Research On The Detection Of Lightning Energetic Radiation And Its Influence On Nuclear Explosion Monitoring

It is now well established that lightning emit transient electromagnetic and optical radiation at the same time,the thunder also generate acoustic signals,which can lead to nuclear monitoring equipment to produce false alarms.Lightning is an important source of interference for nuclear burst detection.During the observation,intense X-ray bursts were detected associated with lightning discharge,and these X-rays are called lightning energetic radiation.The intrinsic link between the mechanism of lightning energetic radiation and other physical signals has become a research hotspot in lightning physics.Focusing on the above issues,the main research work and conclusions in this dissertation are as follows:?1?Based on GEANT4 software,a simulation model of RREA mechanism for lightning energetic radiation was established.We have obtained the detailed results concerning the RREA process,the parameters of the relativistic runaway electron avalanche effect were calculated,a method for estimating the number of bremsstrahlung photons was given.The formulas for calculating avalanche growth length,avalanche growth time,the ration of bremsstrahlung photons to energetic electrons were obtained.These formulas are functions that contain only one variable of electric field strength,which facilitates the calculation and comparative analysis of each parameter.Under the same input conditions,different physical models were used to calculate the RREA mechanism.The impact of different physical models in GEANT4 on the simulation results were evaluated.The calculation results show that the constructor function EM Opt4 adopts the highest accuracy,produces the most bremsstrahlung photons,but the calculation process takes the longest time.?2?According to the characteristics of the lightning energetic radiation,three types of lightning energetic radiation detection systems were developed.By using FPGA to control high speed ADC,we designed a lightning energetic radiation automatic detection system.No return stroke current signal was required as an external trigger.The screening algorithm could effectively identify lightning energetic radiation signals in real time,avoiding consuming a large amount of storage space for storing the background data.The system was designed with a pulse amplitude analysis module,which could acquire gamma-ray spectrum data,and could use the characteristic energy of different radiation source to calibrate the system.?3?For the first time in China,an energetic radiation burst from a natural cloud-to-ground lightning was successfully detected.The maximum energy exceeds 30MeV,with a duration of several hundred?s,which was similar to the TGFs observed by satellite platforms.It is the first double-peak terrestrial gamma-ray flashes observed at ground level,that has been reported so far.The analysis shows that the negative pulse signals of the stepped leaders have a one-to-one correspondence with the energetic radiation pulse signals,which proves that the stepped leader is the source of lightning energetic radiation,and the energy of gamma rays increases with the magnitude of the stepped leader signals.?4?For the first time in China,three energetic radiation signals have been successfully observed.Triggered lightning energetic radiation signals can be roughly divided into two types:The X-ray burst signal gradually changes from a pileup signal to a continuous saturated current signal,and the X-ray pulses are independent of each other with the highest energy up to 16 MeV.In addition,the negative pulse signals of the stepped leaders have a one-to-one correspondence with the high energy radiation pulse signals.The durations of the two types X-ray bursts of triggered lightning are different,and the difference in duration is about 6 times.?5?A Monte Carlo simulation model for lightning energetic radiation atmospheric transport was established,and a theoretical calculation method was used to analyze whether the lightning energetic radiation could interfere the the early nuclear radiation detection equipment on the nuclear monitoring vehicle.The calculation results show that the lightning energetic radiation observed on August 13,2016 as an example can generate false alarm signals for early nuclear radiation detection systems within 3 km from the lightning channel.The amount of air absorbed dose by the lightning energetic radiation transmitted to the ground is only in the order of 10^-4?Gy,and such a low level of radiation can not produce serious biological effects on humans.We calculate the deposition of energy in the detectors by the lightning energetic radiation at different distances from triggered lightning channel.The calculation results show that when the lightning energetic radiation detection system is installed,the distance from the triggered lightning channel should not exceed 5 km,otherwise it is difficult to detect the effective signal,and provides a basis for setting up multiple sets of detection systems on the test site.The triggered lightning that was observed in 2017 could interfere with the early nuclear radiation detection system within 2 km of the lightning channel.The triggered lightning experiment can be used to test the early nuclear radiation coincidence detection device,and it can be used as a simulating source for identification research.