Space sandwich

日期:2017-11-14 05:21:51 作者:濮捆箅 阅读:

By Duncan Graham-Rowe OPTICAL fibres sandwiched between sheets of heavy metals could soon be helping to reveal the secrets of blazars, the active galaxies around black holes. NASA’s ultra-sensitive gamma-ray detector, which will ride on its Gamma-ray Large Area Space Telescope (GLAST), comprises a 125-layer sandwich of optical fibres and thin sheets of heavy metals such as lead or tantalum. The rays scatter as they strike the dense metal atoms, producing showers of charged particles. These cause flashes, or scintillations, as they pass through the fibres, sending light down them to detectors. The fibres run at right angles to each other in a grid, so the location of a scintillation can be plotted in each layer, allowing NASA to determine where the gamma-ray beam came from and its intensity. GLAST will be the first space telescope to employ fibres in this way, though the technique has already been used in particle physics laboratories. It will detect gamma rays over a broad range of wavelengths with greater accuracy than has been possible to date. GLAST will also offer a 160° view of the sky—beating the 40° maximum currently possible with silicon detectors. The telescope’s designer, Geoffrey Pendleton of the University of Alabama in Huntsville, says it should be launched by 2005. In Britain, Gerry Skinner of the University of Birmingham, who specialises in gamma-ray telescopes,