The design of a photoneutron source for the narcotic drugs detection in a large-truck

摘要

A photoneutron source based system is proposed to address the problem of detecting drugs concealed in the large trucks. By utilizing the heavy water convertor to convert X-rays to photoneutrons, a photoneutron source with neutron yield about 10~(11) n/s can be realized with a 7 MeV/100μA e-LINAC. To meet the requirements of in situ application for the large-truck inspection, the photoneutron production, neutron moderation, and both X-rays and photoneutrons shielding are carefully researched to achieve a high analyzing sensitivity inside the truck, whereas at the same time maintain a low dose rate on the boundary of the control zone to ensure the public safety. A NaI(TI) detector array is used to measure the thermal neutron induced radiative capture gamma-rays to analyze the concentrations and distributions of various elements of the inspected objects inside the truck. By analyzing the gamma-ray spectra of a 6.23 kg methamphetamine simulant shielded by various thickness of steel, the feasibility of this system to find the concealed Cl-rich drugs inside a large truck is confirmed. The false positive and false negative rate can be as low as 0.1% even the methamphetamine simulant is shielded by a 5-cm-thick steel.