HK1082035B - Radiographic equipment - Google Patents

Description

Radiographic apparatus

Technical Field

The present invention relates to a radiographic apparatus. In particular, the present invention relates to radiographic equipment for detecting concealed objects, substances and materials. For example, the present invention may be used to detect weapons, explosives, contraband, drugs, or other items, substances, and materials that are concealed in objects such as air parcels, air freight, or marine containers.

Background

X-ray, gamma ray and neutron based techniques have been proposed to address this problem (hussei, e., 1992, Gozani, t., 1997, An, j.et al, 2003). The most widely used technique is the X-ray scanner, which forms an image of the object under examination by measuring the transmission of X-rays from a source through the object to a spatially segmented detector. Dense, higher atomic number materials, such as metals, attenuate X-rays very strongly. Thus, X-ray scanners are ideal for detecting objects such as guns, knives and other weapons. However, X-rays provide little ability to distinguish between organic and inorganic components. With X-rays, the separation of illegal organic materials, such as explosives or narcotics, from common benign organic materials is not possible.

Component identification systems are being developed for verifying goods transported on pallets. A system known as NELIS (neutron component analysis system) utilizes a 14MeV neutron generator and 3 gamma ray detectors to measure induced gamma rays from cargo (Dokhale, p.a. et al, 2001; Barzilov, a.p., Womble, p.c. and vouropoulos, g., 2001). NELIS is not an imaging system and is used in conjunction with an X-ray scanner to assist in identifying gross compositional anomalies.

Pulsed Fast Neutron Analysis (PFNA) cargo inspection systems have been developed (Gozani, t., 1997, Sawa et al, 1991) and commercialized by the Ancore Corporation. The PFNA system uses a collimated beam of nanosecond pulsed fast neutrons and measures the spectrum of the resulting gamma rays. The PFNA method allows the ratio of key organic components to be measured. Nanosecond pulsed fast neutrons are required to facilitate the determination of the location of specific regions contributing to the measured gamma ray signal by time-of-flight spectroscopy. In practice, this technique is limited by the very expensive and complex particle accelerator, limited neutron source intensity and low gamma ray detection efficiency, and the resulting slow scan speed.

Neutron radiography systems have the advantage of directly measuring transmitted neutrons and are therefore more efficient than techniques that measure secondary radiation, such as neutron-induced gamma rays. Fast neutron radiography has the potential to determine line-of-sight "organic" images of objects (Klann, 1996). In contrast to X-rays, organic materials, especially those with a high hydrogen content, subject neutrons to very strong attenuation.

Fast neutron and gamma ray radiography systems were developed by Rynes et al (1999) to supplement PFNA. In this system, nanosecond-pulsed fast neutrons and gamma rays from an accelerator are transmitted through an object, and detected neutron and gamma ray signals are separated by arrival time. The resulting system is claimed to combine the advantages of both radiographic and PFNA systems. However, it is limited to very expensive and complex particle accelerators.

Bartle (1995) proposed the use of fast neutron and gamma ray transmission techniques (Millen et al, 1990) to detect the presence of contraband in luggage and the like. However, this technique has not been used for imaging, and its practical application to contraband detection has not been studied.

Mikerov, v.i. et al (2000) investigated the feasibility of fast neutron radiography using a 14MeV neutron generator and a fluorescent screen/CCD camera detection system. Mikerov found that these applications were limited by the low detection efficiency of 2mm thick phosphor screens for neutrons, and the high sensitivity of the phosphor screens to X-rays produced by neutron generators.

Neutron radiography systems using a 14MeV generator and thermal neutron detection are commercially available (Le tourneuro, p., Bach, p.and Dance, w.e., 1998). However, the fact that fast neutrons slow down (thermalization) before performing radiography limits the size of the object being imaged to a few centimeters. There are no commercially available fast neutron radiography systems that address fast neutron detection.

Most work on neutron radiography is done in the laboratory using neutrons from nuclear reactors or particle accelerators, which are not suitable for cargo handling applications (Lefevre, h.w., et al, 1996, Miller, t.g., 1997, Chen, g.and Lanza, r.c., 2000, Brzosko, j.s.et al, 1992).

To improve the ability of fast neutron radiography systems to provide discrimination between multiple organic materials, systems using multiple neutron energy sources and detectors with means for discriminating between different neutron energies have been proposed (Chen, g.and Lanza, r.c., 2000, Buffler, 2001). A key drawback of these systems is that they rely on sophisticated energy discriminating neutron detectors and/or they use sophisticated high energy accelerator based neutron sources.

Perion et al (Perion, 2000) propose scanners using either a high energy (MeV) X-ray Bremsstrahlung (Bremsstrahlung) source or a radioisotope source. By adjusting the average source energy by means of rapidly inserting and removing filters of low atomic number, or by measuring the energy of the detected X-rays, the transmission through the scanned object at two different X-ray energies can be measured, in which case Compton scattering dominates, and in which case pair-generation (pair-production) is significant. This information can be used to infer the material density and the average atomic number of the material in each pixel of the scanned image. The main drawback of this solution is the low contrast between the different components, even when very high energy X-ray sources are used. The cost of Perion detector arrays is also very high. Alternatively Perion suggests that measurement of the transmission of X-rays and neutrons (either directly in the bremsstrahlung target or by insertion of neutron-generating filters) can yield similar information. The main drawback of this method is that the energy of the neutrons generated via the (gamma, n) reaction is low. This limits the ability of neutrons to pass through thick cargo and increases the difficulty of adequately detecting transmitted neutrons. In particular, the disclosed stacked scintillator detector is unlikely to be able to recognize neutrons when there are many strong X-ray beams. A disadvantage of dual-energy X-ray and X-ray/neutron schemes is that X-rays and neutrons cover a wide energy range. This means that it is not possible to model transmission using simple exponential relationships and it is not possible to directly extract quantitative cross-sectional information that can be used for material identification.

Disclosure of Invention

The present invention is a radiographic apparatus, including:

a source of substantially single-energy fast neutrons produced by deuterium-tritium or deuterium-deuterium fusion reactions, the source of single-energy fast neutrons comprising a sealed tube generator or similar generator for producing neutrons;

an X-ray or gamma ray source of sufficient energy to substantially pass through an object to be imaged;

an alignment block which surrounds the source of neutrons and the source of X-rays and gamma-rays and which provides one or more slots for emitting a substantially fan-shaped radiation beam;

a detector array comprising a plurality of individual scintillator pixels for receiving radiation energy emitted from the source and converting the received energy into light pulses, the detector array being aligned with the fan-shaped radiation beam emitted from the source collimator and collimated to substantially prevent radiation not directly transmitted from the source from reaching the array;

a conversion means for converting the light pulse generated in the scintillator into an electric signal;

a transport device for transporting the object between the source and the detector array;

computing means for determining from the electrical signals the attenuation of the neutron beam and the X-ray or gamma-ray beam and generating an output representative of the mass distribution and composition of an object placed between the source and the detector array; and

a display device for displaying an image based on the mass distribution and composition of the scanned object.

An advantage of the present invention is that neutrons are substantially of a single energy. Thus, neutron transmission can be modeled using a simple exponential relationship, and moreover, information useful for material identification is obtained more accurately.

The apparatus according to at least one embodiment of the present invention has the added advantage of measuring transmitted neutrons directly, and is therefore more efficient when compared to prior art systems that measure secondary radiation, such as neutron-induced gamma rays.

The radiographic equipment may utilize one or more neutron energies. In the example of dual neutron energy technology, the radiographic apparatus may utilize two tubes, one for producing neutrons of substantially 14MeV through the deuterium-tritium fusion reaction and a second for producing neutrons of substantially 2.45MeV through the deuterium-deuterium fusion reaction. Measurement of neutron transmission at the second energy can be used to enhance the capabilities of single energy transmission techniques.

The X-ray or gamma-ray source may include a source of radioisotopes, such as⁶⁰Co or¹³⁷Cs having sufficient energy to substantially pass through the object to be imaged.⁶⁰Co or¹³⁷The Cs source may have an energy of about 1MeV, although other energies may be used depending on the source. Alternatively, an X-ray tube for producing bremsstrahlung radiation, or an electron linac may be used.

Calibration of the X-ray or gamma ray source and the neutron source is advantageously used to minimize scatter. Moreover, proper calibration of the source and detector ensures a narrow beam geometry and, therefore, greater accuracy in determining neutron and gamma ray attenuation through the object. Moreover, a highly collimated fan beam provides increased radiation safety. The calibration block may be made of thick paraffin, thick concrete, iron sand concrete shielding block, steel, lead, etc. Similarly, the or each detector array may be housed within a detector shield having a slot to facilitate providing calibration. The detector calibration shield may be made of iron and may have a thickness greater than about 100 mm. The width of the slot may be selected to allow neutrons and gamma rays to pass directly from the source to the detector and to protect the detector array from scattered radiation. The detector slots can have approximately the same width as the detector array. The source collimator slot may be narrower.

The detector array may include one or more scintillator pixel columns.

The same detector array is capable of measuring neutrons as well as X-rays or gamma rays. Energy discrimination may be used to distinguish the signals, or the detector may operate sequentially on neutrons as well as X-rays or gamma rays. An advantage of using the same detector array for measuring neutrons as well as X-rays or gamma-rays is that a reduction in the cost of the detector array can be achieved.

Optionally, separate detector arrays may be used to measure neutrons and X-rays or gamma-rays, respectively, with or without separate neutron detector calibrators and X-ray or gamma-ray detector calibrators.

The scintillators can be selected such that their spectral response closely matches the photodiode. The scintillators can further be surrounded by masks to cover at least a portion of each scintillator, each mask having a first reflective surface for reflecting escaping light pulses back to the scintillator. The mask will have an opening to allow the light of the scintillator to be detected by the photodiode. The mask may include a layer of PTFE tape and/or Tyvek paper. Advantageously, the efficiency of plastic scintillators with masks for neutrons may be greater than 10%. The material surrounding the scintillator is used to ensure that light escaping the scintillator is reflected back to be detected. In examples where each detector array includes an orange light emitting plastic scintillator and silicon photodiodes, the device may advantageously have a higher performance efficiency, allowing images to be acquired more quickly. Moreover, the device can be manufactured at relatively inexpensive cost.

Silicone oil, GE-688 grease, silicone, optical adhesives such as eljen ej-500 adhesive, and the like, may be used to optically couple the photodiodes to the respective scintillators.

In case the radiographic apparatus comprises a single detector array for measuring neutrons as well as X-rays or gamma-rays, the scintillator may be a plastic scintillator or a liquid scintillator.

In another example, where the radiographic equipment includes two neutron sources and an X-ray or gamma ray source, the scintillator may be a plastic or liquid scintillator. In this example, the scintillator may be coupled to a photomultiplier tube.

In case the radiographic equipment comprises a discrete neutron and gamma ray detector array, the neutron scintillator may preferably be a plastic scintillator or a liquid scintillator, while the gamma ray scintillator may be a plastic scintillator, a liquid scintillator or an inorganic scintillator, such as cesium iodide, sodium iodide or bismuth germanate. Alternatively, the X-ray or gamma-ray detector may be an ionization chamber.

The radiation receiving face of each scintillator, or "area" of each scintillator, corresponds to a single pixel. The area of each scintillator may typically be less than about 20mm by 20 mm. The smaller area results in improved spatial resolution.

The thickness of each scintillator may be in the range of 50 to 100mm, and may be a function of detection efficiency and light collection efficiency. In examples where the object to be imaged is a pallet or ULD (such as is typically used in airport environments), the radiation receiving face of the scintillator array may have dimensions of about 120mm x 3300mm and may comprise about 1000 pixels. At or near 10¹⁰The content of a single ULD can be imaged in a time period of about 1 minute with a combination of neutron source energies of 14MeV neutrons per second.

Alternatively, separate neutron and gamma ray scintillators can be used, including, for example, about 1000 neutron pixels and about 500 gamma ray pixels. In practice, the gamma ray pixels can be made smaller than the neutron pixels, which advantageously provides a high resolution aerial image.

In another example, the conversion device may include a photomultiplier tube and a wavelength shifting optical fiber (WSF). In this example, light from a row or column of scintillator rods may be collected by the WSF and transmitted to the multi-anode photomultiplier tubes. By indexing the rows and columns that produce the light pulses, the scintillator rods that intercept the radiation can be inferred.

The conversion means may comprise a low noise and high gain amplifier for amplifying the output signal. The conversion means may comprise a computer to perform image processing and display the image to the operator on a computer screen.

The detector may be temperature controlled to reduce noise and improve stability. For example, the photodiode and preamplifier may be cooled to about-10 ℃ or less.

In one example, when scanning an object to be imaged, one or more outputs are obtained by measuring, for example, the transmission of 14MeV neutrons through the object and the transmission of 1MeV X-rays or gamma rays through the object. For dual energy neutron scanning, the transmission of 2.45MeV neutrons through the object is also measured. The invention is not limited to the use of such energy.

In the case where a single detector array is used for receiving radiation energy from an X-ray or gamma ray source and a neutron source, the object may be scanned more than once.

In the case where separate detector arrays are used for receiving radiation energy from the neutron source and the X-ray or gamma-ray source, the output signals may comprise a first output from the first scintillator array and a second output from the second scintillator array, wherein the first output is related to the neutron count rate in each pixel position of the detector and the second output is related to the X-ray or gamma-ray count rate in each pixel position of the detector.

Each source input may be processed separately. For each pixel of the array, a simple scintillation spectrum may be acquired separately to infer the count rate of neutrons and X-rays or gamma rays with respect to each pixel. This information can then be combined to form a complete two-dimensional neutron image and a complete two-dimensional X-ray or gamma ray image. The resulting image may have a vertical resolution determined by the pixel size, and a horizontal resolution determined by the pixel size and the frequency with which the array is read out.

The computer can also perform automatic material identification. For example, the transmission output may be converted to a mass attenuation coefficient image for each pixel for display on a computer screen, with different pixel values mapped to different colors. In particular, a mass attenuation coefficient image may be obtained from a count rate measured using the transmission of each of 14MeV neutrons and X-rays or gamma rays, or 14MeV neutrons, 2.45MeV neutrons, and X-rays or gamma rays.

Mass attenuation coefficient image analysis allows identification of a variety of inorganic and organic materials. The analysis may include forming a cross-sectional ratio image between the pair of mass attenuation images. Depending on whether a single neutron source or two neutron sources are utilized, a cross-sectional ratio image may be formed from the mass attenuation coefficient images of the neutron source and the X-ray or gamma ray source, or from the mass attenuation coefficient images of the first and second neutron sources, and the first or second neutron source, and the X-ray or gamma ray. For example, 14MeV neutrons and X-rays or gamma rays, 14MeV neutrons and 2.45MeV neutrons, and 2.45MeV neutrons and X-rays or gamma rays. Advantageously, the ratio is independent of the mass of the object.

The proportions with which the cross-sectional ratio images are combined may be operator adjusted to maximize contrast and sensitivity in the images for a particular inspection object.

An image may be formed that is a combination of the two cross-sectional ratio images.

Two regions in an image containing a first substance may be identified, but only one region may contain a second substance. By performing the cross-sectional subtraction, the image of the first substance can be effectively removed, leaving an image of the second substance available for identification. The quality of the second substance may be obtained from the X-ray or gamma-ray transmission data.

In one example, the neutron source and the detector are stationary and the transport is configured to move the object in front of the neutron source and the gamma ray source. In another example, the object may be stationary and the conveyor is configured to move the source and detector synchronously on one of the two sides of the object. In another example, multiple sets of detectors may be positioned around a centrally positioned source to allow scans of multiple discrete objects to be acquired simultaneously. This has the advantage of increasing throughput. In this example, the transport apparatus may be configured to move the objects between the neutron source and the respective detectors. Alternatively, the source and detector may be rotated around the object to be examined to allow multiple views to be obtained.

The rate at which an object can move in front of a neutron source, or a neutron source and an X-ray or gamma-ray source, depends in part on the intensities of the neutron and gamma-ray sources. The intensity of a single 14MeV neutron source may have a value of 10¹⁰On the order of neutrons per second, which is in fact as high as possible in order to improve counting statistics.

The rate at which the object can be moved in front of the neutron source and the X-ray or gamma-ray source further depends on the number of scintillators and the radiation receiving faces of the scintillator array. Further, the length of the array depends in part on the length of the object to be imaged.

The object may be scanned between the neutron and gamma ray sources and the detector and may pass through a shielding channel. The conveyor may include a pair of rails for positioning a trolley or platform upon which the objects may be transported. Alternatively, the conveying means may comprise a conveyor belt or other similar arrangement for conveying or dragging objects through the passageway. The conveyor may be automated whereby the objects are smoothly transported in front of the neutron source at a controlled uniform rate.

The invention may also be applied to the non-invasive inspection of marine cargo, air cargo containers (ULDs) or smaller containers or packages, as well as the detection of contraband, explosives and other objects, substances and materials. It may provide improved features with respect to illicit materials, such as organic materials in a predominantly inorganic matrix, and provide detection and identification for specific classes of organic materials. It is particularly useful for detecting explosives, drugs and other contraband items concealed in air parcels, air or sea containers.

It is a further advantage of at least one embodiment of the present invention that the use of a neutron generator for generating neutrons is capable of being turned on and off.

It also provides increased automation of the inspection process while reducing reliance on human operators.

Moreover, it may provide a fast scan rate, whereby a high throughput may be achieved. It is simple, low cost, and uses a safe radiation source; and it is a simple, low cost radiation detection system. Which can operate at high measurement rates and low false alarm probabilities.

Brief Description of Drawings

Several examples of the invention will now be described by reference to the accompanying drawings, in which:

fig. 1 is a perspective view of a radiographic apparatus;

FIG. 2 is a schematic diagram of one module of a detector array of a radiographic device;

FIG. 3 is a bar graph of calculated ratios R, i.e., 14MeV neutrons vs. explosive materials for large quantities of benign, drug and explosive materials⁶⁰The ratio of the mass attenuation coefficients of Co gamma rays;

FIG. 4 is a plot of the calculated ratio R, i.e., 14MeV neutrons vs. compositional range⁶⁰The ratio of the mass attenuation coefficients of Co gamma rays;

FIG. 5a is a display output of a gamma ray scan of a motorcycle and FIG. 5b is a display output wherein the image is colorized according to a mass attenuation coefficient ratio R for 14MeV neutrons and gamma rays;

FIG. 6a is a schematic illustration of a selection of material samples and common objects disposed on a wooden rack; FIG. 6b is a display output of a gamma ray scan; FIG. 6c is a display output wherein the image is colorized according to the mass attenuation coefficient ratio R for 14MeV neutrons and gamma rays;

FIG. 7a is a schematic illustration of a selection of material samples, concealed contraband, alcohol, and simulated and actual explosives; FIG. 7b is a display output of a gamma ray scan; FIG. 7c is a display output wherein the image is colorized according to the mass attenuation coefficient ratio R for 14MeV neutrons and gamma rays;

FIG. 8a is a photograph of a ULD containing a mix of household electrical metal goods, concrete blocks and hidden contraband; FIG. 8b is a display output of a gamma ray scan; FIG. 8c is a display output wherein the image is colorized according to the mass attenuation coefficient ratio R for 14MeV neutrons and gamma rays; FIG. 8d is a further processing of FIG. 8c to emphasize the display output of the organic material;

FIG. 9a is a photograph of a ULD with a combination household item and concealed drug; FIG. 9b is a display output of a gamma ray scan; FIG. 9c is a display output wherein the image is rendered according to the mass attenuation coefficient ratio R for 14MeV neutrons and gamma rays R; FIG. 9d is a further processing of FIG. 9c to emphasize the display output of the organic material;

FIG. 10a is a photograph of a ULD with a combination household item and concealed drug; FIG. 10b is the display output of a gamma ray scan; FIG. 10c is a display output wherein the image is colorized according to the mass attenuation coefficient ratio R for 14MeV neutrons and gamma rays R; FIG. 10d is a further processing of FIG. 10c to emphasize the display output of the organic material;

FIG. 11 is an image of a mass of benign, drug and explosive materials with two cross-section ratios, i.e., a cross-section of 2.45MeV neutrons/14 MeV neutrons versus a cross-section of 14MeV neutrons/X-rays or gamma-rays;

FIG. 12a is a simulated count rate DT neutron image of a suitcase; FIG. 12b is a simulated count rate image of a neutron image in the DD for the suitcase; FIG. 12c is a simulated count rate X-ray image of a suitcase; FIG. 12d is a DT/X-ray sectional image and FIG. 12e is a DD/DT sectional image; and is

FIG. 13a is a simulated 14MeV neutron image of an air freight container; FIG. 13b is an X-ray image of the same container; and FIG. 13c is a combined image of the same container.

Best mode for carrying out the invention

Fig. 1 illustrates a general layout of a radiographic apparatus 10. The apparatus 10 includes two separate radiation generators, the first being an A-325MF Physics neutron generator with a D-T neutron emission module for generating a neutron energy source 12 having an energy of 14 MeV. The neutron generator is operated at a voltage of 80-110 kV. The second radiation generator is 0.82GBq (or 22mCi)⁶⁰A Co source 14 for generating a gamma ray source and located to the right of and adjacent to the neutron generator. Neutron generator and⁶⁰the Co source 14 is disposed within a source shield housing 16.

A 1600mm long and 20mm wide detector array is placed near the radiation source and housed within a detector shield housing 20. The detector array 18 (which is shown more clearly in figure 2) is constructed from 80 plastic scintillator rods 19 (only a portion of which is shown), each scintillator rod 19 having a radiation receiving area of 20mm x 20mm and a length of 75 mm. The radiation receiving area of each scintillator rod 19 corresponds to a single pixel in the image frame. The term "image frame" is used to describe a two-dimensional array that contains the number of counts measured in each pixel that are accumulated over a fixed time interval. The scintillator bar 19 is made of an orange plastic scintillator in order to match the spectral response of the silicon photodiode 21 to the respective plastic scintillator. The photodiodes 21 are optically coupled to the respective scintillators 19 by an optical adhesive. A reflective mask is drawn over each orange scintillator rod and photodiode combination to minimize any loss of light from escaping the scintillator rod.

In the primary embodiment, scintillation light generated in the rod 19 by incident neutrons or X-rays or gamma rays is detected by a photodiode 21 attached to the end of the rod 19. In a first variation, light from a row or column of scintillators is collected by a wavelength-shifting optical fiber and transmitted to a photodiode. By indexing the rows and columns that produce the light pulses, the scintillator rods that intercept the radiation can be inferred. In a second variation, light from a number of scintillator rods is collected by wavelength shifting or transparent optical fibers and directed to position sensitive photodiodes or multi-anode photomultiplier tubes to allow multiple scintillator rods to be read out by a single detector. In a third variation, light from several rows or columns of scintillator rods is collected by wavelength shifting optical fibers and transmitted to position sensitive photodiodes or multi-anode photomultipliers. By indexing the rows and columns of light pulses produced, the scintillator rods that intercept the radiation can be inferred.

Since the respective photodiode 21 does not have internal gain, the signal conditioning electronics 23 include a preamplifier that is used in conjunction with a high gain amplifier in order to amplify the output signal with respect to neutrons and gamma rays.

The device 10 comprises a ULD 28 having a width of up to 2.5m and a height of 1.7 m. Each ULD 28 to be imaged rests on a platform 30, the platform 30 having runners for engaging a pair of rails 32. In fact, in an airport, ULDs can be scanned while they are mounted on their respective trolleys that are used to transport the ULDs within the airport. The ULDs and their trolleys may be driven onto a platform which traverses the radiation beam at a known speed. This will minimize the handling of ULDs in airports.

A further shield in the form of a channel 34 is provided. The channel 34 is long enough so that the device can be operated without the need for a door at either end. This maximizes the number of ULDs passing through the device 10.

Calibration cuts (not shown) are cut into the source and detector shields to define fan-shaped radiation beams, respectively, directed from the sources 12 and 14 to the radiation detector 18. The detector calibration cut-out 38 and the detector 18 extend over the entire height of the channel 34. Slots (not shown) are provided on the sides of the shield 34 which mate with the calibration cut-outs and serve to pass radiation from the sources 12, 14 to the detector 18.

Each of the shields 16, 20, and 34 attenuates and absorbs gamma rays and neutrons. The shielding materials used include concrete, iron and polyethylene. The radiation shields 16, 20 and 34 provide radiation protection for the operator of the equipment or other personnel in the vicinity thereof.

In operation, an object to be imaged is placed on the platform 30, and the platform 30 is then maneuvered through the tunnel 34. In the full-scale prototype scanner described herein, the platform 30 is typically operated at a speed that takes about 40 seconds of acquisition time per 10mm increment. This corresponds to a speed of 0.25 mm/sec; therefore, it takes about 21/2 hours to acquire an image of the entire ULD. In practice, the speed at which a ULD is conveyed through an apparatus can be increased by more than a factor of 100 by increasing the strength of the neutron source and by increasing the area of the detector array.

As the object passes through the channel 34, a scintillation spectrum is acquired separately for each element of the 80-pixel array. These spectra are read out and reset each time the platform 30 moves 10mm, and are used to infer the neutron and gamma ray count rates for each pixel. The information in each vertical band is then assembled to form a complete two-dimensional neutron and gamma ray image.

The resulting image has a vertical resolution of 20mm, determined by the pixel size, and a horizontal resolution of 10mm, determined by the frequency used to read out the 80-pixel array. As discussed below, deconvolution of this final image is performed to correct for any blurring that occurs as a result of the combination of the motion of the stage 30 and the 20mm width of the pixel during the scan.

It is assumed that the neutron and gamma ray intensities transmitted through the object and detected by a particular pixel of each image are I and respectively_nAnd I_gAnd the neutron and gamma ray intensities transmitted and detected in a particular pixel of each image without the presence of an object are I respectively_onAnd I_og。

Thus, the attenuation of a substantially single-energy fast neutron through an object of density ρ can be calculated using the following equation:

I_n/I_on＝exp(-μ₁₄ρx) (1)

similarly, the attenuation of a substantially single energy gamma ray through an object can be written as:

I_g/I_og＝exp(-μ_gρx) (2)

where μ 14 is the neutron mass attenuation coefficient at 14MeV, and μ_gIs the gamma mass attenuation coefficient. In this way, the mass attenuation coefficient ratio can be calculated directly:

R＝μ₁₄/μ_g＝In(I_n/I_on)/ln(I_g/I_og) (3)

where R is directly related to the composition of the object and which allows the identification of a wide variety of inorganic and organic materials and compositions.

Fig. 3 and 4 illustrate the ability of R to recognize a wide variety of inorganic and organic materials. Natural materials that are predominantly carbohydrate-based, such as cotton, paper, wood and many foods, proteins based on natural materials, such as wool, silk and leather, and synthetic organic materials, primarily polymers, can be widely recognized. As illustrated, inorganic materials, such as ceramics, porcelain, and metal objects, are readily distinguished from organic materials.

Gamma ray images carry a large portion of information about shape and density due to their higher count rate and lower background scatter. For each pixel in the image, a quantity is calculatedln(I_g/I_og) Which is proportional to the total mass per unit area of material along the line from the radiation source to the pixel in question. A "Mexican-hat" sharpening filter is applied to the image to improve the sharpness of objects and reduce the effects of motion and pixel size level blurring that affect the horizontal resolution of the image.

The pixel-by-pixel ratio of neutron and gamma ray images carries information about the average composition of each pixel, independent of the amount of intervening material.

Due to the relatively low count statistics in the neutron images, there is considerable pixel-by-pixel noise in the component images. Therefore, a 5 × 5 pixel gaussian smoothing filter is applied to the image. This reduces the resolution of the composition information in the final image, while it significantly improves the visibility of subtle variations in the composition of objects having dimensions greater than about 50 mm.

The results from 6 scans are shown in FIGS. 5-10. The gray scale images illustrate the results of a single gamma ray scan, as well as the results that can be obtained by a conventional X-ray scanner. Areas with little or no intervening material appear white, while denser material appears darker shades of gray. The color image combines gamma ray shape, and density information, as well as compositional information from the neutron/gamma ratio image. The density of the colors shows the density of the material, with white corresponding to no intervening material, and the denser regions having saturated colors. The color of a pixel corresponds to the R value for that pixel, with lower R values colored blue, intermediate values colored cyan-green-yellow, and higher values colored orange. The exact mapping between R-values and colors is different for each image, and the color scale is adjusted to show the maximum information in each case. For ULD scans, enhanced organic images are also presented. This emphasizes the organic image areas, which are colored yellow, orange and red.

Fig. 5a illustrates the result of a separate gamma ray scan of a motorcycle. FIG. 5b illustrates the shape and density information of gamma rays combined with compositional information from a neutron/gamma ratio image scan of a motorcycle. The image provides a good indication of the overall imaging capabilities of the device. In particular, fine details such as the front braking lines 52 are shown very clearly in fig. 5, even though they are much smaller than the 20mm pixel size. The metal frame 54 and engine 56 of the vehicle are shown in blue in FIG. 5 b; while the fuel 58 in the tank, rubber tires 60, plastic seat 62 and plastic lights are shown as orange. The oil 64 in the sump (immediately above the kickstand) appears as a green block when averaged with the metal surrounding it. In contrast, from a conventional gamma ray image, like FIG. 5a, it is difficult or impossible to discern between the oil 64 and the sump.

Fig. 6 a-6 c illustrate the selection of material samples and common objects to be arranged on a wooden rack. Again, as illustrated in fig. 6c, metals such as iron 66, lead 68, and aluminum 70 are shown as dark blue. Intermediate materials such as concrete 72, glass 74 (in computer display 75) and ceramic powder (alumina, Al)₂O₃)76 are shown as light blue. Finally, organic materials, including compositional mimics of heroin 77, methamphetamine 78, cocaine 80, and TNT 82, exhibit a variety of colors from green to orange, depending on the R value of the material. By density and by composition, two ceramic figurines on the top shelf can be clearly identified, one filled with iron sand 84 and the other with sugar 86.

Fig. 7 a-7 c illustrate another material selection, which includes hidden contraband, alcohol, and simulated and actual (Detasheet) explosives. Three hollow concrete blocks are placed on the top shelf. The left hand side block contains hidden organic material 94 (drug substitute); the middle block is empty and the right hand block contains alumina powder 96. These three blocks provide a simple model of drugs concealed in porcelain or ceramic objects, hollow empty objects and hollow empty objects with thickened walls. The gamma ray of fig. 7b clearly distinguishes between an empty block 95 and filled blocks 94 and 96, but it does not distinguish between fillingA block 94 with drug substitute and a block 96 filled with alumina. In contrast, the neutron image of fig. 6c clearly reveals hidden organic fillers 94, which appear as yellow/orange patches. On the left-hand side of the middle shelf two containers are placed, one filled with pure alcohol 98 (methylated alcohol) and one with water (H)₂O). Alcohol 98 is clearly shown as being more "organic" (higher R value) and its predominant color is orange, while water 100 with a lower R value is predominantly green. On the same shelf, the simulated explosives 102 and the real explosives 104 are displayed in the same color, which shows that the simulated explosives are good substitutes for the real explosives. On the bottom shelf is a box containing 12 carafes, of which only four are visible, two filled with simulated spirit 106 (40% ethanol, 60% water) and two filled with water 108. Again, the bottle 106 filled with alcohol was shown to have a higher R value (more green/orange) than water 108 (mainly blue). This is in contrast to the bottle shown in fig. 7b, which is barely recognizable.

Fig. 8 a-8 d, 9 a-9 d, 10 a-10 d illustrate imaging results of ULDs filled with multiple objects. In all of these figures above, the filling of the ULD is intentionally made relatively simple to simplify the discussion of the results obtained. In particular, most of the packaging materials (cardboard boxes, foam, polystyrene, etc.) that are commonly found have been omitted, so that objects in the ULD can be clearly seen. It should be appreciated that, in practice, most ULDs are quite chaotic.

Fig. 8 a-8 d illustrate ULDs filled with various home electronics (refrigerator 120 and several computers 122), metal parts, hollow concrete blocks 124 (instead of porcelain tubes or hollow statues or sculptures), and tools. Two-pack plastic beads replacing drugs 126 are hidden in a computer and a concrete block. A propane cylinder 128 is also housed inside the ULD. Fig. 8a illustrates a photograph of a ULD scanner. Fig. 8b shows the result of a gamma ray scan only. The absence of a pack of drug substitutes 126 is particularly evident. The propane cylinder 128 may be identified based on its shape, although the organic nature of its contents is not clear. Fig. 8c and 8d are colored according to the neutron/gamma ratio R, with the result that in fig. 8c the inorganic material is shown as blue (drug substitute 126 and gas cylinder 128) and the organic material is shown as orange (computer 122 and block 124). The proportions used to combine the two images are adjusted by the operator to maximize contrast and sensitivity with respect to the yellow and red colored organic materials and to minimize the effect of clutter caused by overlapping objects, the result of which is illustrated in fig. 8 d. Two packets of concealed drugs 126 can be clearly identified.

Fig. 9 a-9 d illustrate a ULD with drugs 124 hidden inside two computers 122 and one refrigerator 120. Although it can be seen in the gamma ray image of fig. 8b that the top two computers 122 differ from the bottom two, it is unclear whether this is a true difference in machine structure. However, in fig. 9c and 9d, it is immediately apparent that the difference is due to the large amount of organic material, as shown by the bright orange color of these areas with drug 124. The top two computers 122 were loaded with 1kg packs of plastic beads which were simulated as packs of drugs. This is very different from the predominantly blue color (inorganic or low R value) of the rest of the computer structure 126. Similarly, from the gamma ray image of fig. 9b of the refrigerator 120, it is unclear whether the abnormality in the center of the image is a part of the refrigerator structure. However, in fig. 9c and 9d, it can be seen that this anomaly 124 is clearly organic and is distinct from the main inorganic structures found in the rest of the refrigerator (in particular the lower right compressor 125 and the top freezer compartment). Again, in the enhanced organic image of fig. 9d, the hidden drug 124 is clearly visible. In addition, other organic materials in the ULD (particularly the wooden shelf 128 behind the refrigerator 120 and the water container 127 to the left of the refrigerator 120) are also shown as orange.

FIGS. 10 a-10 d illustrate a second ULD with authentic concealed drugs (1 kg each of heroin and methamphetamine). Heroin 130 is hidden inside a hollow concrete block 132. The methamphetamine 134 is stored in a small box which is placed in a larger box 136 containing the garments. The organic nature of the concealed drugs is evident by the coloration in the component images of fig. 10c and 10 d. Again, the enhanced organic image of fig. 10d effectively reveals hidden drugs 130 and 134, and in particular, heroin 130 inside concrete block 132 is colored yellow. Since the methamphetamine 134 is hidden inside the garment box 136 (immediately behind the front fork of the bicycle 140), in this case, the compositional differentiation is lacking in coloration. However, drug pack 134 may be identified as a potential anomaly based on its shape and higher density.

The radiographic equipment may be used to detect and identify contraband material in at least three ways. First, gamma ray images provide considerable information about the shape, size and density of objects inside such as ULDs. Based on which certain suspicious material can be identified. A specific example is a drug pack concealed inside a space or cavity of a hollow object. Second, coloring gamma ray images based on compositional information derived from neutron measurements provides powerful additional clues in scan image translation and suspicious material identification. In particular, it is greatly helpful to detect organic materials inside a mainly inorganic object. Third, in certain circumstances, the apparatus may be used to measure the neutron/gamma ratio (R-value) of a suspect material to further assist in its identification. This method works best when there is little overlying or underlying material around the measured substance, or when the overlying or underlying material is suitably homogeneous in the immediate vicinity of the measurement region. Under these circumstances, appropriate corrections can be made to the absorption of neutrons and gamma rays in the above and below materials to obtain the R-value of the true species of interest.

The second embodiment applies directly to the dual energy fast neutron transmission embodiment for 14MeV and 2.45 MeV. However, the following discussion applies equally to dual energy transmission of energies other than 2.45 and 14 MeV. However, unlike the single-energy neutron transmission discussed above, three count rates are measured at each pixel, rather than two of the single-neutron transmissions, and two cross-sectional ratios can be calculated.

Suppose the count rate in a particular pixel from each image is r, respectively₁₄、r_2.45And r_X. These rates are related to the (unknown) mass of the material between the source point and the detection point and to the (unknown) mass attenuation coefficients of the material with respect to 14MeV neutrons, 2.45MeV neutrons and X-rays or gamma rays, respectively, written as μ₁₄、μ_2.45And mu_XThe relationship is:

r₁₄＝R₁₄exp(-mμ₁₄) (4)

r_X＝R_Xexp(-mμ_X) (5)

r_2.45＝R_2.45exp(-mμ_2.45) (6)

wherein R is₁₄、R_2.45And R_XThe count rates for 14MeV neutrons, 2.45MeV neutrons, and X-rays or gamma rays, respectively, in the absence of intervening objects.

The section ratio can be calculated directly:

μ₁₄/μ_X＝log(r₁₄/R₁₄)/log(r_X/R_X) (7)

μ_2.45/μ₁₄＝log(r_2.45/R_2.45)/log(r₁₄/R₁₄)(8)

it should be noted that these two ratios are independent of the mass of material present in the beam between the source and detector.

The section ratios given by equations (7) and (8) allow identification of a wide variety of organic and inorganic materials.

FIG. 11 illustrates the ratio of 2.45MeV neutron cross-section to 14MeV neutron cross-section versus the ratio of 14MeV neutron cross-section to the X-ray or gamma ray cross-section for material selection. The availability of two cross-sectional ratios further enhances the ability of the present invention to discriminate between different materials. The analysis of these three mass attenuation coefficient images thus allows to deduce information about the contents of the object under examination.

Considering the simulated images of the suitcase 150 shown in fig. 12 a-12 e, fig. 12 illustrates a further advantage of using dual neutron energy. The images 12a to 12c correspond to equations (4), (5), and (6), and show the transmission of 14MeV neutrons, 2.45MeV neutrons, and X-rays or gamma rays, respectively. The images 12d to 12e correspond to equations (7) and (8), and show cross sections of DT/X-ray and DD/DT, respectively.

The suitcase 150 is filled with clothes made of cotton and wool, and contains a variety of benign and suspicious objects. Bottle 152 contains water and bottle 154 contains spirits. The three pieces visible on the lower right of the suitcase 150 are a paper book 156, heroin 158, and RDX explosives 160. The upper right gun 162 of the suitcase 150 is also visible.

From the conventional X-ray image 12c, it is difficult or impossible to discern between the contents of the two bottles 152, 154, or the contents of three packages 156, 158, 160 of similar density on the right hand side of the case. The neutron images 12a, 12b provide a strong contrast between the different materials, but the best results are obtained with the cross-sectional ratio images 12d and 12 e. In particular, the book 156 shown in fig. 12a and 12b actually disappears in fig. 12d and 12e because the paper has a similar composition to the surrounding clothing, whereas the drugs 158 in fig. 12e and the explosive material 160 in fig. 12d and 12e are clearly recognizable. A clear difference between bottles filled with water 152 and spirit 154 is also seen in fig. 12d and 12 e.

In a first variant of the dual neutron transmission method, the operator forms a new image, which is a linear combination of the two section ratio images. The ratio with which the two images are combined is adjusted by the operator to maximize contrast and sensitivity with respect to contraband material and to minimize the effect of clutter caused by overlapping objects.

FIGS. 13 a-13 b illustrate simulated 14MeV neutron and X-ray images, respectively, of a container 170 taken from the side. The steel tubes 176 dominate the image due to their high density, making it difficult to see the contours of the computer equipment. However, by forming a single image, fig. 13c, from the two cross-section ratio images given by equations (7) and (8), the clutter associated with the steel pipe 176 can be removed to reveal the computer box 174.

This method can be understood by referring to fig. 11. Selecting a linear combination of images (7) and (8) is equivalent to coloring an image pixel according to its distance from any oriented straight line drawn on fig. 11. By selecting this line to be parallel to the two selected materials, any combination of these materials is colored the same color. In the example discussed, this line is chosen to be parallel to the line connecting the steel and the polystyrene packaging of the computer. In this way, the steel pipe can be made to disappear to a large extent before it passes through the computer. Fig. 13c shows the result of this process.

While this example of the invention is discussed, it should be recognized that this embodiment is but one of many which utilize the principles of the invention. Although in the above examples the radiation source is placed on one side of the object to be examined and the detector on the opposite side, in a first variant the source is placed above or below the object to be examined and the detector on the opposite side (below or above, respectively). In a second variant, the source and detector may be rotated around the object to be examined to allow multiple views to be obtained. In a third variation, multiple sets of sources and detectors allow multiple views of the same object to be acquired simultaneously. In a fourth variation, multiple sets of detectors are positioned around a central source to allow views of multiple objects to be acquired simultaneously.

Obviously, in operation, the object to be scanned may pass through the tunnel on a conveyor belt, or the object may be pulled or pushed by using a suitable mechanism.

Although in the above embodiments the two radiation sources are operated sequentially while scanning the object through the analyzer. In a first variation, however, the object is scanned twice by the analyzer, with one source operating per scan. In a second variation, each source has a separate associated detector, and the object is scanned only once. In a third variant, two radiation sources are operated simultaneously, a single detector is used, and energy discrimination is used to distinguish the signals obtained by neutrons and X-rays or gamma-rays.

In a variation (dual neutron energy embodiment), the radiation source comprises three separate radiation generators, one producing 14MeV neutrons, one producing 2.45MeV neutrons, and the last producing high energy X-ray or gamma ray radiation. The neutron source is a sealed tube neutron generator or other compact source with similar characteristics, producing neutrons via D-T and D-D fusion reactions.

The three radiation sources are operated sequentially while scanning the object through the analyzer. In a first variation, the object is scanned three times by the analyzer, with one source operating per scan. In a second variation, each source has a separate associated detector, and the object is scanned only once. In a third variant, two or more radiation sources are operated simultaneously and energy discrimination is used to identify signals obtained from high-energy neutrons, low-energy neutrons and X-rays or gamma rays.

It will be appreciated by persons skilled in the art that numerous modifications and/or changes may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Reference to the literature

An, J., Xiang, X., Wu, Z., Zhou, L., Wang, L., and Wu, H., 2003 "⁶⁰Development on planning of Co container inspection system⁶⁰Co conjugation systems) "use radiation and isotopes58(Applied Radiation andIsotopes58)(2003)315～320。

Bartle, c.m., 1995 "Method and apparatus for detecting concealed substances (Method and apparatus for detecting concealed substances)" us patent 5,479,023 (12/26/1995).

Barzilov, A.P., Womble, P.C., and Vourvopoulos, G., 2001 "NELIS-neutron component analysis System for pallet cargo (NELIS-a neutron element analysis system of models of pallets)", 2001 National Drug Control Policy Office International workshop (2001 Office of National Drug Control Policy International symposium).

Brzosko, J.S. et al, 1992, "Advantages and limitations of 14-MeV neutron radiography" (Advantages and limitations of 14-MeV neutron radiography), "Nuclear Equipment and Methods (Nuclear Instruments and Methods) B72(1992) 119-131.

Buffler, A., 2001 "contraband detection by fast neutron scattering", south Africa second national nuclear technology conference (2)^ndNational Nuclear Technology Conference, NAC, South Africa), 5 months 13-15 days 2001, page D-03.

Chen, G, and Lanza, R.C., 2000, "Fast neutron resonance radiography for element mapping", Final research Co-ordination conference on "Bulk Hydrogen Analysis Using Neutrons", Kampton (Cape town), south Africa, 10 months to 26 days 2000, pages 31 to 38, for "Block Hydrogen Analysis Using Neutrons".

Dokhale, P.A., Csikai, J., Womble, P.C., and Vourvopoulos, G., 2001 "NELIS-illicit drug detection System (NELIS-illicit drug detection System)" AIP Conference Proceedings (AIP Conference Proceedings), 576(2001) 1061-1064.

Gozani, T.1997 "Neutron-based non-invasive inspection techniques", proces of Neutron Research and Industry International conference (Proc. Internat. Conf. on Neutron in Research and Industry), Critical island (Crete), Greece, 1996 6.9-15 days, SPIE series proceedings (SPIE proceedings series)2867(1997) 174-181.

Hussein, E., 1992 "explosive material detection using nuclear radiation: overview (detective explicit material using nuclear view)', SPIE Vol.1736(1992) 130-137.

Klann, r.t., 1996 "fast neutron (14.5MeV) radiography: comparative study (Fastneutron (14.5MeV) radiogram: a comparative study), "fifth-day neutron radiography world conference (5)^thWorld Conference on Neutron radiographics), Berlin, 7 months 17-20 days 1996, 469-483.

Lefevre, H.W. et al, 1997 "use a fast neutron spectrometer system for inspecting luggage for explosives (Using a fast neutron spectrometer system to a robust for explosive)", neutron Research and Industry International conference Proceedings (Proc. Internat. Conf. on Neutrons in Research and Industry), Criste island (Crete), Greece, 1996, 6.9-15.S., SPIE Series Proceedings (SPIE Proceedings Series)2867(1997) 206-210.

Le tourniquet, p, Bach, p, and Dance, w.e., 1998 "Neutron fan beam source for Neutron radiography purposes (Neutron fan beam source for Neutron radiation graphics)" fifth international conference on accelerator research and industrial application (15 th international conference on accelerator for Neutron radiation graphics) "^thInt. Conf. on Application of Accelerator in Research and Industry), Danton (Denton), Texas (Texas), USA, 11 months 4-7 days 1998.

Mikerov, v.i. et al, 2000, "Research prospects for portable-device-based fast neutron radiography (investment of projections of fast neutron radiography on the basis of gaseous reagents)", IAEA Coordinated Research program on "bulk hydroanalysis using Neutrons", Cape town (Cape town), south africa, 10.23-26.2000, report F1-RC-655.3.

Millen, m.j., Rafter, p.t., Sowerby, b.d., Rainbow, m.t., and Jelenich, l., 1990 "Plant trial of a fast neutron and gamma ray transmission measurement for the determination of moisture in lump coke on conveyor belts" (Nuclear geophysical) 4(1990) 215-226.

Perion, d. et al, 2000 "System for differentiating between organic and inorganic materials" (international patent application No. wo 00/43760).

Rynes, J.et al, 1990 "Gamma-ray and neutron radiography as part of a pulsed fast neutron analysis inspection system", Nuclear Instruments and Methods A422(1999) 895-899.

Sawa, Z.P., Gozani, T. and Ryge, P., 1991, "Contraband detection system using direct imaging pulsed fans using direct imaging of neutrons in pulse blocks", U.S. Pat. No.5,076,993, 31/12/1991.

Tickner, j.r. and Sowerby, b.d., 2000 "detection system (a detection system)", australian provisional patent application No.2002953244, filing date: 12 and 10 months in 2002.

Claims (26)

1. A radiographic apparatus comprising:

a first source of neutrons, said first source of neutrons being a substantially single-energy fast neutron source, the fast neutrons being generated by deuterium-tritium or deuterium-deuterium fusion reactions, the single-energy fast neutron source comprising a sealed tube generator for generating neutrons;

a separate X-ray or gamma ray source of sufficient energy to substantially pass through the object to be imaged;

an alignment block which surrounds the source of neutrons and the source of X-rays or gamma-rays and which provides one or more slots for emitting a substantially fan-shaped radiation beam;

a detector array comprising a plurality of individual scintillator pixels for receiving neutron radiation and X-ray or gamma-ray radiation emitted from respective sources and converting the received radiation energy into light pulses, the detector array being aligned with a fan-shaped radiation beam emitted from a self-calibration block and calibrated to substantially prevent radiation not transmitted directly from each source from reaching the array;

a conversion means for converting the light pulse generated in the scintillator into an electric signal;

a transport device for transporting the object between each source and the detector array;

computing means for determining from the electrical signals the attenuation of the neutron beam and the X-ray or gamma ray beam and generating an output representative of the mass distribution and composition of an object disposed between each source and the detector array; and

a display device for displaying an image based on the mass distribution and composition of the scanned object.

2. Radiographic equipment according to claim 1, where the X-ray or gamma-ray source comprises¹³⁷Cs、⁶⁰Co or a similar radioisotope source having an energy of substantially 1 MeV.

3. Radiographic equipment according to claim 1, where the X-ray or gamma ray source comprises an X-ray tube or electron accelerator that produces X-rays through bremsstrahlung radiation on the target.

4. Radiographic equipment according to claim 1, where the neutron source produces neutrons which have substantially higher energy than the X-rays or gamma rays from the X-ray or gamma ray source, where the neutron source and the X-ray or gamma ray source are arranged to pass through the same slot in the calibration block and a single detector array is used, which comprises individual pixels of a plastic or liquid organic scintillator, where a distinction is made between X-rays or gamma rays and neutrons based on the energy with which they deposit on the scintillator.

5. Radiographic equipment according to claim 1, where the source of neutrons and the source of X-rays or gamma rays are arranged to pass through the same slot in the calibration block and a single detector array is used, comprising individual pixels of plastic or liquid organic scintillators, where the source of neutrons and the source of X-rays or gamma rays operate alternately.

6. Radiographic equipment according to claim 1, where the source of neutrons and the source of X-rays or gamma rays are arranged through separate parallel slots in the calibration block and two detector arrays are used, one comprising separate pixels of plastic or liquid organic scintillators for the neutron detectors and one comprising separate pixels of plastic, liquid or inorganic scintillators for the detection of X-rays or gamma rays.

7. Radiographic equipment according to claim 4, where each slot of the collimator of the source and detector is wide enough to ensure full illumination of the detector by the source while minimizing detection of scattered radiation.

8. Radiographic equipment according to claim 1, further including a second source of neutrons, said second source of neutrons being a second sealed tube neutron source that produces neutrons by either of deuterium-tritium or deuterium-deuterium fusion reactions, wherein the second source of neutrons uses fusion reactions complementary to the first source of neutrons.

9. Radiographic equipment according to claim 8, where neutrons from the second neutron source are detected in a separate calibrated detector array comprising individual pixels of plastic or liquid organic scintillators.

10. Radiographic equipment according to claim 9, where one of the first or second neutron sources has an energy of substantially 14MeV and the other neutron source has an energy of substantially 2.45 MeV.

11. Radiographic equipment according to claim 8, where the conversion means comprises a plurality of photodiodes, where the scintillator material is selectable to have an emission wavelength substantially matching the response of the photodiodes.

12. Radiographic equipment according to claim 1, where the conversion means comprises crossed wavelength shifting fibres coupled to a plurality of single anode or multi-anode photomultiplier tubes.

13. Radiographic equipment according to claim 11, where the electrical signals from the conversion means are used to infer the transmission of neutrons from the neutron source and X-rays or gamma rays through the scanned object, or to infer the transmission of neutrons from the first neutron source, X-rays or gamma rays, and neutrons from the second neutron source through the scanned object.

14. Radiographic equipment according to claim 13, where the transmission is used to calculate a mass attenuation coefficient image for each pixel used for display, where different pixel values map to different colours, the image being based on the mass distribution and composition inferred from these calculations.

15. Radiographic equipment according to claim 1, where the computing means comprises a computer for performing image processing and displaying the image on a computer screen.

16. Radiographic equipment according to claim 15, where the output is convertible to a mass attenuation coefficient image for each pixel for display on a computer screen, where different pixel values map to different colours.

17. Radiographic equipment according to claim 16, where the mass attenuation coefficient images are obtainable from count rates measured by transmission for deuterium-tritium neutrons or deuterium-deuterium neutrons and X-rays or gamma rays, or for each of deuterium-tritium neutrons, deuterium-deuterium neutrons and X-rays or gamma rays.

18. Radiographic equipment according to claim 17, where the computer is operable to obtain a cross-sectional ratio image between the pair of mass attenuation coefficient images.

19. Radiographic equipment according to claim 18, where the proportions used to combine the cross-section ratio images are adjustable to maximise contrast and sensitivity to the particular object being examined in the images.

20. Radiographic equipment according to claim 18, where the computer is capable of performing automatic material identification based on the measured cross-sections.

21. Radiographic equipment according to claim 19, where the proportions used to combine the cross-section ratio images are adjustable by the operator.

22. Radiographic equipment according to claim 1, where the source and detector arrays are stationary and the transport mechanism is configured to enable the object to be moved in front of the neutron source.

23. Radiographic equipment according to claim 1, where the object is stationary and the transport mechanism is configured to move the source and detector arrays synchronously on either side of the object.

24. Radiographic equipment according to claim 1, where multiple detector sets are placed around a centrally located source to allow simultaneous acquisition of scans of multiple discrete objects.

25. Radiographic equipment according to claim 1, where the intensity of the deuterium-deuterium and/or deuterium-tritium neutron source has 10¹⁰On the order of neutrons per second, or as high as practically possible.

26. Radiographic equipment according to claim 11, where the scintillators are surrounded by a mask to cover at least a portion of each scintillator, the mask having a first reflective surface for reflecting escaping light pulses back to the scintillator.