Design and Simulation of a Magnetic Diverter Structure for the X-Ray Detecting System

Abstract

Minimization of the charged particle background in the x-ray detecting system is an important issue. Generally, there are four possible sources of damaging radiation for x-ray detecting systems, namely: geomagnetically trapped electrons, galactic cosmic ray particles, solar flare events, and onboard radiation sources that always cause noise and damage to the performance of the payload of a spacecraft. In order to alleviate the background noise of the x-ray detecting system, a magnetic diverter is proposed to shield the electrons. The main idea of this method is, using the Monte Carlo method, to follow the tracks of all the electrons and determine whether the electrons collide with the x-ray tube, how they collide, and other parameters of this collision. The number of deflected electrons can be obtained by computing all the physical parameters of electrons. As a result, the shielding efficiency of background noise can be calculated.

Firstly, the electron motion can be classified into the following three types: (1) electrons hit the detector directly, (2) electrons hit the rest of the area of the detector plane except for the active area of the detector, and (3) electrons hit the inner wall of the x-ray detecting system tube. In addition, in accordance with the relativity principle, the velocity of different electrons with different energies can be obtained. In order to mimic the actual motion of electrons, the incidence direction, incidence position and energy of electrons are assumed random.

Secondly, the whole simulation process is divided into two steps. One step is to simulate the motion of electrons in the x-ray detection system without a magnetic diverter, obtaining the number of electrons that arrive to the detector plane, except for the active detector area, and to the inner tube, respectively. The other step is to simulate the motion of electrons in the x-ray detecting system with a magnetic diverter and the initial magnetic parameters, calculating the number of electrons which arrive to the active area of the detector, to the detector plane except for the active area of the detector, and to the inner tube, respectively. As a result, the total shielding efficiency can be obtained.

Finally, in order to reduce the weight of the x-ray detecting system, the structure of the magnetic diverter has been designed and optimized based on the simulation results.