 the neutrons 106 and points them towards the object under examination, such as luggage 108, so as to irradiate or immerse the luggage and its contents with neutrons. Nitrogen contained within an explosive material 110, placed inside of the luggage 108, interacts with the probing neutron radiation and emits prompt gamma rays 112 of a particular energy level. Non-explosive materials within the luggage may have other elements that also interact with the probing neutron radiation, but the gamma rays emitted from such other elements have a different energy than do those from nitrogen. The number and energy of the gamma rays are measured in detector 114, which detector generates an appropriate output signal for each gamma ray of a particular energy that is received. A computer 116 monitors the output of the detector 114 and, after appropriate signal processing, makes a determination as to whether explosive material is present within the luggage. If so, an alarm 118 sounds, or is otherwise generated (e.g., visually) which alarm alerts operating personnel that explosive material 110 may be present within the luggage 108 so that appropriate action may be taken. Such action may include, for example, automatically diverting the suspect luggage away from the other luggage so that an extensive manual or other search of the luggage and its contents can be made.
As shown in FIG. 2A, one type of an explosive detection system 10 in accordance with the present invention includes a loading station 12 (which may consist of a scale to weigh the luggage) and an unloading station 14 (which may consist of a diverter to separate the alarmed luggage from the rest). The loading station leads to a continuous conveyer belt 16 which extends from the loading station 12 to the loading station 16 and has a continuous motion as indicated by the arrows 18. A central shield structure 20 encloses the explosive detection system and with two external wing portions 22 and 24 extending from the central structure 20 to enclose the conveyer belt 16 leading from and to the loading and unloading stations 12 and 14.
As can be seen in FIG. 2B, wherein the shields 20, 22 and 24 are removed, the explosive detection system is positioned over a central portion of the conveyer belt 16. Specifically, the explosive detection system includes a cavity structure 26 through which the conveyer belt 16 passes. As shown in FIGS. 2A and 2B, various articles of luggage and parcels may be positioned on the loading station 12 and may then be carried thorough the cavity 26 to the unloading station 14 by the conveyer belt 16.
The cavity is formed by external wall members including a top wall 28, side walls 30 and 31 and a bottom wall (not shown) which is positioned below the conveyer belt -6. Extending through the wall members are neutron sources, such as source 32 positioned at the top of the cavity, and as shown in FIG. 3, neutron source 34 spaced from the neutron source 32 and positioned at the bottom of the cavity. Also as shown in FIGS. 2 and 3, detector structures are positioned to form two C-rings of detectors having their opened ends facing the neutron sources. This may be seen in FIG. 3 wherein the side detector structures 36 and 38 together with the bottom detector structure 40 are all associated with the neutron source 32. Similarly, side detector structures 42 and 44 together with the top detector structure 46 are all associated with the neutron source 34.
As shown in FIG. 3, the side detector structures may be provided by two sets of four detectors located in each side detector structure 36 and 38. The bottom detector structure 40 includes two sets of seven detectors. The detectors associated with the neutron source 34 similarly include two sets of four detectors located in each side detector structure 42 and 44 and with two sets of seven detectors located in the top detective structure 46. The detectors associated with the neutron source 32, therefore, form a C-ring of detectors having the opened portion of the C facing upward. In an opposite fashion the detectors associa