Using Relative Luminance to Inform the Design and Evaluation of User Interfaces for Dark-Adapted Operators

The authors report on measurements of light output and spatial resolution of microcolumnar CsI:Tl scintillator detectors for x-ray imaging. In addition, the authors discuss the results of simulations aimed at analyzing the results of synchrotron and sealed-source exposures with respect to the contributions of light transport to the total light output. The authors measured light output from a 490-μm CsI:Tl scintillator screen using two setups. First, the authors used a photomultiplier tube (PMT) to measure the response of the scintillator to sealed-source exposures. Second, the authors performed imaging experiments with a 27-keV monoenergetic synchrotron beam and a slit to calculate the total signal generated in terms of optical photons per keV. The results of both methods are compared to simulations obtained with hybridmantis, a coupled x-ray, electron, and optical photon Monte Carlo transport package. The authors report line response (LR) and light output for a range of linear absorption coefficients and describe a model that fits at the same time the light output and the blur measurements. Comparing the experimental results with the simulations, the authors obtained an estimate of the absorption coefficient for the model that provides good agreement with the experimentally measured LR. Finally, the authors report light output simulation results and their dependence on scintillator thickness and reflectivity of the backing surface. The slit images from the synchrotron were analyzed to obtain a total light output of 48 keV-1 while measurements using the fast PMT instrument setup and sealed-sources reported a light output of 28 keV-1 . The authors attribute the difference in light output estimates between the two methods to the difference in time constants between the camera and PMT measurements. Simulation structures were designed to match the light output measured with the camera while providing good agreement with the measured LR resulting in a bulk absorption coefficient of 5 × 10-5 μm-1 . The combination of experimental measurements for microcolumnar CsI:Tl scintillators using sealed-sources and synchrotron exposures with results obtained via simulation suggests that the time course of the emission might play a role in experimental estimates. The procedure yielded an experimentally derived linear absorption coefficient for microcolumnar Cs:Tl of 5 × 10-5 μm-1 . To the author's knowledge, this is the first time this parameter has been validated against experimental observations. The measurements also offer insight into the relative role of optical transport on the effective optical yield of the scintillator with microcolumnar structure.

Purpose: Miniature plastic scintillation detectors (PSDs) and plastic scintillation detector arrays are highly useful in many radiotherapy applications. However, PSDs can show large detector variability between apparently identical detectors. Such variability may impact on the performance of a PSD array. The purpose of this work is to develop a quality control procedure to increase the uniformity of PSDs. Method and Materials: A uniform procedure for fabricating PSDs was established. A quality control bench was then designed, which comprised a precise positioning mechanism, an ultraviolet LED for stimulating the scintillation light in plastic scintillators and a spectrometer to characterize the relative emission spectra of the PSDs as well as their total light output. The reproducibility of the bench itself was evaluated by measurements of a single detector through numerous mounting, un‐mounting cycles. A batch of 15 PSDs was then built and tested for quality. Results: The quality control bench could be used with an average reproducibility of 0.7%. Stimulation of the plastic scintillators by ultraviolet light produced the same emission spectrum as one obtained from ionizing radiation. Quality control measurements for the 15 PSDs showed no major discrepancies in the relative emission spectrum. However, large variations in total light output were observed. The standard deviation of the total light output was 16%, with a maximum variation of 28%. Of all detectors, 13% had a total light output of 0.85 or less relative to the mean. Conclusion: The precision of a plastic scintillation detector will suffer if its total light output is too low. In this work, we have developed a tight quality control procedure for PSDs that could improve the performances of PSDs and PSD arrays. This procedure can be used to prevent detectors with poor light output from being used.Supported by the NCI (1R01CA120198‐01A2).

The material properties of lead sulfate (PbSO/sub 4/) are attractive for use as a gamma radiation detector. In 99.998% pure PbSO/sub 4/ crystals at room temperature excited by 511-keV annihilation photons, the fluorescence decay lifetime contained significant fast components having 1.8-ns and 19-ns decay times, but with longer components having 95-ns and 425-ns decay times. The peak emission wavelength was 335 nm, which was transmitted by borosilicate glass window photomultiplier tubes. The total scintillation light output increased with decreasing temperature from 3200 photons/MeV at +45 degrees C to 4900 photons/MeV at room temperature and 68500 photons/MeV at -145 degrees C. In an imperfect, 3-mm cube of a naturally occurring mineral form of PbSO/sub 4/ (anglesite) at room temperature, a 511-keV photopeak was seen with a total light output of 60% that of BGO. There was significant sample-to-sample variation of the light output among anglesite samples.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

&lt;div class="htmlview paragraph"&gt;This paper examines the consequences of fabrication effects on the performance of injection molded plastic light pipes for distributive automotive lighting. It discusses the magnitude of these effects on propagating and output light. Molding errors, such as sinks, voids, flow lines, knit lines, and warpage, will be examined through computer modeling and measurement of sample distributive lighting systems.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;Two example light pipe systems will be presented, an instrument cluster pointer system and a regional distributive interior lighting system. For the pointer system, computer modeling results, such as total light output and output exitance distributions will be presented. Modeling results will be presented for both an error free system and system that include the aforementioned molding errors. These results will be compared to determine the output light loss and redistribution. For the regional interior lighting system, total output and exitance measurements of fabricated light pipe systems will be presented for comparison and to illustrate the effects of errors.&lt;/div&gt; &lt;div class="htmlview paragraph"&gt;Since it is impossible or impractical to eliminate all injection molding fabrication errors from manufactured light pipe systems, this paper will conclude with a discussion of the circumstances under which individual errors should be diminished or eliminated.&lt;/div&gt;

Monte Carlo simulation methods are used to investigate the light output characteristics and energy resolution of detector modules that consist of long, narrow bars of sodium iodide crystals. These modules are designed to be components of a proposed modular cylindrical single photon emission computed tomography system suitable for cardiac imaging. The simulations are used to investigate the effects of crystal geometry and detector surface reflection properties on the total light output and energy resolution of the detector modules. The simulations include the effects on scintillation photons due to internal photon absorption at the crystal and light guide surfaces, partial (Fresnel) reflections and total internal reflections at the crystal/quartz exit window interface, refraction in the light guide, and finite quantum efficiency of photomultiplier tubes. For the imaging of 140-keV gamma rays, modules with 3-mm wide crystals and diffusely-reflecting surfaces are expected to have total light output of about 12.1% and energy resolution of about 10.9%. Modules with 4-mm wide crystals are expected to have total light output of about 13.9% and energy resolution of about 9.9%.

This work describes a successful post fabrication method of applying a plasmonic grating to the surface of a mounted AlGaInP LED device. A Carl Zeiss 1540 XB Focused Ion beam system was used to mill holes in a thin gold layer with a periodicity of around 540 nm. Measurements of the total light output of the device compared with a standard un‐textured device show that the plasmonic grating was found to significantly affect the light output characteristics such that the overall light output was reduced. This is attributed to the fact that only p‐polarised light can interact with the hole array. Furthermore, the onset of saturation in the textured device was not evident as compared with the un‐textured device. This is attributed to improved current spreading in the device due to the top gold layer. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Both the effects of gamma irradiation and high-current forward bias on GaP:Zn,0 light emitting diodes (LEDs) have been studied by measuring constant current 76K electroluminescence (EL) spectra below 1000 nm, total light output at room temperature, and capacitance transients using the technique of deep level transient spectroscopy (DLTS). The LEDs were divided into two sets; a control set which was subjected only to forward bias, and a set exposed to gamma irradiation and forward bias. The results indicate that gamma-induced light output degradation occurs through a different mechanism than forward bias-induced degradation of the control LEDs. Gamma irradiation, which has no effect on the Zn-O concentration, degrades the light output through the introduction of competing non-radiative recombination centers which reduce the minority carrier lifetime. In contrast, forward bias-induced light output degradation is primarily due to a reduction in Zn-O concentration through the apparent recombination-enhanced interaction of Zn-O centers with impurities rather than defects.

A physical method to develop a scintillator with both a large light output and a quick response is proposed and demonstrated. A direct-gap semiconductor often exhibits ultrafast scintillation components with subnanosecond decay time constants at very low temperatures. However, the exciton luminescence is significantly quenched at room temperature to lose the practical merits. The authors found that the thermal quenching was effectively prevented by constructing a low-dimensional quantum confinement system and a practical amount of light output was obtained at room temperature without losing the quickness of the radiative recombination of the exciton. Crystals of (C6H13NH3)2 PbI4 having a multiple quantum well structure exhibited three decay components of 390 ps, 3.8 ns and 16 ns with the ratios of 28%, 29% and 43%, respectively. The total light output at 300 K was 11% of that of NaI:Tl

Total light output of GaAs laser diodes has been measured at 300 and 76°K before and after successive neutron irradiations to a cumulative fluence of 6.5×1014 neutron/cm2 (&amp;gt; 10 keV). The range of current densities used extended from well below the laser threshold current density to the maximum allowable value. Both the subthreshold light output and the threshold current density were sensitive to neutron damage in agreement with previous observations. However, at current densities significantly above threshold the light output is much less sensitive to irradiation and, in fact, the light output at 76°K was observed to increase following irradiation. These latter results have significant practical importance for cases in which laser diodes must operate in a radiation environment.

Nano-sized powder of cerium-doped lutetium aluminum garnet scintillator (LuAG) was synthesized using the Sol-Gel method, at various cerium concentrations (0.1 at.%, 0.5 at.%, 1 at.%, and 2 at.%). In this study, scintillation properties, including light yield and decay kinetics, were investigated as functions of dopant concentrations. The scintillation light yield was assessed under α-particles excitation from 241Am (Eα = 5.48 MeV) using a LuAG:0.1% Ce3+ single crystal (SC) scintillator as a reference. Decay kinetics were determined from the photomultiplier tube (PMT) anode. A fast oscilloscope was used to digitize the PMT anode pulses, enabling to perform scintillator decay kinetics analysis. Results indicate that an increase in Ce3+ concentration leads to a decrease in scintillation light yield and the sample doped at 0.1 at.% Ce3+ exhibited the highest relative light yield (89.3% of SC). The decline in light yield was attributed to quenching phenomena induced by the cerium concentration. Decay kinetics results reveal that the timing profiles of all samples consist of three light components and the major contributions to the total light output were observed for the fast components.

Light output from six battery operated dental curing lights

Light output power versus current, emission spectroscopy and far-field emission patterns have been used to characterize microcavity light emitting diodes (MC-LEDs). Evidence that microcavity effects lead to enhanced emission properties is provided by changes in the total emitted light output power, as well as the electroluminescence spectra of the MC-LEDs. Compared to a conventional noncavity type LED structure, enhanced efficiency and narrow spectral linewidths have been observed for the MC-LEDs over a wide range of cavity detunings and cavity Q values. Evidence that control of the cavity detuning leads to temperature insensitive output characteristics is provided by changes in the temperature dependence of the slope efficiencies extracted from the light output versus current characteristics. Variations in the emitted radiation patterns as a function of current injection are also reported demonstrating the important role of the cavity detuning on the emission properties of MC-LEDs.

Using probabilistic sampling-based sensitivity analyses for indoor air quality modelling

Modifications have been made to the Burrus LED structure to enable increases in the total light output to be obtained. Incorporation of a circumferential 45° mirror in the active layer of the GaAs/ GaAlAs double heterostructure, surrounding the light-emitting region, redirects the (normally lost) light confined in the active layer towards the emitting surface. In addition to increased light output, these devices have markedly more linear (≃ 14-dB second-harmonic reduction)light-current characteristics than normal Burrus LED's. For devices with thin (0.2-µm) lightly doped ( N_{A} \simeq 5 \times 10^{17} cm-3) active layers a significant in-plane superluminescence contribution to the light output is found. A theoretical model has been developed which provides an adequate description of the observed device characteristics and enables predictions to be made for further device optimization.

Fast neutrons offer high penetration capabilities for both light and dense materials due to their comparatively low interaction cross sections, making them ideal for the imaging of large-scale objects such as large fossils or as-built plane turbines, for which X-rays or thermal neutrons do not provide sufficient penetration. However, inefficient fast neutron detection limits widespread application of this technique. Traditional phosphors such as ZnS:Cu embedded in plastics are utilized as scintillators in recoil proton detectors for fast neutron imaging. However, these scintillation plates exhibit significant light scattering due to the plastic-phosphor interface along with long-lived afterglow (on the order of minutes), and therefore alternative solutions are needed to increase the availability of this technique. Here, we utilize colloidal nanocrystals (NCs) in hydrogen-dense solvents for fast neutron imaging through the detection of recoil protons generated by neutron scattering, demonstrating the efficacy of nanomaterials as scintillators in this detection scheme. The light yield, spatial resolution, and neutron-vs-gamma sensitivity of several chalcogenide (CdSe and CuInS2)-based and perovskite halide-based NCs are determined, with only a short-lived afterglow (below the order of seconds) observed for all of these NCs. FAPbBr3 NCs exhibit the brightest total light output at 19.3% of the commercial ZnS:Cu(PP) standard, while CsPbBrCl2:Mn NCs offer the best spatial resolution at ∼2.6 mm. Colloidal NCs showed significantly lower gamma sensitivity than ZnS:Cu; for example, 79% of the FAPbBr3 light yield results from neutron-induced radioluminescence and hence the neutron-specific light yield of FAPbBr3 is 30.4% of that of ZnS:Cu(PP). Concentration and thickness-dependent measurements highlight the importance of increasing concentrations and reducing self-absorption, yielding design principles to optimize and foster an era of NC-based scintillators for fast neutron imaging.