The Study Of Four-dimensional Imaging Method For The Low And Medium Atomic Numbers Objects At The Centimeter Scale By Cosmic-ray Muon

The cosmic-ray muon possesses the advantages of high-penetrating and non-destructive,which made using muon as a probe in radiation detection field a favored topic.Recently,the application of cosmic-ray muon imaging technique is the detection of high atomic number objects on the basis of scattering method and the imaging of the geological condition as well as the large volume buildings based on the transmission method.However,the muon imaging method aiming at the low and medium atomic number objects is seldom reported in China.A four-dimensional resolution imaging method for the low and medium atomic numbers objects at the centimeter scale by the cosmic-ray muon and its secondary particles coincide detection technique is proposed in this paper.First of all,a study of the characteristics of muonic secondary particles through Monte Carlo toolkit indicates that the secondary particles are composed of secondary electrons and gamma.The energy of the secondary particles is much higher than the background and the polar angle is more likely to emit along the direction of the incident muon.Besides,the amount of secondary particles also carry the location and atomic number information of the target object.Then,by the coincide detection of the incident muon trajectory and muonic secondary particle,a reconstruction of coincide muon trajectory is performed and a 3D image of the target object through the track density as well as the limited angle imaging method is obtained.The results show that the imaging accuracy of the track density method is high enough to distinguish the iron cube with a length of 5 mm or a 2 mm interval and if the imaging time is longer than 20 days,this method will be capable of distinguishing1 mm interval.But the limited angle imaging method has better universality because it confirms the height information of target by searching for the optimal solution.Both method is more applicable to materials with low or medium atomic number.Furthermore,a 4D imaging is achieved through the ratio of the secondary particles generated from different atomic number.The reconstructed image can clearly specify materials with low,medium or high atomic number.More adoptable to differentiate low and medium atomic number.As for the experiment concept,a imaging system based on the coincide detection of the muon and muonic secondary particles is designed,which consists of three layers of position-sensitive detector and four fast time response plastic scintillation detectors with a box-like shape.A series of primarily work of the relative nuclear electronics plugs is performed,including the test of detectors,muon energy together with momentum spectrum measurement in laboratory and coincided counting of muonic secondary particles.The results indicate that the performances of the existing detectors can fulfill the demand of imaging.The coincided muon flux acquired by the experiment is about 37.5% of the theoretical value,the obtained muon energy spectrum matches the deposited energy simulated by Geant4 and the coincide counting of the muonic secondary particles is almost proportional to the atomic number of target object.