information on cassette age and usage was collected. Where possible, screen manufacture date was supplied by the vendor. One cassette from each centre was measured at a standard laboratory to allow normalization of all measurements. Three centres were found to have cassettes in clinical use whose light outputs varied by an amount incompatible with current Royal Australasian College of Radiologists (RACR) standards. These centres used cassettes whose ages varied widely. No correlation between light output and radiographic usage was found. Older cassettes were found to have a slight increase in light output. A small reduction of light output was measured between screen regions of high and low radiation exposure histories. Replacement of mammographic screens should not be based on an expectation of light output reduction due to age or usage. Rather, all mammographic screens should be replaced simultaneously as indicated by factors such as failure of screen-film contact or the presence of screen-related image artefacts.

Development of a Luminescent Bioassay for Thyroid Stimulating Antibodies

The hyperthyroidism of Graves Disease (GD) is due to thyroid stimulating antibodies (TSAb) which are thyrotropin (TSH) agonists. They are detected routinely by measuring their ability to inhibit TSH binding to the receptor (TBII), which does not reflect their true biological activity. Current bioassays which measure cAMP by RIA, are not suitable for routine use. We have developed a luminescent bioassay for TSAb, by introducing a cAMP responsive luciferase construct into CHO cells stably expressing the human TSH receptor (TSHR). Clone lulu1 displays dose dependent TSH response detectable from 10 μU/ml and maximal at 10 mU/ml when a >25 fold increase in light output is obtained. 34 euthyroid sera were tested to determine a reference range, with values >1.5 relative light units (R.L.U.) being considered positive. An international TSAb standard responded in a dose dependent manner with 10 mIU/ml giving an R.L.U. of >10. The assay was adapted to a 96 well format for automatic readout and 100 treated GD samples (50 TBII negative and 50 TBII positive) were tested, 73% being positive. In contrast only 4% of 79 control sera from individuals with Hashimoto’s, non-thyroid autoimmunity or multinodular goitre produced R.L.U. >1.5. When 44 of the GD sera were compared in a traditional salt-free bioassay, 61% were positive compared with 75% in the new luminescent assay. In conclusion, we have developed a luminescent bioassay for TSAb, using unfractionated serum which is capable of high throughput suitable for routine use.

Development of a luminescent bioassay for thyroid stimulating antibodies.

The hyperthyroidism of Graves Disease (GD) is due to thyroid stimulating antibodies (TSAb) which are thyrotropin (TSH) agonists. They are detected routinely by measuring their ability to inhibit TSH binding to the receptor (TBII), which does not reflect their true biological activity. Current bioassays which measure cAMP by RIA, are not suitable for routine use. We have developed a luminescent bioassay for TSAb, by introducing a cAMP responsive luciferase construct into CHO cells stably expressing the human TSH receptor (TSHR). Clone lulul displays dose dependent TSH response detectable from 10 microU/ml and maximal at 10 mU/ml when a >25 fold increase in light output is obtained. 34 euthyroid sera were tested to determine a reference range, with values >1.5 relative light units (R.L.U.) being considered positive. An international TSAb standard responded in a dose dependent manner with 10 mIU/ml giving an R.L.U. of >10. The assay was adapted to a 96 well format for automatic readout and 100 treated GD samples (50 TBII negative and 50 TBII positive) were tested, 73% being positive. In contrast only 4% of 79 control sera from individuals with Hashimoto's, non-thyroid autoimmunity or multinodular goitre produced R.L.U. >1.5. When 44 of the GD sera were compared in a traditional salt-free bioassay, 61% were positive compared with 75% in the new luminescent assay. In conclusion, we have developed a luminescent bioassay for TSAb, using unfractionated serum which is capable of high throughput suitable for routine use.

Integrating cytosolic calcium signals into mitochondrial metabolic responses.

Stimulation of hepatocytes with vasopressin evokes increases in cytosolic free Ca2+ ([Ca2+]c) that are relayed into the mitochondria, where the resulting mitochondrial Ca2+ ([Ca2+]m) increase regulates intramitochondrial Ca2+-sensitive targets. To understand how mitochondria integrate the [Ca2+]c signals into a final metabolic response, we stimulated hepatocytes with high vasopressin doses that generate a sustained increase in [Ca2+]c. This elicited a synchronous, single spike of [Ca2+]m and consequent NAD(P)H formation, which could be related to changes in the activity state of pyruvate dehydrogenase (PDH) measured in parallel. The vasopressin-induced [Ca2+]m spike evoked a transient increase in NAD(P)H that persisted longer than the [Ca2+]m increase. In contrast, PDH activity increased biphasically, with an initial rapid phase accompanying the rise in [Ca2+]m, followed by a sustained secondary activation phase associated with a decline in cellular ATP. The decline of NAD(P)H in the face of elevated PDH activity occurred as a result of respiratory chain activation, which was also manifest in a calcium-dependent increase in the membrane potential and pH gradient components of the proton motive force (PMF). This is the first direct demonstration that Ca2+-mobilizing hormones increase the PMF in intact cells. Thus, Ca2+ plays an important role in signal transduction from cytosol to mitochondria, with a single [Ca2+]m spike evoking a complex series of changes to activate mitochondrial oxidative metabolism.

Structural dependence of optical bistability of In 0.52Al 0.48As/InP type II MQW diodes grown by gas source molecular beam epitaxy

The structural dependence of optical bistability was studied for the In 0.52Al 0.48As/InP type II multiple quantum well diodes grown by gas source molecular beam epitaxy. Two types of optical bistability were observed. One of them shows a sudden increase of light output with increasing injection current, while the other shows a sudden decrease of light output with increasing injection current. The former is considered to be induced by holes tunneling in the valence band, while the latter is considered to be induced by the resonant tunneling effect of electrons in the conduction band.

Research for a fiber detector for CDF Run II

In the course of research and development of a fiber detector for CDF Run II we have made measurments of the light yield increase due to fiber mirroring, and both the noise and rate capability of visible light photon detectors (VLPCs). We found the reflection coefficient, R=0.65±0.01 could be obtained using aluminum sputtering. We also found that both the noise level and the rate capability of the VLPCs were acceptable for use in CDF for collider Run II.

Light Emitting Electrochemical Cells as Mixed Ionic Electronic Conductors

ABSTRACTPolymer electrochemical cells have been reported to emit light. The current and light output increase rapidly with voltage, apparently beyond 2V. The polymer is an ionic conductor as well as an electronic (electron/hole) conductor, i.e. a mixed ionic-electronic conductor (MIEC).The I-V relations are explained here to be those of an MIEC of a particular defect model placed between two ion blocking electrodes. This MIEC defect model assumes a large concentration of mobile ions and small concentrations of electrons and holes. A p and an n region are formed in the MIEC. However, there is no space charge within the MIEC and it stays neutral. The resulting I-V relations are exponential. A good fit to the experimental data is obtained when electrode over-potential and heating of the polymer under current are taken into consideration.

Characterization of fluor concentration and geometry in organic scintillators for in situ beta imaging

Development of a small area (1-2 cm/sup 2/) in situ beta imaging device includes optimization of the front end scintillation detector, which is fiber optically coupled to a remote photon detector. Thin plastic scintillation detectors, which are sensitive to charged particles, are the ideal detectors due to the low sensitivity to ambient gamma backgrounds. The light output of a new binary plastic scintillator was investigated with respect to increasing concentrations of the fluor (0.5-2.0% by weight) and varying thickness cylindrical configurations of the intended imaging detector. The fluor had an emission maximum increasing from 431 to 436 nm with increasing fluor concentration. The decay time(s) had two components (0.38 and 1.74 ns). There was an /spl sim/20% increase in light output with increasing fluor concentration, measured with both /sup 204/Tl betas and conversion electrons from /sup 207/Bi. The highest light output of this new scintillator was measured to be /spl sim/30% lower than BC404. Simulations predicted the 1.5 mm scintillator thickness at which light output and energy absorption for /spl sim/700 keV electrons (e.g., from /sup 204/Tl, /sup 18/F) were maximized, which corresponded with measurements. As beta continua are relatively featureless, energy calibration for the thin scintillators was investigated using Landau distributions, which appear as distinct peaks in the spectra. As the scintillators were made thinner, gamma backgrounds were shown to linearly decrease.

Threshold Cherenkov detectors for a meson trigger in a magnetic spectrometer

Lucite and water Cherenkov detectors were built for a magnetic spectrometer (KaoS at SIS). The task of the detectors is to improve the proton suppression at the trigger level in experiments on meson production from nuclear collisions. By applying Polyphenyl 1 as wavelength shifter addition to water a light yield increase by a factor of 2 was achieved. Material with a very high reflectance (better than that of Teflon) was tested and applied as a wall covering for the water detectors. The efficiency of the detectors was measured as a function of the particle velocity, and the data were compared to formulae for Cherenkov light emission and detection.

Lyoluminescence characteristics of lactose

The lyoluminescence (LL) of lactose shows a linear γ-ray dose response in the range 1–10 4 Gy. LL standardization measurement of lactose with a luminol sensitizer shows a sharp increase in light output in the pH range 10–11. Effects of radical scavengers and oxygen confirm that the radiation-induced free radicals take part in the LL process and oxygen is essential for initiating the LL mechanism. LL emission spectral measurements indicate an energy transfer from diffusing free radicals to sensitizer molecules to produce light.

An algD-bioluminescent reporter plasmid to monitor alginate production in biofilms

A broad-host range algD-lux bioluminescent reporter plasmid was developed to examine the role of exopolymer production in biofilm function. The algD-lux reporter plasmid will allow rapid on-line in situ detection of environmental factors that induce alginate biosynthesis. The algD promoter was stimulated by factors previously reported to induce alginate production, including ethanol and NaCl, and differences were observed with different nitrogen sources. With growth on minimal media with either glucose or succinate as a carbon source, succinate had a greater inductive effect on the algD promoter. An increase in light output of 1.3-fold and 1.7-fold was seen with cultures amended with 50 and 150 mM NaCI, respectively, compared to cultures with succinate alone. NaCl induction of the algD promoter was confirmed by algD RNA slot blots. Light output increased 2.0-fold and 1.7-fold with 0.25% and 0.5% ethanol, respectively, compared with controls grown with succinate only. While the rate of algD promoter response was initially similar when either NH4 or NO3 was used as a nitrogen source, NH4-grown cultures maintained a higher light output during late log phase compared to NO3-grown cultures.

Light output and collected charge in xenon-doped liquid argon

The light output and the collected charge in xenon-doped liquid argon under 207Bi conversion electron excitation have been studied as a function of an applied electric field with the xenon concentration [Xe] less than 1.9%. With increasing [Xe], the light output was increased and was maximized at [Xe] = 1.9%, having about as twice as much intensity with respect to that in pure argon. The amount of collected charge in xenon-doped liquid argon was nearly equal to that in pure argon up to 2500 ppm of [Xe], above which a slight increase was observed. The increase in light output can be explained by the difference in the conversion efficiency of the POPOP wavelength shifter for 130 nm scintillation photons in liquid argon and for 175 nm scintillation photons in xenon-doped liquid argon.

Influence of magnetic fields on the response of a uranium scintillator electromagnetic calorimeter

The response of a uranium scintillator sampling calorimeter to incident electrons and to the uranium radioactivity was measured in transverse magnetic fields up to 1.4T. The signal from electrons rises by as much as 9% due to the expected increase in light output of plastic scintillators in magnetic fields. For fields below 0.3 T the response to the uranium radioactivity tracks the electron signal to within about 0.5%. At higher fields it drops sharply, reaching −1.5% at 1.4 T. The consequences for the calibration of the ZEUS uranium scintillator calorimeter are discussed. We found no evidence for a change in the electromagnetic sampling fraction for fields below 0.3 T.

Plastic scintillators in magnetic fields

The dependence of the light yield and the transmission on magnetic fields has been measured with different methods up to 0.45 T for the plastic scintillators NE-102A, SCSN-38 and Polivar. The scintillators were excited by 25 MeV protons, 5.9 keV X-rays and UV light. When excited with ionizing radiation an increase of light yield is observed. For SCSN-38 of 2.6 mm thickness it amounts to 0.3%, 0.9%, 1.1% and 3.3% at 1, 10, 100 and 450 mT, respectively. NE-120A behaves similar, whereas an acrylic scintillator shows a stronger field dependence. The effect is independent of the direction of the field but increases for the acrylic scintillator with its thickness. No change in the decay time of the scintillator has been observed. The response of the scintillators did not change when excited by UV light in a magnetic field.

Response of plastic scintillators in magnetic fields

The dependence of the light yield on magnetic field has been measured up to 0.45 T for the plastic scintillators NE-102A, SCSN-38, and Polivar. The scintillators were excited by 25-MeV protons, 5.9-keV X-rays, and UV light. When excited with ionizing radiation an increase of light yield is observed. For SCSN-38 of 2.7-mm thickness it amounts to 0.3%, 0.9%, 1.1%, and 3.3% at 1, 10, 100 and 450 mT, respectively. Ne-102A behaves similarly whereas a polymethyl methacrylate (PMMA)-based scintillator shows a stronger field dependence. >

The isotype Al 0.05Ga 0.95As/Al 0.35Ga 0.65As interface of the LPE-grown double heterostructure at elevated temperature

The isotype interface of a double heterostructure is studied by measuring the capacitance-voltage characteristic ( C/ V technique). For the LPE-grown Al 0.05Ga 0.95As/Al 0.35Ga 0.65As system it is shown that the effective barrier height of the p-type heteroboundary can be estimated even in the range below 25 meV by recording the C/ V characteristic at lower than room temperature. Experimental evidence is given for the first time that the effective barrier height at the isotope p/ P interface of the NpP-type heterostructure may be raised after treatment at elevated temperature. This reaction at the heteroboundary depends on the mechanical stress additionally introduced by the solder. The gradual increase in light output often observed in AlGaAs double heterostructure diodes during operation at elevated temperature can be well approximated by a step-like function of the operation time and a characteristic delay time. The process is mainly thermally controlled with an activation energy of about 0.53 eV. A correspondence is found between the microscopic process at the p/ P interface and the gradual increase in light output. Therefore, it is suggested that the reaction at the isotype interface of LPE-grown AlGaAs heterojunctions is at least partly the origin of the increase in light output during operation at elevated temperature. Both phenomena are not dependent on the operation current and are more effective at low external compressive stress.

Energy resolution of liquid scintillator for α-particles and internal conversion electrons at lower temperatures

The energy resolution of α-particles from241Am,222Rn,218Po and214Po and internal conversion electrons from131mXe with a liquid scintillation system has been studied at temperatures from 13 °C to −65 °C. At lower temperatures the liquid scintillation system has shown to give better energy resolutions both for α-particles and internal conversion electrons compared with the values obtained at ordinary temperature. The phenomena were explained by the increase in light output of liquid scintillator at lower temperatures.

Investigation of problems about the light power output of GaAs-GaAlAs DH surface leds

A modified conventional RF sputtering equipment is used in preparing the Al2O3 antireflection (AR) coating. An increase in the light output by 30–60% at a driving current of 200 mA for the GaAs-GaAlAs DH LEDs coated on the front faces with a AR coating thickness of about λ/4 has been obtained. Under the same AR coating conditions a light output increase of less than 30% for the degraded LEDs of the same type has been determined. It may probably be attributed to the defects formed in the bulk of the Ga1−xAlxAs crystals caused by degradation of diodes which restricts light output increase.

Observation of spontaneous increase of light output of scintillation of solid krypton

Observation of spontaneous increase of light output of scintillation of solid krypton

Competing processes in long term accelerated aging of double heterostructure Ga1−xAlxAs light emitting diodes

Two competing processes have been observed in bias aging of double heterostructure (DH) Ga1−xAlxAs light emitting diodes (LEDs) at elevated temperatures. These high radiance LEDs are used as sources in optical data links. In the past, only a single aging process, slow degradation in light output, has been reported for dark line defect (DLD)-free LEDs of similar type. In contrast, we report for the first time, a second process which gives a gradual increase in light output. As temperature and current are increased this new process increasingly masks the degradation process, until at 270 °C there is a net increase in light output of 50% after about 300 h of aging. We show that the two processes have different time dependences and activation energies, and that their effects on the light output during aging can be separated mathematically. A model for the new process is presented in which nonradiative traps anneal out in a recombination-enhanced defect reaction. This leads to higher injection efficiency and light output at fixed current. Operating lifetimes increase due to the second process; for example, at 25 °C mean-time-to-failure (MTTF) increases by a factor of three to 9×107 h.