Loss Of Collection Efficiency Research Articles

Development of a Real-Time Pixel Array-Type Detector for Ultrahigh Dose-Rate Beams

Although research into ultrahigh dose-rate (UHDR) radiation therapy is ongoing, there is a significant lack of experimental measurements for two-dimensional (2D) dose-rate distributions. Additionally, conventional pixel-type detectors result in significant beam loss. In this study, we developed a pixel array-type detector with adjustable gaps and a data acquisition system to evaluate its effectiveness in measuring UHDR proton beams in real time. We measured a UHDR beam at the Korea Institute of Radiological and Medical Sciences using an MC-50 cyclotron, which produced a 45-MeV energy beam with a current range of 10–70 nA, to confirm the UHDR beam conditions. To minimize beam loss during measurement, we adjusted the gap and high voltage on the detector and determined the collection efficiency of the developed detector through Monte Carlo simulation and experimental measurements of the 2D dose-rate distribution. We also verified the accuracy of the real-time position measurement using the developed detector with a 226.29-MeV PBS beam at the National Cancer Center of the Republic of Korea. Our results indicate that, for a current of 70 nA with an energy beam of 45 MeV generated using the MC-50 cyclotron, the dose rate exceeded 300 Gy/s at the center of the beam, indicating UHDR conditions. Simulation and experimental measurements show that fixing the gap at 2 mm and the high voltage at 1000 V resulted in a less than 1% loss of collection efficiency when measuring UHDR beams. Furthermore, we achieved real-time measurements of the beam position with an accuracy of within 2% at five reference points. In conclusion, our study developed a beam monitoring system that can measure UHDR proton beams and confirmed the accuracy of the beam position and profile through real-time data transmission.

Charge collection inefficiencies induced by intense /sup 12/C bombardment of SSB detectors

Experimental data are presented showing that, for a light heavy ion such as Carbon, large collection-efficiency losses appear in Silicon Surface Barrier detectors for large enough ion fluences. This effect, apparently related to the onset of radiation damage of the detector, shows an S-shape behavior with the fluence above threshold.

Theory of amorphous silicon solar cell (b): a five layer analytical model

Abstract An analytical model for amorphous silicon p–i–n solar cell is developed by dividing the i-layer into five regions. The region close to p+ layer is dominated by charge in the tail states, whereas the region next to it has a space charge due to positively charged dangling bonds. This is followed by a quasi-neutral region with a nearly constant electric field. Then, there is a space charge arising due to negatively charged dangling bonds with a conduction band tail dominated space charge region adjacent to n+ layer. Poisson's equation and continuity equation for electrons and holes are solved to obtain the current–voltage characteristic of the cell. An interesting finding of the analysis is that the electric field in the quasi-neutral region increases significantly in short circuit condition when illuminated by light. This is due to neutralization of dangling bonds in the space charge region. When the voltage across the cell is allowed to develop as one moves from short circuit to open-circuit condition, the electric field in the central part of the cell reduces resulting in a loss of collection efficiency and hence a poorer fill factor.

Instrumentation for multistep excitation of lithium atoms to Rydberg states

We have developed a diode laser apparatus to excite Li from its ground 2S state, through 2P and 3S, to its Rydberg states with three cw diode lasers operating at λ = 671 nm, 813 nm, and 630-635 nm. A He-Ne laser at λ = 633 is sometimes used in place of the 635-nm diode laser for the last step. The output power of each of these lasers was ~1 mW. We describe our technique of locking the first two lasers on Li resonance lines by obtaining a fluorescent signal from the second decay (3S ? 2P) that is normally overpowered by a strong background of fluorescent light from the first decay (2P ? 2S). We used two balanced photodiodes to reject the strong fluorescent light without loss of collection efficiency. A rejection ratio as high as 100 has been obtained.

Electrostatic Precipitation Technology: A Different Viewpoint

The paper presents a viewpoint on electrostatic precipitation derived from Australian experience, particularly with fly ash collection from low sulfur coals. The customary expression of precipitability as an effective migration velocity calculated from the Deutsch equation is replaced by a performance line (or equation) obtained from a semi-logarithmic plot of collection efficiency against a combined function of specific collection area and operating voltage. The important effect of voltage, particle size, and carrier gas additives clearly emerge from the extended Deutsch equation, and the proper value of pilot plant testing is realized. Inclusion of particulate resistivity in the equation is straightforward, and an original calculation of loss of collection efficiency caused by high resistivities is presented. This hindrance is much less than generally thought, because the precipitator field reduces particulate resistivity by a long-known effect hitherto ignored in precipitation technology. The operational resistivity (i.e., with the precipitator working) has been measured and is often 100 to 1000 times less than the so-called in situ resistivity observed at lot applied field. Contrary to entrenched belief, the evidence is strongly against any general association of low sulfur in coal with poor fly ash precipitation.