Non-intrusive method to identify presence of nuclear materials using energetic prompt neutrons from photon-induced fission

Abstract

Methods and systems for non-intrusively detecting the existence of fissile materials in a container via the measurement of energetic prompt neutrons are disclosed. The methods and systems use the unique nature of the prompt neutron energy spectrum from photo-fission arising from the emission of neutrons from almost fully accelerated fragments to unambiguously identify fissile material. The angular distribution of the prompt neutrons from photo-fission and the energy distribution correlated to neutron angle relative to the photon beam are used to distinguish odd-even from even-even nuclei undergoing photo-fission. The independence of the neutron yield curve (yield as a function of electron beam energy or photon energy) on neutron energy also is also used to distinguish photo-fission from other processes such as (γ, n). Different beam geometries are used to detect localized samples of fissile material and also fissile materials dispersed as small fragments or thin sheets over broad regions. These signals from photo-fission are unique and allow the detection of any material in the actinide region of the nuclear periodic table.

1 . A method of determining a possible presence of a material comprising an actinide in a container, comprising:
 a) locating the container such that at least one neutron detector capable of distinguishing between photons and neutrons is positioned to view the said container at a first viewing angle relative to a photon beam;   b) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than a first predetermined cutoff photon energy;   c) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container;   d) for each of a plurality of said detected energetic prompt neutrons, determining an energy of the said detected neutron; and   e) based upon the determined energy of at least one of said detected energetic prompt neutrons exceeding a predetermined value, determining that the material comprising the actinide is possibly present in the container.   
     
     
         2 . The method of  claim 1 , wherein the at least one neutron detector is shielded. 
     
     
         3 . The method of  claim 1 , wherein the predetermined value is a difference between the first predetermined cutoff photon energy and a lower energy. 
     
     
         4 . The method of  claim 3 , wherein the lower energy is a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         5 . The method of  claim 3 , wherein the lower energy is no greater than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         6 . The method of  claim 3 , wherein the lower energy is a predetermined amount less than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         7 . The method of  claim 3 , wherein the lower energy is determined based upon materials potentially present in the container. 
     
     
         8 . The method of  claim 3 , wherein the lower energy is determined based upon materials present in the container. 
     
     
         9 . The method of  claim 1 , wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a bremsstrahlung beam produced by electrons of the first predetermined cutoff energy. 
     
     
         10 . The method of  claim 1 , wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a monochromatic photon beam. 
     
     
         11 . The method of  claim 1 , wherein determining the energy of the said detected neutron comprises measuring a time of flight of the said detected neutron. 
     
     
         12 . The method of  claim 1 , wherein determining the energy of the said detected neutron comprises analyzing an energy deposited in at least one of said at least one neutron detector. 
     
     
         13 . A method of determining a presence of a material comprising an actinide in a container, comprising:
 a) locating the container such that at least one neutron detector capable of distinguishing between photons and neutrons is positioned to view the said container at a first viewing angle relative to a photon beam;   b) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than a first predetermined cutoff photon energy;   c) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container;   d) for each of a plurality of said detected energetic prompt neutrons, determining an energy of the said detected neutron; and   e) based upon the determined energy of at least one of said detected energetic prompt neutrons exceeding a predetermined value,
 i) illuminating at least a portion of the said container with the photon beam; 
 ii) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container; 
 iii) for each of a plurality of said detected energetic prompt neutrons, determining an energy of the said detected neutron; and 
   f) based upon determined energies of at least some of the energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the container, determining that the material comprising the actinide is present in the container.   
     
     
         14 . The method of  claim 13 , wherein the at least one neutron detector is shielded. 
     
     
         15 . The method of  claim 13 , wherein the predetermined value is a difference between the first predetermined cutoff photon energy and a lower energy. 
     
     
         16 . The method of  claim 15 , wherein the lower energy is a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         17 . The method of  claim 15 , wherein the lower energy is no greater than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         18 . The method of  claim 15 , wherein the lower energy is a predetermined amount less than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         19 . The method of  claim 15 , wherein the lower energy is determined based upon materials potentially present in the container. 
     
     
         20 . The method of  claim 15 , wherein the lower energy is determined based upon materials present in the container. 
     
     
         21 . The method of  claim 13 , wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a bremsstrahlung beam produced by electrons of the first predetermined cutoff energy. 
     
     
         22 . The method of  claim 13 , wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a monochromatic photon beam. 
     
     
         23 . The method of  claim 13 , wherein determining the energy of the said detected neutron comprises measuring a time of flight of the said detected neutron. 
     
     
         24 . The method of  claim 13 , wherein determining the energy of the said detected neutron comprises analyzing an energy deposited in at least one of said at least one neutron detector. 
     
     
         25 . A method of determining a possible presence of a material comprising an actinide in a container, comprising:
 a) locating the container such that at least one neutron detector capable of distinguishing between photons and neutrons is positioned to view the said container at a first viewing angle relative to a photon beam;   b) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than a first predetermined cutoff photon energy;   c) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container;   d) for each of a plurality of said detected energetic prompt neutrons, determining a minimum energy of the said detected neutron; and   e) based upon the determined minimum energy of at least one of said detected energetic prompt neutrons exceeding a predetermined value, determining that the material comprising the actinide is possibly present in the container.   
     
     
         26 . The method of  claim 25 , wherein the at least one neutron detector is shielded. 
     
     
         27 . The method of  claim 25 , wherein the predetermined value is a difference between the first predetermined cutoff photon energy and a lower energy. 
     
     
         28 . The method of  claim 27 , wherein the lower energy is a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         29 . The method of  claim 27 , wherein the lower energy is no greater than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         30 . The method of  claim 27 , wherein the lower energy is a predetermined amount less than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         31 . The method of  claim 27 , wherein the lower energy is determined based upon materials potentially present in the container. 
     
     
         32 . The method of  claim 27 , wherein the lower energy is determined based upon materials present in the container. 
     
     
         33 . The method of  claim 25 , wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a bremsstrahlung beam produced by electrons of the first predetermined cutoff energy. 
     
     
         34 . The method of  claim 25 , wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a monochromatic photon beam. 
     
     
         35 . The method of  claim 25 , wherein determining the minimum energy of the said detected neutron comprises analyzing an energy deposited in at least one of said at least one neutron detector. 
     
     
         36 . A method of detecting a presence of a material comprising an actinide in a container, comprising:
 a) locating the container such that at least one neutron detector capable of distinguishing between photons and neutrons is positioned to view the said container at a first viewing angle relative to a photon beam;   b) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than a first predetermined cutoff photon energy;   c) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container;   d) for each of a plurality of said detected energetic prompt neutrons, determining a minimum energy of the said detected neutron;   e) based upon the determined minimum energy of at least one of said detected energetic prompt neutrons exceeding a predetermined value,
 i) illuminating at least a portion of the said container with the photon beam; 
 ii) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container; 
 iii) for each of a plurality of said detected energetic prompt neutrons, determining a minimum energy of the said detected neutron; and 
   f) based upon determined minimum energies of at least some of the energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the container, determining that the material comprising the actinide is present in the container.   
     
     
         37 . The method of  claim 36 , wherein the at least one neutron detector is shielded. 
     
     
         38 . The method of  claim 36 , wherein the predetermined value is a difference between the first predetermined cutoff photon energy and a lower energy. 
     
     
         39 . The method of  claim 38 , wherein the lower energy is a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         40 . The method of  claim 38 , wherein the lower energy is no greater than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         41 . The method of  claim 38 , wherein the lower energy is a predetermined amount less than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         42 . The method of  claim 38 , wherein the lower energy is determined based upon materials potentially present in the container. 
     
     
         43 . The method of  claim 38 , wherein the lower energy is determined based upon materials present in the container. 
     
     
         44 . The method of  claim 36 , wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a bremsstrahlung beam produced by electrons of the first predetermined cutoff energy. 
     
     
         45 . The method of  claim 36 , wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a monochromatic photon beam. 
     
     
         46 . The method of  claim 36 , wherein determining the minimum energy of the said detected neutron comprises analyzing an energy deposited in at least one of said at least one neutron detector. 
     
     
         47 . A method of determining a possible presence of a material comprising an actinide in a container, comprising:
 a) locating the container such that at least one neutron detector capable of distinguishing between photons and neutrons is positioned to view the said container at a first viewing angle relative to a photon beam;   b) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than a first predetermined cutoff photon energy;   c) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container;   d) determining that an energy of at least one of said detected energetic prompt neutrons exceeds a predetermined value; and   e) based upon the determination that the energy of the at least one of said detected energetic prompt neutrons exceeds the predetermined value, determining that the material comprising the actinide is possibly present in the container.   
     
     
         48 . The method of  claim 47 , wherein the at least one neutron detector is shielded. 
     
     
         49 . The method of  claim 47 , wherein the predetermined value is a difference between the first predetermined cutoff photon energy and a lower energy. 
     
     
         50 . The method of  claim 49 , wherein the lower energy is a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         51 . The method of  claim 49 , wherein the lower energy is no greater than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         52 . The method of  claim 49 , wherein the lower energy is a predetermined amount less than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         53 . The method of  claim 49 , wherein the lower energy is determined based upon materials potentially present in the container. 
     
     
         54 . The method of  claim 49 , wherein the lower energy is determined based upon materials present in the container. 
     
     
         55 . The method of  claim 47 , wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a bremsstrahlung beam produced by electrons of the first predetermined cutoff energy. 
     
     
         56 . The method of  claim 47 , wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a monochromatic photon beam. 
     
     
         57 . The method of  claim 47 , wherein determining that the energy of the at least one of said detected energetic prompt neutrons exceeds a predetermined value comprises analyzing an energy deposited in at least one of said at least one neutron detector. 
     
     
         58 . A method of detecting a presence of a material comprising an actinide in a container, comprising:
 a) locating the container such that at least one neutron detector capable of distinguishing between photons and neutrons is positioned to view the said container at a first viewing angle relative to a photon beam;   b) illuminating at least a portion of the said container with the photon beam comprising photons of energies no greater than a first predetermined cutoff photon energy;   c) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container;   d) determining that an energy of at least one of said detected energetic prompt neutrons exceeds a predetermined value;   e) based upon the determination that the energy of the at least one of said detected energetic prompt neutrons exceeds a predetermined value,
 i) illuminating at least a portion of the said container with the photon beam; 
 ii) detecting in at least one of said at least one neutron detector some energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the said container; 
 iii) determining that energies of at least some of said detected energetic prompt neutrons exceed a predetermined value; and 
   f) based upon the determination that the energies of at least some of the energetic prompt neutrons produced by fission reactions from an interaction of the said photon beam with at least a portion of the container exceed a predetermined value, determining that the material comprising the actinide is present in the container.   
     
     
         59 . The method of  claim 58 , wherein the at least one neutron detector is shielded. 
     
     
         60 . The method of  claim 58 , wherein the predetermined value is a difference between the first predetermined cutoff photon energy and a lower energy. 
     
     
         61 . The method of  claim 60 , wherein the lower energy is a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         62 . The method of  claim 60 , wherein the lower energy is no greater than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         63 . The method of  claim 60 , wherein the lower energy is a predetermined amount less than a threshold energy for production of neutrons by a (γ, n) process in a specified material. 
     
     
         64 . The method of  claim 60 , wherein the lower energy is determined based upon materials potentially present in the container. 
     
     
         65 . The method of  claim 60 , wherein the lower energy is determined based upon materials present in the container. 
     
     
         66 . The method of  claim 58 , wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a bremsstrahlung beam produced by electrons of the first predetermined cutoff energy. 
     
     
         67 . The method of  claim 58 , wherein the photon beam comprising photons of energies no greater than the first predetermined cutoff photon energy is a monochromatic photon beam. 
     
     
         68 . The method of  claim 58 , wherein determining that the energy of the at least one of said detected energetic prompt neutrons exceeds a predetermined value comprises analyzing an energy deposited in at least one of said at least one neutron detector.