1. Field of the Invention
The present invention relates to the detection of particles, more particularly, the present invention relates to the detection of neutrons using high cross section converter materials in three dimensional high-efficiency configurations and methods of fabricating such structures.
2. Description of Related Art
Present technology for radiation detection suffers from flexibility and scalability issues. Since neutrons have no charges and do not interact significantly with most materials, special neutron converters such as, pure Boron 10 in solid form are needed to react with neutrons to produce charged particles that can be easily detected by semiconductor devices to generate electrical signals.
A commonly used geometry involves the use of a planar semiconductor detector over which a neutron reactive film has been deposited. Upon a surface of the semiconductor detector is attached a coating that releases ionizing radiation reaction products upon the interaction with a neutron. The ionizing radiation reaction products can then enter into the semiconductor material of the detector thereby creating a charge cloud of electrons and “holes,” which can be sensed to indicate the occurrence of a neutron interaction within the neutron sensitive film. The charges are swept through such configured detectors via methods known by those of ordinary skill in the art and registered as an electrical signal.
Another geometry includes etched trenches, slots, or holes in semiconductor materials having dimensions on the micron scale or larger that are filled with predetermined converter materials and configured with electrodes so as to produce detectors similar to the planar detector geometries discussed above.
A need exists for new and/or improved high-efficiency radiation detectors based on materials having three dimensional hierarchical structures at the micro and at the nano dimensional scale level. The present invention is directed to such a need.
Accordingly, the present invention provides a detector having a plurality of embedded converter materials extending into the substrate from only a single predetermined surface of the substrate. Such a detector provides detection efficiencies greater than conventional detectors because the converter materials are configured in voids having at least one dimension that is less than about a mean free path of the reaction-produced particles.
Another aspect of the present invention provides a neutron detector having a plurality of detectors, such as, neutron detectors, each respective detector being configured with embedded converter materials that extend into the substrate from only a single predetermined surface of a substrate. Such a stacked configuration enables collection and comparisons of signals from one or more detectors arranged in the stacked configuration to detect a large dynamic range of neutron flux intensity.
A final aspect of the present invention is directed to a method for producing a neutron detector that includes: configuring a substrate with a matrix of voids that extend from only a single predetermined surface of the substrate, wherein the substrate is capable of producing electron-hole pairs upon interaction with one or more reaction-produced particles; and embedding converter materials within the voids, wherein the embedded converter materials are configured to release the reaction-produced particles upon interaction with one or more received neutrons; and coupling pairs of non-embedded electrodes to predetermined surfaces of the substrate, wherein each electrode of the pairs of electrodes comprises a substantially linear configuration, and wherein signals from resulting electron-hole pairs as received from respective pairs of electrodes are indicative of the received neutrons.
Accordingly, such methods and apparatus of the present invention enable the use of a large amount of high neutron cross-section converter materials to increase the total neutron capture and thus substantially increase neutron detector efficiency. Moreover, the present invention provides beneficial embedded detector arrangements to detect the directions of incoming neutrons by connecting configured semiconductor elements with electrodes and analyzing received signals from each set of the elements. As another beneficial arrangement, stacking of such detectors in a layered configuration increases the neutron capture volume and thus allows the detection of fluxes of neutrons having a broad range of intensities. Such proposed designs can yield drastic improvements in area, such as flexibility, durability, sensitivity, increased detector area, improved electrical signal output, and energy resolution for the next generation of neutron detectors.
The accompanying drawings, which are incorporated into and constitute a part of the specification, illustrate specific embodiments of the invention and, together with the general description of the invention given above, and the detailed description of the specific embodiments, serve to explain the principles of the invention.
Referring now to the drawings, specific embodiments of the invention are shown. The detailed description of the specific embodiments, together with the general description of the invention, serves to explain the principles of the invention.
Unless otherwise indicated, numbers expressing quantities of ingredients, constituents, reaction conditions and so forth used in the specification and claims are to be understood as being modified by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the subject matter presented herein. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the subject matter presented herein are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
Detectable radiations generated by neutron converter materials upon neutron irradiation usually travel inside the neutron converter materials only for a substantially short distance. Thus, a thick layer of a neutron converter materials (neutron converter materials are defined herein as any material that can react with neutrons to produce secondary radiations, such as gamma rays, charged particles, neutrons of different energy, and/or products from fission or fusion reactions), though perceived to increase the generation of such radiations, actually absorb substantially all of the detectable radiations before they are detected by the semiconductor detection elements.
The present invention explores semiconductor-based micromaterial and nanomaterial elements as an electrical signal generation media that can be utilized for the detection of neutrons so as to provide detectors that substantially eliminate the geometrical problem illustrated in
Recent advances in microtechnology and nanotechnology provide new means to control the dimensionality, morphology, and chemical composition of such embedded materials at the atomic level and are incorporated into the present invention. Such manipulation of materials provides beneficial properties due to a combination of quantum confinement and surface to volume ratio effects. Semiconductor detectors of the present invention can be configured with a predetermined density of pillars that are individually coated with neutron converter materials. Such an arrangement provides a substantially small dead neutron active volume because the charge particles generated in the converter materials do not need to travel far to hit and lose energy in the semiconductor elements. The pillars can thus capture a substantial amount of the secondary radiations such as charged particles upon radiations with fluxes of neutrons.
Another example arrangement of the present invention includes a coating, such as, a polymer coating (e.g., Lucite, polyethylene, etc.) and having as one arrangement a variable thickness that is applied on a predetermined surface of a semiconductor material to detect slow and fast neutrons. Other beneficial detector embodiments of the present invention provide high neutron cross-section converter materials embedded in the chosen semiconductor detector elements. Such embedded converter materials are arranged in a matrix inside the semiconductor elements to enable substantially all of the desired radiations produced via the interactions with neutrons to be captured and detected by configuring such embedded materials to be within configured surroundings that are smaller than about the mean free path of charged particles generated from the reaction between neutrons and the predetermined neutron converter materials. Therefore, theoretically, there is no limitation on the amount of neutron converter materials to incorporate into detectors of the present invention because of the minimization of the dead volume in such three dimensional structures as disclosed herein.
Returning now to the drawings,
Electrodes 20 and 22 are deposited on both sides of semiconductor material 16. A predetermined electrode 22 is grounded 23 and another predetermined electrode 20 is often connected to a pre-amplifier 26, followed by an amplifier 30, a multi-channel analyzer 36, and then a computer 40 to analyze the electrical signals. In a method of operation, upon the impingement of neutron flux (denoted by n and shown with accompanying arrows) from a neutron source 44 onto detector 10, predetermined neutron converter materials (not shown) disposed within voids 12 react with such impinging neutrons react to generate radiations such as charged particles (e.g., alpha particles a as denoted in
The three dimensional structures of the semiconductor material 16 that contains the voids can be configured in many possible beneficial arrangements, such as, pillar structures 52 (only one labeled for simplicity), such as pixilated structures, coupled with a semiconductor material 16, as shown in
Another beneficial embodiment of the present invention is the use of structures, such as pillars, having predetermined dimensions, e.g., dimensions from at least about 10 nm to about 3000 nm in diameter. In such an arrangement, the pillars (or wires) can act as an individual semiconductor detector element if each of them is individually connected to the signal collection electronics.
Analysis of the signals from each pillar or groups of pillars can indicate the presence and directions of the charge particles produced in different regions of the neutron converter materials in the detector. This information can be used to infer the direction of the neutron impinging onto the neutron detector. Moreover, since a wire has a large surface-to-volume ratio, charged particles that are generated in the neutron converter materials and embedded in the dense semiconductor pillar matrix, only need to travel a very short distance in the neutron converter material to reach the semiconductor elements to generate electron-hole pairs and thus the electrical signals. Because such charged particles lose some of their energy when they travel inside a predetermined converter material, the minimization of the travel distance using such pillars and/or wires of the charged particles inside the neutron converter materials increases the active volume of the neutron converter materials and thus the efficiency of the neutron detector. Moreover, by tracking the directions and intensity of the electrical signals in the neutron detector of the design, as described above, the intensity of the neutron flux and the relative energy of the neutron flux can be determined.
The present invention will be more fully understood by reference to the following two example approaches for constructing detector embodiments of the present invention, which are intended to be illustrative of the present invention, but not limiting thereof.
A top-down detector fabrication scheme (illustrated clock-wise) as shown in FIGS. 5(a)-(d).
In an example method for providing such a structure, as shown in FIGS. 5(a)-(d), a monolayer of polystyrene beads having diameters from about 10 nm to about 1000 nm is first deposited onto a semiconductor wafer by either spin coating, dip coating, or drop-drying technique. Then, oxygen and tetrafluoromethane plasma is applied to etch each polystyrene spheres to desired shape and size. The semiconductor is then etched by high density plasma with optimal etching conditions to generate the pillar structures. This fabrication scheme can be applied to generate pillar structures of different diameter and separations with polystyrene beads of different sizes and oxygen plasma etching conditions.
FIGS. 6(a)-6(c) shows scanning electron micrographs of pillar structures being constructed by nanosphere lithography at different stages of the fabrication scheme.
FIGS. 7(a)-(d) show a bottom-up approach for the fabrication of proposed neutron semiconductor detectors. Such a bottom-up detector fabrication scheme, as shown in FIGS. 7(a)-(d), can be used to generate the pillar semiconductor structures, as shown in FIGS. 5(a)-(d). In particular,
As shown by the data in
Accordingly, designing radiation detectors based on materials of three dimensional hierarchical structures at the micro and nano scale has the potential to yield drastic improvements in areas such as flexibility, durability, sensitivity, increased detector area, improved electrical signal output, and energy resolution for the next generation of neutron detectors.
Applicants are providing this description, which includes drawings and examples of specific embodiments, to give a broad representation of the invention. Various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this description and by practice of the invention. The scope of the invention is not intended to be limited to the particular forms disclosed and the invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims.
This application claims priority from U.S. Provisional Patent Application No. 60/675,654, entitled “SEMI-CONDUCTOR NANO-MATERIALS MATRIX FOR NEUTRON DETECTION,” filed on Apr. 27, 2005, and is incorporated by reference in its entirety.
The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG-48 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory.
Number | Date | Country | |
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60675654 | Apr 2005 | US |