Nature : 闪电 有机会影响 反物质 诸平 A Kyoto University-based team has unraveled the mystery of gamma-ray emission cascades caused by lightning strikes. Credit: Kyoto University/Teruaki Enoto 据物理学家组织网（ Phys.org ） 2017 年 11 月 22 日 转载来自日本 京都大学 （ Kyoto University ） 的消息，该大学的研究人员研究发现， 闪电放电 会 引起的光致 核 反应 ， 有可能会对反物质产生影响。 日本 京都大学 的研究 团队 已经 解开 了 由雷击引起的伽马射线发射 流之谜 。 雷雨天气， 一场 疾风暴雨来临 : 天昏地暗，电闪雷鸣，这是司空见惯的自然现象。这一幕虽然大家都很熟悉，并且不断地在人类生存的地球上重复发生，并没有什么神秘感。但是，对于其中引起的光反应之谜，有许多可能还是有待深入研究的空白。 京都大学 的研究已经使神秘加深，他们发现闪电可能导致物质 - 反物质湮灭（ matter-antimatter annihilation ）。 相关研究结果已经于 2017 年 11 月 22 日在《 自然 》（ Nature ） 杂志网站发表 —— Teruaki Enoto, Yuuki Wada, Yoshihiro Furuta, Kazuhiro Nakazawa, Takayuki Yuasa, Kazufumi Okuda, Kazuo Makishima, Mitsuteru Sato, Yousuke Sato, Toshio Nakano, Daigo Umemoto, Harufumi Tsuchiya. Photonuclear reactions triggered by lightning discharge . Nature , 2017 , 551: 481-484 . DOI: 10.1038/nature24630 Abstract Lightning and thunderclouds are natural particle accelerators 1 . Avalanches of relativistic runaway electrons, which develop in electric fields within thunderclouds 2 , 3 , emit bremsstrahlung γ-rays. These γ-rays have been detected by ground-based observatories 4 , 5 , 6 , 7 , 8 , 9 , by airborne detectors 10 and as terrestrial γ-ray flashes from space 10 , 11 , 12 , 13 , 14 . The energy of the γ-rays is sufficiently high that they can trigger atmospheric photonuclear reactions 10 , 15 , 16 , 17 , 18 , 19 that produce neutrons and eventually positrons via β + decay of the unstable radioactive isotopes, most notably 13 N, which is generated via 14 N + γ → 13 N + n , where γ denotes a photon and n a neutron. However, this reaction has hitherto not been observed conclusively, despite increasing observational evidence of neutrons 7 , 20 , 21 and positrons 10 , 22 that are presumably derived from such reactions. Here we report ground-based observations of neutron and positron signals after lightning. During a thunderstorm on 6 February 2017 in Japan, a γ-ray flash with a duration of less than one millisecond was detected at our monitoring sites 0.5–1.7 kilometres away from the lightning. The subsequent γ-ray afterglow subsided quickly, with an exponential decay constant of 40–60 milliseconds, and was followed by prolonged line emission at about 0.511 megaelectronvolts, which lasted for a minute. The observed decay timescale and spectral cutoff at about 10 megaelectronvolts of the γ-ray afterglow are well explained by de-excitation γ-rays from nuclei excited by neutron capture. The centre energy of the prolonged line emission corresponds to electron–positron annihilation, providing conclusive evidence of positrons being produced after the lightning.
看到孟津老师的博客 《 天空中写京城夜空雷电》 惊呼闪电的样子真像神经元的树突和轴突： A single, pyramidal neuron. Illustration by Ramon Y Cajal S., ca. 1899. Cajal 银染色的锥体神经元 http://drsimonsaysscience.org/2015/02/03/i-am-neuron/ 下图应该是海马区的颗粒细胞 http://jonlieffmd.com/wp-content/uploads/2012/10/Newborn-neuron-in-mouse-brain-.gif 视网膜神经节细胞ganglion cell (2) Wong, KY, Dunn, FA, Berson, DM. (2005) Photoreceptor adaptation in intrinsically photosensitive retinal ganglion cells. Neuron 48 (6):1001-10. PMID 16364903 . http://neuronbank.org/wiki/images/3/32/Photoreceptive_ganglion_cell.jpg Neuron. 2003 Jan 9;37(1):15-27. Fireworks in the primate retina: in vitro photodynamics reveals diverse LGN-projecting ganglion cell types. Dacey DM 1 , Peterson BB , Robinson FR , Gamlin PD . (D) Schematic summary of depth of dendritic stratification and mean dendritic field size for each of the 13 ganglion cell populations recognized thus far.
标签: 闪电
