Current Issue : July - September Volume : 2018 Issue Number : 3 Articles : 6 Articles
We review the history of astronomical X-ray polarimetry based on the author�s perspective,\nbeginning with early sounding-rocket experiments by Robert Novick at Columbia University and his\nteam, of which the author was a member. After describing various early techniques for measuring\nX-ray polarization, we discuss the polarimeter aboard the Orbiting Solar Observatory 8 (OSO-8) and\nits scientific results. Next, we describe the X-ray polarimeter to have flown aboard the ill-fated original\nSpectrum-X mission, which provided important lessons on polarimeter design, systematic effects, and the\nprogrammatics of a shared focal plane. We conclude with a description of the Imaging X-ray Polarimetry\nExplorer (IXPE) and its prospective scientific return. IXPE, a partnership between NASA and ASI,\nhas been selected as a NASA Astrophysics Small Explorers Mission and is currently scheduled to launch\nin April of 2021....
Metal laser cutting belongs to mature laser material processing technologies in\nindustry applications. However, without understanding of the mechanism\nunderlying the overall process, the improvement of the cutting quality is restricted.\nIn this paper, an instantaneous melt removal model is presented to\ndescribe the process of material removal and striation formation. In the temperature\nfield calculation, melted metal layer is removed when it grows to an\nassumed thickness. The effects of cutting parameters including cutting speed,\ngas pressure and laser power on the shape of striation are discussed. A novel\nmethod of getting striation free cutting surface is presented. Finally, laser cutting\nexperiments of mild steel is conducted to validate the model. The striation\nvariation trend can be well predicted by the model presented here and the\ndisagreement may be caused by the coupling effect of cutting speed and critical\nthickness value....
ArgonCube Light readout system (ArCLight) is a novel device for detecting scintillation\nlight over large areas with Photon Detection Efficiency (PDE) of the order of a few percent. Its robust\ntechnological design allows for efficient use in large-volume particle detectors, such as Liquid\nArgon Time Projection Chambers (LArTPCs) or liquid scintillator detectors. Due to its dielectric\nstructure it can be placed inside volumes with high electric field. It could potentially replace vacuum\nPhotoMultiplier Tubes (PMTs) in applications where high PDE is not required. The photon detection\nefficiency for a 10Ã?â??10 cm2 detector prototype was measured to be in the range of 0.8% to 2.2% across\nthe active area....
Microquasars are Galactic black hole systems in which matter is transferred from a donor\nstar and accretes onto a black hole of, typically, 10ââ?¬â??20 solar masses. The presence of an accretion disk\nand a relativistic jet made them a scaled down analogue of quasarsââ?¬â?thence their name. Microquasars\nfeature prominently in the scientific goals of X-ray polarimeters, because a number of open questions,\nwhich are discussed in this paper, can potentially be answered: the geometry of the hot corona\nbelieved to be responsible for the hard X-ray emission; the role of the jet; the spin of the black hole....
In the never-ending quest for better detection efficiency and spatial resolution, various\nthermal neutron detection schemes have been proposed over the years. Given the presence of\nsome converting layers (typically boron, but 6LiF is also widely used nowadays), the shift towards\nconcepts based on solid state detectors has been steadily increasing and ingenious schemes thereby\nproposed. However, a trade-off has been always sought for between efficiency and spatial resolution;\nthe problem can be (at least partially) circumvented using more elaborate geometries, but this\ncomplicates the sample preparation and detector construction. Thus, viable alternatives must\nbe found. What we proposed (and verified experimentally) is a detection scheme based on the\nsuperconducting to normal transition. More precisely, using a boron converting layer, the �± particles\n(generated in the (n, �±) reaction) crossing a low critical temperature superconducting strip some\n10 �¼m wide have been detected; the process, bolometric in nature and based on the ionization energy\nloss, is intrinsically fast and the spatial resolution very appealing. In this work, some of the work\ndone so far will be illustrated, together with the principles of the measurement and various related\nproblems. The realization of the detector is based on industrial deposition and photolitographic\ntechniques well within the grasp of a condensed matter laboratory, so that there is substantial room\nfor improvement over our elementary strip geometry. Some of the plans for future work will also be\npresented, together with some improvements both in the choice of the materials and the geometry of\nthe detector....
The PoGO mission, including the PoGOLite Pathfinder and PoGO+, aims to provide\npolarimetric measurements of the Crab system and Cygnus X-1 in the hard X-ray band. Measurements\nare conducted from a stabilized balloon-borne platform, launched on a 1 million cubic meter balloon\nfrom the Esrange Space Center in Sweden to an altitude of approximately 40 km. Several flights have\nbeen conducted, resulting in two independent measurements of the Crab polarization and one of\nCygnus X-1. Here, a review of the PoGO mission is presented, including a description of the payload\nand the flight campaigns, and a discussion of some of the scientific results obtained to date....
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