MSGID: 1:317/3 6427b376   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Mathematical model provides bolt of understanding for lightning-produced   
   X-rays    
      
     Date:   
         March 31, 2023   
     Source:   
         Penn State   
     Summary:   
         In the early 2000s, scientists observed lightning discharge   
         producing X- rays comprising high energy photons -- the same   
         type used for medical imaging. Researchers could recreate this   
         phenomenon in the lab, but they could not fully explain how and   
         why lightning produced X-rays. Now, two decades later, a team has   
         discovered a new physical mechanism explaining naturally occurring   
         X-rays associated with lightning activity in the Earth's atmosphere.   
      
      
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   FULL STORY   
   ==========================================================================   
   In the early 2000s, scientists observed lightning discharge producing   
   X-rays comprising high energy photons -- the same type used for medical   
   imaging.   
      
   Researchers could recreate this phenomenon in the lab, but they could not   
   fully explain how and why lightning produced X-rays. Now, two decades   
   later, a Penn State-led team has discovered a new physical mechanism   
   explaining naturally occurring X-rays associated with lightning activity   
   in the Earth's atmosphere.   
      
      
   ==========================================================================   
   They published their results on March 30 in Geophysical Research Letters.   
      
   The team's finding could also shed light on another phenomenon: the   
   small shock sometimes felt when touching a metal doorknob. Called spark   
   discharge, it occurs when a voltage difference is created between a body   
   and a conductor. In a series of lab experiments in the 1960s, scientists   
   discovered that spark discharges produce X-rays -- just as lightning   
   does. More than 60 years later, scientists are still conducting lab   
   experiments to better understand the mechanism underpinning this process.   
      
   Lightning consists in part of relativistic electrons, which emit   
   spectacular high-energy bursts of X-rays with tens of mega electron-volt   
   energies called terrestrial gamma-ray flashes (TGFs). Researchers have   
   created simulations and models to explain the TGF observations, but there   
   is a mismatch between simulated and actual sizes, according to lead author   
   Victor Pasko, Penn State professor of electrical engineering. Pasko and   
   his team mathematically modeled the TGF phenomenon to better understand   
   how it can occur in observed compact space.   
      
   "The simulations are all very big -- usually several kilometers across --   
   and the community has difficulty reconciling this right now with actual   
   observations, because when lightning propagates, it's very compact,"   
   Pasko said, explaining that lightning's space channel is typically   
   several centimeters in scale, with electric discharge activity producing   
   X-rays expanding around tips of these channels up to 100 meters in extreme   
   cases. "Why is that source so compact? It's been a puzzle until now. Since   
   we're working with very small volumes, it may also have implications   
   for the lab experiments with spark discharges underway since the 1960s."   
   Pasko said that they developed the explanation for how an electric field   
   amplifies the number of electrons, driving the phenomenon. The electrons   
   scatter on individual atoms, which constitute the air, as they experience   
   acceleration. As the electrons move, most of them go forward as they   
   gain energy and multiply, similar to a snow avalanche, allowing them to   
   produce more electrons. As the electrons avalanche, they produce X-rays,   
   which launch the photons backward and produce new electrons.   
      
   "From there, the question we wanted to answer mathematically was, 'What   
   is the electric field you need to apply in order to just replicate this,   
   to launch just enough X-rays backwards to allow amplification of these   
   select electrons?'" Pasko said.   
      
   The mathematical modeling established a threshold for the electric   
   field, according to Pasko, which confirmed the feedback mechanism that   
   amplifies the electron avalanches when X-rays emitted by the electrons   
   travel backward and generate new electrons.   
      
   "The model results agree with the observational and experimental evidence   
   indicating that TGFs originate from relatively compact regions of space   
   with spatial extent on the order of 10 to 100 meters," Pasko said.   
      
   In addition to describing high-energy phenomena related to lightning,   
   Pasko said the work may eventually help to design new X-ray sources. The   
   researchers said they plan to examine the mechanism using different   
   materials and gases, as well as different applications of their findings.   
      
   The other authors on the paper are Reza Janalizadeh, a postdoctoral   
   scholar in the Penn State Department of Electrical Engineering; Sebastien   
   Celestin of the University of Orleans in Orleans, France; Anne Bourdon,   
   of Ecole Polytechnique in Palaiseau, France; and Jaroslav Jansky of the   
   University of Defense in Brno, Czechia.   
      
   The National Science Foundation funded this work.   
      
       * RELATED_TOPICS   
             o Matter_&_Energy   
                   # Energy_Technology # Spintronics # Electricity # Physics   
             o Earth_&_Climate   
                   # Storms # Severe_Weather # Energy_and_the_Environment #   
                   Environmental_Science   
       * RELATED_TERMS   
             o X-ray o Radiography o Gamma_ray o Nuclear_fission o   
             Subatomic_particle o Photoelectric_effect o Thunderstorm   
             o Electricity   
      
   ==========================================================================   
   Story Source: Materials provided by Penn_State. Original written by   
   Sarah Small. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Victor P. Pasko, Sebastien Celestin, Anne Bourdon, Reza Janalizadeh,   
         Jaroslav Jansky. Conditions for Inception of Relativistic Runaway   
         Discharges in Air. Geophysical Research Letters, 2023; 50 (7)   
         DOI: 10.1029/2022GL102710   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/03/230331131501.htm   
      
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