Food irradiation dose uniformity

Abstract

A food irradiation system comprising a plurality of compact linear accelerator systems is described herein. Each of the plurality of compact linear accelerator systems includes: a high energy particle beam source providing a particle beam up to 10 MeV; an emission target assembly configured to generate bremsstrahlung x-rays when impacted by particles of the particle beam; and a drift tube through which the particle beam passes on a path from the high-energy particle beam source to the emission target assembly. The emission target assembly is positioned at the distal end of the drift tube for direct impinging of the particle beam to generate bremsstrahlung x-rays in the directed radiation beam. Each of the plurality of compact linear accelerator systems is individually positioned such that the plurality of compact linear accelerator systems as a group provide directed radiation beam coverage for the total cumulative volume at a prescribed radiation dose level.

Description

[0001] Cross - reference to related applications

[0002] This application is a non - provisional application of U.S. Provisional Patent Application No. 63 / 403,405, entitled "FOOD IRRADIATION DOSE UNIFORMITY", filed on September 2, 2022, the entire content of which is incorporated herein by reference. Technical field

[0003] The present disclosure generally relates to the treatment of food to eliminate biological pathogens. More particularly, the present disclosure relates to performing such treatment using high energy. Background art

[0004] The present disclosure discusses systems and their associated operating methods that meet several needs for performing high - energy electron beam and x - ray phytosanitary treatment and food irradiation to eliminate pests, invasive species, fungi, molds, and other hazards, thereby strengthening global food safety and extending shelf life. Current phytosanitary and irradiation methods mainly include hot water immersion (which damages texture and food properties), cold treatment (flash freezing), methyl bromide exposure (fumigation), Co - 60 gamma - ray irradiation (radioactive source), and bremsstrahlung x - ray irradiation with low - energy anodes (x - ray tubes) or high - energy targets (electron beam converters in electron accelerators). In addition, high - energy x - rays and their electrons can be used to replace other methods for material sterilization methods (such as chemical ethylene oxide treatment) for bulk materials, medical devices, skin care products, fabrics, additives, bio - organic materials, and raw materials, seeds, etc.

[0005] X-rays and gamma rays are preferred treatment means that can address / overcome the drawbacks of chemical treatment having a persistent carcinogenic pathway. However, current technologies based on 3 - 5 MCi radioactive Co-60 pose significant safety / transfer risks and have limited global supply. Treatments using electron bremsstrahlung x-ray generators through traditional electrostatic systems (in the case of x-ray tube / window converters) have been limited to the range of 150 kV to 350 kV. The former is implemented using traditional x-ray tube technology used in the medical and inspection industries. Electrostatic systems in the 1 to 5 MeV range (such as Pelletron or Tandetron) can achieve efficiency similar to low-frequency DC through the use of transmission converters made of materials such as W or Ta, but at the cost of physical size and weight. The total power of these systems is usually limited and not suitable for high-power irradiation. High-current electromagnetic / RF accelerators operate in the 1 to 10 MeV range, using transmission-type x-ray converters (up to 7.5 MeV) and transmission electron beam windows (up to 10 MeV). The latter systems are usually service equipment using super-large recirculating electron devices (such as Rhodotrons) or S-band linear accelerator equipment. Due to electron generation and the relatively large system size required for acceleration, a single beam is usually used to transmit the electron beam into a magnetic deflection scanning horn (horn), which diffuses electron heating over a large area and focal length to generate x-rays, or rasterizes the electron beam onto the object to be directly irradiated through a thin window. To achieve economies of scale, large electron accelerators require 250 to 1000 kW to generate 40 to 240 kW of power on a transmission Ta bremsstrahlung converter or thin foil window. Due to the large magnetic steering horn and power levels greater than 40 kW, large equipment operates quasi-continuously in a single-sided manner for irradiating trays or large cargo.

[0006] Irradiation of food or materials is usually subject to minimum dose requirements to achieve sprout inhibition, insecticidal effects, extended shelf life, pathogen reduction, and pest elimination. Similarly, food or materials are usually subject to maximum dose limits in terms of quality, taste, structure, etc. Therefore, the trays or boxes receiving radiation will have a radiation dose profile over the entire volume (challenging for single-sided irradiation). The challenge of achieving sufficient-dose irradiation using single-sided irradiation can be mitigated by running the trays or boxes of materials through the scanning system 2 to 4 times and rotating the materials 90 or 180 degrees relative to the large accelerator in subsequent scans. This process reduces the throughput of the physical plant (1 / 4x) and increases the physical cost and floor space for transportation and material handling (4x). Improvements in the physical size, power handling, and complexity of the irradiation system can reduce this negative impact.

[0007] From an operating expenditure (OpEx) perspective, energy conversion efficiency is important for continuous operation of the equipment or high-load operation over a year. Electrostatic acceleration offers an AC to DC conversion rate greater than 75%, CW operation, and broad acceptance for electron beam generation. Electromagnetic (RF) power efficiency is lower, with an AC to RF conversion rate far less than 50%, resulting in higher operating costs. Additionally, the electron cost is also higher, approximately $3 to $10 per watt, which is higher compared to the cost of $1 to $2 per watt for DC. The efficiency of electromagnetic (MW) is even lower. However, electromagnetic power supplies offer the advantage of reduced system size. Traditional electrostatic accelerators have an increasingly large size, and accelerating energies exceeding a few MeV also make these systems costly. Traditional RF / MW accelerators have very high power (>40 kW) to achieve economies of scale in irradiation. Innovations in electrostatic, laser-based, and RF / MW accelerators may support / enable new irradiation modalities and thus address the shortcomings of the current systems described herein.

[0008] The systems and methods of operation of the present disclosure address the problems of known systems, utilize advances in high-voltage / high-gradient materials and electron accelerator kinetics, and provide efficient power coupling / transfer. The design of the x-ray converter helps to provide a new approach for improving the 5 MeV bremsstrahlung photon source recognized by the IAEA (International Atomic Energy Agency) for pallet irradiation of food to achieve phytosanitary and pathogen reduction. The system according to the present disclosure provides an x-ray source up to 7.5 MeV and an electron beam direct irradiation system up to 10 MeV. Summary of the Invention

[0009] According to the present disclosure, a food irradiation system including a plurality of compact linear accelerator systems is described herein. Each compact linear accelerator system of the plurality of compact linear accelerator systems includes: a high-energy particle beam source providing a particle beam up to 10 MeV; an emission target assembly configured to generate bremsstrahlung x-rays when struck by particles of the particle beam; and drift tubes through which the particle beam passes along a path from the high-energy particle beam source to the emission target assembly. The emission target assembly is positioned at a distal end of the drift tube for direct impingement of the particle beam to generate bremsstrahlung x-rays in a directed radiation beam. The individual systems of the plurality of compact linear accelerator systems are positioned separately such that the plurality of compact linear accelerator systems, as a group, provide directed radiation beam coverage for a total cumulative volume at a specified radiation dose level.

[0010] In addition, a pallet irradiation system is described that includes the food irradiation system summarized above and a transport device configured to carry a pallet supporting an object to be irradiated. Brief Description of the Drawings

[0011] While the appended claims particularly set forth the features of the present disclosure, the present disclosure and its objects and advantages will be best understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0012] Figure 1 is a graph of the prior art, typically used to show the positive effects of low-temperature pasteurization and food irradiation on fruits, vegetables, meats, grains, and spices.

[0013] Figure 2 is a photograph and schematic diagram of a prior art Co-60 irradiator facility using batch transport, where the photograph is of Co-60 tubes emitting Cherenkov light in a storage pool.

[0014] Figure 3A is a prior art graphical rendering of two 40 to 80 kW S-band microwave linear accelerators in a single-sided emission configuration for irradiating one or two laterally moving trays.

[0015] Figure 3B is a prior art graphical rendering showing details of an irradiation processing facility with transport means, bends, and revolving doors for rotating materials 90 degrees and 180 degrees for dose control in a thick shielded bunker room.

[0016] Figure 4 is a prior art graphical rendering showing a 160 to 240 kW high-power recirculating RF accelerator in a side-emission configuration with a large magnetic steering horn on a single converter target for material transport in a very thick shielded bunker room.

[0017] Figure 5 is a prior art graphical rendering depicting a system for improving dose uniformity in a single-sided emission configuration by rotating a single pallet stack 360 degrees through a stop-and-scan process.

[0018] Figure 6A is a prior art graphical illustration depicting the energy-angle correlation and spatial distribution of the x-ray bremsstrahlung spectrum as a function of the electron energy incident on a thin target.

[0019] Figure 6B is a prior art illustration of the relative x-ray intensity of a 0.8 mm thick tungsten target at a given electron energy, including the percentage of forward and backward x-rays.

[0020] Figure 6C is a prior art illustration of the variation of x-ray intensity with angle for a set of different target converter materials, showing the dependence of Z on the total yield and the angular distribution of forward / backward radiation.

[0021] Figure 6DIt is a prior art illustration of the total x-ray conversion efficiency divided into forward radiation and backward radiation for a fixed 5 MeV electron beam incident on W targets of different thicknesses.

[0022] Figure 6E It is a prior art illustration of the total x-ray conversion efficiency divided into forward radiation and backward radiation for a fixed Ta target thickness at variable electron energies, showing the influence on the x-ray spectral distribution.

[0023] Figure 7A It is a prior art illustration depicting the x-ray dose profile from a 5 MeV electron beam incident on a 0.8 mm Ta converter into a reference water volume, showing an asymmetry of 10 times that of single-sided irradiation and a reduction to 2 times for double-sided irradiation.

[0024] Figure 7B It is a prior art graphic summary along the dose centerline of Figure 7A to highlight the two-sided improvement in dose superposition for dose uniformity.

[0025] Figure 8A It is a prior art schematic illustration depicting a general state-of-the-art electron utilization scheme, where an electron beam is generated in a particle accelerator, the electrons enter a beam steering horn through the particle beam, and reach a converter assembly (for x-rays) or a thin window for emitting the electrons into the air.

[0026] Figure 8B It is a prior art photograph of an S-band linear accelerator for emitting an electron beam. Due to its size, weight, and vertical installation above the transportation vehicle, the linear accelerator is lowered through the roof of the facility with the aid of a crane gantry.

[0027] Figure 8C It is a prior art photograph of an electron beam scanning horn, showing the coils and core of the electron beam scanning system, a tightly focused electron grating pattern on a thin extraction foil, and air jet cooling for electron beam irradiation.

[0028] Figure 8D It is a prior art illustration of the emission target area at the end of a scanning horn with a Ta converter, direct water cooling, and a stainless steel backing.

[0029] Figure 9A Schematically depicts an emission target assembly for emitting electron radiation according to the present disclosure, highlighting the basic structural elements for coupling with an electron beam accelerator of a compact linear accelerator system, including a vacuum-facing boundary, an optional heat conductor, a cooling layer, and an end cap layer leading to the atmosphere according to the present disclosure.

[0030] Figure 9BSchematically depicts an emission target assembly for emitting x-ray radiation for the present disclosure, highlighting the basic structural elements for coupling with an electron beam accelerator of a compact linear accelerator system, including a vacuum-facing cover layer, a converter material, an anti-corrosion interface layer, a cooling layer, and an end cap layer leading to the atmosphere according to the present disclosure.

[0031] Figure 9C Also shown is an emission target assembly for emitting x-ray radiation using a liquid converter target material according to the present disclosure, where the liquid converter target material can also be used as a direct cooling structure by flowing to an external radiator; also shown is additional low-energy x-ray attenuation for beam hardening.

[0032] Figure 9D Schematically depicts the geometry of the converter target material within the emission target assembly according to the present disclosure to present an inclined surface for the incident electron beam, thereby modifying the effective thickness for on-axis bremsstrahlung generation and modifying the anisotropy of the bremsstrahlung x-ray energy-angle spectrum by the angle.

[0033] Figure 10A Also shown is another aspect of the present disclosure according to the present disclosure, that is, modifying the anisotropy of the bremsstrahlung x-ray energy-angle spectrum by designing the crystal structure orientation or bulk structure orientation of the converter material to be substantially orthotropic to the electron beam.

[0034] Figure 10B Also shown is another aspect of the present disclosure according to the present disclosure, that is, modifying the anisotropy of the bremsstrahlung x-ray energy-angle spectrum by designing the crystal structure orientation or bulk structure orientation of the converter material to be substantially orthogonal to the electron beam.

[0035] Figure 11A and Figure 11B Schematically depicts a compact linear accelerator system including an electron accelerator directly coupled to an extended nozzle drift tube, using beam diffusion to irradiate the emission target assembly to generate the energy-angle distribution of bremsstrahlung photons at different acceleration energies of 5 MeV and 3 eV respectively according to the present disclosure.

[0036] Figure 12A and Figure 12B Schematically depicts a shielding collimator closely coupled to the extended nozzle drift tube according to the present disclosure to affect the bremsstrahlung energy-angle distribution, thereby controlling the forward photons and the equivalent dose profile.

[0037] Figure 12C and Figure 12D Schematically depicts a shielding collimator closely coupled to the extended nozzle drift tube according to the present disclosure for physical collimation and constraining the forward photons into a symmetric-shaped beam or an asymmetric-shaped beam for irradiating an object and obtaining a specific dose profile.

[0038] Figure 12E Schematically depicts a shielding collimator with a toothed structure according to the present disclosure to facilitate the capture of backscattered radiation, thereby minimizing scatter and redirecting it as forward radiation with a lower effective energy.

[0039] Figure 13 Schematically depicts a compact linear accelerator system according to the present disclosure including an electron accelerator directly coupled to an extended nozzle drift tube, utilizing beam spreading to irradiate an emission target assembly, thereby generating a forward electron beam for different acceleration energies.

[0040] Figure 14A Schematically depicts a compact linear accelerator system according to the present disclosure including an electron accelerator directly coupled to an extended nozzle drift tube, the drift tube containing a beam deflector capable of moving the electron beam to irradiate an emission target assembly in an extended beam region, thereby generating a rasterized electron beam of different acceleration energies.

[0041] Figure 14B Schematically depicts a compact linear accelerator system according to the present disclosure including an electron accelerator directly coupled to an extended nozzle drift tube, the drift tube containing a beam deflector capable of spreading the electron beam to irradiate an emission target assembly within an extended beam region, thereby generating multiple and / or overlapping electron beams for different acceleration energies.

[0042] Figure 15A Schematically depicts a super-compact irradiation device according to the present disclosure suitable for phytosanitary and sterilization treatments, the device including one or more compact linear accelerator systems arranged around an object transport device.

[0043] Figure 15B Schematically depicts a variable placement of a compact linear accelerator system according to the present disclosure azimuthally around an in-line object transport device for high-throughput phytosanitary and sterilization treatments.

[0044] Figure 15C Schematically depicts a super-compact irradiation device according to the present disclosure suitable for, for example, Figure 15A the phytosanitary and sterilization treatments depicted, in which one or more compact linear accelerator systems longitudinally revolve around an object transport device for in-line exposure.

[0045] Figure 16 Schematically depicts a super-compact irradiation device according to the present disclosure suitable for Figure 15A phytosanitary and sterilization treatments from A to C, in which one or more compact linear accelerator systems are vertically stacked beside an object transport device for in-line exposure to irradiate larger objects, such as stacked pallets.

[0046] Figure 17A and Figure 17B schematically depicts a dynamic energy angle control for adjusting a directed radiation beam towards an object to be treated using a relative position shielding collimator according to the present disclosure, thereby adjusting the relative dose across the object.

[0047] Figure 18A and Figure 18B schematically depicts a central feature of the present disclosure according to the present disclosure, namely that a plurality (four in this example) of compact linear accelerator systems are positioned in close proximity to the object such that a plurality of directed radiation beams with overlapping radiation fields will equalize the standardized dose level across the object, thereby improving the dose uniformity ratio and reducing the spread between D max and D min .

[0048] Figure 19A and Figure 19B The scheme of Figures 18A to 18B is further extended by adding additional compact linear accelerator systems positioned around the object to be irradiated to further equalize the standardized dose across the object, thereby improving the dose uniformity ratio, throughput, and processing speed; wherein, according to the present disclosure, individual adjustments to each compact linear accelerator system "source", collimation adjustments for energy-angle correlation, adjustments to the accelerating energy, low-energy filter adjustments for beam hardening, adjustments to the beam current (flux), adjustments to the beam position, adjustments to the exposure time, etc. are supported.

[0049] Figure 20 schematically depicts a super-compact irradiation device according to the present disclosure suitable for phytosanitary and sterilization treatments, the device comprising a plurality of compact linear accelerator systems arranged around an object transport device for on-line exposure, for example 20 to 40 4 kW units will project a beam power of 80 to 160 kW, as an alternative to a traditional large single-sided irradiation platform with low cost and small facility size.

[0050] Figure 21A and Figure 21B schematically depicts a super-compact irradiation device according to the present disclosure employing local radiation shielding with a small diameter access port for a compact linear accelerator system having an emission target assembly and a shielding collimator, the shielding collimator greatly reducing the burden of backscattered photons and stray radiation on the facility, personnel, and equipment, thereby enabling the compact linear accelerator systems to be placed in close proximity to each other to achieve overlapping radiation fields, high area and volume density, for dose uniformity and throughput.

[0051] Figure 22Schematically depicts another embodiment of the present disclosure that uses magnetoelectronic transport to direct and guide an electron beam to an emission target assembly that is farther from or at an angle to an electron accelerator to generate a directed radiation beam in accordance with the present disclosure.

[0052] Figure 23A and Figure 23B and Figure 23C Also shown is an extension to multiple compact linear accelerator systems in accordance with the present disclosure, which are arranged to generate an overlapping radiation field from multiple directed radiation beams, the multiple directed radiation beams surrounding an area that may contain an object to be irradiated. Figure 22 is a flowchart summarizing the operation of a method for achieving improved dose uniformity ratio and improved linear exposure time for a super-compact irradiation device in accordance with the present disclosure.

[0053] Figure 24 is a flowchart summarizing the operation of a method in accordance with the present disclosure that uses a radiation detector placed near an object to be irradiated.

[0054] Figure 25 is a detailed schematic illustration of a device in accordance with the present disclosure for achieving radiation dose differential adjustment and monitoring the dose conditions actually delivered to an irradiated object.

[0055] Figure 26 is a schematic illustration of a method and a device in accordance with the present disclosure for performing operational dose control (e.g., 400 Gy ± 20 Gy) and auditable verification for each irradiated object.

[0056] Figure 27 is in accordance with the present disclosure Figure 25 of the method and Figure 26 of the device for performing operational dose control (e.g., 400 Gy ± 20 Gy) and auditable verification for each irradiated object. Detailed Description

[0057] The following description (including details of the drawings) should not be considered restrictive, but is for the sole purpose of describing the principles of the described embodiments.

[0058] Food safety is of utmost importance to our country. For phytosanitary applications, such as fruit and vegetable handling, disinfection and quarantine are required. Typically, fumigation is carried out (which is why vegetables are washed before consumption). However, in mid-2022, methyl bromide was phased out for environmental reasons, causing significant disruptions to the import of certain fruits and vegetables. Co-60 irradiation is the natural solution. However, the supply of cobalt-60 gamma-ray sources is limited, and the cost increased from $1.8 per curie in 2022 to $6.4 per curie, and will peak at $10 per curie in 2024 due to global supply and demand.

[0059] The present disclosure relates to a system for ultra-compact devices and irradiation methods for phytosanitary and food safety processing with small size / low power / low cost, which promotes distributed packing point irradiation as an add-on to existing refrigeration / container facilities and is a facilitator for small-scale medical sterilization, industrial non-destructive testing, and material processing.

[0060] The present disclosure provides access to a system small enough to be installed through doors and existing radiation shields to retrofit Co-60 gamma-ray facilities disrupted by global supply chain difficulties while reducing capital expenditure and operating expenditure costs, enabling more end-users to adopt accelerator irradiation for its Figure 1 benefits as shown in the figure, which is commonly used to represent the positive effects of low-temperature pasteurization and food irradiation on fruits, vegetables, meats, grains, and spices.

[0061] Food has a lower / upper limit of irradiation dose set by recognized national agencies (e.g., in the United States, it is the U.S. Food and Drug Administration (FDA), the U.S. Department of Agriculture (USDA), the Animal and Plant Health Inspection Service (APHIS), etc.). The dose uniformity ratio (i.e., the ratio of the highest dose to the lowest dose in a sample) provides a good indicator for the evaluation approach. A high DUR also means spending more time on an object to reach the minimum irradiation dose target that meets the recognized agency's criteria. An overly high DUR may exceed the threshold of food damage. More importantly, a lower DUR generally leads to a higher facility throughput of the irradiation facility, reduced energy costs, and a higher gross profit margin.

[0062] Figure 2 is an illustration of a Co-60 irradiator facility using batch transport and a photograph of Co-60 tubes emitting Cherenkov light in a storage pool. Co-60 systems typically operate in a batch mode, in which objects (products) are loaded onto transportable shelves and moved into a shielded irradiation chamber. The radioactive Co-60 material is lifted from the storage pool to the middle of the room, and the material is irradiated with a large amount of MeV gamma rays. Co-60 systems typically expose the pallet to the radiation through 1, 2, or 4 sides of the pallets in the room to improve the dose uniformity of the entire package. The DUR value of Co-60 systems is typically 2.0 to 2.5. For Co-60, the gamma-ray energy is almost monoenergetic (2 near photons), resulting in a relationship between a specific depth and the dose profile at a given effective density on the pallet. For denser materials, due to different depth profiles, this results in a higher dose near the outer edge of the pallet than in the middle. Single-sided irradiation exacerbates this defect, and two-sided and four-sided irradiation improves this defect. Rotating the pallet 90 degrees four times allows passage through the irradiation zone to achieve the dose. In 2023, the cost of cobalt-60 in the global market increased by more than four times and is constrained by limited supply under trade restrictions.

[0063] There are two main MeV accelerators available: an S-band microwave electron linear accelerator (linac) from 40 to 80 kV, and an RF recirculating electron accelerator (Rhodotron) from 120 to 240 kW. Rhodotron technology operates at 400 kHz, minimizing switching losses and skin depth effects, achieving higher efficiency - nearly twice as good as traditional S-band linacs at GHz frequencies; however, this comes at the cost of size, minimum power, and upfront capital expenditure. Large electron accelerators greater than 10 kW typically use bending / steering magnets to rasterize the electron beam to spread the heat load over a large area - and are used in conjunction with a horn-shaped converter target to produce a fan beam. The magnetic steering system and large-area format target are expensive, large, and heavy enough to require a crane for installation. Additionally, the thermal management system represents a large portion of the overall system. The emission target assembly can include an x-ray converter to capture electrons and convert them to bremsstrahlung, or it can include a thin vacuum window for direct electron beam irradiation processing. The latter has the advantage of direct electron-to-electron energy transfer, resulting in higher efficiency, while the former is an electron-to-photon-to-electron energy transfer, with the reduced solid angle leading to a lower overall energy transfer efficiency. The advantage of x-rays is that photons can penetrate deep into an object before generating Compton electrons to convert local energy into dose; however, electrons (charged) decelerate and attenuate immediately near the object surface, resulting in an exaggerated dose profile and a very high DUR rating.

[0064] Figure 3A Is a graphical rendering of two 40 to 80 kW S-band microwave linacs in a single-sided emission configuration for irradiating one or two trays traversing laterally through a large magnetic scan horn. Traditional techniques for full-tray (40”x48”x96”) irradiation from a single-point electron beam source (40 to 240 kW input electron beam) use a scan horn to spread the heat and dose loading, which results in dose loss / inefficiency at the tray / object corners. This results in over-dosing in certain areas and under-dosing in others. For food safety, all objects must receive a minimum dose and not exceed a maximum dose. Imposing constraints on the object leads to the system requiring tray rotation and a wide fan beam, resulting in wasted radiation, cost, and expense. Figure 3BIs a graphical rendering of the prior art, showing details of an irradiation processing facility with a vehicle, a bend, and a revolving door for rotating materials 90 and 180 degrees for dose control within a thick shielded bunker room. A pallet of materials will pass through the scanning system 2 to 4 times, where in subsequent channels, the materials will be rotated 90 or 180 degrees relative to the large accelerator. This process reduces the throughput of the physical plant (1 / 4x), and increases the physical cost and footprint for transportation and material handling (4x). As described subsequently in this disclosure, this can be improved through a system-level approach.

[0065] Figure 4 Is a graphical rendering of the prior art, showing a 160 to 240 kW high-power recirculating RF accelerator in a side-emitting configuration, with a large magnetic steering horn on a single x-ray converter target for material transport in a very thick shielded bunker room. A single-particle beam with a magnetic deflector is used to generate a fan beam of 5 or 7.5 MeV Ta x-ray bremsstrahlung on the horn target. The higher peak energy of the photons results in greater penetration and Compton scattering at the center of the pallet, thus improving the DUR compared to Co-60. The 5 MeV x-ray system typically achieves DUR values of 1.8 to 3.5. The 7.5 MeV x-ray system can achieve DUR values of 1.4 to 2.5. The lowest values are obtained using 360-degree point irradiation with a single-station irradiation with a rotating pallet.

[0066] Figure 5 Is a graphical rendering depicting a system for improving dose uniformity in a single-side-emitting configuration by a stop-and-scan process of rotating a single pallet stack 360 degrees. These systems reduce throughput due to mechanical segmentation and suffer from beam losses at the edges (i.e., top, bottom, sides) caused by the single fan beam emitted by the large magnetic steering horn.

[0067] For direct electron beam irradiation, the main driving factor is the very high electrical efficiency of conversion to dose. However, for large pallets and dense objects, the electron beam penetration depth is shallow, and its dose distribution is steep, which results in excessive DUR values and overexposure at the edges and underexposure in the middle.

[0068] For x-ray irradiation, understand the energy-angle correlation and the conversion from electron beam to photons. Figure 6A Illustratively depicts the energy-angle correlation and spatial distribution of the x-ray bremsstrahlung spectrum as a function of the electron energy incident on a thin target. Figure 6B Graphically summarizes the relative x-ray intensity of a 0.8 mm thick tungsten target at a given electron energy, including the percentage of forward and backward x-rays. Figure 6C Graphically depicts the variation of x-ray intensity with angle for a set of different target converter materials, showing the dependence of Z on the total yield and the angular distribution of forward / backward radiation.Figure 6D Graphically depicts the total x-ray conversion efficiency, divided into forward and backward radiation, of a fixed 5 MeV electron beam on W targets of different thicknesses. Figure 6E Graphically depicts the total x-ray conversion efficiency, divided into forward and backward radiation, at a fixed Ta target thickness for variable electron energies, illustratively showing the effect on the x-ray spectral distribution.

[0069] To understand how to use the spatial and energy angular distribution of x-rays, Figure 7A Graphically depicts the x-ray dose profile from a 5 MeV electron beam into a 0.8 mm Ta converter into a reference water volume, showing an asymmetry 10 times that of single-sided irradiation and a reduction in the received dose difference achieved with double-sided irradiation to a factor of 2. Figure 7B Graphically summarizes the results obtained with double-sided irradiation along the dose centerline to highlight the two-sided improvement in dose uniformity due to dose superposition. This can be improved through a system-level approach according to the present disclosure provided below. Figure 7A From a system-level approach, there are many challenges with electron beam incidence of 40 to 240 kW on an emission target.

[0070] There are many challenges with electron beam incidence of 40 to 240 kW on an emission target from a system-level approach. Figure 8A Is a schematic of the prior art depicting a general state-of-the-art electron utilization scheme where an electron beam is generated in a particle accelerator and the electrons enter a beam steering horn through a particle beam and reach a converter assembly (for x-rays) or a thin window for emitting the electrons into the air.

[0071] Figure 8B Is a photograph of a known S-band linear accelerator for emitting an electron beam that, due to its size, weight, and vertical installation above the transport device, lowers the system through a crane gantry through the roof of the facility.

[0072] Figure 8C Is a photograph of a known electron beam scanning horn for electron beam irradiation, including the coils and core of an electron beam scanning system that provides a tightly focused electron raster pattern on a thin extraction foil, as well as an air jet cooling device.

[0073] Figure 8DSchematically depicts the emission target region of a scanned horn tip with a Ta converter, direct water cooling, and a stainless steel backing. In the forward 2π solid angle direction, the conversion efficiency of electrons to X-ray bremsstrahlung: is approximately 10% for W at 5 MeV, and 13% for a Ta high-temperature target at 7.5 MeV. The available fraction of the converted forward photons is approximately 1 / 2 of this value, approximately 6% and 8% respectively. This is due to the dominance of low-energy X-rays below 1 MeV, which cannot penetrate deeply into palletized objects and result in shallow doses - thus causing DUR deviations and being filtered out - and a large number of photons emitted at a solid angle greater than 1 sr not reaching the object. Increasing the electron energy improves the forwardness of the photons, transfers more of the spectrum above 1 MeV, and increases the penetration power for pallet objects. Using tungsten and uranium above 5 MeV results in neutron emission due to electronuclear photodisintegration. Before significant neutron emission is initiated, tantalum and bismuth can accept up to 7.5 MeV. Due to the neutron effect, the IAEA limits the electron energy to 5 MeV, and only in selected countries is the limit increased to 7.5 MeV for tantalum targets. Higher energies result in "harder" X-ray spectra to generate and are also more forward-directed. Photons of higher energy can penetrate more deeply into pallets suitable for irradiating materials or materials of higher density objects. The stronger the forward direction of the X-rays, the greater the potential for irradiating objects (such as pallets) using radiation conversion. For lower energy X-rays, the radiation distribution is more spherical, with additional losses caused by photons traveling in the wrong direction. Improvements to traditional converter targets can increase the overall system-level efficiency.

[0074] High-gradient DC accelerator technology and high-gradient X-band microwave accelerator technology can achieve kW-level (1 to 10 kW) MeV electron (5 to 10 MeV) acceleration at a shape factor length scale of 1 m X 0.5 m X 0.5 m, while reducing capital expenditure and operating expenditure costs. Therefore, there is an option for an ultra-compact irradiation device that includes multiple kW-level compact linear accelerators that use new converter sources to generate electron beams or X-ray photon beams for irradiation, and provide multiplexed radiation beams around the object to improve DUR, while maintaining high facility throughput through a single-pass online system. In addition, having a distributed set of radiation beams and associated corresponding radiation detectors provides real-time volumetric dose feedback and the opportunity for adjustment.

[0075] First, turn attention to the emission target assembly. A 1 to 10 kW class electron accelerator source does not require the very large and complex magnetic scan horns shown in the prior art systems discussed above because the power density is much lower, and the emission target can be physically smaller. Utilizing high heat flux cooling solutions and phase change materials, its active area diameter is approximately 0.1 to 10 cm. The smaller active area size minimizes the atmospheric pressure across the vacuum boundary, thus allowing for a much thinner material compared to the prior art, which is 40 to 400 times larger in size. Figure 9A Schematically depicts an emission target assembly 931 according to the present disclosure, which is configured to emit radiation in the form of a forward electron beam 937, highlighting the basic structural elements coupled to the electron beam trajectory 936 (from an accelerator (not shown on the left) through the drift tube 934) of a compact linear accelerator system, including a vacuum-facing boundary 915, an optional heat conductor 917, an optional cooling layer 918, and an optional end cap layer 919 leading to the atmosphere. Here, the vacuum-facing boundary is a thin foil with a low vapor pressure and high heat tolerance, and has sufficient structural strength to hold the atmospheric pressure on one side and high vacuum on the other side, such as Al, Ti, Be, or an alloy, brazed into the assembly and connected to the vacuum drift tube 934. The vacuum-facing boundary 915 can be coated with a thin capping layer of vacuum-facing dimensions to resist oxidation, corrosion, contamination, or other weakening of the vacuum seal.

[0076] Figure 9B Schematically depicts an emission target assembly 931 configured to emit x-ray radiation 938 according to the present disclosure, highlighting the basic structural elements coupled to the electron beam trajectory 936 (from an accelerator (not shown on the left) through the drift tube 934) of a compact linear accelerator system, including a vacuum-facing boundary 915, a converter material 916, an optional heat conductor 917, a cooling layer 918, and an end cap layer 919 leading to the atmosphere. Again, the vacuum-facing boundary 915 can be coated with a thin capping layer on the vacuum side to resist oxidation, corrosion, contamination, or other weakening of the vacuum seal.

[0077] Figure 9CAlso illustratively depicted is an emission target assembly 931 configured to emit x-ray radiation 938 using a liquid converter target 968, which can also be used as a direct cooling structure by flowing to an external radiator (not shown). Also shown is an additional low-energy x-ray attenuation structure 965 for beam hardening, which can be placed at the distal end after the anti-corrosion interface layer 962. A high melting point, low vapor pressure material for the cover layer 960 is located on top of the vacuum-facing boundary 915. Surrounding the assembly is an emission target assembly housing 969, which is configured to provide a seal and a flow path for the liquid converter target 968. The liquid can be a pure metal such as Hg, or a cryogenic alloy with a phase change expansion margin (such as a Bi, Pb, In, Sn eutectic), or a heterogeneous liquid with a high-Z material. In the case of liquid mercury at room temperature, the photofission threshold increases to above 5.5 MeV. Thus, similar to U, the target is suitable for the IAEA standard of 5 MeV. However, Bi is similar to Ta and can be increased to 7.5 MeV without problems. The advantage of the liquid converter is that it reduces the need for a separate cooling layer, which adds additional material in the path of the x-rays and the object.

[0078] Figure 9D The geometry of the converter target 916 within the emission target assembly 931 is schematically depicted. The emission target assembly 931 is configured to provide an inclined surface for the incident electron beam 936 to modify the relationship between the effective thickness and the angle of on-axis bremsstrahlung generation, thereby modifying the bremsstrahlung x-ray energy-angle spectrum anisotropy. The illustratively depicted configuration affects the sidelobe photon flux and has an impact on reducing radiation shielding. Here, the entire assembly is shaped as a V-shaped or conical-like structure and is encapsulated in an assembly housing 969, including a vacuum-facing boundary layer 915, having a cover layer 960, an optional thermal layer 917, a cooling layer 918, and an end cap layer 919. The geometry of this illustrative example diffuses the thermal load from the electron beam over a larger surface area to obtain greater heat conduction and convective extraction, and provides two different path lengths for the generated photons and the scattered electrons.

[0079] It should be noted that the thermal layer and the cooling layer can include radiators, heat pipes, vapor chambers, liquid cooling, or heat transfer materials. In addition, low-energy attenuators can be used to scatter / minimize low-energy photons from the reaction object to reduce the shallow surface radiation dose. The low-energy attenuators are used to harden the spectrum and can be integrated with the assembly housing 969, or can be located outside the compact linear accelerator system and can be placed downstream of the directed radiation beam.

[0080] Selecting the crystal structure of the converter material at the atomic lattice parameter, as well as the orientation or stratification of the macroscopic grains, will have a significant impact on the energy-angle spectrum of the emitted radiation. Figure 10AAnother aspect of the present disclosure is also shown, which is to modify the bremsstrahlung x-ray energy-angle distribution 1047 and spectral anisotropy by designing the crystal structure orientation 1066 or bulk structure orientation 1067 of the converter material 1061 to be orthotropic with respect to the electron beam. Figure 10B Another aspect of the present disclosure is also shown, which is to modify the bremsstrahlung x-ray energy-angle distribution 1047 and spectral anisotropy by designing the crystal structure orientation 1066 or bulk structure orientation 1067 of the converter material 1061 to be substantially orthogonal to the electron beam. These two mutually exclusive atomic arrangements affect the channeling of the emitted bremsstrahlung to promote forward directivity, or to direct low-energy photons in the x-y plane relative to the electron beam z-axis. The former is beneficial for improving the effective electrical conversion efficiency from electron beam to photons, and the latter is more beneficial for minimizing the lower-energy shallow dose to the object affecting DUR.

[0081] Figure 11A and Figure 11B An example of a compact linear accelerator system is schematically depicted, which includes an electron accelerator 1130 directly coupled to an extended nozzle drift tube 1134 that injects electron trajectories 1136 for beam spreading 1146 to irradiate an emission target assembly 1131, and for different acceleration energies of 5 MeV and 3 MeV respectively, generates the energy-angle distributions 1147 of bremsstrahlung forward photons 1138 and backward photons 1139. The emitted radiation 1133 covers the energy-angle distribution 1147 shown by the range of the arrow and the gray area.

[0082] The compact linear accelerator system can be (for example) an X-band linear accelerator using split-cavity high-gradient acceleration units, or a high-gradient DC linear accelerator with a sealed vacuum tube to achieve MeV acceleration on a desktop. Compared with the current state-of-the-art magnetic steering horns, the tight coupling enables a small-diameter emission target assembly to be adapted to be tightly coupled with a shielding collimator to achieve minimized size and weight. Figure 12A and Figure 12B A shielding collimator 1232 tightly coupled to an extended nozzle drift tube 1234 positioned (as shown by arrow 1248) relative to an emission target assembly 1231 is schematically depicted to affect the bremsstrahlung energy-angle distribution 1247 to control the forward photons 1238 and the resulting collimated radiation beam 1229. This adjustment of the shielding collimator 1232 and the relative positioning (according to arrow 1248) can adjust the equivalent dose profile downstream of the object by modifying the finally generated collimated radiation beam 1229.

[0083] In addition, the style of the shielding collimator used can vary depending on the required set of collimated radiation beam spatial characteristics. Figure 12C and Figure 12DSchematically depicts a shielded collimator 1232 closely coupled to an extended nozzle drift tube (not shown) to physically collimate the forward photons in the ultimately generated directed radiation beam 1229 and transform it into a beam of symmetric shape or asymmetric shape for irradiating an object and obtaining a specific dose profile depending on the collimator exit shape 1271. Generally, since the shielded collimator is typically made of tungsten with high z and density, a conical beam is used for simplicity and processing cost. In Figure 12E additional physical structures / features for mitigating side lobes and scattered radiation can be found, Figure 12E is a schematic depiction of a shielded collimator 1232 with a toothed structure 1270 to facilitate the capture of backscattered radiation 1239, thereby minimizing scatter 1240 and redirecting it as forward radiation with lower effective energy.

[0084] Figure 13 Schematically depicts a compact linear accelerator system 1320, which includes an electron accelerator 1330 directly coupled to an extended nozzle drift tube 1334 that utilizes beam divergence 1346 from an electron trajectory 1336 to irradiate an emission target assembly 1331 to generate a forward electron beam 1337 of different accelerating energies. It should be noted that the spatial distribution of the forward electron beam 1337 is fixed based on the impact of the electron beam on the target within the emission target assembly 1331. By multiplexing multiple compact linear accelerator systems 1320 together into a stitching line or a quasi - continuous region for irradiation, this limited field of view can be alleviated.

[0085] Figure 14A Shows a hybrid approach. A schematic depiction of a compact linear accelerator system 1420, which includes an electron accelerator 1430 directly coupled to an extended nozzle drift tube 1434 that contains a beam deflector 1421 capable of moving an electron beam trajectory 1436 with beam divergence 1446 to irradiate an emission target assembly 1431 in an extended beam region 1422, thereby generating a forward electron beam 1437 rasterized over a raster beam region 1472 for different accelerating energies. It should be noted that the approach of this method is similar to the magnetically scanned horn with a programmed raster pattern summarized / discussed above to create an effective forward electron beam distribution.

[0086] Figure 14BSchematically depicts a compact linear accelerator system 1420, which includes an electron accelerator 1430 directly coupled to an extended nozzle drift tube 1434. The drift tube 1434 contains a beam deflector 1421 capable of diffusing an electron beam trajectory 1436 to irradiate an emission target assembly 1431 in an extended beam region 1422, thereby generating simultaneous, multiple, and / or overlapping forward electron beams 1437 for different acceleration energies. The beam deflector 1421 can also be extended to an x-y steering electrode 1424 to diffuse the electron beam trajectory 1436 into an x-y electron beam 1425, which enters a disordered magnetic array 1423 to be transformed into an r-θ electron beam, and the r-θ electron beam widely irradiates the emission target assembly 1431. The final result of this embodiment is that, in the quasi-steady state, the forward electron beam reaches a wider and broader irradiation region.

[0087] After describing examples of several emission sources, attention is now turned to the system-level architecture / components for performing irradiation, which include components of multiple integrated compact linear accelerator systems having material transport equipment. Figure 15A Schematically depicts a super-compact irradiation device 1501 suitable for phytosanitary and sterilization treatments, including one or more compact linear accelerator systems 1520 arranged around an object 1510 transport device 1512 for online exposure of the object. The compact linear accelerator system 1520 includes an electron accelerator, an emission target assembly, a shielding collimator, and generates a directional radiation beam 1529 that irradiates the object 1510 moving along the transport device 1512.

[0088] Multiple compact linear accelerator systems provide radiation doses from multiple angles. Figure 15B Schematically depicts the azimuthal placement 1502 of the compact linear accelerator system 1520 around the online object 1510 transport device 1512 for high-throughput phytosanitary and sterilization treatments.

[0089] Figure 15C Schematically depicts Figure 15A The configuration in is a super-compact irradiation device 1501 suitable for phytosanitary and sterilization treatments, in which one or more compact linear accelerator systems 1520 pivot around the object 1510 transport device 1512 into a longitudinal orientation 1573 for online exposure. Multiple directional radiation beams 1529 are aligned along the transport device 1512 to generate an overlapping radiation field 1528. According to the above illustrative example, the compact linear accelerator 1530 can be freely oriented along the transport equipment 1512 to control the dose to the object 1510.

[0090] Figure 16 Schematically depicts according to Figure 15A 、 15BConfigurations of 16C suitable for phytosanitary and sterilization treatments with a super-compact irradiation geometry / device, where one or more compact linear accelerator systems 1630 are vertically stacked beside an object 1610 for on-line exposure, thereby irradiating larger objects, such as stacks on a pallet 1611. The directed radiation beam 1629 from the emission target assembly 1631 can employ a beam deflector 1621, which can generate overlapping radiation beams 1629 that can be leveled and balance dose non-uniformities.

[0091] Figure 17A and Figure 17B Schematically depicts the dynamic energy-angle 1745 control using a relative position shielding collimator 1748 to adjust the directed radiation beam (e.g., beam 1729) towards the object 1710 to be treated, thereby adjusting the relative dose profile across the entire object 1710 using an overlapping radiation field 1728 and controlling the energy-angle distribution 1747. Each compact linear accelerator system 1730 can adjust its shielding collimator 1732 to affect the dose profile.

[0092] Figure 18A and Figure 18B Schematically depicts a feature of the present disclosure that involves multiple (four in this example) compact linear accelerator systems 1820 positioned in close proximity to an object 1810 such that multiple directed radiation beams 1829 use an overlapping radiation field 1828 to level the normalized dose (see the position-dependent dose bar graph 1849) across the entire object 1810 to improve the dose uniformity ratio (DUR) and reduce the difference between D max and D min The dose control points 1844 correspond to the columns of the normalized dose 1849 in the figure. By adjusting the relative position 1848 (z-cm) of the shielding collimator 1832, the beam energy (MeV), beam current (mA), and duty cycle (%DF) of the electron accelerator 1830, as well as the presence or absence of any low-energy shielding, and adjusting the longitudinal orientation 1873 and azimuthal placement 1801, the normalized dose depicted in the bar graph 1849 can be adjusted.

[0093] Figure 19A and Figure 19B Also extended Figure 18A and Figure 18B 's scheme to further improve dose uniformity, reduce the difference between D max and D min by providing additional compact linear accelerator systems 1920 positioned around the object 1910 to be irradiated, increasing throughput and improving processing speed. As Figures 18A to 18BAs indicated, individual adjustments of each compact linear accelerator system 1920 "source", adjustments of the relative position 1948 of the shielding collimator 1932 for energy-angle control 1945, adjustments of the accelerating energy, adjustments of the low-energy filter 1927 for beam hardening, adjustments of the beam current (flux), adjustments of the beam position, adjustments of the exposure time, rasterization or beam deflection, adjustments of the longitudinal orientation 1973 and the azimuthal placement 1901, and other techniques described herein can affect the normalized dose as shown in the bar graph 1949. The dose control point 1944 corresponds to the optimization of the normalized dose 1949 over the entire object 1910. Each directed radiation beam 1929 from the electron accelerator 1930 and the emission target assembly 1931 will generate a tunable overlapping radiation field 1928.

[0094] Figure 20 Schematically depicted is an ultra-compact irradiation device suitable for phytosanitary and sterilization treatments, which includes a number of compact linear accelerator systems arranged around an object transport device for on-line exposure. For example, 20 to 40 4 kW units will project a beam power of 80 to 160 kW, as an alternative to traditional large single-sided irradiation platforms with a low-cost, small facility size. Here, the directed radiation beams 2029 from multiple compact linear accelerator systems 2020 create an overlapping radiation field 2028 on one or more objects 2010 stacked on a tray 2011 and move on a transport device 2012. In this illustrative example, the compact linear accelerator systems are configured to include an array of multiple units positioned around the transport device 2012 to form an on-line, continuous, fast ultra-compact irradiation system.

[0095] For example, a 160 kW high-power recirculating electron accelerator system may require an upfront capital expenditure of $5 million for the machine, plus $4 million for the facility layout, transport device, and radiation shielding. A $100,000 4 kW compact linear accelerator system (which is multiplexed 40 times) will cost $4 million and, due to its compact design, requires only a single pass instead of 2 to 4 passes, as well as additional floor space and storage space requirements, and has a cost of $2 million for the facility layout, transport device, and radiation shielding. The $3 million capital expenditure savings is 50% of the $6 million installation cost of the ultra-compact irradiation device, and the system is scalable, with throughput expanded by adding units to encourage adoption.

[0096] Figure 21A and Figure 21BSchematically depicts an ultra-compact irradiation device employing a local radiation shield 2113 with a small-diameter access port 2114 for a compact linear accelerator system 2120 having an emission target assembly 2131 and a shielding collimator 2132, which greatly reduces the burden of backscattered photons and stray radiation on the facility, personnel, and equipment; and enables the compact linear accelerator systems 2120 to be placed closely together to achieve an overlapping radiation field 2128, high area and volume density, thereby achieving dose uniformity and throughput for an object 2110 on a transport device 2112. The small-diameter emission target assembly 2113 can be inserted through the small-diameter access port 2114 and closely coupled to the shielding collimator 2132 to provide excellent overall radiation shielding and sealing within the object 2110 transport device 2112 passageway. This reduces the total facility radiation shielding required.

[0097] Figure 22 Schematically depicts another illustrative example according to the present disclosure that uses magnetic electron transport to direct and guide an electron beam to an emission target assembly further away from or at an angle to an electron accelerator to generate a directed radiation beam. In this figure, a magnetic structure 2235 provides guidance for an electron trajectory 2236 along a non-linear drift tube 2234 towards the emission target assembly 2231 for the emitted radiation 2233 in the form of a forward-directed electron beam 2237 or forward photons 2238 and backscattered photons 2239.

[0098] Figure 23A Also shown is Figure 22 features introduced in and extended to multiple compact linear accelerator systems 2230 that are arranged to generate an overlapping radiation field from multiple directed radiation beams 2329 surrounding a region containing an object to be irradiated. As a specific example, Figure 23B and Figure 23C shows an electron accelerator 2330 longitudinally positioned along a transport axis 2312 and an electron beam delivery drift tube 2334 having a 90-degree turn for entry into an emission target assembly 2331 that emits radially inwards towards a central object 2310. Multiple compact linear accelerator systems can be arranged around the object to achieve more uniform irradiation, up to approximately 360-degree irradiation.

[0099] Figure 24A flowchart of an operation that summarizes a method for providing improved overall system efficiency for food irradiation, phytosanitary treatment, object exposure, and sterilization. The method begins at 2480, where a compact linear accelerator system is positioned around an object transport device. Thereafter, during 2481, the appropriate weight and volume of the object are measured, and an effective density distribution is determined using other data inputs. This can be from a variety of means, optical, mass sensors, distribution information, inventory information, attenuation scans with x-rays, etc. The method also includes, during 2482, using the target unit dose for treatment (determined by regulatory or customer requirements), the mass / density distribution over the object volume (acquired during 2481), the position of the compact linear accelerator around the transport device (from operation 2480), and the required transport speed, to calculate the required dose parameters for the compact linear accelerator system for the object of interest. The method also includes calculating the required dose strategy for a given device configuration based on 2482 and recommending adjustments to the beam space as well as the energy-angle distribution (operation 2483), energy filtering for beam hardening (operation 2484), acceleration energy and penetration (operation 2485), beam current and beam-on time (fluence) (operation 2486), combining beam deflectors or adjusting the beam path to rasterize over the object (operation 2487), and independent operation of each accelerator.

[0100] The method also includes adjusting (during 2483) the shielding collimator to shape the beam distribution and energy in space; introducing a low-energy filter or replacing the low-energy filter with different materials and thicknesses to achieve shallow dose attenuation (during 2484), adjusting the acceleration energy during irradiation for photon peak spectral profiles or the electron range vs. depth relationship (during 2485); modulating the beam current (and duty cycle %) for a given transport speed or dwell time (during 2486), and physically rasterizing the object or moving the directed radiation beam over the object by beam deflection or overlapping radiation fields (during 2487). Thereafter, the ultra-compact irradiation device is activated to irradiate the object 2490. The method starting with the arrangement of the compact linear accelerator system positioned around the object transport device 2492 achieves an improvement in the dose uniformity ratio and a shortening of the linear exposure time. Part of the calculation (operation 2482) is to generate an effective density distribution over the 3D tray / packaging / object volume by measuring and calculating the required dose strategy for a given device configuration. The disclosed system includes a plurality of compact linear accelerator systems, which, in combination with the method described herein, are capable of independently adjusting the operation of each accelerator to achieve independent beam space as well as energy-angle distribution, energy filtering for beam hardening, acceleration energy, beam current, and overlapping radiation fields.

[0101] At Figure 24Building on the method, the irradiation device can incorporate an in-situ feedback mechanism to determine the 2D area and 3D volume dose distributions of the irradiated object for quality control, dose mapping, and certification. One challenge in phytosanitary irradiation is dose verification and documentation of dose verification. The method described herein will complement external NIST-traceable dosimetry tags and provide additional value-added quality assurance for food safety users. Figure 25 is a block diagram of a schematic of another embodiment of the present disclosure, detailing a method that uses radiation detectors placed near the object to be irradiated, in combination with a reference calibration source and the actual object to be irradiated, to measure and evaluate the transmitted, scattered, and backscattered photon responses from the operation of a compact linear accelerator system to calculate the effective dose response of the entire object, enabling the calculation of differential adjustments to operating parameters (e.g., E MeV (t), I mA (t), accelerator beam time, beam steering, beam space, and energy angle adjustments, low-energy x-ray filters, collimation changes, etc.), and continue exposure to achieve sufficient dose, DUR profile, and exposure time. Operating each compact linear accelerator system independently enables the calculation of the adjoint flux of the differential object response function and the 3D dose mapping of the entire object. Using this differential irradiation response of multiple compact linear accelerator systems, an effective dose strategy can be designed by adjusting the accelerator conditions parametrically to achieve a minimum dose threshold, not exceeding the dose upper limit, achieving optimized DUR, and minimizing the exposure time.

[0102] The method starts with a compact linear accelerator system around an object transport device positioned in the irradiation area (operation 2480), and emission detectors are positioned around the irradiation area (operation 2488), the emission detectors having a specific collimation and acceptance to define a volume scan area for collecting the transmitted and scanned radiation. Each compact linear accelerator system operates independently and is scanned with electron energy (MeV) and beam current (mA) as test variables (operation 2489) to generate directed radiation that interacts, transmits, and scatters with the object and a calibration reference source. The method also includes measuring and evaluating the response of the test variables from each compact linear accelerator system at the radiation detector (operation 2492). In combination with other potential metrics, such as a desired 3D volume density distribution, during 2481, the method requires predicting a dose response from the test variables and other dose calculations based on the radiation detected during 2493. Using this data, a dose profile of the 3D object to be irradiated can be inferred as baseline operating parameters of the compact linear accelerator system. The method also includes calculating the adjustments required to the operating parameters of each compact linear accelerator system to achieve sufficient dose, DUR profile, and exposure time (operation 2495). The method also describes making these adjustments (also during operation 2495) to operating parameters such as acceleration energy, beam current, beam path, shielding collimator position, beam-on time, beam steering, low energy filtering, duty cycle %, etc. The object can be irradiated (during 2490), and differential measurements can be made during irradiation to perform adjoint calculations, make additional adjustments, and repeat / continue irradiation (during 2496) to further achieve the goal of a sufficient dose distribution throughout the object, define minimum / maximum dose, optimize DUR, and / or minimize linear exposure time, and achieve throughput and energy efficiency (operation 2492).

[0103] Figure 26 is configured to effect differential adjustment of the radiation dose and monitor the actual delivery to Figure 25Detailed schematic diagram of the apparatus for the dose conditions of the irradiated object described in detail. In the above illustrative example, the compact linear accelerator 2620 emits radiation 2633, which penetrates the object 2610 and is transmitted along path 2641, scattering events 2640 occur and the forward scatter 2652 passes through the object 2610, or scattering events 2640 occur and the backscatter 2643 comes from the object 2610, or scattering events 2640 occur within the reference calibration source 2655 to generate calibration radiation 2656. The transmitted or scattered radiation is detected by a series of discrete detectors 2650 or detector arrays 2657, where appropriate detector collimation 2651 is set / located around the object 2610 to be irradiated, creating a detector acceptance region 2652, thereby creating a 2D dose integration volume 2653 and a 3D object voxel dose region 2654. For Figure 25 the method in, the superposition principle can be used to calculate the differential object adjoint response function for the contribution of each compact linear accelerator to irradiating the object. In addition, the reference calibration source 2655 also serves as a reference material in the collimated radiation beam 2629, providing a known calibration check for detector drift, gain, and degradation over time in the absence of an object in the transport device and the irradiation area.

[0104] Figure 27 is configured to perform Figure 25 the method and Figure 26 the apparatus for operating dose control (e.g., 400 Gy ± 20 Gy) and auditable verification for each irradiated object. Operating each compact linear accelerator system independently enables the calculation of the adjoint flux for the differential object response function and the 3D dose mapping of the entire object. The differential object adjoint response function can be calculated for the contribution of each compact linear accelerator to irradiating the object. Using this differential irradiation response of multiple compact linear accelerator systems, an effective dose strategy can be designed by adjusting each accelerator condition parametrically to sum and achieve a minimum dose threshold, not exceeding the dose upper limit, to achieve an optimized DUR, and to minimize the exposure time. Real-time feedback enables the external processing unit to calculate the differential adjustment to the operating parameters (e.g., E MeV (t), I mA (t), accelerator beam time, beam steering, beam space and energy angle adjustment, low-energy x-ray filter, collimation change, etc.), and continue the exposure to reach a sufficient dose, DUR profile, and exposure time.

[0105] In Figure 27In this case, a directed radiation beam 2729 is emitted into an object 2710. The transmitted, scattered, and calibrated radiation is picked up by one or more detectors 2750, where detector collimation 2751 defines a specific field for generating a 2D dose integration volume and a 3D object voxel dose region. As each compact linear accelerator system 2720 operates, differential dose responses can be measured and estimated simultaneously based on an adjoint calculation of the individual contributions of the detectors to the specific compact linear amplifier. An external processing unit 2758 quickly calculates the differential responses from each compact linear accelerator and calculates adjustments to the compact linear amplifier system to optimize specific constraints: throughput, DUR maximum, minimum Gray dose, not exceeding the maximum Gray dose, etc. The external processing unit 2758 sends commands to the compact linear accelerator system 2720 to adjust parameters and execute a dose plan. The system can also measure the sum of the dose response functions of all compact linear accelerators to determine if any drift or additional corrections are needed. This method and apparatus can self-manage inconsistencies in object products, such as mixed fruits and vegetables, differences between different boxes or batches.

[0106] In summary, using a 0.1 to 10 kW class source can improve the efficiency of a small-diameter emission target assembly tightly coupled to a shielding collimator and reduce shielding / facility costs. Multiple linear accelerator sources can be configured in an arrangement around the object to be irradiated to provide excellent dose uniformity and irradiation speed using customized electron energies, collimation, and beam currents, enabling precise dose control. Using multiple tightly coupled electron accelerators and energy-angle selection, accelerator energy control, and beam control, with low-energy shallow dose filtering, a DUR close to 1 can be achieved. The online transport of large trays can be used for a smaller facility footprint. Using a small target converter on the extended nozzle of an electron accelerator can remove the very large scanning (raster) horns used in traditional systems, and the accelerator integrates a compact and modular facility shield. Additionally, using a 0.1 to 10 kW class compact electron accelerator, multiple sources can be multiplexed around the object for scanning on the move without switching transport conveyors, rotating trays, or object bins, thereby minimizing start / stop and movement time losses, and reducing the overall footprint of the transport conveyor system compared to 2-point and 4-point rotating gates with expensive transport conveyors and flipping mechanisms (for sealed bins) with parallel paths. Similarly, the labor costs for unloading, unpacking, repackaging, and reloading can also be alleviated.

[0107] It should be understood that the above description relates to examples showing preferred configurations of the system. However, it is contemplated that other embodiments of the present invention may differ in details from the above examples. As previously mentioned, all references to the present invention are for the purpose of referring to the specific examples of the present invention being discussed at that time and do not imply any limitation on the scope of the present invention. All language regarding distinctions and disparagements of each feature is intended to indicate a lack of preference for those features, but does not exclude them entirely from the scope of the present invention unless otherwise stated.

[0108] In the context of describing the present invention (especially in the context of the following claims), the terms "a", "an", "the", and similar references should be construed to cover both the singular and the plural unless otherwise specified herein or the context clearly dictates otherwise. Unless otherwise specified, the terms "comprising", "having", "including", and "consisting of" should be construed as open-ended terms (i.e., "including but not limited to"). Unless otherwise specified herein, the recitation of numerical ranges herein is merely intended as a shorthand method of referring individually to each separate numerical value within the range, and each separate numerical value is incorporated into the specification as if it were recited individually herein. Unless otherwise specified herein or the context clearly dictates otherwise, all methods described herein can be performed in any suitable order. The use of any and all examples, or exemplary language (e.g., "such as") provided herein is merely intended to better illustrate the present invention and does not pose a limitation on the scope of the present invention unless otherwise required. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the present invention.

[0109] Accordingly, the present invention includes all modifications and equivalents of the subject matter recited in the appended claims of the present invention as permitted by applicable law. In addition, unless otherwise indicated herein or otherwise clearly contradicted by the context, any combination of the above elements in all possible variations is included in the present invention.

Claims

1. A food irradiation system, the food irradiation system comprising a plurality of compact linear accelerator systems, Among them, Each of the plurality of compact linear accelerator systems includes: A high-energy particle beam source that provides a particle beam up to 10 MeV; An emission target assembly configured to generate bremsstrahlung x-rays when struck by particles of the particle beam; and A drift tube through which the particle beam passes on a path from the high-energy particle beam source to the emission target assembly, wherein the emission target assembly is positioned at a distal end of the drift tube for direct impingement of the particle beam to generate the bremsstrahlung x-rays in a directional radiation beam, and wherein one of the plurality of compact linear accelerator systems is positioned separately such that the plurality of compact linear accelerator systems, as a group, provide directional radiation beam coverage for a total cumulative volume at a specified radiation dose level.

2. The system according to claim 1, wherein, A shielding collimator is provided external to the drift tube and near the emission target assembly, wherein the shielding collimator defines a radiation dispersion pattern of the bremsstrahlung x-rays in the directional radiation beam.

3. The system according to claim 2, wherein The shielding collimator is configured to be adjusted relative to the emission target assembly.

4. The system according to claim 3, wherein, The radiation dispersion pattern is modified in terms of space and energy.

5. The system according to claim 3, wherein Adjusting relative to the emission target assembly helps to adjust the radiation pattern of the bremsstrahlung x-rays in the directional radiation beam.

6. The system according to claim 1, wherein The emission target assembly includes a converter target material that generates the bremsstrahlung x-rays when struck by particles of the particle beam.

7. The system according to claim 6, wherein, The orientation of the converter target material is anisotropic.

8. The system according to claim 1, wherein The high-energy particle beam source is an electron accelerator.

9. The system according to claim 1, wherein The emission target assembly allows particles of the particle beam to pass through.

10. The system according to claim 1, wherein, The drift tube is configured as an extended nozzle.

11. The system according to claim 1, wherein, The path of the particle beam from the high-energy particle beam source to the emission target assembly is a curved path defined by an external magnetic field source.

12. The system according to claim 11, wherein, The high-energy beam sources of the plurality of compact linear accelerator systems are maintained in positions close to other high-energy beam sources, and wherein, on the respective curved paths of the respective drift tubes, the respective light beams are directed to separately positioned emission target assemblies oriented to provide the directional radiation beam coverage for the total cumulative volume at a specified radiation dose level.

13. The system according to claim 1, the system further comprising a local radiation shield positioned to contain the energy of the directional radiation beam within an irradiation processing space.

14. The system according to claim 1, wherein, At least one compact linear accelerator system includes a beam deflector positioned before the emission target assembly and configured to change the trajectory of the particle beam toward a specific location on the emission target assembly.

15. The system according to claim 1, the system further comprising at least one radiation detector positioned to receive energy from one or more compact linear accelerator systems, wherein, The radiation detector provides information indicating that the directional radiation beam coverage is provided for the total cumulative volume at a specified radiation dose level.

16. The system according to claim 15, wherein, The radiation detector is positioned within a detector collimator to define a volume from which the radiation detector receives the directional radiation beam of the compact linear accelerator system.

17. The system according to claim 16, further comprising a calibration unit positioned within the total cumulative volume, the calibration unit generating calibration radiation sensed by the radiation detector.

18. A pallet irradiation system, the pallet irradiation system comprising: a transport device configured to carry a pallet supporting an object to be irradiated; and a food irradiation system according to any one of claims 1 to 17.

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