The Security Inspection System Using X-ray Pseudo Dual-energy Transmission Technology

X-ray　detection　methods　have　increasingly　been　used　as　an　effective　means　for　the　automatic　detection　of　contrabands　such　as　explosive　and　handgun.　X-ray　devices　have　demonstrated　the　ability　to　characterize　a　kind　of　material　at　the　molecular　and　atomic　levels,　which　is　particularly　important　for　detecting　plastic　explosives,　where　object　shape　information　cannot　be　used.　X-ray　devices　are　relatively　inexpensive　compared　to　many　other　detection　technologies　for　detecting　illicit　materials.　So　a　number　of　devices　are　now　commercially　available.　The　purpose　of　this　research　has　been　to　investigate　methods　for　using　X-ray　dual-energy　transmission　technologies　more　effectively.　　Followed　by　an　introduction　and　brief　overview　of　X-ray　and　X-ray　detection　technologies,　the　principle　of　X-ray　transmission　image　is　expatiated.　Then,　an　algorithm　is　developed　to　correct　the　non-uniformity　of　transmission　detectors　in　our　scanning　system.　A　given　object　may　be　randomly　placed　anywhere　on　the　conveyor　belt,　resulting　in　a　variation　in　the　detected　signals.　An　adaptive　modeling　technique　is　used　to　decrease　this　distance　effect.　　Using　X-ray　transmission　technology,　a　material's　effective　atomic　number　or　Zeff-related　information　can　be　determined.　The　X-ray　source　output　energy　in　our　scanning　system　is　not　monochromatic,　resulting　in　spectrum　overlap　and　output　signal　unbalance　between　high　and　low　energy　levels,　which　will　degrade　the　performance　of　dual-energy　X-ray　sensing.　A　numerical　optimization　method　to　remove　thickness　effect　of　objects　has　been　developed　to　improve　the　system　performance.　The　technology　used　is　called　R　and　Rψ　sensing　technology.　It　uses　dual-energy　transmission　technology　to　obtain　characteristic　value　of　an　object,　i.e.　R　and　Rψ.　The　material　type　of　this　object　can　then　be　determined　using　R　or　Rψ　plane.　The　characteristic　value　R　or　Rψ　is　computed　using　signals　from　dual-energy　transmission　modality.　R　or　Rψis　related　to　Zeff,　and　classification　rules　have　been　obtained　to　separate　organic　substance,mixture　and　metal.　　At　the　end　of　this　dissertation,　the　discussion　of　image-processing　methods　is　focused　on　to　get　a　much　more　legible　transmission　image.