to direct irradiation to the logs of the whole vehicle which requires an irradiation tunnel with large cross section for access of the locomotive therefore the conventional maze structure cannot be used as a part of the tunnel consequently the present invention employs the shielding structure containing the tunnel walls with buttresses barriers and the shielding door to meet the safety requirement at the entrance and exit as well as other portions outside the tunnel therefore when the accelerators are in operation the leakage radiation level outside the tunnel meets the relevant requirements according to the international regulations u201c international basic safety standards for protection against ionizing radiation and for the safety of radiation sources u201d iaea no 115 1996 thus ensuring safety of public and operators the structural principle of the traction device of the invention is shown in fig6 the exemplified traction device 6 includes a traction locomotive 13 a hook 14 a current collector 15 a sliding guide rail 16 and an anti collision device 17 the sliding guide rail 16 is fixed to the ground along the spread direction of the tunnel 7 for providing electrical and communication connection with the current collector 15 of the traction locomotive 13 the current collector 15 is provided at one side of the traction locomotive 13 to be in contact with the sliding guide rail 16 to keep the communication and supply of the driving power the anti collision device.