Patent Number: 
Section: description

The present invention concerns an apparatus and method for irradiation of products. FIG. 4 shows a top view of the complete apparatus. Products to be irradiated arrive in packages, like trays 1. Typical trays used by the US Post Service are 610 mm long (24 inches), 292 mm wide (11xc2xd inches) and 133 mm high (5xc2xc inches). Trays 1 are put on the entry conveyor of a detection device 2. The detection device performs the function of measuring maximum effective thickness of the trays 1. The detection device may be an X-ray inspection system such as those used in the food industry or for checking luggage at the airports. These devices may use an X-ray tube having an energy in the range of 50 kV-200 kV. The imaging device may be a linear diode array, with phosphor screen, or a CCD camera. Suitable devices are those provided by Perkin Elmer (Linescan 107) or by LIXI, Inc. (FIS Series Inspection System). The company Detection Technology, Inc. provides linear arrays of x-ray detectors (X-scan). At the exit of the detection device 2, a diverter 5 directs trays having at least an area with an effective thickness above a given threshold to the X-ray processing line (right hand side) and trays 1 having everywhere an effective thickness below said threshold to the e-beam processing line (left hand side). This diversion may be performed by a piston arm pushing trays to the side, or by driving a conveyor in the appropriate direction. The threshold is chosen so that the effective thickness measured for the tray 1 is below the optimum thickness Ropt for the given energy. Optimum thicknesses depend on beam energy and are 2 g/cm2, 3.9 g/cm2, 4.8 g/cm2 for 5, 10 and 12 Mev, respectively, as stated in ASTM E 1649. At the entrance of the X-ray processing line, a palletising machine 3 performs the function of placing trays 1 as a three by two array on slave trays 6, and stacking a number of such arrays vertically. The trays 1 are lined up and stacked by a robotic arm 4. The number of layers of such a stack is limited by the vertical scan height of the X-ray line. However, in order to reduce delays, the decision may be taken to start processing of an incomplete stack. In that case, the vertical scanning height of the beam for the X-ray irradiation may be adapted so as to correspond to the actual stack height. In an alternate embodiment of the invention, the stacks are brought to a gas sterilant device. At the entrance of the e-beam processing line, trays 1 are grouped in a three by two array on slave trays 6, but in only one layer. The width of three trays 1 side by side is 879 mm which is a convenient value for an e-beam scan horn 13 and 18. Both the path for X-ray processing and the path for e-beam processing share a common entry maze 7 and a common exit maze 8 into and out of the irradiation rooms. The e-beam irradiation room 9 is located on level xe2x88x921, as depicted on FIG. 5. A lowering device 11 and elevator 12 bring the slave trays 6 down to the e-beam irradiation room and back up again. In the e-beam irradiation room 9, the product packages are irradiated from above. The X-ray irradiation room 10 is located on level 0. A scan horn 18 produces a horizontal electron beam scanned in a vertical plane. A conversion window 14 made of a high-Z material performs the function of converting the energy of the electrons to X-rays, by bremsstrahlung. For treating the pallets to full depth, pallets are put on a turntable 15, and turned during the number of turns required for reaching the required dose. The irradiation source 17 is a Rhodotron. The beam is either directed to the e-beam scan horn 13 and irradiation room 9 with a bending dipole magnet or to the X-ray scan horn 18 and irradiation room 10 with another set of bending magnets. Outside the shielding, a separation wall 16 separates the untreated product in the loading area from the treated products in the unloading area. Using the apparatus and method of the invention, the most efficient path, i.e. the e-beam path, is used for processing the majority of the trays. These are treated by a beam directed along the shortest dimension of the tray 1. In case the effective thickness of a set of packages, as measured by the detection device 2, is above the optimum thickness Ropt, the set of packages may be flipped over, for performing double-sided irradiation. The invention allows to achieve throughput and to guarantee minimal dose, even under the very high constraints required for treating mail against biological threats. The invention is not to be construed as limited to the above detailed description. More specifically, in an alternate configuration, the e-beam conveyor may be on level 0, as the detection device 2 and palettising machine 3, the X-ray conveyor being on level 1. In this configuration, only the product stacks for x-ray processing have to be brought up and down again after irradiation. The Rhodotron is on level 1. In another variation, another electron accelerator, such as a Dynamitron may replace the Rhodotron.