Neutron detector using neutron absorbing scintillating particulates in plastic

Abstract

A neutron detector composed of a matrix of scintillating particles imbedded in a lithiated glass is disclosed. The neutron detector detects the neutrons by absorbing the neutron in the 6 Li isotope which has been enriched from the natural isotopic ratio to a commercial ninety five percent. The utility of the detector is optimized by suitably selecting scintillating particle sizes in the range of the alpha and the triton. Nominal particle sizes are in the range of five to twenty five microns depending upon the specific scintillating particle selected.

1 . A neutron detector comprising: 
 a glass medium;    a first material which yields at least one of a triton, an alpha particle and a fission fragment when said first material absorbs a neutron, said first material being incorporated into said glass medium;    a second material embedded within said glass medium, said second material consisting of scintillating particles which scintillate when traversed by said at least one of a triton, an alpha particle and a fission fragment, said second material being defined by small particulates such that said glass medium surrounding said small particulates when emitting charged particles from the constituent within said glass medium is thin relative to a range of said charged particles;    a transparent plastic into which said glass medium, said first material and said second material are dispersed; and    a surface coating disposed on said transparent plastic for reflecting scintillation light pulses.    
   
   
       2 . The neutron detector of  claim 1  wherein said glass medium contains a constituent that absorbs a neutron and subsequently and promptly emits a charged particle from the group consisting of Li-6 and B-10.  
   
   
       3 . The neutron detector of  claim 2  wherein said glass medium is a lithiated sol-gel glass, and wherein a composite mass of said lithiated sol-gel glass and said scintillating particles is polymerized to a mass and heat-treated to form a rigid structure.  
   
   
       4 . The neutron detector of  claim 3  wherein said scintillating particulates are uniformly mixed within said glass medium.  
   
   
       5 . The neutron detector of  claim 2  wherein said scintillating particulates are finely powdered and mixed into said glass medium to form a glass medium/scintillation particulate mixture, said glass medium being in a melted state, said glass medium/scintillation particulate mixture then being solidified.  
   
   
       6 . The neutron detector of  claim 2  wherein said scintillating particulates are finely powdered, and wherein said glass medium is powdered, said scintillating particulates and said glass medium being mixed to form an aggregate mixture, said aggregate mixture being melted and then solidified.  
   
   
       7 . The neutron detector of  claim 2  wherein said scintillating particulates are finely powdered, said scintillating particulates being mixed into a sol-gel precursor to glass, said sol-gel precursor containing a constituent of said glass medium, said scintillating particulates being locked into said glass medium as polymerization occurs.  
   
   
       8 . The neutron detector of  claim 2  wherein said scintillating particulates are overcoated by said glass medium, said scintillating particles being processed to a size in the range of from nominally five to twenty five microns in diameter referenced to spherical particulates, said range being selected to optimally absorb charged particles emitted within said glass medium.  
   
   
       9 . The neutron detector of  claim 2  wherein said scintillating particles are selecting from the group consisting of: cerium doped strontium sulfide, bismuth doped strontium sulfide, cerium activated calcium sulfide, europium activated calcium sulfide, bismuth germanate, cerium activated yttrium silicate, aluminum perovskite, cerium activated yttrium aluminum garnet, terbium activated yttrium aluminum garnet, cerium activated lutetium oxyorthosilicate, europium activated yttrium oxide, europium activated calcium fluoride, gallium activated zinc oxide, thallium-activated cesium iodide, europium activated lanthanum oxsulfide, manganese-lead activated calcium silicate, europium-activated gadolinium oxysulfide, europium activated indium borate, cerium-activated calcium sulfide, and zinc sulfide activate with silver.  
   
   
       10 . The neutron detector of  claim 9  wherein said scintillating particles are mechanically sized in the range of from five to twenty five microns, said range being selected to optimally absorb charged particles emitted within said glass medium and such that charged particles are subjected to ionization from reaction products of absorption in said glass medium.  
   
   
       11 . The neutron detector of  claim 1  wherein said scintillating particulates are a scintillating molecular compound including at least one of PPO and POPOP, said scintillating molecular compound having attached a molecular entity containing lithium such that each of said scintillating particles is a mass composed of fluor/lithium molecules distributed within said transparent plastic.  
   
   
       12 . The neutron detector of  claim 1  wherein said transparent plastic includes a plurality of transparent plastic elements, said glass medium, said first material and said second scintillator material being dispersed in said plurality of transparent plastic elements, whereby detection of neutrons in each of said plurality of transparent plastic elements is identified individually and the occurrence of the absorption of a neutron is temporally identified with respect to a repeating fiducial timing signal thus allowing each neutron detection event in each of said plurality of transparent plastic elements to be analyzed with respect to each other.  
   
   
       13 . The neutron detector of  claim 2  wherein said glass medium defines a rigid structure and is mechanically pulverized into glass particulates in the range five to twenty five microns, such as particulates being a composite of the lithiated glass and said scintillating particles.  
   
   
       14 . The neutron detector of  claim 13  wherein said glass medium comprises composite particles such that absorption of a neutron results in an ionization path yielding a light pulse characteristic of said scintillating particles.  
   
   
       15 . The neutron detector of  claim 1  wherein said transparent plastic is selected from the group consisting of at least polystyrene, polyvinyl toluene and polymethylmethacrylate.  
   
   
       16 . The neutron detector of  claim 1  wherein said surface coating contains titanium dioxide.  
   
   
       17 . The neutron detector of  claim 1  further comprising at least one wavelength shifting fiber and at least one light detecting element, said wavelength shifting fiber being secured in optical communication between said transparent plastic and said light detecting element, whereby scintillation light generated within said transparent plastic travels through said wavelength shifting fiber toward said light detecting element.  
   
   
       18 . The neutron detector of  claim 17  wherein said light detecting element is selected from the group consisting of a photomultiplier tube, a multi-anode photomultiplier, a silicon photodiode, a microchannel plate, and an avalanche photodiode.  
   
   
       19 . The neutron detector of  claim 17  wherein said transparent plastic includes an array of transparent plastic slabs, each of said array of transparent plastic slabs for detecting neutrons, each of said array of transparent plastic slabs having one said wavelength shifting optical fiber.  
   
   
       20 . The neutron detector of  claim 19  wherein said array of transparent plastic slabs is an 8×8 array of said transparent plastic slabs, each of said 8×8 array of transparent plastic slabs being optically connected to a single multi-anode photomultiplier tube, said multi-anode photomultiplier tube defining 64 individual pixels of detection, a direction of a neutron source being ascertainable by determining a relative intensity of detected neutrons in each of said 8×8 array of transparent plastic slabs, a portion of said 8×8 array of transparent plastic slabs facing the neutron source yielding the highest intensity of counted signals.  
   
   
       21 . The neutron detector of  claim 1  wherein said transparent plastic includes a plurality of transparent plastic elements, said glass medium, said first material and said second scintillator material being dispersed in said plurality of transparent plastic elements, each of said plurality of transparent plastic elements being optically coupled to a multi-anode photomultiplier, whereby detection of neutrons in each of said plurality of transparent plastic elements is identified individually and the occurrence of the absorption of a neutron is temporally identified with respect to a repeating fiducial timing signal synchronized with a pulsing of an external neutron source thus allowing each neutron detection event in each of said plurality of transparent plastic elements to be analyzed temporally with respect to each other.  
   
   
       22 . The neutron detector of  claim 21  wherein each of said plurality of transparent plastic elements is configured to enclose a volume allowing a high probability of capture of all neutrons borne from spontaneous fission events and induced fissions events from active external injection of neutrons from a pulse neutron tube.  
   
   
       23 . The neutron detector of  claim 22  wherein neutron event data is collected and stored in a record such that correlated neutron events may be calculated to acquire a quantitative measurement of a quantity of material spontaneously emitting neutrons and a quantitative measurement of fissile content within said enclosed volume having been stimulated to emit neutrons.  
   
   
       24 . The neutron detector of  claim 23  wherein individual neutron detection events are correlated in time with neutron pulses from either of a pulsed deuterium-deuterium and a deuterium-tritium neutron tube.