Multiple station gamma ray absorption contraband detection system

A multiple station gamma ray absorption contraband detection system utilizes a proton source and disk-shaped target to provide a 360 degree resonant gamma ray cone which is suitable for use in four separate gamma ray absorption contraband detection stations simultaneously. The target has two beryllium walls coated with .sup.13 C and .sup.34 S so as to facilitate the detection of nitrogen and chlorine in a manner which reliably and effectively identifies contraband such as explosives and drugs via gamma ray absorption.

FIELD OF THE INVENTION 
The present invention relates generally to the detection of contraband, 
e.g., drugs and explosives, via the selective absorption of gamma rays. It 
relates more particularly to an improved target which facilitates the 
construction of multiple contraband detection stations utilizing a common 
proton source for the generation of gamma rays. 
BACKGROUND OF THE INVENTION 
The need to detect contraband such as drugs and explosives is well 
appreciated. Drugs are routinely smuggled through various ports of entry 
such as airports, border crossings, and boat docks. Efforts to control the 
flow of such contraband have increased substantially over the years. 
Various means, including manual searches, drug sniffing dogs, and X-ray 
devices are frequently utilized in an attempt to locate such contraband. 
The smuggling of explosives, particularly aboard aircraft, has become of 
great concern recently. This is particularly true in light of recent 
airline bombings involving great loss of life. Again, various techniques 
such as manual searching, dogs, and X-rays are routinely used in order to 
prevent such smuggling. 
However, as those skilled in the art will appreciate, such contemporary 
contraband detection techniques are much less effective than desirable. 
Manual searching is extremely time consuming and costly. Manual searching 
is also intrusive, and therefore objectionable to the owners of the 
searched containers. 
The use of dogs to search for drugs and/or explosives requires that a 
trained and experienced dog and handler be utilized. This is very 
inefficient and also strictly limits the quantity of baggage that can be 
so searched. 
The use of X-rays has been found to be unreliable, since it is possible to 
disguise or camouflage drugs and/or explosives in a manner which makes 
them extremely difficult to detect therewith. Even experienced X-ray 
machine operators are not capable of detecting such camouflaged contraband 
in some cases. 
In view of the above-mentioned deficiencies in the art, various 
non-intrusive scanning techniques have been developed which are more 
accurate than contemporary X-ray techniques. It is known to utilize 
neutron activation and selective gamma ray absorption to identify 
elements, typically chlorine, oxygen, and/or nitrogen, which are generally 
present in such contraband. Examples of devices which utilize gamma rays 
to detect contraband are provided in U.S. Pat. Nos. 5,040,200 issued on 
Aug. 13, 1991 to Ettinger et al.; 5,068,883 issued on Nov. 26, 1991 to 
DeHaan et al.; 5,159,617 issued on Oct. 27, 1992 to King et al.; 5,251,240 
issued on Oct. 5, 1993 to Grodzins; and 5,282,235 issued on Jan. 25, 1994 
to Schmor et al. 
However, although such gamma ray absorption techniques are non-intrusive 
and generally reliable, they are extremely expensive to practice. A gamma 
ray absorption contraband detection device which is suitable for use in 
high-capacity applications, such as airports, boat docks, and border 
crossings, must utilize a comparatively strong gamma ray source, such as a 
proton accelerator. Such a device generates gamma rays by focusing a beam 
of energetic protons upon a target. The incident proton beam excites the 
material of the target according to well known principles, thereby causing 
it to produce gamma rays. 
In order to prevent rapid deterioration of the target, contemporary systems 
utilize a drum-shaped target which rotates, so as to limit the exposure of 
any particular portion of the target to the proton beam, thereby 
increasing the surface area upon which the proton beam is incident and 
consequently facilitating cooling thereof. Further, water cooling is 
typically utilized to facilitate heat dissipation from the target. One 
example of a watercooled target is provided in U.S. Pat. No. 4,323,780 
issued on Apr. 6, 1982 to Tombaugh et al. 
However, a problem common to contemporary targets is that they form a 360 
degree gamma ray beam which, due to interaction with the target structure 
(shape), typically approximately 53 degrees of the gamma cone beam is 
suitable for use. This limits use to only a single contraband detection 
station. Thus, according to the prior art, each individual contraband 
detection station requires a separate, dedicated target and proton 
accelerator. Because of the high cost associated with the construction and 
maintenance of a proton accelerator suitable for use in such contraband 
detection, it would be extremely beneficial to provide a single proton 
accelerator suitable for use in the generation of a gamma ray beam which 
may be used in multiple contraband detection stations. 
SUMMARY OF THE INVENTION 
The present invention specifically addresses and alleviates the 
above-mentioned deficiencies associated with the prior art. More 
particularly, the present invention comprises a multiple station gamma ray 
absorption contraband detection system. The contraband detection system 
comprises a proton source, e.g., a linear proton accelerator, and a target 
upon which protons from the proton source are incident. The target of the 
present invention comprises a disk formed of an alloy of beryllium which 
is configured to be rotatable within the proton beam. The disk provides a 
360 resonant gamma ray cone so as to facilitate the operation of plural 
detection stations simultaneously therewith. 
According to a preferred embodiment of the present invention, the plural 
contraband detection stations each utilize between approximately 45 
degrees and approximately 90 degrees, preferably approximately 53 degrees, 
of the gamma ray beam. As those skilled in the art will appreciate, four 
contraband detection stations can readily be accommodated when each 
station utilizes approximately 53 degrees of the 360 degrees resonant 
gamma ray cone. 
A conveyor is preferably utilized to transport a test article, i.e., 
baggage, into that portion of the gamma ray cone used by a particular 
station. At least one detector is configured to sense gamma rays which 
have passed through the test article. The conveyor is preferably 
configured so as to translate and rotate the test article within the 
proton beam, such that the proton beam passed through substantially all 
portions of the test article. 
A plurality of gamma ray detectors, preferably two horizontal rows of 
detectors generally defining an arc, are preferably utilized, so as to 
more efficiently scan the test article, thereby increasing performance. 
The use of such a plurality of gamma ray detectors further facilitates 
tomographic imaging, so as to further enhance reliability. 
According to the preferred embodiment of the present invention, the system 
also comprises a plurality of containers, preferably drums, into which the 
individual test articles are placed, so as to facilitate their being moved 
into the gamma ray cone at each detection station. Thus, a plurality of 
suitcases, preferably approximately 18, are placed into a drum and 
processed together, so as to increase the throughput of the system. 
A conveyor system preferably comprises at least one incoming conveyor belt 
for bringing each container to a position near the translation and 
rotation tables, and a first handler for each incoming conveyor belt for 
moving the container from the incoming conveyor belt to a selected one of 
the rotation and translation tables. At least one outgoing conveyor belt 
receives the scanned containers from the rotation and translation tables, 
via a second handler. Those skilled in the art will appreciate that 
various mechanical handling devices are suitable for transferring drums 
between a conveyor belt and a table. 
According to the preferred embodiment of the present invention, four tables 
disposed approximately 90 degrees apart from one another about a common 
center rotate and translate each container during the scanning process. 
Two incoming conveyor belts, disposed approximately 180 degrees apart from 
one another about the common center each bring the containers near two of 
the tables. The first handler associated with each of the incoming 
conveyor belts then moves an incoming container from the conveyor belt to 
a selected one of the two nearby tables. Four outgoing conveyor belts are 
preferably then utilized to remove the containers from the detection 
stations. Preferably, an operator at each station monitors the operation 
thereof and is notified, preferably via an audible signal and a computer 
monitor, when contraband is detected at that station. Alternatively, a 
single operator can monitor a plurality of such contraband detection 
stations. 
The target is formed so as to be generally disk shaped and preferably has a 
cavity formed therethrough within which water flows, so as to provide 
cooling therefor. According to the preferred embodiment of the present 
invention, the disk comprises two generally planar beryllium walls 
defining the cavity through which cooling water flows. The disk preferably 
comprises coatings of .sup.13 C and .sup.34 S so as to facilitate the 
detection of .sup.14 N and .sup.35 Cl via gamma ray absorption. 
These, as well as other advantages of the present invention will become 
more apparent from the following description and drawings. It is 
understood that changes in the specific structure shown and described may 
be made within the scope of the claims without departing from the spirit 
of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The detailed description set forth below in connection with the appended 
drawings is intended as a description of the presently preferred 
embodiment of the invention, and is not intended to represent the only 
form in which the present invention may be constructed or utilized. The 
description sets forth the functions and sequence of steps for 
constructing and operating the invention in connection with the 
illustrated embodiment. It is to be understood, however, that the same or 
equivalent functions may be accomplished by different embodiments that are 
also intended to be encompassed within the spirit and scope of the 
invention. The multiple station contraband detection system of the present 
invention is illustrated in FIGS. 2 through 11 which depict a presently 
preferred embodiment of the invention. FIG. 1 depicts the use of a 
contemporary cylindrically configured target in a single station 
contraband detection system. 
Referring now to FIG. 1, according to contemporary methodology, a proton 
beam 10 is incident upon a target 12 which is configured generally as a 
cylinder. The cylinder is typically comprised of copper or copper alloy 
having coatings of .sup.13 C and .sup.34 S, so as to produce gamma rays 
which are absorbed by nitrogen and chlorine. The cylinder is rotated so as 
to provide thermal dissipation and thereby prevent heat buildup at any 
particular location thereon. The proton beam 10 excites a 360 degrees fan 
of gamma radiation 14 having a useful dispersion angle or field of view of 
approximately 53 degrees. In the prior art, the rotating target axis is 
tilted so that 53 degrees of gamma rays are reflected by the target. The 
gamma ray fan is only usable over about 53 degrees due to scattering and 
attenuation covered by the target structure. As those skilled in the art 
will appreciate, a field of view of 53 degrees is only sufficient to 
provide for the scanning of a single container or drum 16 having a 
plurality of separate test articles or bags 18 contained therein. The drum 
16 is rotated within the field of view of the gamma radiation 14 about the 
axis 20 thereof and is also translated up and down along the axis 20 
thereof, so as to insure the complete and reliable detection of contraband 
contained within the baggage 18. An array of gamma ray detectors 22 
measures the intensity of the gamma rays after they have passed through 
the rotation and translation drum 16. 
Thus, as the drum 16 is rotated and translated, contraband such as illegal 
drugs and explosives pass through the path of the gamma rays 14. The gamma 
rays 14 are selectively absorbed by compounds containing elements such as 
chlorine and nitrogen, such that the gamma rays 14 are attenuated prior to 
being sensed by gamma ray detectors 22. 
Thus, an operator is notified as to the possibility of baggage 18 within 
the drum 16 containing contraband. The baggage 18 may then be manually 
inspected in order to verify the presence of contraband. 
However, one problem associated with such contemporary contraband detection 
methodology is the cost per article inspected. Since a large proportion of 
the costs associated with the operation of such a gamma ray absorption 
contraband detection system are associated with the construction and 
maintenance of the linear accelerator and target, it would substantially 
reduce the cost per article tested if the number of detection stations for 
a particular linear accelerator could be substantially increased. However, 
due to the contemporary use of a target configured as a cylinder, the 
angle of dispersion of gamma rays from the target is strictly limited, 
such that each linear accelerator can support only a single detection 
station. 
Referring now to FIG. 2, according to the present invention a target 100 is 
configured so as to be generally disk shaped. It produces a resonant cone 
102 of 360 degrees when struck by proton beam 101. The resonant cone 102 
of 360 degrees may be easily divided into four portions, each portion 
having a field of view of approximately 53 degrees, so as to facilitate 
detection at four separate stations 104 simultaneously. 
Referring now to FIG. 3, the angle with respect to the normal 103 (which 
defines the sharpness of the resonant cone) at which the 360 degrees 
resonant cone is formed is dependent upon which target coating, i.e., 
.sup.13 C or .sup.34 S, is excited. This in turn is dependent upon the 
energy of the proton beam, as discussed below. Thus, the proton beam 101 
striking the disk-shaped target 100 produces either a resonant cone having 
an angle of 80.66 degrees for the detection of nitrogen or a resonant cone 
having an angle of 82 degrees for the detection of chlorine. 
The linear accelerator (220 of FIGS. 4 and 5) is configured so as to 
provide a DC current .gtoreq.10 mA and so as to provide a stream of 
protons at either 1.75 MeV or 1.89 MeV.+-.12 KeV. Proton beam emittance is 
preferably 0.12 .pi.millimeter milliradians (rms). The use of a 1.75 MeV 
proton beam excites an 80.7 degree resonant gamma ray cone from the .sup.3 
C coating of the target for the detection of nitrogen, while the use of a 
1.89 MeV proton beam excites an 82 degree resonant gamma ray cone from the 
.sup.34 S coating of the target for the detection of chlorine. Thus 
depending upon which proton beam energy is selected (and consequently 
which target coating is excited), the resultant resonant gamma rays are 
preferentially absorbed by either nitrogen or chlorine, thereby 
facilitating their detection. 
Since the angles at which the gamma rays are produced by the target are so 
close (80.7 degrees for nitrogen and 80.66 degrees for chlorine), a common 
array of segmented gamma ray detectors may be utilized to detect gamma 
rays passing through the drum 16, as discussed in detail below. 
According to the preferred embodiment of the present invention, the target 
100 comprises two spaced apart, generally parallel walls 102 formed of 
beryllium having a single front surface coated with .sup.13 C and .sup.34 
S. A cavity 104 is formed intermediate the two walls 102 to accommodate 
water flow therein for cooling the target 100. The target is preferably 1 
to 3 feet in diameter and 1/8 to 1/2 inch in thickness. 
Referring now to FIG. 4, the present invention generally comprises a beam 
production subsystem 200 for providing gamma rays to each of the 
contraband detection stations 202, 204, 206, and 208. An operational 
control and support system 210 facilitates operation of the multiple 
station contraband detection system as described in detail below. The 
detector and data acquisition subsystem 212 collects data from the 
detector arrays 106 and provides the same to image construction and 
interpretation subsystem 214 for processing. 
The beam production system 200 comprises the proton accelerator 220 and the 
target 100. The proton accelerator provides a beam of protons 101 having 
energies of either 1.75 MeV or 1.89 MeV, so as to facilitate the detection 
of either nitrogen or chlorine, respectively. Vacuum services 222 provide 
the vacuum necessary for the generation of the proton beam 101 and 
communication of proton beam 101 to the target 100. Cooling services 224 
provide the required cooling for the proton accelerator 220. Beam 
diagnostics 226 monitor the proton beam 101 so as to assure proper 
operation of the proton accelerator and auxiliary equipment. 
The operational control and support section 210 comprises accelerator 
control 230 for providing control of the proton accelerator 220. A safety 
system 232 having a radiation monitoring subsystem 234 monitors safety 
related items. Power distribution 236 provides power to the proton 
accelerator 220 and support equipment. Master control and user interface 
238 provides the primary means for the operator to control the multiple 
station contraband detection system of the present invention. Container 
control 240 controls movement of the drums 273 (FIG. 8) on the conveyors 
301 and 303, and the rotation and translation tables 272, as discussed in 
detail below. Container handling 242 facilitates movement of the 
containers from the incoming conveyor belts 301 to the rotation and 
translation tables 272 and from the rotation and translation tables 272 to 
the outgoing conveyor belts 303. 
Detector arrays 106 preferably comprise bismuth germanium oxide (BGO)gamma 
ray detectors for sensing the intensity of the gamma rays after they have 
passed through the baggage contained within the drums 273. According to 
the preferred embodiment of the present invention, two adjacent horizontal 
rows of such detectors define the array 106. This has been found to 
provide sufficient resolution so as to reliably indicate which bag 
contained in a drum 273 most likely contains sensed contraband. 
The detection and data acquisition subsystem 212 comprises data acquisition 
electronics 250 for receiving the outputs of the detector arrays 106 and 
for conditioning the same. 
Image construction and interpretation subsystem 214 utilizes recognition 
algorithms 252 for determining the likelihood that a sensed detector 
signal indicates the presence of contraband. The recognition algorithms 
252 provide an output indicative of the sensed signals to imaging and 
display system 254 so as to alert an operator of the likely presence of 
contraband. Data storage and processing 256 provides for the storage of 
data indicative of likely contraband being contained within a particular 
piece of baggage, for future evidentiary purposes. 
Referring now to FIG. 5, a plurality of individual contraband detection 
stations 300 are preferably disposed upon one floor 302 of a building 
while the proton accelerator 220 is located upon the floor below 304. A 
work station 306 allows an operator to control and monitor the proton 
accelerator 220 on the lower floor and a work station 308 allows an 
operator to control and monitor the contraband detection system 300 on the 
upper floor 302. Optionally, a plurality of operators may be accommodated 
for the proton accelerator and/or the contraband detection stations. For 
example, four work stations 308 may be provided, one for each contraband 
inspection station. 
Protons provided by accelerator 220 travel through proton conduit 260, bend 
262, and proton conduit 264, and are then directed upon target 100 (better 
shown in FIGS. 6 and 7). The target 100 is disposed within vacuum vessel 
266 comprised of gamma ray transparent beryllium walls 268. 
Drums 273 disposed upon rotation and translation tables 272 are rotated 
about their axis and also move up and down in order to assure that they 
are adequately scanned by gamma rays 208 produced by the impact of the 
proton beam 101 upon the target 100. 
A ball screw linear drive 274 moves each rotation and translation table 272 
up and down while a rotation motor 276 effects rotation of each rotation 
and translation table. Gamma ray detectors 106 sense the intensity of the 
gamma rays 208 after they have passed through the drum 272. As discussed 
in detail below, contraband contained within baggage contained in the 
drums 273 selectively absorbs gamma rays so as to vary the sensed 
intensity thereof and thereby provide an indication as to the presence of 
such contraband. The outputs of the gamma ray detectors 106 are provided 
to data acquisition electronics 250 (FIG. 4) and the output of the data 
acquisition electronics 250 is provided to the recognition algorithms 252 
and the data storage and processing system 256. 
Referring now to FIGS. 6 and 7, the target 100 is generally configured as a 
disk which is rotatable about its center via shaft 402, which is rotatable 
via rotation motor 404. Rotation motor 404 and shaft 402 are preferably 
mounted upon translation platform 406 which is movable via translation 
motor 408. Thus, the target 100 can be rotated and translated so as to 
vary the impact point 410 at which the proton beam 101 strikes the target 
100. In this manner, localized heat buildup is minimized since the proton 
beam is not allowed to impact upon any particular portion of the target 
100 for a prolonged period of time. 
The target is disposed within vacuum vessel 266, having beryllium side wall 
268. The beryllium side wall 268 is transparent to the gamma radiation 
generated when the proton beam 101 strikes the target 100. Thus, the gamma 
radiation is free to pass through the test articles to be incident upon 
gamma ray detectors 106. 
Referring now to FIG. 8, the conveyor and container handling system for 
transporting drums 273 to the rotation and translation tables 272 for, 
positioning the drums 273 upon the rotation and translation tables 272, 
for removing the drums 273 from the rotation and translation tables 272, 
and for transporting the drums 273 away from the rotating and translation 
tables 272, is illustrated. 
According to the preferred embodiment of the present invention, the 
multiple station gamma ray absorption contraband detection system 
comprises four individual detection stations 300. Two input conveyor 301 
are configured such that each input conveyor 301 services two adjacent 
detection stations 300. Each detection station 300 has a dedicated output 
conveyor 303. 
The drums 273 are transported by the input conveyors 301 to a position 
proximate to rotation and translation tables 272. Drum handling equipment, 
not shown, then transfers each drum from the input conveyor 301 to a 
selected one of the two adjacent rotation and translation tables 272. 
Preferably, the handling equipment alternates between the two rotation and 
translation tables 272 such that one drum is placed upon that rotation and 
translation table 272 to the drum's 273 left, then the next drum is placed 
upon the rotation and translation table 272 to the drum's 273 right, and 
the process repeats indefinitely. 
Once a drum 273 is positioned upon a rotation and translation table 272, 
the table 272 then begins to rotate and translate in a manner which 
facilitates accurate and reliable scanning of the items contained within 
the drum 273. Once scanning process is complete, handling equipment (not 
shown) then moves the drum 273 from the rotation and translation table 272 
to a dedicated output conveyor 303 which then moves the drum 273 away from 
the contraband detection station. Guides 440 stabilize and restrain the 
drums 273 as they are loaded onto the rotation and translation tables 272 
and removed therefrom. 
The contraband detection process is preferably monitored at a dedicated 
work station 308 by a dedicated operator. 
Referring now to FIGS. 9 and 10, testing has shown that illegal drugs, as 
indicated by the small solid triangles, and explosives, as indicated by 
the small circles, tend to be positioned apart from common material, as 
indicated by small squares, when plotted on a nitrogen density versus 
total density graph. Similarly, drugs and explosives tend to be located at 
different positions from other materials on a chlorine density versus 
total density plot. These differences in the responses of common 
materials, explosives, and drugs to gamma rays facilitates the reliable 
detection of such contraband materials. The recognition algorithms 252 
check to see if the response of a test article is located at the position 
on the nitrogen density versus total density and chlorine density versus 
total density plots which is indicative of such contraband. Then if 
contraband is indicated, the baggage is manually inspected. 
Referring now to FIG. 11, as the time per scan slice increases, the 
detection rate increases, thereby providing more reliable and effective 
detection of contraband. As would be expected, the false alarm rate 
decreases with increased time per scan. 
It is understood that the exemplary multiple station gamma ray absorption 
contraband detection system described herein and shown in the drawings 
represents only a presently preferred embodiment of the invention. Indeed, 
various modifications and additions may be made to such embodiment without 
departing from the spirit and scope of the invention. For example, various 
different physical configurations of the conveyor and handling system are 
contemplated. Additionally, those skilled in the art will appreciate that 
fewer or more than four detection stations may be accommodated by the 360 
degrees resonant gamma ray cone of the present invention. Thus, these and 
other modifications may be obvious to those skilled in the art and may be 
implemented to adapt to the present invention for use in a variety of 
different applications.