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    • 专利摘要:
    The invention relates to a method for evaluating the mass concentration of uranium of an ore sample by gamma spectrometry. The method comprises the following steps: a) measuring (600) an energy spectrum of gamma radiation of the sample using a detector, said energy spectrum comprising at least one energy line at 92 keV and a line; at 98 keV, each line having a net area; (b) (610) is evaluated by calculating a quantity characterizing the mass concentration of uranium in the sample using the net area of the energy line at 92 keV and the net area of the energy line at 98 keV of the spectrum measured energy.
    公开号:FR3078408A1
    申请号:FR1851744
    申请日:2018-02-27
    公开日:2019-08-30
    发明作者:Thomas Marchais；Bertrand Perot；Cedric Carasco；Pierre-Guy Allinei；Herve Toubon
    申请人:Commissariat a lEnergie Atomique CEA；Orano Mining SA；Commissariat a lEnergie Atomique et aux Energies Alternatives CEA；
    IPC主号:
    专利说明:

    Method for evaluating the mass concentration of uranium in an ore sample by gamma spectrometry
    The present invention relates to a method for evaluating the mass concentration of uranium in an ore sample by gamma spectrometry.
    Uranium occurs naturally in the form of three isotopes: 238 U, 235 U and 234 U, the latter being from the 238 U decay chain. 238 U is very widely majority and represents more than 99.2% of total uranium.
    The 238 U and the 235 U disintegrate successively in different chemical elements called son elements until the chemical element obtained is stable. Each disintegration is most often accompanied by the emission of high energy photons also called gamma radiation. The energy spectrum is typically between a few tens of keV and more than 2000 keV. The unit of measurement of radiation is expressed in counts per unit of time, for example in counts per second.
    It is possible to use the aforementioned type of process in mining exploration and exploitation to characterize the uranium content of rock samples. In the case of mineral prospecting, these measurements are carried out in situ or on rock samples, for example from boreholes. These measurements typically characterize the uranium potential of a region. In mining, the process can for example be used at the factory to sort the ore according to its uranium content and thus adapt the processing of the ore accordingly.
    The standards NF M60-790-3 and NF ISO 18589-3 describe for example a measurement by high resolution gamma spectrometry based on the detection of an energy line at 1001 keV of a descendant of the uranium chain, 234m However, the low intensity of this line leads to long measurement times, up to several hours for samples of low mass (ie a few hundred grams) or of low uranium content (less than 1000 ppmu). The choice of this line rather than those much more intense of 214 Pb or 214 Bi, descendants of 238 U located at the end of the radioactive chain, comes from the risk of imbalance in the decay chain of 238 U. In case of imbalance, a measurement of the uranium content based on the gamma radiation of a child element located at the end of the decay chain leads to an erroneous value of the uranium content. This imbalance is generally observed for deposits with a low uranium content subject to differential leaching phenomena (eg uranium deposit of the “roll fronts” type) which constitute a significant part of the uranium deposits mined in the world.
    In the article entitled “Determining 234 Th and 238 U in Rocks, Soils and Sediments via the Doublet Gamma at 92.5 keV” Analyst, 131, n ° 6, 2006, 757-63, Kaste et al. also describe the use of the energy line at 1001 keV at 234m Pa and demonstrate the feasibility of using an alternative by measuring the energy line at 92 keV of the spectrum.
    The object of the invention is to provide a faster method for evaluating the mass concentration of uranium in a sample by reducing the time required for measurement, in particular for samples with a low uranium content. To this end, the invention relates to a method of the aforementioned type comprising the following steps:
    a) an energy spectrum of gamma radiation of the sample is measured using a detector, said energy spectrum comprising at least one energy line at 92 keV and one energy line at 98 keV, each line having a net area;
    b) a quantity characterizing the mass concentration of uranium of the sample is evaluated by calculation using the net area of the energy line at 92 keV and the net area of the energy line at 98 keV of the measured energy spectrum.
    Thus, the method according to the invention makes it possible to determine the mass concentration of uranium by using two low energy energy lines which are more intense and not subject to the phenomenon of imbalance. The number of counts per unit of time measured is significantly higher, which significantly reduces the measurement time of a sample.
    According to particular embodiments, the method according to the invention comprises one or more of the following characteristics, taken in isolation or according to all the possible technical combinations:
    - step b) of evaluation comprises a sub-step c) in which a first mass concentration of uranium Cmj (92 keV) is calculated using the net area of the energy line at 92 keV and a second mass concentration of uranium Cmu (98keV) using the net area of the energy line at 98 keV of the measured energy spectrum,
    - the quantity evaluated is an interval of mass concentration of uranium, the interval being delimited by a lower bound equal to the first mass concentration of uranium and by an upper bound equal to the second mass concentration of uranium,
    the method further comprises a step d) in which the heterogeneity of the sample is characterized on the basis of the amplitude of the mass concentration range of uranium,
    - step d) of characterizing the heterogeneity of the sample comprises a sub-step e) of calculating a coefficient representative of the heterogeneity of the sample using the first and second mass concentration of uranium,
    - the coefficient representative of the heterogeneity of the sample is preferably the ratio: (Cmj (98 keV) / Cmu (92 keV),
    - the method includes at least one step f) in which the value of the coefficient representative of the heterogeneity of the sample is tested to determine a state representative of the heterogeneity chosen from a heterogeneous state and a homogeneous state,
    - in step f), the value of the coefficient representative of the heterogeneity of the sample is compared to a predetermined threshold value,
    - the method further comprises, when the state representative of the heterogeneity corresponds to a heterogeneous state:
    - a step g) in which the sample is crushed and homogenized, and
    - steps a) to f) are repeated.
    - the second mass concentration of uranium is calculated taking into account a spontaneous emission of X-rays linked to 234m Pa, a spontaneous emission of two X-rays linked to 223 Ra, the spontaneous emission of two linked X-rays at 226 Ra and the contribution of an X-ray fluorescence phenomenon caused by at least one gamma radiation emission from at least one descendant of uranium.
    The invention also relates to a device for evaluating the mass concentration of uranium in a sample, said device comprising:
    - A detector adapted to measure an energy spectrum of gamma radiation of the sample, said energy spectrum comprising at least one energy line at 92 keV and one energy line at 98 keV, each line having a net area;
    - an evaluation module by calculating a quantity characterizing the mass concentration of uranium using the net area of the energy line at 92 keV and the net area of the energy line at 98 keV of the measured energy spectrum.
    According to particular embodiments, the device can include one or more of the following characteristics:
    - the evaluation module includes a sub-module for calculating a first mass concentration of uranium Cmj (92 keV) using the net area of the energy line at 92 keV and for calculating a second mass concentration in uranium Cmj (98 keV) using the net area of the energy line at 98 keV in the measured energy spectrum,
    - the quantity evaluated by the module is a mass concentration interval in uranium, the interval being delimited by a lower bound equal to the first mass concentration in uranium Cmj (92 keV) and by an upper bound equal to the second mass concentration in uranium Cmu (98 keV),
    - The device also includes a module for characterizing the heterogeneity of the sample based on the amplitude of the mass uranium concentration range.
    The invention will be better understood on reading the description which follows, given solely by way of example, and made with reference to the drawings among which:
    FIG. 1 is a schematic representation of the device used to implement the method according to the invention, FIG. 2 is a schematic representation of a method for evaluating the mass concentration of uranium in an ore sample, FIG. 3 is a graphical representation of a typical gamma energy spectrum simulated with the Monte-Carlo N-Particle code (MCNP) for a sample having a mass concentration of uranium equal to 1000 ppmj, FIG. 4 is a graphical representation of a spectrum type gamma energy simulated with the Monte-Carlo N-Particle code (MCNP) for a sample with a mass concentration of uranium equal to 10,000 ppmd, Figure 5 is a representation of a low energy gamma spectrum simulated with the Monte-Carlo code N-Particle (MCNP) of the two uranium parentage chains ( 238 U in thick line, 235 U in thin line) and of the total spectrum of the two chains convoluted by the resolution of the die tector (in dashes), Figure 6 is a representation of the contribution of four emissions present in the line at 98 keV for a sample with an average content equal to 1000 ppm U5 obtained by modeling with MCNP, Figure 7 is a representation of the contribution of four emissions present in the line at 98 keV for a sample having an average content equal to 10,000 ppm U5 obtained by modeling with MCNP, Figure 8 is a representation of the mass concentration of uranium Cmu (92 keV) obtained with the method according to the invention from the line at 92 keV and Cmu (98 keV) obtained with the method according to the invention from the line at 98 keV, as a function of the theoretical mass concentration Cmj measured with the line at 1001 keV
    In the following description, the terms “mass concentration” and “content” are considered to be synonymous. Similarly, the terms “line”, “energy line”, “peak” or “energy peak” are considered to be synonymous in the following.
    In the description, the emission intensities of gamma ray or X-ray are expressed as a percentage of the number of decays of the father nucleus.
    A device 10 for evaluating the mass concentration of uranium in a sample 16 according to the invention is shown in FIG. 1.
    The device 10 comprises a germanium detector 12 configured to measure an energy spectrum of gamma radiation from the sample 16, said energy spectrum comprising at least one energy line at 92 keV and one energy line at 98 keV, each line having a net area measurable by a Gaussian adjustment.
    The net area corresponds to the contribution which comes only from the radionuclides or from the fluorescence considered, after subtraction of the continuous background, for example ad hoc using processing software.
    The detector 12 has a resolution suitable for separately measuring the energy line at 92 keV and the energy line at 98 keV.
    The resolution is for example the resolution FWHM (Full Width at Half Maximum, in English) or LTMH (Total Width at Half-Height, in French)
    For example, the detector 12 is a hyper pure germanium (GeHP) detector.
    Typically, the FWHM resolution of a hyper pure germanium detector is around 1 keV for the 92 keV and 98 keV energy lines.
    For example, the detector 12 is a Falcon 5000® manufactured by the company Canberra®. This type of detector is for example described in detail in “Falcon 5000 HPGe based nuclear identifier: a portable tool for safeguards measurements” (2008) by Bosko et al. in "Proceedings of the international conference on facility operationssafeguards interface".
    The Falcon 5000® detector includes a hyper pure germanium crystal with dimensions 60 mm in diameter and 30 mm thick.
    Referring to Figure 1, the device 10 is adapted to receive a sample
    16.
    Sample 16 is for example a drill core or crushed ore from the exploration or exploitation of a mine placed in a container, for example cylindrical (Figure 1).
    Advantageously, the device 10 also comprises a shim 14, for example made of PVC or polycarbonates (for example made of makrolon®), on which the sample 16 rests.
    The wedge 14 has for example a variable height. This makes it possible to bring the sample 16 and the detector 12 into contact.
    The device 10 further comprises an enclosure 18, for example cylindrical, defining an opening 20 in which the wedge 14 is placed.
    The opening 20 is typically closed by means of an enclosure element 22.
    The enclosure 18 and the enclosure element 22 are typically made of copper.
    Copper absorbs X-rays of lead fluorescence (72.80 keV, 74.97 keV, 84.45 keV and 87.30 keV lines).
    The device 10 further comprises a plurality of lead bricks 24, for example 5 cm thick, arranged around the enclosure.
    The lead bricks 24 reduce the background noise.
    The device 10 further comprises a module 26 for evaluation, by calculation, of a quantity characterizing the mass concentration of uranium using the net area of the energy line at 92 keV and the net area of the energy line at 98 keV of the measured energy spectrum.
    Advantageously, the evaluation module 26 comprises a sub-module 28 for calculating a first mass concentration of uranium using the net area of the energy line at 92 keV and for calculating a second mass concentration in uranium using the net area of the energy line at 98 keV of the measured energy spectrum.
    According to one embodiment, the quantity evaluated is an interval of mass concentration of uranium, the interval being delimited by a lower bound equal to the first mass concentration of uranium and by an upper bound equal to the second mass concentration of uranium and the device 10 further comprises a module 30 for characterizing the heterogeneity of the sample 16 on the basis of the amplitude of the mass concentration interval of uranium.
    The modules 26, 28 and 30 are programmed to implement the method according to the invention, described in the following.
    FIG. 2 shows the steps of the method for evaluating the mass concentration of uranium in a sample 16 by gamma spectrometry according to the invention.
    The method according to the invention comprises a step a) 600 of measuring an energy spectrum of gamma radiation of the sample 16 using a detector 12, said energy spectrum comprising at least one energy line at 92 keV and an energetic line at 98 keV, each line having a net area.
    FIGS. 3 and 4 show spectra 201, 301 of gamma radiation of a standard sample of uranium ore for contents of 1000 ppmj and 10000 ppmu respectively.
    One distinguishes in particular the energy line 203, 303 of 234m Pa at 1001 keV conventionally used in spectrometry, the line 205, 305 to 92 keV and the line 207, 307 to 98 KeV (on the left) used in the process according to the invention .
    It is observed that the net area of the energy lines 205, 305 to 92 keV and the energy lines 207, 307 to 98 keV is advantageously greater than that of the line 203, 303 to 1001 keV, generally of the order of a factor 30 to 40 for the 92 keV line and a factor of 4 to 10 for the 98 keV line. These observations were made on more than 80 samples of crushed ore measured in the laboratory by the Applicant with the Falcon 5000 detector. These variations in factors are due to the differences in uranium content (from 100 to 14,000 ppm), in volume, in density , heterogeneity and radioactive imbalance between samples.
    FIG. 5 presents a modeling of the emissions that make up the line 205, 305 to 92 keV, carried out with the Monte-Carlo N-Particle code (MCNP) for a homogeneous standard sample.
    The MCNP code is a code which makes it possible to model the transport of X and gamma rays emitted in the sample to the detector then their interaction (energy deposits) in the germanium crystal (“MCNP6TM, User's manual - Version 1.0 - LA-CP-13-00634, Rev. 0 Denise B. Pelowitz, editor ”. May-2013).
    The 205, 305 to 92 keV line is mainly dominated by the emissions of two radionuclides:
    - a spontaneous emission 401 of an X-ray at 93.35 keV (which contributes to the signal at 92 keV due to the resolution of the detector) linked to the 235 U. This emission comes from the reorganization of the electronic procession of the thorium atom following the a decay of 235 U around 231 Th. Its emission intensity is tabulated and is equal to / 93 / cev ( 2 92 ^) - 5.56%;
    - a 403 emission of a gamma doublet of 234 Th at 92.38 keV and 92.80 keV (located at the top of the 238 U chain). The total emission intensity of the gamma doublet Î92fcev ( 2 9oTÙ) is 4.83%.
    Since 235 U and 234 Th are located at the top of the uranium decay chains, the 92 keV line area is not subject to potential imbalances in this chain.
    In FIG. 5, the spontaneous emission 401 at 93.35 keV is shown in a thin line. The emission 403 of the gamma doublet of 234 Th at 92.38 keV and 92.80 keV is represented in thick line.
    The dashes represent the total spectrum 205 of the two chains convoluted by the resolution of the detector. It is then observed that all the lines merge into a peak at 92.5 keV called “line at 92 keV” for the sake of simplification in the description.
    Figures 6 and 7 show the relative importance of the emissions that make up the 207, 307 to 98 keV line, based on models carried out with the MCNP code, respectively for a sample of average content equal to 1000 ppmd and 10000 ppmd.
    Line 207, 307 at 98 keV is dominated by four emissions:
    - 501 XKa1 fluorescence of uranium at 98.439 keV, however simulated by MCNP at 99 keV;
    - a spontaneous 503 X emission at 98.439 keV linked to 234m Pa (at the top of the 238 U chain) which follows the internal conversion of its son nucleus 234 U. The corresponding emission intensity is l98kev ( 234 ™ Pa) = 0.23%;
    - a spontaneous emission 505 of two X-rays linked to 223 Ra at 97.530 keV and
    97.853 keV ( 235 U chain). This emission comes from the reorganization of the electronic procession of the radon atom following the decay a of 223 Ra towards 219 Rn. The total emission intensity is tabulated at Ig 8 kev ( 2 88 Ra ) = 2.85%,
    - a spontaneous emission 507 of two X-rays linked to 226 Ra at 97.530 keV and
    97.853 keV ( 238 U chain). This emission comes from the reorganization of the electronic procession of the radon atom following the a decay of 226 Ra towards 222 Rn. The total emission intensity is tabulated Ig kev 2 (2 88 Ra) = 0.036%.
    The fluorescence 501 XKa1 of uranium at 98.439 keV, the spontaneous emission 503 X at 98.439 keV linked to 234m Pa and the spontaneous emission 507 of two X-rays linked to 226 Ra at 97.530 keV and 97.853 keV, all three linked to the 238 U, are shown in thick lines.
    The spontaneous emission 505 of two X-rays linked to 223 Ra at 97.530 keV and
    97.853 keV is shown in thin lines.
    A total spectrum 207, 307 convoluted by the resolution of the detector is shown in dashes.
    It is noted in particular in FIG. 7, for an average content equal to 10,000 ppmu, the preponderance of an auto-fluorescence phenomenon compared to the other contributions.
    Each gamma radiation emitted by one of the child elements of the 238 U and 235 U decay chain can, in general after Compton scattering and then photoelectric absorption, cause X-ray fluorescence of the uranium atoms in the sample. This phenomenon does not follow a simple linear evolution like spontaneous emissions but increases in a quadratic way with the uranium content, because on the one hand, the source of fluorescence becomes more intense, and on the other hand the quantity of uranium increases.
    The method comprises a step b) 610 of evaluation by calculation of a quantity characterizing the mass concentration of uranium using the net area of the energy line 205, 305 to 92 keV and the net area of the energy line 207 , 307 to 98 keV of the measured energy spectrum.
    Advantageously, step b) 610 of evaluating the method according to the invention comprises a sub-step c) 615 of calculating a first mass concentration of uranium using the net area of the energy line 205, 305 to 92 keV and calculation of a second mass concentration of uranium using the net area of the energy line 207, 307 to 98 keV of the energy spectrum measured.
    For example, the quantity evaluated is an interval of mass concentration of uranium, the interval being delimited by a lower bound equal to the first mass concentration of uranium and by an upper bound equal to the second mass concentration of uranium.
    The shape of an energy line is close to that of a Gaussian. The energy lines are located on a continuous background composed by the events due to Compton scattering from photons at higher energies to lower energies and by ambient background noise.
    The first mass concentration of Crriu uranium (92 keV), expressed in ppmu (ie in mgu per kg of sample) is calculated using the net area Sn (92 keV) of the line 205, 305 to 92 keV and the formula next :
    9 .. (92 keV)
    Cm „(92 keV) = ---------------------- Te x M ech x (CE 234n + CE 233u ) with:
    - a calibration coefficient ce 234tk E ff92keV x LzfcevCgo'Fft) x ln (2) X JMfl _ r qzt y Ί n ~ 4 V 1.0072 X 10 6 X Μ X T1 ( 2 ^ U) '
    Eff 9 2kev (in S -1 .gu 1 or s _1 .ppmu 1 .g ech ' 1 );
    ^ zls ^ x E ff93keV * l93kev (. 2 llu) x ln (2) x JNa
    - a calibration coefficient ce 233 = 0072 x 10 & χ Μ ^ χΤι ^ υ} --- = 3,160 x 10 “ 5 x
    Eff-Hkev (in S -1 .gu 1 or s 1 .ppmu 1 .g eC h _1 )
    In these coefficients, the following notations are used:
    - Effect 92 kev, detector efficiency at 92 keV (dimensionless: number of shots in the peak at 92 keV per gamma photon of 92 keV emitted in the sample);
    - Ef f 93keV , detector efficiency at 93 keV (dimensionless: number of strokes in the peak at 93 keV per gamma photon of 93 keV emitted in the sample);
    - JVa, the Avogadro constant;
    - In, the natural logarithm;
    ^ kevdoTh ·) and h-îkev ^ l ^ E), the emission intensities described above;
    - Μ ( 2 92 υ), molar mass of 2 | f 77;
    - 7-1 (^ 2 ^), the half-life of 2 ^ (in s);
    ττΞϋτΚ ' the ratio of the activities of isotopes 235 U and 238 U in natural uranium (which is equal to 0.046);
    -Te / counting time (in s);
    - M ech : mass of the sample (in g);
    The second mass concentration of uranium Cmu (98 keV) is calculated using the net area S n (98keV) of the line 207, and the net areas S net (E ^ of the lines at 186 keV, 242 keV, 298 keV, 352 keV, 609 keV and 1120keV (fluorescence source term)
    Sn (98 keV)
    Cm „(98 keV) = ------------------- r ---------- 2 ------------ -------------------------- Mech x TEfofluofE-i'd.h) x SnettefE-i)] + Te x Al ecft x (CE 23impa + CE 223Ra + CE 226Ra ~) with:
    - ^ hfiuoÇE dh), energy fluorescence yield E r and a height h and a density dd'échantillon, defined below (in PPMU 1 .M exch, ie in gu 1);
    -S net (Ε γ ~), net area of the line at energy E r (186 keV, 242 keV, 298 keV, 352 keV, 609 keV and 1120 keV);
    C £ '234m Pa ' . _ 2341 x (in s - '. Gu ·). 1.0072 X 10 6 XM ( 22 ®U) XT1 ( 22 | U) 1 198 / cel / MU / 2
    Effsskev, detection efficiency at 98 keV (dimensionless) x E ff '”<kev x ln (2) x JMa xi 98ke v ( 2 ^ a)
    -ce 223b = 92 ------------------- = 1,620 x 10 ”” 5 x Eff 98keV (in s -1 .gu 1 )
    223 Ra 1.0072 x 1O 6 xMp ^ u) xTi ( 2 ^ u) mu / A ^ 238, ^ isotope activity ratio 223 Ra (chain of 235 U) and 238 U, which is = t / zlsm = 0.046 in the case of a natural enrichment in 235 U (0.72%) and an A (g 2 U) A (92 ^) secular balance of the chain of 235 U in which the 223 Ra is found;
    226 Sa xln (2) xT4ax / 98fc Λ ( 92 ^ 98fceV_______________________
    1.0072 X 10 6 XMX Γ1 ( 2 92 ^) = 4.447 X 10 “ 5 x Eff 98keV (in s 1 .gu 1 )
    - / 98fcer ( 234 9iTa) and I 9 skev (. 2 88 Ra the emission intensities described above.
    Thus, the first mass concentration of uranium is calculated taking into account a spontaneous emission of an X-ray of 235 U and an emission of a gamma ray doublet of 234 Th.
    Advantageously, the second mass concentration of uranium is calculated by taking into account a spontaneous emission of X-rays linked to 234m Pa, a spontaneous emission of two X-rays linked to 223 Ra and the spontaneous emission of two X-rays linked to 226 Ra and the contribution of an X-ray fluorescence phenomenon caused by at least one gamma radiation emission from at least one descendant of uranium.
    In order to quantify the capacity of an energy photon E to make uranium fluoresce, a fluorescence yield η Πυο (Ε γ , ά, h) specific to the geometry and the nature of the sample (uranium content , filling height, density, mineralogy) is defined as the ratio between the net surface at 98 keV and the net surface at energy Ε γ in the spectrum measured by the detector, normalized by the uranium content and the mass of l 'simulated sample.
    The fluorescence yield is calculated by numerical simulation with the MCNP code, described above, for different types of samples, for example by varying the filling height, the mineralogy, the density or even the uranium content.
    Modeling with the MCNP software was carried out in order to highlight the influence of the heterogeneity of the sample on the calculation of the mass concentration of uranium using the two formulas described above.
    Two types of heterogeneity were simulated using the H1 and H2 models. For both models, the total mass of uranium in the sample is identical.
    The first model H1 corresponds to a nugget of UO 2 (density equal to 11) which concentrates all the uranium in the center of the sample. The rest of the sample is composed of SiO 2 sand.
    Considering in a homogeneous case (density of 1.4 and height of 6 cm) a content of 1000 ppmU, then the radius of the nugget of UO 2 which allows to concentrate all the mass in uranium (0.798 gu) is 0.264 cm.
    The second model H2 corresponds to a nugget of UO 2 (density equal to 11) with a radius of 0.2 cm, or a mass of uranium of 0.343 g u . As the nugget radius is smaller than in the first H1 model, the rest of the uranium (0.455 g u ) is diluted in the SiO 2 sand. Thus, if we consider in the homogeneous case a uranium content of 1000 ppmu for a density of 1.4 and a filling height of 6 cm, this is equivalent to concentrating 43% of the mass of total uranium in the sample in the nugget and 57% in the SiO 2 sand.
    The following table represents the uranium contents obtained in the case of homogeneous and heterogeneous samples (models H1 and H2), simulated by MCNP, for 100, 1000 and 10000 ppmu, using the formulas CmU (92 keV) and CmU (98 keV) described above. The fluorescence yields and the efficiencies used are those calculated in the homogeneous case for a uranium content of 1000 ppmu.
    Homogeneous H1 H2 Simulated mass concentration (ppmu) 92 keV 98 keV 92 keV 98 keV 92 keV 98 keV 100 102 123 36 1145 X X 1000 1013 1042 198 6965 690 3645 10000 8892 9643 895 19220 X X
    The results with homogeneous samples show that the formulas
    CmU (92 keV) and CmU (98 keV) are representative of the uranium content. However, when the sample becomes heterogeneous, the use of the only net area of the line at 92 keV induces an underestimation of the uranium content whereas using the only net area at 98 keV induces an overestimation. When the uranium is concentrated in the center of the sample, the passive emissions undergo a strong self-absorption in the nugget because it has a high density and an average atomic mass. Conversely, X-ray fluorescence is favored in the case of a dense nugget in the center of the sample where the Compton scattering and photoelectric absorption phenomena are maximum.
    Furthermore, the inventors noted a concordance between an experimentally measured sample (not shown) and the heterogeneous model H2. Indeed, a sample of known uranium content (909 ppmj) gives 708 ppmj with Cmu (92 keV) and 2,920 ppmu with Cmu (98 keV). The values are similar to those observed in the table for the UO 2 nugget of the H2 model studied by simulation and therefore suggests a probable heterogeneity of the sample measured.
    Advantageously, step b) of evaluation comprises the determination of a mass concentration interval of uranium, the interval being bounded by a lower bound equal to the first mass concentration of uranium and by an upper bound equal to the second mass concentration of uranium.
    Advantageously, the method further comprises a step d) 620 for characterizing the heterogeneity of the sample on the basis of the amplitude of the mass concentration range of uranium.
    Typically, the range of the interval increases with heterogeneity.
    Advantageously, step d) 620 for characterizing the heterogeneity of the sample comprises a sub-step e) 625 for determining a coefficient representative of the heterogeneity of the sample using the first and second mass concentrations uranium.
    The coefficient is preferably a Cmj (98 keV) / Cmu (92keV) ratio between the second mass concentration of uranium Cmj (98 keV) and the first mass concentration of uranium Cmu (92 keV).
    As a variant, the coefficient is equal to [Cmj (98 keV) / Cmj (92 keV)] - 1.
    Preferably, the method comprises a step f) 630 in which the value of the coefficient representative of the heterogeneity of the sample 16 is tested to determine a state representative of the heterogeneity chosen from a heterogeneous state and a homogeneous state.
    Thus, for example, considering that the coefficient representative of heterogeneity is the ratio Cmu (98 keV) / Cmu (92 keV), step f) 630 consists in comparing the value of said coefficient with a predetermined threshold value.
    The threshold value is advantageously calculated beforehand using numerical simulations.
    If the coefficient representing heterogeneity is equal to Cmu (98 keV) / Cmu (92 keV), the predetermined threshold value is for example between 1.2 and 1.7, advantageously equal to 1.5.
    Thus, in the case where the predetermined threshold value is fixed at 1.5, if the coefficient Cmu (98keV) / Cmu (92keV) is greater than said predetermined threshold value, it can be considered that the state of the sample corresponds to a heterogeneous state.
    Conversely, if the coefficient Cmu (98 keV) / Cmu (92 keV) is less than said predetermined threshold value, the state of the sample corresponds to a homogeneous state.
    Typically, if the determined state corresponds to a homogeneous state, the process is stopped.
    Advantageously, if the determined state corresponds to a heterogeneous state, the method then comprises:
    - a step g) 640 of crushing and homogenization of the ore sample, and
    - repeating steps a) to f).
    Step g) 640 of crushing and homogenization thus avoids a "nugget" effect.
    In the context of the invention, step g) of crushing and homogenization of the sample and steps a) to f) can be repeated until the state of the sample corresponds to a state homogeneous.
    In the context of the invention, the term “crushing” designates any method making it possible to reduce the test sample into fragments of variable size which can range from the order of a few centimeters to a fine powder whose particle size is for example of 600 pm or even 100 pm.
    The inventors have carried out an experimental validation of the formulas Cmu (92 keV) and Cmu (98 keV); To do this, more than 80 rock samples from mines located in Mongolia and Niger were tested, in order to scan a wide range of mass concentration, ranging from a few tens of ppmu to more than 10,000 ppmu.
    FIG. 8 shows the mass concentrations of uranium obtained with the formulas Cmu (92 keV) and Cmu (98 keV) as a function of the theoretical mass concentration Cmj obtained using the peak at 1001 keV.
    The results show that these two formulas allow to find the theoretical concentration (global values close to the line y = x) but also the probable presence of several heterogeneities whose Cmu value (98 keV) clearly deviates from the theoretical Cmu value (1001 keV) (see Figure 8).
    Thus the method according to the invention makes it possible to significantly reduce the measurement time, by a factor 4 to 10 for the line at 98 keV and by a factor 30 to 40 for that at 92 keV, compared to the line at 1001 keV used conventionally (it is recalled that these factors have been observed on samples measured in the laboratory and vary according to their homogeneity, uranium content and imbalance). Furthermore, the method makes it possible to estimate a mass concentration interval of uranium and by the same, to also provide an indicator of the quality of the measurement relating to a potential heterogeneity of the ore sample. The process according to the invention ultimately makes it possible to obtain a more precise value for the uranium concentration than if the content evaluated with the usual line at 92 keV is used only.
    权利要求:
    Claims (14)
    [1" id="c-fr-0001]
    1. - Method for evaluating the mass concentration of uranium in a sample (16) of ore by gamma spectrometry, the method comprising the following steps:
    c) an energy spectrum of gamma radiation of the sample (16) is measured (600) using a detector (12), said energy spectrum comprising at least one energy line (205, 305) at 92 keV and an energetic line (207, 307) at 98 keV, each line having a net area;
    d) a quantity characterizing the mass concentration of uranium in the sample (16) is calculated (610) using the net area of the energy line (205, 305) at 92 keV and the net area of the line energy (207, 307) at 98 keV of the measured energy spectrum.
    [2" id="c-fr-0002]
    2. - The method of claim 1, wherein step b) of evaluation comprises a sub-step c) (615) in which a first mass concentration of uranium Cmu (92 keV) is calculated using the net area of the energy line (205, 305) at 92 keV and a second mass concentration of uranium Cmu (98 keV) using the net area of the energy line (207, 307) at 98 keV of the measured energy spectrum.
    [3" id="c-fr-0003]
    3. - Method according to claim 2, wherein the quantity evaluated is a mass concentration interval in uranium, the interval being bounded by a lower bound equal to the first mass concentration in uranium and by an upper bound equal to the second concentration mass in uranium.
    [4" id="c-fr-0004]
    4. - Method according to claim 3, further comprising a step d) (620) in which the heterogeneity of the sample (16) is characterized from the amplitude of the mass concentration range of uranium.
    [5" id="c-fr-0005]
    5. - Method according to claim 4, wherein step d) (620) of characterizing the heterogeneity of the sample (16) comprises a sub-step e) (625) of calculation of a coefficient representative of the heterogeneity of the sample (16) using the first and the second mass concentration of uranium.
    [6" id="c-fr-0006]
    6. - Method according to claim 5, wherein the coefficient representative of the heterogeneity of the sample (16) is the ratio: (Cmu (98 keV) / Cmu (92 keV).
    [7" id="c-fr-0007]
    7. - Method according to claims 5 or 6, comprising at least one step f) (630) in which the value of the coefficient representative of the heterogeneity of the sample (16) is tested to determine a state representative of the heterogeneity chosen from a heterogeneous state and a homogeneous state.
    [8" id="c-fr-0008]
    8. - Method according to claim 7, wherein in step f) (630), the value of the coefficient representative of the heterogeneity of the sample (16) is compared to a predetermined threshold value.
    [9" id="c-fr-0009]
    9. - Method according to claim 7 or 8, further comprising, when the state representative of the heterogeneity corresponds to a heterogeneous state:
    a step g) (640) in which the sample (16) is crushed and homogenized, and
    - steps a) to f) are repeated.
    [10" id="c-fr-0010]
    10. - Method according to any one of claims 2 to 9, wherein the second mass concentration of uranium is calculated by taking into account a spontaneous emission of X-rays linked to 234m Pa, a spontaneous emission of two radiations X linked to 223 Ra, the spontaneous emission of two X-rays linked to 226 Ra and the contribution of an X fluorescence phenomenon caused by at least one gamma radiation emission from at least one descendant of uranium.
    [11" id="c-fr-0011]
    11. - Device (10) for evaluating the mass concentration of uranium in a sample (16), said device comprising:
    - a detector (12) adapted to measure an energy spectrum of gamma radiation of the sample (16), said energy spectrum comprising at least one energy line (205, 305) at 92 keV and an energy line (207, 307) at 98 keV, each line having a clean area;
    - a module (26) for evaluation by calculation of a quantity characterizing the mass concentration of uranium using the net area of the energy line (205, 305) at 92 keV and the net area of the energy line ( 207, 307) at 98 keV of the measured energy spectrum.
    [12" id="c-fr-0012]
    12. - Device (10) according to claim 11, wherein the evaluation module (26) comprises a sub-module (28) for calculating a first mass concentration of uranium Cmu (92 keV) using the area net of the energy line (205,
    305) at 92 keV and calculating a second mass concentration of uranium Cmu (98 keV) using the net area of the energy line (207, 307) at 98 keV in the measured energy spectrum.
    5
    [13" id="c-fr-0013]
    13.- Device (10) according to claim 12, in which the quantity evaluated by the module (26) is a mass concentration interval in uranium, the interval being delimited by a lower bound equal to the first mass concentration in uranium Cmu (92 keV) and by an upper bound equal to the second mass concentration of uranium Cmu (98 keV).
    [14" id="c-fr-0014]
    14, - Device (10) according to claims 12 or 13, further comprising a module (30) for characterizing the heterogeneity of the sample (16) from the amplitude of the mass concentration range of uranium .
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    同族专利:
    公开号 | 公开日
    FR3078408B1|2021-06-11|
    WO2019166462A1|2019-09-06|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    US20060231768A1|2005-03-24|2006-10-19|Bil Solutions Limited|Providing information|FR3104737A1|2019-12-11|2021-06-18|Orano Mining|Method and system for evaluating a parameter representative of the mass uranium concentration of a sample of uranium material by gamma spectrometry|
    FR3104739A1|2019-12-17|2021-06-18|Orano Mining|Method for evaluating the uranium content by gamma spectrometry in a wellbore and associated device|
    法律状态:
    2019-01-25| PLFP| Fee payment|Year of fee payment: 2 |
    2019-08-30| PLSC| Publication of the preliminary search report|Effective date: 20190830 |
    2020-01-13| PLFP| Fee payment|Year of fee payment: 3 |
    2021-01-22| PLFP| Fee payment|Year of fee payment: 4 |
    2022-01-12| PLFP| Fee payment|Year of fee payment: 5 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1851744|2018-02-27|
    FR1851744A|FR3078408B1|2018-02-27|2018-02-27|METHOD OF EVALUATING THE MASS URANIUM CONCENTRATION OF A SAMPLE OF ORE BY GAMMA SPECTROMETRY|FR1851744A| FR3078408B1|2018-02-27|2018-02-27|METHOD OF EVALUATING THE MASS URANIUM CONCENTRATION OF A SAMPLE OF ORE BY GAMMA SPECTROMETRY|
    PCT/EP2019/054797| WO2019166462A1|2018-02-27|2019-02-27|Method for assessing the mass concentration of uranium in a material containing uranium by gamma spectrometry|
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