| Nowadays,the major obstruction of limiting X-ray phase-contrast imaging to be better practical development would be lack of X-ray source with high brightness and high spatial coherence,and because new microstructed X-ray tube can provide X-ray beam with high spatial coherence.So it gradually becomes research hotspot of X-ray phase contrast source.However,on account of research of energy deposition of incident electron in anodic target is relative to be less infrequent and not enough deep,therefore while designing microstructured X-ray source,researchers have to refer to the value of empirical fomula of electronic range to decide practical parameter,and the disadvantage of this method is difficult to avoid to appear larger error and lower efficiency.And because the structure and the size of micron level in microstructed X-ray source affects the strength and angular distribution of output X-ray vitally,therefore the most urgent problem is how to deeply research electron trajectory and distribution of energy deposition of ineraction of energetic electron with anodic target.In this paper,we started from multiple scattering theory of electrons and studied,by Monte Carlo method,numerically calculate trajectory and distribution of energy deposition of energetic electrons within Tungsten,Molybdenum,Copper,Diamond(responsable for distribution of thermal energy and initial X-ray strength).The calculation result indicate that when electrons interacting with atom of target,99% of electron energy deposited in the area of approximate cylinder,and the field of producing X-ray is larger than the spot of electron beam in the interface of target,and the size of this field is directly related to the energy of incident electron,material of target and so on.At the same time,we can find out that the distribution of deposition energy in the incident direction is not directly diminishing but to increasing,and it becomes diminishing to a certain depth.Thus the maximum value of deposition energy is located in a certain depth below surface of target.On the other hand,when the energy of incident electrons become the same,the maximum value of deposition energy is not always positively related to atomic number and desity of target,for examble,the atomic number and desity of Diamond is far less than Molybdenum and Copper,but on the contrary,the maximum value of deposition energy of Diamond is higher.Then,combining the simulation results of four materials and Dulong-Petit law,we acquire the critical value of andic current respectly are Diamond,Molydenum,Copper,Tungsten from higher to lower while electrons of 20 to 100 keV are injected into different target of material.And according to contrastive analysis,we find that Tungsten target with thickness of 5?m can absorb 99% energy of electrons of 100 keV,so it's suitable as microstructed target.And the critical value of anodic current of Diamond is the highest,so it's suitable as materials of heat dissipation.On this base,we deeply research between the relationship of the angular distribution of output X-ray strength and spectrum and the energy of incident electron and the thickness of target in the microstructed tungsten target with period of 3?m and duty ratio of 1:2,and find that its' angular distribution of X-ray strength present to be Gaussian distribution,X-ray mainly concentrate on the field of the angle of ±15 in the positive Z direction,and the distribution of X-ray on the plane which perpendicular to Z direction of 50 cm is similar to “M” type.All the results can be used as excellet reference for research and design of microstructure x-ray tubes and micro-focus X-ray tube with spot of X-ray below 10?m and coherent x-rays of high brightness. |
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