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141.
Yu. I. Neshpor O. R. Kalekin A. A. Stepanian V. P. Fomin N. N. Chalenko 《Astronomy Letters》2003,29(4):236-240
We present the observations of Cygnus X-3 carried out with the GT-48 gamma-ray telescope at the Crimean Astrophysical Observatory in 1994–1995. The mean gamma-ray flux at energy E>1012 eV is shown to be approximately equal to 1.3×10?11 cm?2 s?1. The flux in 1994 was much lower than that in 1995, being (6.2±2.6)×10?12 cm?2 s?1; i.e., it was statistically insignificant. The flux in 1995 was (2.7±0.7)×10?11 cm?2 s?1. Thus, the very high energy gamma-ray emission from Cyg X-3 is variable. These measurement results can be used to obtain upper limits on the flux from Cyg X-3 in 1994–1995. 相似文献
142.
Robert K. Smither Khaliefeh Abu Saleem Dante E. Roa Mark A. Beno Peter Von Ballmoos Gerry K. Skinner 《Experimental Astronomy》2005,20(1-3):201-210
A major goal of the MAX program is to detect and measure gamma rays produced following the nuclear reactions that take place in a supernova explosion. To detect a reasonable number of supernovae, sensitivities of the order of a few times 10-7 γ cm-2sec-1 are needed – much better than possible with current instruments. The approach in the MAX program is to use a crystal diffraction lens to collect photons over a large area and concentrate them on a small well-shielded detector, greatly improving the signal to noise ratio. The crystals need to have both high diffraction efficiency and a relatively broad energy bandwidth. With mosaic crystals there is a trade-off between bandwidth and diffraction efficiency – one can have either high efficiency or large bandwidth, but not both without losing too much intensity through atomic absorption. A recent breakthrough in our understanding of crystal diffraction for high-energy gamma rays has made it possible to develop crystals that have both high diffraction efficiency and a relatively broad energy bandwidth. These crystals have near perfect crystal structure, but the crystalline planes are slightly curved. Such curved planes can be obtained in 3 different ways, by using mixed crystals with a composition gradient, by applying a thermal gradient, and by mechanically bending a near perfect crystal. A series of experiments have been performed on all three types of crystals using high-energy x-ray beams from the Advanced Photon Source at the Argonne National Laboratory. Experiments performed at 3 energies, 93 keV, 123 keV and 153 keV, with both the thermal gradient Si crystals and with the mechanically bent Si crystals, demonstrated that one can achieve diffraction efficiencies approaching 100% with moderate energy bandwidths (ΔE/E = 1.4%) and low atomic absorption (transmission = 0.65), in excellent agreement with theory. The use of this type of diffraction crystal is expected to increase the sensitivity of gamma ray telescopes by a factor of 5 over that possible with normal mosaic crystals. 相似文献
143.
Ernst-Jan Buis Marco Beijersbergen Stefan Kraft Alan Owens Francesco Quarati Sytze Brandenburg Reint Ostendorf 《Experimental Astronomy》2005,20(1-3):333-339
Recent developments of cerium-doped lanthanum-halide scintillators like LaBr3:Ce show a remarkable performance in gamma-ray spectroscopy. When high energy resolution in combination with stopping power is required they provide excellent gamma-ray detector candidates for the use in space missions. Moreover, irradiation tests have shown that such detectors are radiation tolerant. In this paper we discuss a possible application of LaBr in nuclear astrophysics missions. We show results on recent proton irradiation tests at KVI in Groningen (NL) and discuss the damage and activation effects after irradiation. A possible implementation for a focal plane detector in a gamma-ray telescope and the expected performance is presented. 相似文献
144.
145.
蓝牙技术在便携式伽玛射线全谱仪中应用可行性研究 总被引:4,自引:0,他引:4
作者在本文中分析了现有便携式伽玛能谱仪在实际应用中所存在的问题,剖析了最新的蓝牙通信技术,探讨了蓝牙技术在解决该仪器所存在的问题的可行性。 相似文献
146.
During the GRIF experiment onboard the Mir orbiting station, cosmic gamma-ray bursts (GRBs) were observed in the photon energy range 10–300 keV. We developed a technique for selecting events, cosmic GRB candidates, based on output readings from the PX-2 scintillation spectrometer, the main astrophysical instrument. Six events interpreted as cosmic GRBs were identified at a threshold sensitivity level of ≥10?7 erg cm?2. The GRIF burst detection rate recalculated to all the sky is ~103 yr?1 (fluence ≥10?7 erg cm?2). This rate matches the BATSE/CGRO estimate and significantly differs from the value predicted by the S?3/2 dependence, which holds for a spatially uniform source distribution. The GRB detection rate at low peak fluxes is compared with the results of analysis for BATSE/CGRO “nontriggered” events and with predictions of major cosmological models. We conclude that the PX-2 observational data on faint cosmic GRBs are consistent with predictions of models with the highest frequency of GRB occurrence at z ≥1.5–2. 相似文献
147.
Hakkila J. Meegan C. Horack J. Pendleton G. Briggs M. Paciesas W. Emslie G. Mallozzi R. 《Astrophysics and Space Science》1995,231(1-2):369-372
Constraints are found on the gamma-ray burst luminosity function from an analysis of the combined BATSE/PVO intensity distribution. If bursts originate in an extended Galactic halo, then the intrinsic luminosity range is narrow, with bursts spanning only a factor of five or less in luminosity. If bursts originate in a simple Friedmann cosmology with = 1 and = 0, then very few luminosity constraints exist.National Research Council Fellow at NASA/MSFC 相似文献
148.
J. Hakkila V. Vo C. Meegan J. Horack G. Fishman D. Hartmann G. Pendleton M. Briggs W. Paciesas 《Astrophysics and Space Science》1995,231(1-2):23-26
A repeater statistic (derived from the two-point angular correlation function and accounting for location errors) is used to identify constraints on the rate of burst repetition from the BATSE 1B catalog. Because of the anisotropic sky exposure, repeating sources should create additional effects in the large-scale distribution of close burst pairs.National Research Council Fellow at NASA/MSFC 相似文献
149.
150.
氡气灾害是一种广泛分布的地质灾害。室内氡气浓度偏高会使居民患肺癌的几率增高,而室内氡气主要来自房屋地基所在的地质单元。笔者在美国犹他大学研究所工作期是,研究了瑞丁普朗花岗片麻岩带近地表氡的浓度与铀含量的关系以及铀的分布与居民癌症死亡率之间的相关关系。铀的区域性分布是利用航空伽马能谱测量资料求得的,说明利用航空伽马能谱测量资料开展氡气灾害区域评价的可能性。文中还举例说明氡气调查在制定建设规划方面的作 相似文献