Patent Number: 
Section: claims

1. A system for detecting concealed threats in an object by simultaneously performing active and passive radiation detection, the system comprising:an X-ray source with a modulating device to produce a pencil beam of radiation for scanning the object, said modulating device configured to block the pencil beam at regular intervals;a distance sensor adapted to emit a beam of light and adapted to determine a plurality of times for said light to scatter off a plurality of surfaces of said object and return to said sensor, wherein said plurality of times are indicative of a plurality of distances from said distance sensor to said plurality of surfaces;a detector module for generating signals indicative of radiation backscattered by the object when the object is scanned with the pencil beam of radiation and for generating signals indicative of passive radiation that is emitted from threats within said object when the pencil beam of radiation is blocked, wherein said detector module comprises at least one detector; anda controller configured to cause said system to measure backscattered radiation only when the x-ray pencil beam is on, and to measure only passive radiation when the x-ray pencil beam is blocked, wherein said controller further uses the plurality of distances to implement an adaptive region based averaging method such that a size of each region is a function of a distance to the X-ray source thereby resulting in signals from regions far from the X-ray source being averaged over a larger region. 2. The system of claim 1 wherein the detector module comprises a detector array, wherein said detector array is capable of detecting both backscattered x-rays and passive radiation. 3. The system of claim 1 wherein the passive radiation detector is at least one of a gamma ray detector, a neutron detector, or a gamma-neutron detector. 4. The system of claim 3 wherein said neutron detector is used to passively measure neutrons simultaneously with backscatter radiation and passive gamma rays. 5. The system of claim 1 wherein the modulating device comprises a disc with at least one pinhole. 6. The system of claim 1 wherein the modulating device comprises a cylindrical chopper with at least one helical slit. 7. The system of claim 1 wherein the modulating device is rotated to produce a pencil beam that is blocked at regular intervals and wherein said system does not illuminate the object with radiation when the pencil beam is blocked. 8. A system for detecting concealed threats in an object by simultaneously performing active and passive radiation detection, the system comprising:an X-ray source with a modulating device to produce a pencil beam of radiation for scanning the object;a distance sensor adapted to generate a plurality of distances from said distance sensor to portions of said object;a detector module comprising an X-ray detector for detecting radiation backscattered by the object when scanned with the pencil beam and generating backscatter signals indicative thereof;a passive radiation detector for detecting radiation emitted from threats inside said object when the pencil beam is switched off and generating passive radiation threat signals indicative thereof; anda controller for switching the X-ray source on and off at regular intervals and, wherein said controller further uses the plurality of distances to implement an adaptive region based averaging method such that a size of each region is a function of a distance to the X-ray source thereby resulting in signals from regions further from the X-ray source being averaged over a larger region. 9. The system of claim 8 further comprising control electronics to measure backscattered radiation only when the beam is on, and to measure only passive radiation when the x-ray pencil beam is off. 10. The system of claim 8 wherein the detector module comprises a detector capable of detecting both backscattered x-rays and passive radiation. 11. The system of claim 8 wherein the passive radiation detector is at least one of a gamma ray detector, a neutron detector, or a gamma-neutron detector. 12. The system of claim 8 wherein the controller is further adapted to use the plurality of distances to geometrically correct an image of the object. 13. A method for detecting concealed threats in an object by simultaneously performing active and passive radiation detection, the method comprising:modulating an X-ray source to produce a pencil beam of radiation for scanning the object, such that the pencil beam is blocked at regular intervals;measuring distances to a plurality of surfaces of said object;detecting radiation backscattered by the object when scanned with the pencil beam;detecting passive radiation emitted from threats inside said object when the pencil beam is blocked; andusing a filter to implement an adaptive region based averaging method using said distances such that a size of each region is a function of a distance to the X-ray source thereby resulting in signals from regions far from the X-ray source being averaged over a larger region. 14. The method of claim 13 wherein radiation is detected by using a dual-purpose detector adapted to detect both backscattered x-rays and passive radiation. 15. The method of claim 13 wherein the passive radiation is detected using a separate passive radiation detector that is at least one of a gamma ray detector, a neutron detector, or a combined gamma-neutron detector. 16. The method of claim 13 wherein said neutron detector passively measures neutrons simultaneously with backscatter radiation and passive gamma rays. 17. The method of claim 13 wherein only backscattered radiation is measured when the x-ray pencil beam is on, and only passive radiation is measured when the beam is blocked. 18. The method of claim 13 wherein the beam is modulated using a modulating device that comprises a disc with at least one pinhole. 19. The method of claim 13 wherein the beam is modulated using a modulating device that comprises a cylindrical chopper with helical slits. 20. The method of claim 13 wherein the modulating device is rotated to produce a pencil beam and is adapted to block said pencil beam at regular intervals.