Results 1 - 10 of 842
Results 1 - 10 of 842. Search took: 0.024 seconds
|Sort by: date | relevance|
[en] Highly precise monitoring of arrival times of pulses from pulsars will allow for gravitational-wave detection in the nano-Hertz regime in the near future. Due to the complex nature of such pulsar-timing experiments and to the large number of effects that can affect these data (starting with magnetospheric effects at the pulsars themselves but extending across the entire signal path down to the final gravitational-wave detection algorithm), any treatment of the measurement uncertainties relevant to such a gravitational-wave detection has been lacking and incomplete so far. In this review, we provide an exhaustive description of the currently known influences on measurement precision in pulsar-timing experiments in general and in gravitational-wave detection through pulsar-timing specifically. While some of these effects remain poorly understood and largely unquantified at present, we discuss both analytic and observational quantifications where available. (topical review)
[en] Aerogel production in Novosibirsk began in 1986 as a part of the development of the Cherenkov threshold counters used in the KEDR detector. The aerogel produced in Novosibirsk had excellent optical parameters. The Cherenkov counter systems based on the aerogel operate successfully in the SND experiment (VEPP-2000 -collider), in the KEDR detector (VEPP-4M -collider), and in the AMS-02 experiment at the International Space Station. In this paper, we have overviewed particle identification systems based on the aerogel that have been developed at the Budker Nuclear Physics Institute. We have also described the principles of a new type of ring-imaging Cherenkov detector based on Focusing Aerogel (FARICH).
[en] The characterization of mobile charge carriers of semiconductor materials has spurred the development of numerous two dimensional carrier profiling tools. Here, we investigate the mobile charge carriers of several samples by multi-harmonic electrostatic force microscopy (MH-EFM) and scanning microwave impedance microscopy (sMIM). We present the basic principles and experiment setups of these two methods. And then several typical samples, i.e. a standard n-type doped Si sample, mechanical exfoliation and chemical vapor deposition grown molybdenum disulfide (MoS2) layers are systemically investigated by sMIM and MH-EFM. The difference and (dis)advantages of these two modes are discussed. Both modes can provide carrier concentration profiles and have sub-surface sensitivity. They also have advantages in sample preparation in which contact electrodes are not required and insulating or electrically isolated samples can readily be studied. The basic mode, physics quantities extracted, dielectric response form and parasitic charges in scanning environment result in difference in experiment results for these two kinds of methods. The techniques described in this study will effectively promote research on basic science and semiconductor applications. (paper)
[en] The scientific instruments onboard the Lomonosov satellite include a complete set of detectors designed to study the gamma and optical emission of cosmic gamma-ray bursts (GRBs). The BDRG gamma spectrometer ensures producing a trigger of a GRB and studying GRB properties in the energy range of 10–3000 keV as well as determining the GRB source coordinates by comparing readings of three differently directed detectors. The SHOK optical cameras (with a field of view of ~20 × 40 degrees) fix a set of images by the GRB trigger preceding the trigger and a post-trigger set at a frequency of about five frames per second. The UFFO instrument incorporates the UBAT telescope with a coding mask for measurements within a range of hard X rays and soft gamma rays and the SMT optical slewing mirror telescope, which can be directed at the GRB source in about 1 s to measure the GRB optical emission at early stages.
[en] Numerical simulation of magnetic systems having corner points is considered. The literature on this topic is reviewed. A method of encapsulating the function behavior near corner points in the difference scheme is proposed for numerical solution of the 2D magnetostatic problem in the iron domain. For the 3D magnetostatic problem in the iron/vacuum domain, the increase in the magnetic field near the corner point is estimated, and a method for construction of an adaptive mesh is proposed. A parallel algorithm is implemented on the graphics-processing unit (GPU) architecture for faster search for the numerical solution of the magnetostatic problem. Numerical simulation is performed for the magnetic system of the SPD detector to be used at the NICA complex (JINR, Dubna).
[en] Detection of special nuclear materials (SNM) requires instruments which can detect and characterize uranium and plutonium isotopes, having at the same time the ability to discriminate among different types of radiation. For many decades, neutron detection has been based on 3He proportional counters sensitive primarily to thermal neutrons. The most common methods for detection of fast neutrons have been based on liquid scintillators with pulse shape discrimination (PSD). The shortage of 3He and handling issues with liquid scintillators stimulated a search for efficient solid-state PSD materials. Recent studies conducted at LLNL led to development of new materials, among which are organic crystals with excellent PSD and first PSD plastics for fast neutron detection. More advantages have been introduced by plastics doped with neutron capture agents, such as 10B and 6Li, that can be used for combined detection of both thermal and fast neutrons, offering, in addition, a unique ‘triple’ PSD for signal separation between fast neutrons, thermal neutrons, and gamma-rays. Among commercially produced materials are large-scale (>10 cm) stilbene crystals grown by the inexpensive solution technique, and different types of PSD plastics which, due to the deployment advantages and ease of fabrication, create a basis for the widespread use as large-volume and low-cost neutron detectors. (author)
[en] Neutron imaging has a long tradition since neutron sources with sui Table beam ports became available in the late 1940s to the 1960s. Based on film in combination with neutron converters, this radiography approach attracted a lot of interesting applications in the industrial field, and in military and nuclear technologies. The alternative and complement to Xray methods has been obvious from the beginning. The real change in neutron imaging techniques and increase in scientific applications has been initiated by new detection systems which are nowadays digital. In this way, a much more efficient use of neutron beams has been enabled and sophisticated methods like neutron grating interferometers, diffractive imaging and imaging with polarized neutrons have been implemented at several places. A high level of quantification is enabled in this way: neutron tomography is nowadays a routine method in science and applications delivering voxel-wise values of attenuation coefficients. However, dedicated neutron imaging beam lines need to be installed, where the detection systems are but one of the key components. Such attractive research facilities are established at only a few places world-wide, but several upcoming projects and installations are on the way to be realized at prominent sources like ESS (Lund, Sweden), SNS (Oak Ridge, USA) and other new neutron sources. The majority of neutron imaging detectors are based on the conversion of the neutrons into visible light—the scintillation process. Since neutron imaging enables the transmission through samples and objects on the macroscopic scale, the field-of-view has to be tuned according to their sizes. This can vary between about 40 cm and 1 cm with the inherent resolution of 500 to 2 μm. The development of suitable scintillation screens is still progressing with respect to inherent resolution, light output and stability. Scintillator solutions for even highly activated samples are under development. The active sensor for the scintillation light can be either in direct contact (a-Si flat panels) or optically coupled via lenses (CCD or CMOS cameras). Due to their high performance and flexibility, cameras are presently the most used devices in neutron imaging. They can be tuned for very long or very short exposure times, be synchronized to repetitive processes, and enable a high dynamic range and a high signal/noise performance. Camera technology is still under development, and performance and prices follow this process in the usual manner. Challenges for the next future are systems with ultimate spatial resolution to be competitive to X-ray methods, the most suitable systems for pulsed beams (in time-of-flight mode), and access to as many beam ports as possible to deliver neutron imaging as a routine method in science and for industry. (author)
[en] In this study, xPbO2 − [(100 − x)(0.5Na2O − 0.5P2O5)] glass samples where x = 0, 5, 10, 15, 20 and 30 mol%, were prepared and their radiation shielding and mechanical properties were investigated. A 3 × 3 inch NaI (Tl) scintillation detector has been used to detect the emitted gamma-ray. The obtained results revealed the increase of both PbO2 content and the photon energy from 0.356 to 1.33 MeV increase the mass attenuation coefficient (MAC), the effective atomic number (EAN), and the radiation protection efficiency (RPE) and in the same time decrease the values of the half-value layer (HVL) and the mean free path (MFP). The G-P fitting method was used to calculate the exposure buildup factor in the photon energy range of 0.015–15 MeV along with the use of SRIM code, ESTAR database and the removal cross-sections to calculate the proton, alpha and electron mass stopping power of the prepared glasses. These parameters are affected mainly with Zn (n = 2 or 4). Moreover, the elastic properties of the glass samples have been calculated by measuring both longitudinal (VL) and shear (VS) velocities using the pulse-echo overlap technique at 5 MHz. The sample that had 30 PbO2 mol% had the highest elastic properties that gives confidence in the possibility of using these glasses for radiation shielding application.
[en] This study applied a vapor cooling condensation system for depositing p-ZnO:LiNO3, i-Ga2O3, and n-Ga2O3:Si layers on sapphire substrates to fabricate solar-blind p-i-n deep-ultraviolet photodetectors (DUV-PDs). The deposited i-Ga2O3 absorption layer was measured to exhibit high performance levels. Therefore, when the resulting solar-blind p-i-n DUV-PDs were operated at a reverse bias voltage of − 5 V, the dark current and the DUV (250 nm)/visible (500 nm) rejection ratio were 1.45 pA and 2.5 × 104, respectively. Moreover, when the solar-blind p-i-n DUV-PDs were operated at a reverse bias voltage of − 5 V, the photoresponsivity, noise power density, noise equivalent power, and specific detectivity were 0.73 A/W, 2.45 × 10−26 A2/Hz, 4.80 × 10−13 W, and 1.97 × 1012 cmHz0.5W−1, respectively. Furthermore, flicker noise was the dominant low-frequency noise source in the photodetectors. These results demonstrated the effectiveness of the proposed solar-blind p-i-n DUV-PDs.
[en] The total dose effect of 60Co γ-rays on 0.8-μm H-gate partially depleted-silicon-on-insulator NMOS devices was investigated at different irradiation doses. The results show that the shift in saturation current at high dose rate is greater than that at low dose rate, due to increase in interface-state density with decreasing dose rate; the scattering effect of interface state on electrons in the channel causes degradation in carrier mobility; and the body current and transconductance of the back gate enhance low-doserate sensitivity when the irradiation is under OFF-bias. A double transconductance peak is observed at 3 kGy(Si) under high dose rates. (authors)