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1.
We report on optical gain calculations of a dilute-nitride mid-infrared laser structure designed to be grown on InAs substrate. The active region is composed of several strain-compensated type-II “W”-like InAsN/GaSb/InAsN quantum wells adapted to operate near 3.3 μm at room temperature. For typical injected carrier density σ = 1.1012 cm − 2, the theoretical laser structure performances reveal a gain value at around 1000 cm − 1 at 300 K, inducing a modal gain value equal to 50 cm − 1. Low radiative current densities lower than 100 A/cm 2 are predicted, indicating that this dilute-nitride structure could operate at 300 K with small threshold current density. 相似文献
2.
Using the Low-Temperature Nuclear Orientation (LTNO) technique one can study various interesting properties of atomic nuclei and nuclear decay which can be deduced from the measurements of the angular distributions of charged particles emitted during the decay. However, the use of particle detectors working in conditions of LTNO devices (which are generally not available commercially) is a necessary precondition for the realization of these experiments. Planar HPGe detectors for detection of charged particles at “liquid helium” temperatures were developed and produced at NPI
e
. Relatively simple technology using vacuum evaporation and diffusion was employed. The performance of detectors at low temperatures was tested and their characteristics measured in a testing cryostat before using them in real experiments. The HPGe detectors were extensively used in a whole range of LTNO experiments with various physical objectives — in offline (IKS Leuven) as well as online (CERN-ISOLDE, Louvain-la-Neuve — LISOL) experiments. In frame of the project “Meson-Exchange Enhancement of First-Forbidden Beta Transitions in the Lead Region”, the measurements of angular distribution of emitted β-particles allowed to determine experimentally the “meson-exchange currents” contribution to the β-decay. In the project “Isospin Mixing in NZ nuclei”, the isospin-forbidden β-transitions of the nuclei in region (A=50–100) were studied in order to obtain information on the isospin structure of the nuclear states. A new project looking for the possible presence of the tensor currents contribution to the β-decay is being prepared for the CERN-ISOLDE facility. 相似文献
3.
Selected crystals have been investigated at 20 mK for their properties of scintillation produced under irradiation. A scintillation signal is found in preliminary studies of YAP:Ce, GSO:Ce, CaF 2:Eu and Al 2O 3:Ti crystals thanks to high sensitivity light detectors. The full mixed “light-and-heat” bolometric technique has been applied to further characterize materials already employed in rare event researches: CaWO 4, BGO, undoped Al 2O 3 (sapphire). All these crystals show powerful discrimination properties for /γ or nuclear recoil/γ detection, with a special mention to undoped Al 2O 3, hitherto untested, which revealed an unexpected strong light emission. A weaker light signal has been found on LiF and TeO 2 bolometers too, sufficient to separate alpha from gamma events in these crystals. 相似文献
4.
Recent efforts in the Transition Edge Sensor (TES) bolometer/calorimeter community have focused on developing detectors whose noise properties are near the fundamental limits. These include the in-band phonon noise, the out-of-band Johnson noise, and the 1/f noise. We have investigated the noise performance of Mo/Au-bilayer TES bolometers designed for infrared detectors. These detectors use normal metal regions for the suppression of excess noise, which are oriented either parallel to (“bars”) or transverse to (“stripes”) the direction of current flow. Two nearly identical detectors, one with stripes and one with bars, were fabricated at the NASA/GSFC detector development facility. Significantly lower noise is found with the normal metal regions oriented transversely. We compare the detailed noise measurement and quantitative analysis of the noise level in each device as a function of the detector resistance. Our preliminary result is that the best detector features only moderate excess noise in both the in-band region and in the out-of-band region. This noise performance is suitable for instruments with multiplexed TES arrays, such as GSFC's FIBRE and SAFIRE. 相似文献
5.
Nd 3+ : YVO 4 is one of the most interesting laser hosts for micro and diode-pumped solid state lasers. We have studied magnetic and optical properties of Nd 3+ in three zircon type crystals YMO 4 (M=V, As, P). In particular, Nd 3+ ions exhibit in the three hosts a multisite character observed in the absorption and emission spectra. However, the emission and its dynamics are strongly dependant on the reabsorption mechanisms. In Nd : YVO 4, single crystals containing 7 ± 1 × 10 18 Nd 3+ ions/cm 3, the lifetime is 95 ± 2 μs in good agreement with the calculated radiative lifetime. Electron Paramagnetic Resonance (EPR) measurements are performed to identify the nature of the different substitution sites for Nd 3+ ions. Nd 3+ ions are found to be inhomogeneously distributed in tetragonal D 2d symmetry sites, in isolated ions, “shallow clusters” and pairs. Proportions of the different local environments depend on the total neodymium concentration. For instance, 15% of the Nd 3+ ions are gathered in Nd 3+–Nd 3+ pairs for 7.2 ± 0.2 × 10 19 Nd 3+ ions/cm 3. 相似文献
6.
The objective of this work is to develop a gamma ray spectrometer (GRS) suitable for use on planetary rover missions. The main characteristics of this detector are low weight, small volume low power and resistance to cosmic ray radiation over a long period of time. We describe a 3 cm diameter by 3 cm thick CdWO 4 cylindrical scintillator coupled to a PMT as a GRS for the energy region 0.662–7.64 MeV. Its spectral performance and efficiency are compared to that of a CsI(Tl) scintillator 2.5 cm diameter by 6 cm thick coupled to a 28 mm×28 mm PIN photodiode. The comparison is made experimentally using 137Cs, 60Co, 6.13 MeV gamma rays from a 13C(,γn)O 16* source, 7.64 MeV thermal neutron capture gamma rays emitted from iron bars using a 252Cf neutron source, and natural radioactivity 1.46 MeV 40K and 2.61 MeV 232Th gamma rays. We use a Monte Carlo method to calculate the total peak efficiency of these detectors and the full energy, first and second escape peak efficiencies. The experimental and calculated results agree well. We investigated the usefulness of these detectors for a GRS on a Mars lander mission. Although both detectors meet desired specifications, it was found that CdWO 4 has advantages over CsI(Tl) being a more compact detector of higher efficiency. Using a shaping amplifier of 24 ms, CdWO 4 spectrometer exhibited a 6.8% FWHM at 662 keV. At 6.13 MeV, CdWO 4 detector possesses an intrinsic total and full energy peak efficiencies of 16.7% and 6.3%, respectively. These efficiencies are nearly a factor of 1.6 and 4 greater than the corresponding efficiencies of the CsI(Tl) detector. A proposed gamma ray spectroscopy system to be placed on a rover, consists of a central detector surrounded by a Compton suppressor shield. The central detector is a cylindrical CdWO4 detector and the Compton suppressor shield is made of segmented CdWO4, coupled to PIN photodiodes. The shield also prevents thermal neutron activation of the central detector. 相似文献
7.
Semiconductor-based thermal neutron detectors provide a compact technology for neutron detection and imaging. Such devices can be produced by externally coating semiconductor-charged-particle detectors with neutron reactive films that convert free neutrons into charged-particle reaction products. Commonly used films for such devices utilize the 10B(n,) 7Li reaction or the 6Li(n,) 3H reaction, which are attractive due to the relatively high energies imparted to the reaction products. Unfortunately, thin film or “foil” type thermal neutron detectors suffer from self-absorption effects that ultimately limit neutron detection efficiency. Design considerations that maximize the efficiency and performance of such devices are discussed. Theoretical and experimental results from front coated, back coated, and “sandwich” designs are presented. 相似文献
8.
The traditional method used to determine the Uranium enrichment by nondestructive analysis is based on the “enrichment meter principle” [1]. It involves measuring the intensity of the 186 keV net peak area of 235U in “quasi-infinite” samples. A prominent factor, which affects the peak intensity, is the presence of gamma absorbing material (e.g., container wall, detector cover) between the sample and the detector. Its effect is taken into consideration in a commonly called “wall thickness” correction factor. Often calculated on the basis of approximations, its performance is adequate for small attenuation factors applicable to the case of narrow beams. However these approximations do not lead to precise results when wide non-parallel beams are attenuated through thick container walls. This paper is dedicated to the calculation by numerical integration of the geometrical correction factor (Kwtc) which describes the effective mean path length of the radiation through the absorbing layer. This factor was calculated as a function of various measurement parameters (types and dimensions of the detector, of the collimator and of the shielding) for the most commonly used collimator shapes and detectors. Both coherent scattering (Rayleigh) and incoherent scattering (Compton) are taken into account for the calculation of the radiation interaction within the detector. 相似文献
9.
Particle launch experiments were performed to study application of the enhanced hypervelocity launcher (EHVL), i.e. the third-stage addition to the two-stage gun, for launching micron to millimeter sized particulates at velocities unobtainable with a standard two-stage light gas gun launch. Three types of particles or fliers were tested along with several barrel designs. For micron scale particles fine-grain polycrystalline ceramics were impacted and fractured, launching particulate clouds at velocities of 15 km/s. Multiple titanium particles 400 μm diameter embedded in plastic were “shotgun” launched to velocities of 10 km/s. Flier plates of 3 mm diameter by 1 mm thick Ti6Al4V were launched to 19 km/s. All experiments used a second-stage projectile with graded density facing impacting a flier in an impact generated acceleration reservoir. This paper describes the modification and adaptation of the Sandia EHVL to provide micrometeoroid simulation capabilities. 相似文献
10.
The grain size dependence of the tensile properties and the deformation mechanisms responsible for those properties are examined for Mg alloy, AZ31B, sheet. Specifically, the Hall–Petch effect and strain anisotropy ( r-value) are characterized experimentally, and interpreted using polycrystal plasticity modeling. {1 0 . 2} extension twins, {1 0 . 1} contraction twins, and so-called “double-twins” are observed via microscopy and diffraction-based techniques, and the amount of twinning is found to increase with increasing grain size. For the sheet texture and tensile loading condition examined, {1 0 . 2} extension twinning is not expected, yet the polycrystal plasticity model predicts the observed behavior, including this ‘anomalous’ tensile twinning. The analysis shows that the Hall–Petch strength dependence, of the polycrystal as a whole, is primarily determined by the grain size dependence of the strength of the prismatic slip systems. 相似文献
11.
The structural, magnetic and transport properties of Co/GaAs (1 0 0) and Co/glass thin films have been investigated. The structural measurements reveal the crystalline nature of Co thin film grown on GaAs, while microcrystalline nature in case of glass substrate. The film grown on GaAs shows higher coercivity (49.0 G), lower saturation magnetization (3.65 × 10 −4) and resistivity (8 μΩ cm) values as compared to that on glass substrate (22 G, 4.77 × 10 −4 and 18 μΩ cm). The grazing incidence X-ray reflectivity and photoemission spectroscopy results show the interaction between Co and GaAs at the interface, while the Co layer grown on glass remains unaffected. These observed results are discussed and interpreted in terms of different growth morphologies and structures of as grown Co thin film on both substrates. 相似文献
12.
The influence of changes in the pattern of ferroic domain structure on the Raman spectra of β-LiNH 4SO 4 and (NH 4) 3H(SO 4) 2 single crystals were studied. It was shown that the Raman spectra of β-LiNH 4SO 4 passed from the ferroelastic phase differ from those of “as-grown” crystal and those of the crystal, which was in the paraelectric phase. Significant changes could be observed in the Raman bands related to triply degenerated ν3 and ν4 vibrations of the SO 4 tetrahedron. Detailed temperature studies of the Raman spectra of β-LiNH 4SO 4 close to the paraelectric–ferroelectric phase transition, exhibit anomaly of some internal vibrations of SO 4 in the temperature range where a regular large-scale structure is observed. Different types of evolution of the ferroelastic domain structure and temperature behaviour of the donor and acceptor vibrations were shown while heating and cooling the (NH 4) 3H(SO 4) 2 crystal. Different values of temperature hysteresis were found in temperature studies of the ferroelastic domain structure (Δ TS 3–5 K) and in Raman spectra studies (Δ TS 12 K). No changes were observed in the pattern of ferroelastic domain structure at the temperature TII–III 265 K, at which C2/ c → P2/ n structural phase transition takes place. On the other hand, at TIII–IV 135 K additional domains with W′-type of domain wall orientation were found. 相似文献
13.
Highly stable ΔE− E telescope systems consisting of plastic scintillation detectors are operated as flux monitors in a “white” neutron beam between 15 and 50 MeV. Multiple telescope systems consisting of large area silicon ΔE detectors and NaI E detectors are set up in a scattering chamber to investigate charged particle reactions induced by fast neutrons up to 50 MeV. 相似文献
14.
It has been demonstrated by Low-Temperature Scanning Synchrotron Microscope that the spatial profiles of Nb/Al/AlO x/Al/Nb detectors are abnormally large in an energy range between 2 and 10 keV, and thus the detectors produce no clear total absorption peaks. Below 2 keV, on the other hand, full illumination experiments have afforded the evidence that the spatial uniformity is significantly improved, for example, an 100 μm square junction has an intrinsic energy resolution of 5.4 eV at 200 eV. These results reconfirm that carefully designed junction detectors with a reasonable size are ideal for energy-dispersive spectroscopy in a soft X-ray range. 相似文献
15.
The “edge-on” illuminated microchannel plate (MCP) position-sensitive detector (PSD) is used for gamma-ray imaging for the first time. The superior position resolution of the MCP is combined with high detection efficiency due to the “edge-on” illumination mode. The results of imaging a 15 μCi 137Cs source (662 keV quantum energy) are presented. 相似文献
16.
We report measurements in a high-energy beam of the sensitivity of the edge region in “edgeless” planar silicon pad diode detectors. The edgeless side of these rectangular diodes is formed by a cut and break through the contact implants. A large surface current on such an edge prevents the normal reverse biasing of this device above the full depletion voltage, but we have shown that the current can be sufficiently reduced by the use of a suitable cutting method, followed by edge treatment, and by operating the detector at a low temperature. A pair of these edgeless silicon diode pad sensors was exposed to the X5 high-energy pion beam at CERN, to determine the edge sensitivity. The signal of the detector pair triggered a reference telescope made of silicon microstrip detector modules. The gap width between the edgeless sensors, determined using the tracks measured by the reference telescope, was then compared with the results of precision metrology. It was concluded that the depth of the dead layer at the diced edge is compatible with zero within the statistical precision of ±8 μm and systematic error of ±6 μm. 相似文献
17.
Boron lined ionisation chambers with an overall diameter of 85 mm and maximum length of 165 mm have been developed and tested. The chamber consists of 34 numbers of parallel plate aluminium electrodes spaced at a distance of 2 mm and mounted on SS rods and radiation resistant polyetheretherketone (PEEK) spacers. One surface of the signal electrode and both the surfaces of the +HT electrodes are dip coated with boron. It is filled with nitrogen gas at a pressure of 128 cm of Hg. Tests at the 60Co source facility at gamma fields ranging from 200 R/h to 830 kR/h showed that the chamber required 500 V to obtain 90% of the saturation current at 830 kR/h. The gamma compensation factor was measured as 0.12–7% for various gamma fields for polarising voltages of +400 and −350 V. Neutron measurements at the Apsara Thermal Column showed that the linearity of the chamber response as a function of reactor power was within 2%. The neutron sensitivity was measured as 3.9 fA/nv. 相似文献
18.
ChemFECs (chemical field effect capacitors) or EIS (Electrolyte-Insulator-Semiconductor) devices were coated with calix[ n]arene macrocycles for cation sensors development. Silicon nitride surface electrodes were spin-coated with p-tert-butylcalix[ n]arene molecules for n = 8, 9 and 11. Electrochemical capacitance measurements were carried out to evaluate the sensitivity of the calix[ n]arene layers towards specific cations as calcium and copper ions. Sensor responses were due to the “host-guest” specific interaction between the rigid cavity of calix[ n]arene receptors (ligand) and chemical ion species. The developed chemical sensors have demonstrated good analytical characteristic in terms of: stability, selectivity and lifetime. In addition, experimental results were fitted using the site binding model in order to determine complex association constants, pK (1.9 ≤ pK ≤ 6.39) and surface density of ligands, NL (9.10 14 ≤ NL ≤ 2.10 16). All results obtained in this work were compared with those obtained using silicon dioxide EIS electrodes coated with the same calix[ n]arene receptors using both spin-coating and thermal evaporation deposit processes. 相似文献
19.
Large one- and two-dimensional position-sensitive neutron detectors have been developed. Their shapes are a long block and a square and their sizes are 100×10×7.5 cm 3 and 100×100×10 cm 3 for one- and two-dimensional detectors, respectively. Both liquid and plastic scintillators are employed as detector materials. Position resolutions are examined by using monoenergetic neutron beams with energies of 61.6 MeV. The obtained position resolutions in FWHM are 3–5 cm and 4–14 cm for one- and two-dimensional detectors, respectively. Position resolutions are poor near the corner of the two-dimensional detector irrespective of scintillator materials. Scintillation light responses have been compared with predictions of Monte Carlo calculations. Neutron polarimeters at an intermediate energy have been developed by utilizing the position sensitivity of these detectors. 相似文献
20.
A novel scanning slit X-ray imaging system based on an “edge-on” microchannel plate detector was developed and tested. Images were acquired at 50 kV(p) X-ray tube voltage with a limiting spatial resolution of 7 lp/mm. The pixel noise was measured to be 0.3 count/pixel/s for a 50×70 μm 2 pixel size. This photon counting detector can be considered to be virtually noise free. 相似文献
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