In-situ quality assurance and spectrum analysis by prompt gamma neutron activation analysis for material samples

Abstract

A method of non-destructive testing (NDT) using prompt gamma neutron activation analysis (PGAA) and a suite of algorithms based on various mathematical algorithms, includes: analyzing stored spectra for net peak areas; determining aggregate type from the analyzed stored spectra; calculating dominant element ratios; solving for dominant element mass fractions; calculating elemental mass fractions; solving a linear equations system including a coefficient matrix; and determining material components.

Description

[0001] IN-SITU QUALITY ASSURANCE AND SPECTRUM ANALYSIS BY PROMPT GAMMA NEUTRON ACTIVATION ANALYSIS FOR MATERIAL SAMPLES

[0002] Related Applications

[0003] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 607,221 (filed December 7, 2023), which is herein incorporated by reference in its entirety.

[0004] Federally-Sponsored Research and Development

[0005] This invention was made with United States Government support from the National Institute of Standards and Technology (NIST), an agency of the United States Department of Commerce. The Government has certain rights in this invention.

[0006] Copyright Notice

[0007] This patent disclosure may contain material that is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves any and all copyright rights.

[0008] Field of Invention

[0009] The present invention relates generally to petrography, and more particularly to petrography by prompt gamma neutron activation analysis.

[0010] Background

[0011] Petrography, a term originating in geology for microscopic composition analysis, in the context of concrete, refers to quantifying bulk constituents such as cement, aggregates, and water for the purpose of verifying the intended design and predicting the service life for existing structure. Conventional methods for concrete petrography can be grouped into three categories: chemical, microscopy, and bulk elemental analysis. The chemical methods typically involve a reaction that attacks a single constituent such as the cement. In this case, the acid-soluble calcium content is taken as the surrogate for the cement. Also included in this category is the measurement of water by the method of loss on ignition (LOI).

[0012] The microscopy methods involve image analysis of a thin section of the concrete. In a conventional method using modal analysis the operator uses an optical microscope to identify the grains of the individual constituents or cement paste matrix by visual inspection. Using a grid superimposed on the slide, the operator counts the number of points that fall on each constituent. These counts are then used to calculate the area or volume fractions from which the mass fractions are computed. The counting of points is time-consuming and requires skilled operators.

[0013] Conventional bulk elemental analysis methods (along with some other conventional microscopy methods) use X-ray fluorescence (XRF).

[0014] Summary of Invention

[0015] The conventional chemical methods are labor-intensive, involving crushing and grinding and may be prone to interference such as the presence of acid-soluble calcium in the aggregates. Conventional microscopy methods that require counting of points are time-consuming and require skilled operators. Further, neither optical microscopy nor XRF can identify water. Moreover, the thin sections are difficult to prepare because of the great differences in hardness and friability between the aggregate grains and the cement paste. Finally, conventional XRF spectrum is less informative than an exemplary gamma ray spectrum, especially regarding the light elements. Characteristic gamma ray energies are 2-3 orders of magnitude higher than the X-rays for the same element. This minimizes any matrix effects and eliminates the need for extensive sample preparation such as fusion into glass beads. Also, the elemental masses can be calculated from the gamma ray counts from first principles. Moreover, exemplary methods are uniquely capable of detecting hydrogen (H), which is critical for determining the water content of the concrete. XRF cannot detect H, and hence it must be supplemented by loss on ignition (LOI) measurements. According to an aspect of the invention, a method of non-destructive testing (NDT) using prompt gamma neutron activation analysis (PGAA) and a suite of algorithms based on various mathematical algorithms includes the steps of: analyzing stored spectra for net peak areas; determining aggregate type from the analyzed stored spectra; calculating dominant element ratios; solving for dominant element mass fractions; calculating elemental mass fractions; solving a linear equations system including a coefficient matrix; and determining material components.

[0016] Optionally, the method includes calculating a water mass fraction, and wherein the step of determining material components includes determining concrete mix components.

[0017] Optionally, the step of calculating a water mass fraction includes using an H mass fraction from the calculated elemental mass fractions.

[0018] Optionally, the step of solving a linear equations system includes selecting a coefficient matrix and calculating an inverse of the coefficient matrix.

[0019] Optionally, the step of solving for dominant element mass fractions uses a sub-composition method.

[0020] Optionally, the step of determining concrete mix components includes determining proportions of cement, limestone, sand, and water of the concrete.

[0021] According to another aspect, a method of quality assurance of a material sample automated for non-expert operation includes the steps of: acquiring a reference gamma spectrum from a reference batch of known composition; acquiring a sample gamma spectrum from a sample of unknown composition; normalizing the acquired sample gamma spectrum to the reference sample gamma spectrum by a signature peak common to both spectra, resulting in a normalized sample gamma spectrum; subtracting the reference gamma spectrum from the normalized sample gamma spectrum, resulting in a difference spectrum; searching the difference spectrum for negative peaks; measuring an area of the negative peaks; and rejecting the sample if an area of the negative peaks exceeds a tolerance level.

[0022] Optionally, the signature peak is an H peak.

[0023] According to another aspect, a method for automated scanning of material samples using a portable neutron source with moderated neutron beam output, sample changing mechanism, and a gamma detection system for spectra acquisition includes the steps of: irradiating a concrete sample with a neutron beam from the portable neutron source; acquiring a gamma spectrum of a first sample of the material samples with the gamma detection system; and processing the acquired gamma spectrum, wherein the steps of irradiating, acquiring, and processing are repeated for multiple sections of the first sample.

[0024] Optionally, the step of processing includes identifying and counting peaks in the acquired gamma spectrum.

[0025] Optionally, the method includes moving the first material sample out of an irradiation / detection area; moving a second material sample into an irradiation / detection area; and wherein the steps of irradiating, acquiring, and processing are repeated for the second material sample.

[0026] Optionally, the method includes loading a sample handling subsystem with a set of material samples.

[0027] Exemplary embodiments aim at replacing conventional destructive methods for concrete petrography with a single nondestructive method. Exemplary embodiments involve measuring the elements in the concrete by prompt gamma neutron activation. The elemental data are then converted into mass fractions of the constituents by various mathematical methods. Exemplary embodiments include the use of a neutron generator and an automated scanning system.

[0028] The foregoing and other features of the invention are hereinafter described in greater detail with reference to the accompanying drawings.

[0029] Brief Description of the Drawings

[0030] FIG. 1 shows a schematic representation of an exemplary measurement system.

[0031] FIG. 2 shows a block diagram of an exemplary performance-specific operation method.

[0032] FIG. 3 shows a block diagram of an exemplary method of off-line analysis for concrete petrography.

[0033] FIG. 4 shows a block diagram of an exemplary method of performing quality assurance (QA). Detailed Description

[0034] The descriptions given herein should not be understood to be limited to using concrete samples or be limited to concrete petrography. Rather, the invention is sometimes described in reference to concrete petrography and analysis of concrete material samples. However, exemplary embodiments of the invention include material samples of various compositions and embodiments have many applications such as, for example, steel analysis and sorting recycling materials. Such embodiments may have alternative or additional steps as would be understood by those having ordinary skill in the art upon reading and understanding this disclosure. For example, a recycling application might include an additional step of sorting materials after identification.

[0035] Concrete petrography is used for characterizing and quantifying the constituents in concrete, which are various proportions of cement, coarse and fine aggregates, chemical and mineral admixtures, and water. These proportions are then used to calculate important properties of the concrete including cement content and water / cement ratio, which are necessary for verifying the intended design (for newly cast structure) and for predicting the service life (for existing structure). Chloride diffusion is a critical precursor to corrosion of steel reinforcement in concrete structures, e.g., and prompt gamma activation analysis for in-situ determination of chloride distribution, specifically, is discussed at length in Chen-Mayer, H.H., Berke, N.S. & Livingston, R.A. PGAA measurement of chloride diffusion profiles in concrete cylinders. J Radioanal Nucl Chem 332, 5239-5245 (2023). https: / / doi.org / 10.1007 / s10967-023-09023-y. the contents of which are incorporated by reference herein in its entirety. R&D in concrete chemistry and process engineering is constantly evolving to create more durable and lower-carbon emission materials and casting methods, resulting in more varieties of products that need rapid petrography. Exemplary embodiments redefine the traditional process for petrography by enabling non-destructive in- situ analysis. This is achieved by using a highly penetrating neutron beam that can produce prompt gamma emissions for simultaneous multiple-elemental analysis with the concrete structure intact. The data are then processed to obtain the original proportions of the constituents. Exemplary embodiments address both the measurement process and data processing. Included herein are innovations in hardware for scanning and in algorithms for data analysis including matrix inversion, linear least-squares and other mathematical methods of solving systems of linear equations.

[0036] In addition to being able to analyze the composition, exemplary instances of scan spectrum can be used to identify a specific concrete mix, or components. This provides what is known as a “fingerprint” for the material. This then can be used with spectrum matching as a quality control and qualify assurance method, providing results before the concrete is placed or material used.

[0037] Currently, destructive analysis methods are conventional, with limited surface techniques for in-situ analysis. In contrast, exemplary embodiments may look deeply into the bulk structure without time consuming and cost prohibiting destructive analysis, generating profit for companies that adapt exemplary methods.

[0038] Exemplary spectrum matching techniques add something that currently is not available; there are conventional tools to access the water content in fresh concrete, but they do not show that the concrete meets the job specification. For example, one can keep the water in the right range, but change the other material contents and that would not be known until after the concrete is placed.

[0039] Referring to FIG. 1 , an exemplary prompt gamma neutron activation analysis (PGAA) system 100 is shown in schematic. A commercially available neutron generator is preferred for use as a neutron source 101 although other options are also possible and known to those skilled in the art. Preferably, the neutron generator uses a deuterium-deuterium (DD) fusion reaction, although any suitable source may be used (e.g., a deuterium-tritium (DT) reaction, a cold neutron beam, a nuclear fission reactor, a particle accelerator-based fusion device, a radioisotope, or the like), keeping in mind that not all of these are suitable for on-site application.

[0040] Samples 103 may be in the form of concrete cylinders and may be moved in and out of the neutron beam by an optional automated sample handling system 102. Gamma rays from the samples 103 are detected by the detector 105 and detected signals processed by associated electronics. In preferred embodiments, the detector 105 may be a High Purity Germanium (HPGe) detector, for example, having relatively higher energy resolution over a conventional Sodium Iodide (Nal) detector.

[0041] The entire system may be optionally enclosed in a room shield 104 which protects the operators from gamma and neutron radiation.

[0042] Scanning PGAA (SPGAA) is an elemental analysis method or mode of operation of PGAA which includes irradiating a sample 103 with thermal neutrons that are captured by the nuclei in the sample. In this process gamma rays are emitted with characteristic energies. The gamma ray energy spectrum is detected and used to quantify the elements present in the sample. PGAA is sensitive to all the major and minor elements, including hydrogen, found in concrete.

[0043] In SPGAA, a gamma ray collimator 107 in the form of a narrow slit is placed between the gamma ray detector 105 and the sample 103, ensuring only a narrow slice of the sample is measured at each step. Scanning may be achieved by moving the sample 103 relative to the collimator 107 and detector 105. Preferably, the sample 103 is moved while the collimator 107 and detector 105 remain stationary. A complete gamma ray spectrum is acquired for each slice of the sample. Each spectrum is then analyzed to obtain the mass fractions of selected elements in the slice. The list of elements includes, but is not limited to: H, C, Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni and Sr. These 17 elements, along with oxygen, typically account for 99.5% of the total mass of the concrete. PGAA is not sensitive to oxygen; however, these other elements are fully oxidized so the oxygen content can be calculated from stoichiometry.

[0044] The SPGAA system may be controlled automatically or remotely by an operator who sits at a workstation located outside the room shielding 104.

[0045] The data acquisition system 150 of the workstation can provide online analysis of the gamma ray spectrum. The data can then be analyzed offline for concrete petrography and / or quality assurance.

[0046] As mentioned above, exemplary systems use a neutron generator (NG). However, there are some issues in the transition from reactor-based SPGAA to NG-based SPGAA. These issues include higher gamma-ray background and lower thermal neutron flux. Exemplary embodiments, therefore, may include the use of an NG and a set of PGAA system design options that can reduce the counting time per sample to around 10 minutes. The lower neutron flux is the result of two factors. One is the limited neutron generation rate which is orders of magnitude lower than the fission reactor. The other is that the neutrons produced by fusion reactions are “fast" i.e., they have very high kinetic energies: 14.7 MeV for the DT reaction and 2.54 MeV for the DD reaction. These fast neutrons are slowed down, or moderated, to thermal equilibrium at room temperature to be useful for PGAA. At 293 K the neutron energy spectrum has a peak at 25.3 meV. This energy is 8 or 9 orders of magnitude lower than the fast neutrons. In the moderating process a significant number of neutrons are lost by capture in the moderator material. Ideally the DD NG would be preferred for PGAA because its fast neutrons have a lower energy than the DT neutrons, and thus require less moderating. However, the maximum neutron production rate for DD generators is also lower than DT generators. An advanced version of DD NG has recently been developed that uses Radio Frequency (RF) to accelerate the ions. This is capable of a thermal neutron flux of 1X107cm-2s-1, which (when combined with the various gain factors below) approaches the 109cm-2s-1flux of the reactor with a cold source. There are several hardware and software options that can be used to increase the PGAA counting rate based on this type of NG. These options are presented in Table 1.

[0047] Table 1: Options for Optimizing NG-based PGAA Performance. The total estimated gain is the product of each factor.

[0048] Since the revenue of a commercial facility may come from charging a fee per sample analyzed, an objective is to minimize the cost per sample. Ways to minimize labor costs include automated sample handling and data analysis. Minimizing the fixed costs per sample involves maximizing the throughput of samples. As discussed above the fluence rate of the NG is expected to be 1% of the reactor-based beam and since the counting time is linearly proportional to the fluence, everything else being equal, the counting time would be 100 times greater. However, there are a number of ways to significantly reduce this time by optimization of the layout of the facility, selection of detectors and the counting process.

[0049] Geometric optimization involves the port-to-sample distance and the sample-to-detector distance fluxes decrease by x-2. Thus, by cutting these distances in half, it would be possible to increase the count rate by a factor of 16. However, moving the detector closer to the moderator may increase the background and the risk of fast neutron damage. Another modification to the layout would be to use more than one beam port. The emission of neutrons from the moderator is omnidirectional. It would thus be possible to triple or quadruple the throughput by using 3 or 4 beam ports. This would involve an increase in capital cost for the additional detectors.

[0050] Concerning the selection of detector 105, a scintillator such as LaBr3could be used in place of the HPGe detector. These are both more efficient and faster. It was shown in previous research that a LaBr3detector increased the count rate by a factor of 4 over the HPGe. This substitution involves a drawback of reduced energy resolution, but this can be compensated by deconvolution methods in the spectrum analysis. Finally, the count rate could be doubled simply by adding another detector (as illustrated in Fig. 1, the detector 105 is shown in two places).

[0051] The counting procedure could also be modified. Because uncertainty scales with the square roots of the counts, by accepting an uncertainty of 3% instead of 1%, the counting time could be reduced by a factor of 10. To put this increase in uncertainty in perspective, a precision of 10% in the mass fraction is a common goal in the design of sampling procedures with conventional methods. Also, the counting could be set up to end at a fixed number of counts in a specified peak rather than after a fixed live time. Finally, the effective counts could be doubled by using the whole spectrum method of data analysis discussed below. Turning now to FIG. 2, a process 200 of SPGAA on concrete samples is illustrated.

[0052] The sample handling subsystem may be loaded with a set of samples usually in the form of cylinders at block 201.

[0053] The power to the neutron generator (NG) may be turned on, and the voltage and current adjusted for optimum neutron beam performance at block 202. Note that the NG may not emit radiation when the power is off.

[0054] The automated sample handling subsystem may move the first sample into position for irradiation at block 203.

[0055] The start command may be given to the controlling software to begin acquisition of a spectrum at block 204. The end of the counting period may be set as a specified amount of time or a specified number of counts in the main peak of interest.

[0056] At the end of counting, an initial online analysis of the spectrum may be made to identify peaks and to determine the counting statistics at block 205. The data file may optionally be stored for offline analysis. This initial analysis may be automated by using machine learning / artificial intelligence for efficiency. For further information on using machine learning / artificial intelligence, please see Mahynski, N. , Monroe, J. , Sheen, D. , Paul, R. , Chen-Mayer, H. and Shen, V. (2023), Classification and Authentication of Materials using Prompt Gamma Ray Activation Analysis, Journal of Radioanalytical and Nuclear Chemistry, [online], https: / / doi.org / 10.1007 / s10967 -023-09024-x, the contents of which are incorporated by reference herein in its entirety.

[0057] The sample may be moved to the next position at block 206 and steps 204 and 205 may be repeated.

[0058] When all the locations on the sample have been measured, it may be moved into a shielded container to allow the decay of induced radioactivity to a safe level and a new sample may be moved into the beam to repeat steps 203 to 206.

[0059] After all the samples have been scanned and put in storage, the NG power may be turned off at block 207 to enable the loading of a new set of samples at block 208. Samples shown herein are depicted as being cylindrical (and may be sized at approximately 2 inches (5 cm) in diameter, e.g.) because the typical concrete specimen has a cylindrical shape; however, exemplary samples may take any appropriate shape and / or size (e.g. large blocks or slabs on the order of 25 cm on a side, or very small samples in the form of pellets of powdered concrete with a mass less than a gram). This typical cylindrical shape is usually because the sample was originally cast in a cylinder mold or was drilled as a core from a structure. For QA / QC the fresh concrete would be contained in a Teflon tube. Thus, the simplest scanning procedure would be to move the specimen in a linear motion in the direction of its longitudinal axis (although moving along another axis is also possible). Thus, a spectrum would be acquired for a disc-shaped volume, or slice, at each step. This assumes that the slit collimator allows the detector to view the complete width of the specimen. However, because of the heterogeneity of concrete, it is preferable to rotate the specimen (in the example case here, around its longitudinal axis) continuously during counting to average out local differences in the aggregate / cement paste fractions.

[0060] As pointed out above, to achieve a 10% precision it may be necessary to have a sample size of hundreds of grams. With SPGAA, it could be possible to measure a stack of slices and then average them. However, at a 2 mm height per slice and a counting time of 15 minutes each, it would take over 6 hours to scan a 5 cm x 5 cm cylinder, which would not be practical. The alternative would be to record the spectrum while rotating the sample and also moving it linearly continuously. The result would be a helical scan of the entire volume. An exemplary system to accomplish this can be constructed from off-the-shelf positioning equipment components. The acquired spectrum may be used for prompt gamma emission tomographic reconstruction.

[0061] In addition to performing an actual scanning, the system may also mount the specimen and then remove it after irradiation to a holding area to let the radioactivity decay to manageable levels. In previous work in which the specimen was handled manually, this period for decay was found to be around 45 minutes. Therefore, using an automated system could increase the throughput by a factor of at least 3. Turning now to FIG. 3, an exemplary method 300 applying PGAA to the field of concrete petrography is shown.

[0062] At block 301, an off-line analysis may be performed on stored spectra for net peak areas.

[0063] At block 302, aggregate type may be determined, distinguishing between silicate or carbonate.

[0064] At block 303, dominant element ratios may be calculated.

[0065] At block 304, solving for dominant element mass fractions may be carried out using the sub-composition method. The alternative method is to perform whole spectrum fitting with the publicly available nuclear library and detector modeling, either by developing custom software or more efficiently, by commercial software. Additionally, artificial intelligence may be developed for this task to speed up the process, when sufficient data is accumulated for model training and testing.

[0066] At block 305, the elemental mass fractions may be calculated.

[0067] At block 306, the water mass fraction may be calculated from the H mass fraction.

[0068] At block 307, the coefficient matrix may be selected and the inverse matrix calculated.

[0069] At block 308, The constituents’ mass fractions may be calculated.

[0070] At block 309, a report on the best estimate of the concrete mix components may be generated. In particular, the proportion of cement, limestone, sand, and water may be reported.

[0071] Overall, the first part (block 301 - 305) of the method is the calculation of elemental masses or mass fractions in the sample from the net counts in each peak. This may be done with an appropriate calibration procedure. The next part (306-309) is to compute the mass fractions of the four constituents (fine aggregate, coarse aggregate, water and cement) that comprise the original mix design. Ideally each constituent would have a unique element to identify it. However, the solid constituents can have some elements in common, for example, Ca and Si, although in different proportions. The straightforward method of conversion, matrix inversion, requires a square matrix (the number of measured elements, m, is equal to the number of constituents, n) makes only limited use of the data, since the elements measured usually exceeds the n=4 constituents in the concrete mix. Therefore, the strategy is mainly focused on solving an overdetermined (m>n) system of linear equations. Advanced algorithms such as linear least squares can provide more robust analytical utility. The mass fractions of the constituents are estimated by minimizing the chi squared statistic between the actual elemental composition of the sample and a composition calculated from the elemental signatures of the constituents. The linear least squares approach can be extended to using the whole spectrum for each constituent rather than just the peak data.

[0072] The method 300 has several advantages over the conventional XRF method currently used for elemental analysis of concrete. The gamma ray spectrum, originated from the nuclear structure, is more complicated than XRF that reflects the atomic structure, but it also contains more information, especially about the light elements which are less accessible by XRF. The characteristic gamma ray energies are in the MeV range versus keV’s of X rays for the same element, which minimizes matrix effects and eliminates the need for extensive sample preparation such as fusion into glass beads. In theory, the elemental masses can be calculated from the gamma ray counts from first principles. Moreover, PGAA is uniquely capable of detecting H, which is critical for determining the water content of the concrete, whereas XRF cannot detect H, and hence it must be supplemented by loss on ignition (LOI) measurements .

[0073] The method 300 described above may include the use of advanced algorithms to calculate the mass fractions from the PGAA data. These algorithms would replace simple matrix inversion with methods such as linear least squares for greater accuracy. Such software may speed up the reduction of the data, and thus the cost per sample, by reducing the amount of manual work spent in reformatting the data and creating spreadsheets. Numerous other statistical tools have been developed and are publicly available for solving linear equations. The use of these algorithms in blocks 306-309, either interactively or in batch mode for automation, enables on-the-flight concrete petrography.

[0074] The function of exemplary spectrum analysis software may be to identify the peaks in the gamma ray spectrum corresponding to the elements of interest and integrate each one to yield the net counts, or area, of each peak. Commercial software packages are available for this purpose.

[0075] A typical PGAA spectrum consists of hundreds of peaks, but only 10-20 are needed for the element of concrete. Moreover, the most prominent peaks may have interferences. Thus, the first step in the application of spectral analyses to concrete may involve going through the spectrum by hand to identify the most useful peaks based on the knowledge of concrete chemistry and the PGAA properties of each element. This information may be saved as regions of interest (ROI) in a data file that could be reloaded each time the analysis is run. This manually created ROI file is time-consuming to prepare.

[0076] A limitation of commercial software is that they only report the counts in the photopeak. However, this results in an underestimate of actual gamma ray flux for a given energy, because some of the photons lose energy in the detector because of Compton scattering. The scattered photons are counted as part of the background. One approach to account for these scattered photons is library matching, in which the observed spectrum is fit against a spectrum measured on a sample with known composition of elements of interest. This approach has been shown to increase the effective count rate by a factor of 2. The library spectra are unique to a given PGAA setup.

[0077] Turning now to FIG. 4, shown is an application of SPGAA to the QA / QC of fresh concrete samples in method 400.

[0078] At block 401, a QA sample may be placed in a location (for example, an automated sample handling system) for testing and exposed by a neutron source, e.g., by turning on the neutron source in an exemplary PGAA system.

[0079] At block 402, a reference gamma spectrum is acquired from a correctly prepared reference batch.

[0080] At block 403, a sample for measurement is prepared or acquired. In exemplary embodiments, a sample of unknown fresh concrete may be poured, preferably into a Teflon container.

[0081] At block 404, a spectrum of the sample is acquired.

[0082] At block 405, the acquired spectrum of the sample may be normalized by the H peak. At block 406, the reference gamma spectrum may be normalized by its H peak and subtracted from the sample spectrum, resulting in a difference spectrum.

[0083] At block 407, the difference spectrum may be searched for negative peaks.

[0084] At block 408, the sample batch may be rejected if negative peaks exceed a tolerance level.

[0085] Since the method 400 is not affected by the physical state of the material, the unhardened mix can simply be poured into a Teflon container for scanning. A comparison of the spectrum to a well-known control spectrum (fingerprint) is all that is required.

[0086] In addition to confirming that the sample meets the specifications of the mix design, PGAA can also test for nitrogen-bearing additives such as calcium nitrite, a corrosion inhibitor, or amines used as grinding aids or inhibitors. Also cement manufacturers could label their products with trace elements that PGAA can detect. This may be used to verify that the correct cement type was used for a given job.

[0087] Since the neutron generator may be portable, an exemplary SPGAA laboratory is a mobile laboratory that may be set up at a construction site or the like for rapid turnaround of QA / QC tests.

[0088] The processes described herein may be embodied in, and fully automated via, software code modules executed by a computing system that includes one or more general purpose computers or processors. The code modules may be stored in any type of non-transitory computer-readable medium or other computer storage device. Some or all the methods may alternatively be embodied in specialized computer hardware. In addition, the components referred to herein may be implemented in hardware, software, firmware, or a combination thereof.

[0089] Many other variations than those described herein will be apparent from this disclosure. For example, depending on the embodiment, certain acts, events, or functions of any of the algorithms described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the algorithms). Moreover, in certain embodiments, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors or processor cores or on other parallel architectures, rather than sequentially. In addition, different tasks or processes can be performed by different machines and / or computing systems that can function together.

[0090] Any logical blocks, modules, and algorithm elements described or used in connection with the embodiments disclosed herein can be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, and elements have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. The described functionality can be implemented in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the disclosure.

[0091] The various illustrative logical blocks and modules described or used in connection with the embodiments disclosed herein can be implemented or performed by a machine, such as a processing unit or processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A processor can be a microprocessor, but in the alternative, the processor can be a controller, microcontroller, or state machine, combinations of the same, or the like. A processor can include electrical circuitry configured to process computerexecutable instructions. In another embodiment, a processor includes an FPGA or other programmable device that performs logic operations without processing computer-executable instructions. A processor can also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Although described herein primarily with respect to digital technology, a processor may also include primarily analog components. For example, some or all of the signal processing algorithms described herein may be implemented in analog circuitry or mixed analog and digital circuitry. A computing environment can include any type of computer system, including, but not limited to, a computer system based on a microprocessor, a mainframe computer, a digital signal processor, a portable computing device, a device controller, or a computational engine within an appliance, to name a few.

[0092] The elements of a method, process, or algorithm described in connection with the embodiments disclosed herein can be embodied directly in hardware, in a software module stored in one or more memory devices and executed by one or more processors, or in a combination of the two. A software module can reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of non-transitory computer-readable storage medium, media, or physical computer storage known in the art. An example storage medium can be coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium can be integral to the processor. The storage medium can be volatile or nonvolatile.

[0093] While one or more embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation. Embodiments herein can be used independently or can be combined.

[0094] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. The ranges are continuous and thus contain every value and subset thereof in the range. Unless otherwise stated or contextually inapplicable, all percentages, when expressing a quantity, are weight percentages. The suffix (s) as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including at least one of that term (e.g., the colorant(s) includes at least one colorants). Option, optional, or optionally means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event occurs and instances where it does not. As used herein, combination is inclusive of blends, mixtures, alloys, reaction products, collection of elements, and the like.

[0095] As used herein, a combination thereof refers to a combination comprising at least one of the named constituents, components, compounds, or elements, optionally together with one or more of the same class of constituents, components, compounds, or elements.

[0096] All references are incorporated herein by reference.

[0097] The use of the terms “a,” “an," and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. It can further be noted that the terms first, second, primary, secondary, and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. It will also be understood that, although the terms first, second, etc. are, in some instances, used herein to describe various elements, these elements should not be limited by these terms. For example, a first current could be termed a second current, and, similarly, a second current could be termed a first current, without departing from the scope of the various described embodiments. The first current and the second current are both currents, but they are not the same condition unless explicitly stated as such.

[0098] The modifier about used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity). The conjunction or is used to link objects of a list or alternatives and is not disjunctive; rather the elements can be used separately or can be combined together under appropriate circumstances.

[0099] Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.

Claims

ClaimsWhat is claimed is:

1. A method of non-destructive testing (NDT) using prompt gamma neutron activation analysis (PGAA) and a suite of algorithms based on various mathematical algorithms, the method comprising the steps of: analyzing stored spectra for net peak areas; determining aggregate type from the analyzed stored spectra; calculating dominant element ratios; solving for dominant element mass fractions; calculating elemental mass fractions; solving a linear equations system including a coefficient matrix; and determining material components.

2. The method of claim 1 , further comprising the step of calculating a water mass fraction, and wherein the step of determining material components includes determining concrete mix components.

3. The method of claim 2, wherein the step of calculating a water mass fraction includes using an H mass fraction from the calculated elemental mass fractions.

4. The method of any preceding claim, wherein the step of solving a linear equations system includes selecting a coefficient matrix and calculating an inverse of the coefficient matrix.

5. The method of any preceding claim, wherein the step of solving for dominant element mass fractions uses a sub-composition method.

6. The method of any one of claims 2-5, wherein the step of determining concrete mix components includes determining proportions of cement, limestone, sand, and water of the concrete.

7. A method of quality assurance of a material sample automated for non-expert operation, the method comprising the steps of: acquiring a reference gamma spectrum from a reference batch of known composition; acquiring a sample gamma spectrum from a sample of unknown composition; normalizing the acquired sample gamma spectrum to the reference sample gamma spectrum by a signature peak common to both spectra, resulting in a normalized sample gamma spectrum; subtracting the reference gamma spectrum from the normalized sample gamma spectrum, resulting in a difference spectrum; searching the difference spectrum for negative peaks; measuring an area of the negative peaks; and rejecting the sample if an area of the negative peaks exceeds a tolerance level.

8. The method of claim 7, wherein the signature peak is an H peak.

9. A method for automated scanning of material samples using a portable neutron source with moderated neutron beam output, sample changing mechanism, and a gamma detection system for spectra acquisition, the method comprising the steps of: irradiating a concrete sample with a neutron beam from the portable neutron source; acquiring a gamma spectrum of a first sample of the material samples with the gamma detection system; and processing the acquired gamma spectrum, wherein the steps of irradiating, acquiring, and processing are repeated for multiple sections of the first sample.

10. The method of claim 9, wherein the step of processing includes identifying and counting peaks in the acquired gamma spectrum.

11. The method of either one of claims 9 or 10, further comprising the steps of: moving the first material sample out of an irradiation / detection area; moving a second material sample into an irradiation / detection area; and wherein the steps of irradiating, acquiring, and processing are repeated for the second material sample.

12. The method of any one of claims 9-11 , further comprising the step of loading a sample handling subsystem with a set of material samples.

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