A Geiger mode planar InGaAs/InP avalanche photodiode （APD） with a cascade peripheral junction structure to suppress edge breakdowns is designed by finite-element analysis. The photodiode breakdown voltage is reduced...A Geiger mode planar InGaAs/InP avalanche photodiode （APD） with a cascade peripheral junction structure to suppress edge breakdowns is designed by finite-element analysis. The photodiode breakdown voltage is reduced to 54.3V by controlling the central junction depth, while the electric field distribution along the device central axis is controlled by adjusting doping level and thickness of the lnP field control layer. Using a cascade junction structure at the periphery of the active area, premature edge breakdowns are effectively suppressed. The simulations show that the quadra-cascade structure is a good trade-off between suppression performance and fabrication complexity, with a reduced peak electric field of 5.2 × 10^5 kV/cm and a maximum hole ionization integral of 1. 201. Work presented in this paper provides an effective way to design high performance photon counting InGaAs/InP avalanche photodiodes.展开更多
A simple method employing a pair of pancake-style Geiger-Mueller (GM) counters for quantitative measurement of radon activity concentration (activity per unit volume) is described and demonstrated. The use of two GM c...A simple method employing a pair of pancake-style Geiger-Mueller (GM) counters for quantitative measurement of radon activity concentration (activity per unit volume) is described and demonstrated. The use of two GM counters, together with the basic theory derived in this paper, permit the detection of alpha particles from decay of and progeny ( <sup>218</sup>Po, <sup>214</sup>Po) and the conversion of the alpha count rate into a radon concentration. A unique feature of this method, in comparison with standard methodologies to measure radon concentration, is the absence of a fixed control volume. Advantages afforded by the reported GM method include: 1) it provides a direct in-situ value of radon level, thereby eliminating the need to send samples to an external testing laboratory;2) it can be applied to monitoring radon levels exhibiting wide short-term variability;3) it can yield short-term measurements of comparable accuracy and equivalent or higher precision than a commercial radon monitor sampling by passive diffusion;4) it yields long-term measurements statistically equivalent to commercial radon monitors;5) it uses the most commonly employed, overall least expensive, and most easily operated type of nuclear instrumentation. As such, the method is par-ticularly suitable for use by researchers, public health personnel, and home dwellers who prefer to monitor indoor radon levels themselves. The results of a consecutive 30-day sequence of 24 hour mean radon measurements by the proposed GM method and a commercial state-of-the-art radon monitor certified for radon testing are compared.展开更多
We design and fabricate 4H-SiC UV avalanche photodiodes （APDs） ~qth positive beveled mesa, which exhibit low leakage current and high avalanche gain when working in the Geiger mode. The single photon counting perfor...We design and fabricate 4H-SiC UV avalanche photodiodes （APDs） ~qth positive beveled mesa, which exhibit low leakage current and high avalanche gain when working in the Geiger mode. The single photon counting performance of the SiC APDs is studied by using a passive-quenching circuit. A new method to determine the exact breakdown voltage of the APD is proposed based on the initial emergence of photon count pulses. The photon count rate and dark count rate of the APD are also evaluated as a function of quenching resistance.展开更多
Recently,we analyze the α-decay data of even-Z nuclei and propose the new Geiger-Nuttall law where the effects of the quantum numbers of α-core relative motion are naturally embedded in the law [Physical Review C 85...Recently,we analyze the α-decay data of even-Z nuclei and propose the new Geiger-Nuttall law where the effects of the quantum numbers of α-core relative motion are naturally embedded in the law [Physical Review C 85,044608(2012)].In this paper,we firstly test whether the new law without any change of parameters can be applied to the α-decays of odd-Z nuclei which are more complicated than those of even-even nuclei.Then the nuclear shell effect around N=126 is analyzed for very proton-rich nuclei with Z=85-92 based on the data of α-decay energies and half-lives.A long-lived island beyond the stable line is proposed where the half-lives of nuclei on this island are abnormally long.The mechanism of the appearance of the island and its significance to other mass ranges are discussed.展开更多
The aim of this pilot study conducted by the consortium for capacity building was to develop a prototype concept and methodology for the classification and visualization of the geographic impacts of El Nio on annual...The aim of this pilot study conducted by the consortium for capacity building was to develop a prototype concept and methodology for the classification and visualization of the geographic impacts of El Nio on annual climates and seasonality. Our study is based on the Kppen–Geiger climate classification scheme for a set of selected countries affected by strong El Nios in Latin America. By identifying and visualizing the annual and seasonal changes in regional, national, or subnational climate regimes that generally accompany an El Nio event,this research proposes an efficient way to detect and describe climate shifts and variability across time and space. Such knowledge provides a support tool for risk analysis and can potentially enhance government efforts of climate risk management, including disaster risk reduction activities that prevent, mitigate, and improve coping responses to El Nio-related hydrometeorological threats.Details of the conceptual approach and methodology to classifying and mapping El Nio's impacts are described and explained using the Central American and circumCaribbean region as a case study. The potential applications for disaster risk reduction as well as its limitations and future work are also discussed.展开更多
This Letter introduces a trigger-controlled Geiger-mode avalanche photodiode （GM-APD）. A hierarchical look- back-upon tree recurrence method is given to predict the performance of trigger-controlled GM-APDs under di...This Letter introduces a trigger-controlled Geiger-mode avalanche photodiode （GM-APD）. A hierarchical look- back-upon tree recurrence method is given to predict the performance of trigger-controlled GM-APDs under different trigger-count upper limits. In addition, the normalized detection probability is defined to evaluate the detection performance of trigger-controlled GM-APDs in typical weak optical signal detection （impulse noise and continuous noise situations）. Theoretical analyses show that the trigger-controlled GM-APD improves the detection performance of GM-APDs in weak optical signal detection via the optimization of the trigger-count upper limit, compared with single-trigger and multi-trigger GM-APDs.展开更多
文摘A Geiger mode planar InGaAs/InP avalanche photodiode （APD） with a cascade peripheral junction structure to suppress edge breakdowns is designed by finite-element analysis. The photodiode breakdown voltage is reduced to 54.3V by controlling the central junction depth, while the electric field distribution along the device central axis is controlled by adjusting doping level and thickness of the lnP field control layer. Using a cascade junction structure at the periphery of the active area, premature edge breakdowns are effectively suppressed. The simulations show that the quadra-cascade structure is a good trade-off between suppression performance and fabrication complexity, with a reduced peak electric field of 5.2 × 10^5 kV/cm and a maximum hole ionization integral of 1. 201. Work presented in this paper provides an effective way to design high performance photon counting InGaAs/InP avalanche photodiodes.
文摘A simple method employing a pair of pancake-style Geiger-Mueller (GM) counters for quantitative measurement of radon activity concentration (activity per unit volume) is described and demonstrated. The use of two GM counters, together with the basic theory derived in this paper, permit the detection of alpha particles from decay of and progeny ( <sup>218</sup>Po, <sup>214</sup>Po) and the conversion of the alpha count rate into a radon concentration. A unique feature of this method, in comparison with standard methodologies to measure radon concentration, is the absence of a fixed control volume. Advantages afforded by the reported GM method include: 1) it provides a direct in-situ value of radon level, thereby eliminating the need to send samples to an external testing laboratory;2) it can be applied to monitoring radon levels exhibiting wide short-term variability;3) it can yield short-term measurements of comparable accuracy and equivalent or higher precision than a commercial radon monitor sampling by passive diffusion;4) it yields long-term measurements statistically equivalent to commercial radon monitors;5) it uses the most commonly employed, overall least expensive, and most easily operated type of nuclear instrumentation. As such, the method is par-ticularly suitable for use by researchers, public health personnel, and home dwellers who prefer to monitor indoor radon levels themselves. The results of a consecutive 30-day sequence of 24 hour mean radon measurements by the proposed GM method and a commercial state-of-the-art radon monitor certified for radon testing are compared.
基金Supported by the National Basic Research Program of China under Grant Nos 2011CB301900 and 2011CB922100the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘We design and fabricate 4H-SiC UV avalanche photodiodes （APDs） ~qth positive beveled mesa, which exhibit low leakage current and high avalanche gain when working in the Geiger mode. The single photon counting performance of the SiC APDs is studied by using a passive-quenching circuit. A new method to determine the exact breakdown voltage of the APD is proposed based on the initial emergence of photon count pulses. The photon count rate and dark count rate of the APD are also evaluated as a function of quenching resistance.
基金Supported by National Natural Science Foundation of China(NSFC) projects (Nos.11035001,11120101005 and 11175085)the Priority Academic Development of Jiangsu Higher education Institutions
文摘Recently,we analyze the α-decay data of even-Z nuclei and propose the new Geiger-Nuttall law where the effects of the quantum numbers of α-core relative motion are naturally embedded in the law [Physical Review C 85,044608(2012)].In this paper,we firstly test whether the new law without any change of parameters can be applied to the α-decays of odd-Z nuclei which are more complicated than those of even-even nuclei.Then the nuclear shell effect around N=126 is analyzed for very proton-rich nuclei with Z=85-92 based on the data of α-decay energies and half-lives.A long-lived island beyond the stable line is proposed where the half-lives of nuclei on this island are abnormally long.The mechanism of the appearance of the island and its significance to other mass ranges are discussed.
基金the support provided by the Office of US Foreign Disaster Assistance,Bureau for Democracy,Conflict and Humanitarian Assistance,US Agency for International Development
文摘The aim of this pilot study conducted by the consortium for capacity building was to develop a prototype concept and methodology for the classification and visualization of the geographic impacts of El Nio on annual climates and seasonality. Our study is based on the Kppen–Geiger climate classification scheme for a set of selected countries affected by strong El Nios in Latin America. By identifying and visualizing the annual and seasonal changes in regional, national, or subnational climate regimes that generally accompany an El Nio event,this research proposes an efficient way to detect and describe climate shifts and variability across time and space. Such knowledge provides a support tool for risk analysis and can potentially enhance government efforts of climate risk management, including disaster risk reduction activities that prevent, mitigate, and improve coping responses to El Nio-related hydrometeorological threats.Details of the conceptual approach and methodology to classifying and mapping El Nio's impacts are described and explained using the Central American and circumCaribbean region as a case study. The potential applications for disaster risk reduction as well as its limitations and future work are also discussed.
文摘This Letter introduces a trigger-controlled Geiger-mode avalanche photodiode （GM-APD）. A hierarchical look- back-upon tree recurrence method is given to predict the performance of trigger-controlled GM-APDs under different trigger-count upper limits. In addition, the normalized detection probability is defined to evaluate the detection performance of trigger-controlled GM-APDs in typical weak optical signal detection （impulse noise and continuous noise situations）. Theoretical analyses show that the trigger-controlled GM-APD improves the detection performance of GM-APDs in weak optical signal detection via the optimization of the trigger-count upper limit, compared with single-trigger and multi-trigger GM-APDs.
