System and method for identifying nuclear threats

Abstract

The present invention relates to a method and device for detecting a radiation source, the device for identifying a radiation source of the present invention comprises a Type II detector, a first photomultiplier tube or SiPm reader associated with the Type II detector, a first digitizer circuit associated with the first photomultiplier tube and adapted to convert light pulses into a digital signal, a first power supply circuit associated with the first photomultiplier tube, a Type I detector, a second photomultiplier tube or SiPm reader associated with the Type I detector, a second digitizer circuit associated with the second photomultiplier tube and adapted to convert light pulses into a digital signal, a second power supply circuit associated with the second photomultiplier tube, a programmable digital processor associated with the first and second photomultiplier tubes, a user interface, GUI, and a control panel for exchanging information and data with a user.

Description

Technical Field

[0001] The present invention relates to the technical field of methods and devices for detecting and measuring radioactivity and radiation sources.

Background Art

[0002] Between 1993 and 2006, 1080 cases of illicit trafficking and unauthorized activities related to nuclear and radioactive materials were confirmed worldwide (source: IAEA). Of these, 18 cases involve substances that can be used in the manufacture of bombs, namely plutonium and highly enriched uranium (HEU). The IAEA has also reported 124 cases involving substances that could potentially be used in the manufacture of so-called "dirty bombs," i.e., bombs that detonate conventional explosives to disperse radioactive materials. The IAEA has concluded that these substances pose a potential and ongoing threat to the security of the international community.

[0003] Therefore, considerable efforts have been made in all countries, particularly in the United States and the European Community, to monitor the transportation of goods by land, air, and sea. In this regard, particular attention has been paid to ensuring that the instruments used for monitoring do not give false alarms. In fact, in the initial stage, automated instruments are usually used. A typical example is the radiation portal, which consists of one or more detection units and forms a gate through which the object to be analyzed must pass. When an alarm occurs, it is necessary to inspect the suspicious substance using a portable device in order to accurately identify the nature of the substance. If the radiation source cannot be identified, it is necessary to physically inspect the suspicious substance, which requires a significant amount of time and cost.

[0004] Therefore, there is a need for a reliable tool that can surely identify the nature of the inspected substance.

[0005] Portable devices for identifying radiation sources whose characteristics are defined by the IEC62327 standard are known and commercially available. In these devices, a spectroscopic detector for gamma rays, such as an organic or inorganic scintillator like NaI(Tl) or LaBr3, is used. This type of detector obtains the identification of radioactive substances by recognizing the photopeaks generated by the characteristic transitions of various radioactive isotopes present in the detected spectral range. Since the response of inorganic scintillators to neutrons is statistically irrelevant, these systems are not used to detect the possibility of the presence of neutrons. In fact, the interaction between neutrons and the inorganic crystal lattice is basically due to inelastic scattering from the excited energy levels of the atomic nuclei that make up the scintillator. Since the cross-section of this inelastic scattering is very small, statistically few occur, generating characteristic gamma rays that are indistinguishable in energy from direct gamma rays. For all these reasons, it is impossible to separate the contribution of neutrons from gamma rays due to the surrounding background. For this reason, radiation monitoring devices sometimes add a neutron detector (generally 3 a 3He proportional counter) to detect the presence of a neutron source.

[0006] The identification of neutron sources is characteristic of industrial radioactive isotopes (e.g., 252 Cf or Am / Be sources), and certain types of nuclear waste (where neutrons are emitted by (α,n) type reactions), and so-called special nuclear materials, especially plutonium, and is actually fundamental because of this.

[0007] The main drawback of the above system is that it provides no information suitable for identifying a neutron source in the absence of a relevant distinct gamma signal. The reason is that in such a device, the neutron detector and the gamma detector are completely separated, and the information provided is also separated. Neutron detectors that have been used in portable systems so far only provide an indication of the number of neutrons present, and information regarding gamma rays must be obtained from an inorganic scintillator. That is, one of the distinctive features of this type of system is that the neutron detector has very low sensitivity to gamma rays, and conversely, the gamma detector has weak sensitivity to neutrons. This is very important especially in identifying special nuclear materials. According to the IEC62327 standard, the identification of special nuclear materials is only provided by gamma ray spectrometry in the case of a source shielded by 5 mm of iron. However, in the case of a larger shield or a heavier metal (e.g., lead or tungsten), the gamma ray emission may be too weak to lead to a direct identification. In all these cases, the currently available technology only detects excess neutrons and cannot be used to distinguish the type of neutron source and perform an accurate identification.

[0008] To date, all portable or transportable, or fixed-installed portal monitor measuring devices and systems used for on-site measurements use only separate and exclusive analysis for gamma ray sources and neutron sources. Those measuring devices and systems identify gamma isotopes and count neutrons separately, usually 3 using a He detector, but there is no correlation between the two. The same standards such as ANSI and IEC mention the ability to measure the presence of gamma ray sources and neutron sources, but do not consider complex scenarios such as the reliable determination of neutron emitters (i.e., the identification of the (α-n) reaction). Furthermore, regarding neutron measurements, the same IEC and ANSI standards only impose conditions on the counting performance for detecting the presence or absence of neutron emitters, and do not impose conditions for defining the type of their origin (i.e., performing an identification). Summary of the Invention

Problems to be Solved by the Invention

[0009] Accordingly, an object of the present invention is to provide a method based on a computational algorithm that enables the detection of a radiation source, as has been done heretofore with portable, transportable, and fixed-installed portal monitors / systems, not only to simply identify its generality but also to accurately identify its type. These algorithms based on the mixed detection and identification of gamma rays and neutrons enable the accurate identification of radioactive substances even in the absence of clearly identifiable gamma-ray emissions.

[0010] Another object of the present invention relates to implementing such a method in a portable device (less than 10 kg), a transportable device (less than 20 kg), or a radiation portal monitor.

[0011] Another object of the present invention is to provide a new method for detecting a radiation source that can be implemented by a single detector for simultaneously detecting gamma-ray emissions and neutron-ray emissions from the same source.

[0012] Another object of the present invention is to be able to distinguish different types of neutron sources even in the absence of clearly identifiable gamma-ray emissions.

Means for Solving the Problems

[0013] The present invention relates to a method and a device for detecting a radiation source, which is based on the simultaneous use of two or more radiation detectors of different types, and in particular consists of possible configurations of detectors of type I, II, and / or III (see the following definitions of detectors). Since different types of detectors are integrated into a single device in this way, it is possible to identify special nuclear materials (SNMs) contained in devices that terrorists may use, such as radioactive dispersion devices (RDDs) and improvised nuclear devices (INDs), in a single simultaneous measurement. This single measurement is carried out simultaneously by all the detectors installed in the device, includes both gamma rays and neutrons, and is an almost instantaneous measurement that generates an alarm within seconds, even potentially in the presence of shielding and / or masking. Furthermore, it is possible to completely identify the gamma-ray and neutron sources and instantaneously evaluate the total dose or the independent equivalent ambient dose H * (10) from both gamma rays and neutrons.

[0014] The identification of neutron sources is essential for identifying special nuclear materials or products resulting from fuel cycle processing. Such products are generated by the reprocessing of nuclear fuel irradiated in a reactor or by so-called "spent fuel", which is irradiated nuclear fuel that has reached the end of its life and has been removed from the reactor core. Other sources of these products include 252 radioactive isotopes for industrial use such as Cf, sources where neutrons are emitted by (α, n)-type reactions, i.e., AmLi, AmBe, representative isotopes of special nuclear materials (SNMs) such as plutonium-239 and uranium-235.

[0015] The particularity and uniqueness of the present invention lie in the implementation of an algorithm for analyzing gamma and neutron count data by simultaneously processing neutron counts and multiplicities in a parallel and continuous manner and analyzing the related gamma-ray spectrum with the help of a selected isotope library. Selection criteria are applied to these analyses to maximize the probability of identifying the source in terms of both the properties of gamma rays and neutrons and to associate a specific confidence level CL (CL = probability of accurately identifying the nuclide).

[0016] The idea underlying the present invention is that, in addition to obtaining the identification of both neutrons and isotopes in the emission range, it is possible to ensure identification under specific critical detection conditions, namely, the so-called masking conditions where a gamma-ray source with strong natural, medical, and industrial properties is added to the neutron beam emission source. Under this condition, since the neutron / gamma-ray multiplicity changes significantly, problems occur in recognizing the neutron source. Therefore, the idea of introducing a second detector into the measurement system can be selected, for example, as a scintillator having a resolution of 8% or more (i.e., NaI(Tl) with a typical FWHM of 7% at Cs-137, CeBr with a typical FWHM of 3% at Cs-137, or CsI, SrI, or LaBr with a typical FWHM of 2.5 - 3% at Cs-137(661KeV), etc.), to identify the peak of the gamma-ray source and subtract them from the n-gamma-ray measurement section to obtain correction of the neutron / gamma-ray multiplicity.

[0017] For example, by identifying the 1.001 MeV photopeak of metastable protactinium Pa-231m, the algorithm determines whether HEU (highly enriched uranium) (emitting 100 gammas / second at 1 MeV for 1 gram of U-238) is effective or not.

[0018] By mounting a thermal neutron detector (Type III) in parallel with the Type I detector, the ratio of thermal neutrons to fast neutrons can be obtained, and when the neutron emitter is SNM, it becomes easier to identify it in a special way.

[0019] Each SNM has its own radioactive signature, that is, a characteristic neutron and gamma-ray emission spectrum, by which it can be identified. Neutron emission is by both spontaneous fission and alpha-particle-induced fission, about 2×10 5 n / s for 12 kg of WGU (uranium weapon grade), about 2×10 5It becomes n / s. It should be recalled that the IEC62327 standard requires a neutron alarm to be activated within 2 seconds for a radiation source emitting at 20,000 n / s at a distance of 25 cm. For most of the isotopes of interest, the neutrons emitted are accompanied by gamma rays with an average of 6.5 photons and an energy of 1 MeV from nuclear fission. When tungsten is used as the shielding material, in the cases of WGU and WGPu, the emissions become 30 γ / s and 100 γ / s respectively.

[0020] Gamma emissions can be shielded more easily in a way that is confused with the surrounding background. Therefore, the identification of WGU and WGPu needs to be carried out by detecting neutrons with a background that is about three orders of magnitude smaller than that of gamma rays. The greatest difficulty lies in the identification of WGU because the number of neutrons emitted is small, especially when tungsten is used as the shielding / tamping material. In this case, the SNM material can only be identified at close range. For this need, a portable survey system is required. The reason is that it can detect gamma rays and neutrons, distinguish them simultaneously and accurately identify them, and accurately associate the types of special nuclear materials (SNM).

Advantages of the Invention

[0021] The present invention provides both parallel analysis and sequential analysis of both the counts and spectroscopic analysis obtained from two or more gamma-ray detectors and gamma-ray / neutron detectors, performs comparative verification, and further enables the evaluation of the reliability in identification (both gamma and neutrons) through the unique experimental calibration process of measurement and automatic calibration equipment.

Brief Description of the Drawings

[0022] Further features and advantages of the present invention will become apparent by reading the following detailed description provided with the aid of the drawings as non-limiting examples.

[0023]

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[0024] The following description of exemplary embodiments refers to the accompanying drawings. The same reference numerals in different drawings identify the same or similar elements. The following detailed description is not intended to limit the present invention. The scope of the present invention is defined by the appended claims.

[0025] In the following description, the reference numerals 1.a) - 16.a), 1.b) - 5.b), and 1.c) - 8.c) used in the flowcharts of FIGS. 1 - 4 are inserted within square brackets in the text.

Mode for Carrying Out the Invention

[0026] The present invention relates to a method and a device for detecting a radiation source, based on simultaneously using two or more radiation detectors of different types, and in particular consisting of possible configurations of detectors of type I, II, or III. More specifically, the detectors used simultaneously according to an embodiment of the present invention are as follows.

[0027] Type I detectors can generate a gamma-ray spectrum that can be used in the system of the present invention. These detectors are organic or inorganic scintillators based on luminescent materials and are coupled to a device of the signal readout system (not limited to, for example, PMT or SiPM). The luminescence material can be selected from NaI(Tl), NaIL, CsI, LaBr3, CLLB, BaF2, CdWO4, CaF2(Eu), CaWO4, CdWO4, Gd2O2S, LaCl3(Ce), PbWO4, LuI3, LSO, LYSO, YAG(Ce), ZnS(Ag), ZnWO4, BGO, CeBr3, etc. Type I detectors can also be high-resolution semiconductor detectors such as ultra-high purity germanium, especially HpGe, CdZnTe, TlBr, etc.

[0028] Type II detectors can count both gamma rays and neutrons with appropriately and accurately designed processing electronics (typically, but not limited to, digitizers) such as organic or inorganic liquid scintillators or plastic scintillator detectors. By way of example, but not limited to, there is the organic liquid scintillator detector EJ309 that we used for verification. In fact, other similar scintillation detectors can also be used if they have scintillation characteristics such that, when combined with a digitizer appropriately designed using PSD pulse shape discrimination, they can separate gamma-ray and neutron pulses from the same detector and correlate these pulses with very accurate timing up to 10 nanoseconds.

[0029] Type III detectors are gas detectors that have a thermal neutron detection function or include gas, solid, or plastic scintillator detectors that are efficient for the detection of thermal neutrons.

[0030] The combination of two detectors, for example, a combination of any one selected from among one of Type I and one of Type II, enables the following. In the case of Type I, obtaining a gamma-ray spectrum in the energy range from 0 keV to 10 MeV. In the case of Type II, obtaining a gamma-ray spectrum with low resolution, which is sufficient to see the Compton edge of the radiation and, at the same time, being able to detect neutrons with sufficient efficiency.

[0031] The method according to the present invention is based on a computational algorithm that enables detecting a radiation source by accurately identifying not only its generality but also its type.

[0032] A preferred embodiment of the method for identifying a radiation source according to the present invention utilizes the following data collected from the Type I detector and the Type II detector. Data from a Type I detector (gamma-ray spectroscopy detector) that generates the following: Spec1: Identification spectrum obtained by a Type I detector in the case of a gamma-ray alarm. Background (Type I): What is continuously obtained by a Type I detector in order to have a reference spectrum in the absence of an alarm, even without an alarm. Spec2 = Spec1 - Background (Type I): Normalized by acquisition time. Data from a Type II detector (gamma-ray / neutron detector) that generates the following: Spec3: Gamma-ray identification spectrum obtained by a Type II detector in the case of a neutron-only alarm or a gamma-ray and neutron alarm. Spec4: Neutron identification spectrum obtained by a Type II detector in the case of a neutron-only alarm or a gamma-ray and neutron alarm. Background (Type II): What is continuously obtained by a Type II detector in order to have a reference spectrum in the absence of an alarm.

[0033] Furthermore, a preferred embodiment of a method for identifying a radiation source according to the present invention includes the following steps. Detecting a gamma-ray emitting source with a Type I detector; Detecting a plurality of impulses generated from a Type II detector related to each neutron emission and gamma-ray emission from the radiation source; Identifying a first portion of the plurality of impulses related to each neutron emission and a second portion of the plurality of impulses related to each gamma-ray emission, the step of identifying the first portion and the second portion of the impulses including calculating, for each impulse, a total integrated value Ltot of each impulse; A first number n of impulses belonging to the first portion n (Total number of events in Spec4) and a second number n of impulses belonging to the second portion γ (Total number of events in Spec3) are determined; Total integrated value L totThe first average value E n and the second average value E γ are calculated in a step where

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[0034] The identification algorithm of the type II detector provides the identification region of each SNM defined by the values of par x and par y For each region of each SNM, depending on the variation of the measurement rate of gamma rays or neutron rays, it is possible to define sub-regions obtained from the variation of par x , par y or both of them. The variations of the measurement rates of gamma rays and neutron rays are closely correlated with the presence of a shielding material or a moderator, which is a heavy substance that causes a shift in the values of par x and par y .

[0035] (Gamma ray spectrum correction from the contribution of the masking gamma ray source) By using an inorganic scintillator detector of type I such as CeBr3, the results of the method for identifying neutron emitters can be corrected at the high end of the range or when there is a masking source.

[0036] The gamma ray spectrum can, under certain conditions, include both radiation from the neutron ray emission source and radiation from any masking source. Therefore, the masking source can modify the identification results of the neutron ray source.

[0037] By using a type I detector, the gamma-ray source can be identified through its energy spectrum and gamma-ray emission. Further, starting from the knowledge of the energy of the gamma-rays of the identified masking source and the Klein-Nishina distribution of each gamma-ray, the normalization template of the spectral distribution of the type II detector

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[0038] From the count of each photopeak, the photopeak efficiency measurement (cps / phi) of the type I detector, and the count efficiency measurement of the type II detector, a multiplication factor for estimating the contamination of the gamma-ray spectrum of type II by the masking source

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[0039] Coefficient

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[0040]

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[0041] When contamination is suspected, it becomes possible to subtract its contribution in the measured gamma-ray spectrum of type II and perform the same identification as has already been carried out.

[0042] The differences between the prior art detection methods and detectors and the method of the present invention are summarized in the following chart.

Table 1

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[0043] The flowcharts of the attached FIGS. 1 to 4 show the flowchart of one embodiment of the method according to the present invention starting from an alarm event which is the detection of a neutron source.

[0044] The method according to this specification is adapted to function correctly with any type I detector. The tests were performed on many detectors and the measurement results and parameterizations reported in this specification are related to the scintillator CeBr3 with average resolution.

[0045] In one embodiment, the method according to this specification utilizes two gamma-ray energy spectra [1.a)]. The first spectrum spec1 is obtained during a same period (for example, during 1 minute of data acquisition, although other periods can also be selected), and the second spectrum spec2 is obtained by subtracting the last environmental background (for example, 3 minutes after data acquisition, although other periods can also be selected), appropriately rescaled to be equal to spec1. Further, the background is calculated and subtracted to obtain spec2 [2.a)]. An example of the steps of the algorithm is described below, where the values of the parameters and equations adopted here are related to the specific selection of the CeBr3 type I detector. Generally, these equations and parameters can be changed according to the selection of the type I detector. For example, peak fitting can be performed by Gaussian fitting or Poisson fitting, and the background can be calculated in polynomial form or step function from degree 0 to degree 3.

[0046] 1) Search for gamma-ray peaks on Spec2 This can be done using a search function [3.a)]. This function limits the number of possible peaks by two parameters σ and thr. The first parameter selects peaks based on the width (the smaller σ is, the smaller the peak width). The second parameter discards peaks with an amplitude less than thr·h, where h is equal to the height of the highest peak. σ is set to 2, 5, and 7 spectrum channels (1 channel = 3 keV) for the energy intervals [0, 330[, [330, 1100[, and [1100, 5100[ keV respectively, and thr is set to 0.0002.

[0047] 2) First verification of spec2 peaks Performed for each peak position p obtained in step 1) 1,i Fitting, for example, Gaussian fitting [4.a)], is performed within the energy interval [a i ; b i , where a i = p 1,i - 5 / 3σt (p 1,i ), b i = p 1,i + 5 / 2σ t (p 1,i ) where σ t (p 1,i ) is the theoretical resolution value represented by the standard deviation at energy p 1,i . ((b i - a i ) < 40 keV, ai = p 1,i - 11 keV, b i = p 1,i + 10 keV). The standard deviation σ i , the centroid position E i , and the Gaussian integral value Inti are discarded immediately if they are non - physical values (E i or Int i is negative, E i < a i , E i > b i , E i > 5100 keV) or Int i < 30 counts and obtained from the fit [5.a)].

[0048] Next, check the peak energy resolution

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[0049] 3) Second verification of the spec1 peak The gamma-ray spectrum is switched from spec2 to spec1, and the second verification is performed with the gamma-ray energy spectrum spec1. For example, the fitting procedure is executed with a function defined as follows [6.a)]. f(E)=Gauss(E;E i,f ,σ i,f ,Int i,f )+m·E+q In the energy interval [E 1,i ,E 2,i , let E 1,i =E i -3.5σ t (E i ), E2=E i +3.5σ t (E i ). In the fitted function f(E), the Gaussian represents the photopeak, and the last term m·E+q is a linear function for estimating the local background. The fitting parameters m, q, σ i,f ,E i,f are initialized as follows. ·m=(c 2,i -c 1,i ) / (E 2,i -E 1,i ), where c 2,i and c1,i are the spectral counts at energies E 2,i and E 1,i respectively, and ·q = c 1,i -(m·E 1,i ), ·σ i,f , E i,f is the parameter σ obtained from the previous fit i and E i respectively.

[0050] Furthermore, let y1 = m·E1 + q and y2 = m·E2 + q. When y1 or y2 is negative, repeat the fitting procedure up to 5 times and force the fitting parameters to conform to these constraints. 1. When y1 < 0 and y2 < 0 → m = 0, q = 0, 2. When y1 < 0 and y2 ≥ 0 → max(m) = 1.01·y2 / (E2 - E1) counts / keV, both m and q are initialized to 0, 3. When y1 ≥ 0 and y2 < 0 → min(m) = -1.01·y1 / (E2 - E1) counts / keV, both m and q are initialized to 0.

[0051] Int i,f peaks with negative values, or peaks where E i,f is outside [E 1,i , E 2,i , are immediately discarded. At this point [7.a)], the integrated value S i,f of the product of Gaussian Gaussian(E; E i,f , σ i,f , Int i ) and the integrated value B i of the linear background m·E + q, within the energy interval [E min,i , E max,i , where E min,i = E i,f - 3.5σ i,f and E max,i = E i,f + 3.5σ i,fIt is calculated as such. These two values are used to reject false peaks detected by statistical fluctuations. Another parameter Sig called "significance" i is calculated. This parameter is i / √(S i +B i ), and is equal to the ratio between the signal integral value S i and the statistical uncertainty of the total count within [E min,i ,E max,i : Sig i Peaks with Sig < 6 are rejected [8.a)]. Also, the parameter Sig / ch (used later, see point 5), which is the ratio of the number of spectral channels included in the same energy range [E min,i ,E max,i to Sig, is also calculated.

[0052] Finally, the check of the peak energy resolution

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[0053] 4) Further peak search (second cycle of steps 2 and 3) First, subtract all Gaussian functions associated with all gamma peaks that were not previously rejected (those with the energy E obtained in point 2) from both spec1 and spec2 (subtraction within the energy range [0.5 - E, 1.5 - E]) [9.a)]. Next, repeat each of points 1), 2), and 3) using the updated spectra spec1 and spec2 and different sets of parameters of the search function. Here, σ is set to 10 and 12 spectral channels for the energy ranges [0, 1100[ and [1100, 5100[ keV, respectively, and thr is set to 0.006. i The reason for performing this operation is to improve the identification ability of the algorithm. By subtracting the peaks, peaks with insufficient separation can also be recognized (for example, Na 1275 keV and Co 1332 keV, see Figure 1). min,i , 1.5 - E max,i for subtraction) [9.a)]. Next, repeat each of points 1), 2), and 3) using the updated spectra spec1 and spec2 and different sets of parameters of the search function. Here, σ is set to 10 and 12 spectral channels for the energy ranges [0, 1100[ and [1100, 5100[ keV, respectively, and thr is set to 0.006.

[0054] The reason for performing this operation is to improve the identification ability of the algorithm. By subtracting the peaks, peaks with insufficient separation can also be recognized (for example, 22 Na 1275 keV and 60 Co 1332 keV, see Figure 1).

[0055] 5) The integrated value in the region of interest (ROI) from 180 to 243 keV. 239 Pu concentration [4.c)] (The larger the value of P 208 / B 208 , the greater the contribution of the Pu isotope should be shown). To evaluate this, two integrated values P 241 and B 208 are calculated within the energy range [180 keV, 243 keV].) P 208 and B 208 and B 208 are calculated as the total number of counts within the ROI using spec2 and Background (the same as the one obtained by first subtracting spec2), respectively [10.a)].

[0056] 6) Search for multiplets. 4) For each peak with the detected energy E i,f , the algorithm searches for a peak with the energy E j,f (E i,f > E j,f ) at Ei,f -E j,f <6.5σ i,f Search for peaks such that this is the case. In this case [11.a)], E i,f and E j,f Discard the two peaks of and repeat point 3) in the same way. The only difference is the fitting function, which is defined as follows. f(E)=Gauss i (E;E i,f ,σ i,f ,Int i,f )+Gauss j (E;E j,f ,σ j,f ,Int j,f )+m·E+q Gauss i and Gauss j The function parameters of are initialized with the respective parameters obtained at the end of the fitting procedure described in point 2), m and q are initialized as described in 3), and the energy interval for fitting is equal to [E 1,i ,E 2,j . Also, the verification procedure is the same as that described in 3) for both peaks of E i,f and E j,f .

[0057] 7) Rejection of potentially overlapping peaks. E i,f and E j,f Two peaks whose energies differ by less than 1.0·σ i,f are each discarded. These two peaks are replaced by a new peak with parameters (E i,f ,σ i,f ,Int i,f ,Sig,Sig / ch) calculated as the average of the respective parameters of the two discarded peaks [12.a)].

[0058] 8) Identification of Compton edge and backscattered peak. For each identified peak with energy E i,f >200 keV, the theoretical Compton edge E C , and the backscattered peak EBS is calculated. Next, the energy E j,f (E j,f <E i,f ) for each peak, σ t (E j,f ) is taken as the theoretical resolution value (σ t (E) = FWHM t (E) / 2.354820045), and the distances from E C and E BS are evaluated as follows, respectively. d C = |(E j,f + σ t (E j,f )) - E C | d BS = |E j,f - E BS | Here, adding σ C to d t (E j,f ) takes into account the energy shift due to the finite resolution of the detector. Therefore, peak E j,f is regarded as the Compton edge related to photopeak E i,f , and is discarded if the following relationship is true. d C < 1.0·σ t (E j,f )

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[0059] In this case, the backscattered peak E j,f is not rejected, and its index j is stored in memory for subsequent analysis [13.a)].

[0060] 9) Source identification At this point, the set of peak positions E i (i.e., all Es detected at the end of 8) i,f (where i = 1,…, N and N = the number of previously detected peaks) is available. The algorithm compares these values with the known peaks p j,h of gamma-ray sources stored in the library (where j = 1,…, M and M = the number of known sources, and h = 1,…, H and H = the number of peaks belonging to the j-th known gamma-ray source s j ).

[0061] For each s j , p j,h is such that if the latter is the closest to p j,h among all Es i and |E i - p j,h | < 1.5 - σ i , then E i is identified as the same, and σ i = the σ of the i-th peak i,f . If n peaks are identified (n > 0), two parameters Sig and Sig / ch are calculated as the n-averages of Sig and Sig / ch (explained in 3). Then, to consider the identification quality of s j , another parameter χ is introduced. It is calculated as follows.

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[0062] [14.a)] Finally, if the following condition is true, the s j gamma-ray source is identified. · χ < 0.002 · Sig / ch ≥ 0.17 · n / L ≥ 0.59

[0063] Furthermore, an empirical "confidence value" CL is associated with the identified source. This is defined as CL = min(CL1, CL2). Here,

Number

[0064] Finally [15.a)], the number of backscatter peaks detected in 8) and belonging to s j is denoted as n BS and if (n - n BS ) / L < 0.59, the name S j of the identified source s j is replaced by the character string "Backscatter (possible S j masked)".

[0065] 10) Identification of minor sources. Repeat step 9 a total of L times (L = the number of gamma source libraries) in descending order or priority. For each iteration, all peaks E j associated with each identified source s id,i are removed from set E i before the next iteration of the source identification routine [16.a)]. The library is created as follows (from left to right, source name, source type, gamma energy (unit: keV) between angle brackets). · Library 1: Am - 241 Industrial [59.5409] Ba - 133 Industrial [80.8966, 302.8508, 276.3989, 356.0129, 383.8485] Co - 56 Industrial [846.75, 511.0, 1238.26, 1771.40] Co - 57 Medical [122.06065] Co - 60 Industrial, Medical [1173.228, 1332.492] Cs-137 for industry, medical [661.657] Eu-152 for industry, medical [121.78, 344.27, 778.9045, 963.38, 1112.076, 1407.95] K-40 normal [1460.822] Mn-54 for industry [834.848] Na-22 for medical [511.0, 1274.537] Pu-241 SNM [103.68, 208.0, 332.376] Pu-239 SNM [56.0, 375.05, 413.71] Ra-226 normal [295.21, 351.92, 609.31, 1764.49] Th-232 normal [238.63, 338.3, 583.0, 911.07, 968.0, 2614.66] U-235 SNM [143.767, 185.72] U deteriorated, natural, or LEU SNM [1001.026, 766.361] Y-88 for industry, medical [898.042, 1836.07] · Library 2: Ag-108m for industry [433.93, 614.37, 722.95] Ag-110m for industry [657.75, 884.67, 937.48, 1384.27] Au-198 for industry [411.80] Ba-133 for industry [80.8966, 302.8508, 356.0129] Ba-140 for industry [537.38] Be-7 normal [477.61] Bi-207 for industry [569.70, 1063.66] Co-56 for industry [846.75, 1238.26, 1771.40] Co-60 for industry, medical [1173.228] Cs-134 Industry [569.32, 604.70, 795.85] Eu-152 Industry, Medical [121.78, 344.27, 963.38, 1407.95] Ga-67 Medical [93.31, 184.58, 300.23] Hg-203 Industry [279.20] Ir-192 Industry, Medical [295.96, 308.46, 316.51, 468.07] La-138 Industry, Medical [788.74, 1435.80] La-140 Industry [487.03, 815.83, 1596.49] Lu-177 Medical [112.9498, 208.3662] Mo-99 Medical [739.50, 140.51] Na-22 Medical [511.0] Nd-147 Industry [91.11, 531.03] Pb-203 Medical [279.20] Ru-103 Industry [497.08] Ru-106 Industry, Medical [511.85, 621.84] Sb-124 Industry [602.72, 722.78, 1691.02] Sb-125 Industry [427.89, 600.56, 635.90] Sc-46 Industry [889.28, 1120.55] Sn-113 Industry, Medical [391.69] Ta-182 Industry [1121.28, 1189.04, 1221.42] U-235 SNM [185.72] Yb-169 Industry, Medical [130.52, 177.21, 197.95] Zr-95 Industry [724.20, 756.73] ·Library 3: I-131 Medical [364.48] U Degraded, Natural, or LEU SNM [1001.026] Zn-65 industry [1115.55]

[0066] (Merging of the identification of gamma-ray sources (Type I detector data) and neutron sources (Type II detector data)) Before presenting the final identification result to the user, compare the identification results a) and b) of the gamma-ray source and the neutron source [1.c)]. The former is executed when an alarm for gamma rays and / or neutrons occurs [1.a)], and the latter is executed every time a neutron-ray alarm occurs [1.b)].

[0067] At the end of a), the set S of the identified sources γ m (m = 1, …, k, where k = the number of identified sources) is available. As explained in 9) and 10) above, each source in this set is described by its type, CL value, Sig parameter, and library number l. On the other hand, b) returns the neutron source S n along with its own CL value as the result. S n can be equal to only one of the following sources. S n can be equal to only one of the following sources (「Cf-252」, 「Pu」, 「U」, 「AmBe」, 「AmLi」) (or, if the algorithm fails to identify the source, equal to 「unknown」). This algorithm can also identify shielded sources [7.b)], but more specifically, in the following cases. Cf-252 shielded with a neutron moderator. Cf-252, Pu, and AmBe shielded with Pb.

[0068] The merging of the identification of gamma-ray sources and neutron sources consists of the following operations. 1. Verification of the AmLi source. This gamma-ray source and neutron source are such that S n = 「AmLi」 and at least two sources among 「U-235」, 「Be-7」, and 「Cs-137」 are in S γ mAs long as it belongs to it, it is correctly identified. In this case [2.c)], "U-235", "Be-7", "Cs-137" are removed from the set S γ m and S n remains "AmLi", and in other cases, S n is regarded as "unknown" [3.c)]. 2. Determination of the masking conditions for the neutron source and warning of Sn masked by the gamma source. S n is not "unknown", and S γ k if there is at least one gamma source different from S n in S n add "masked" to the name [4.c)]. 3. Identification of Na-22 / Co-60 with a high count rate of Co-60 / Na-22. Since the two peaks of Na-22 / Co-60 have a finite resolution of the detector, if one gamma source is stronger than the other, only one may be detected. Therefore, only one peak (Na-22 at 511 keV and Co-60 at 1173 keV) of Na-22 and Co-60 is added to the second library. In this way, by identifying Na-22 / Co-60 from the second library and Co-60 / Na-22 from the first library, the two sources are identified [7.c), 8.c)]. The possibility of Ru-103 existing in S γ m is removed from the identified source when Na-22 is identified from the second library and Co-60 is identified from the first library respectively. 4. Estimation of the Pu-239 concentration. This step is executed when at least one Pu isotope Pu-n is identified by a) and there is no other gamma source with a gamma peak between 180 and 243 keV in S γ m (according to the current library: Ga-67, Lu-177, Th-232, U-235, Yb-169). In this case [5.c)], the concentration of Pu-239 is defined in the following five classes based on the ratio P 208 / B 208 calculated by the gamma source identification algorithm (above 5). i. Weapon-grade Pu (WGPu) S n = Pu where "Pu-239" is S γ m belongs to P 208 / B 208 < 0.11. When S n the word "WGPu" is added to the source name of S ii. 80 - 90% enriched "Pu-239" is S γ m belongs to 0.11 ≤ P 208 / B 208 < 0.18. When S n the string "80 - 90% Pu-239" is added to the source name of S iii. 65 - 80% enrichment 0.18 ≤ P 208 / B 208 < 0.31. When S n the string "65 - 80% Pu-239" is added to the source name of S iv. 55 - 70% enrichment 0.31 ≤ P 208 / B 208 < 0.45 s. When S n the string "55 - 70% Pu-239" is added to the source name of S v. < 60% enrichment P 208 / B 208 ≥ 0.45. When S n the string "< 60% Pu-239" is added to the source name of S

[0069] The final enrichment is reduced by 10% in the following two cases [6.c)]: S n when it is identified as a shielded source, or Sig γ taking Sig as S γ m the maximum value of the Sig parameter among all gamma sources (excluding Am-241 and Pu-n) in S Pu taking Sig as S γ m the corresponding value of the Pu source in S γ / Sig Pu when the ratio is less than 1.0

[0070] The present invention also includes the identification of SNM in scenarios where shielding and masking are present, i.e., scenarios typically considered in the presence of potential terrorist acts or nuclear "smuggling" situations.

[0071] This system analyzes in real time like a chart, where the ratio R of the number of gamma-ray counts to the number of neutron counts c is shown on the X-axis and the ratio R of the average energy of gamma rays to the average energy of neutrons E is shown on the Y-axis.

[0072] In this way, as in the case of the attached Figure 5, it is possible to accurately determine the position of the source being observed in a fairly enclosed space and thus associate it with that particular situation. The grouping or clustering of points related to the measured values of Cf252 can be seen in a well-defined region obtained even in the absence of shielding and masking. Figure 6 shows the positioning of points in the presence of a lead shield, Figure 7 shows the presence of a polyethylene (PE) neutron moderator shield, and Figure 8 shows the presence of different sources for creating a masking scenario for a neutron source, which is solved in this case by the method and system of the present invention by simultaneous spectroscopic evaluation.

[0073] The attached Figures 9 to 17 summarize the experimental observations using the algorithm for SNM identification according to the present invention.

[0074] Figure 9 shows the planar distribution of all identifications (data: measurements with ENEA, Legnaro, Seibersdorf, and AmLi, Oak Ridge). In each chart, the ratio R of gamma-ray counts to neutron counts c is shown on the X-axis and the ratio R of the average energy of gamma rays to the average energy of neutrons E is shown on the Y-axis. These values were obtained using data (in this particular case for 1 minute) obtained with a liquid scintillator (EJ-309) during the identification measurement. In particular, from the gamma-ray energy spectrum, the spectrum saved at the end of the appropriately rescaled surrounding background (in this particular case for 3 minutes of acquisition) is subtracted.

[0075] The boxes shown on the chart represent the regions in planes R C , R E for identifying different types of neutron sources. For the identification of AmBe, since the relative boxes overlap those of Cf-252 and Pu, the average neutron energy is used as a third parameter (E n > 650 keV ee in which case, AmBe).

[0076] In the chart of Figure 10, actually, measured values with neutron counts > 8 cpm are selected. In this case, the set threshold is less stringent than that of the neutron cps alarm (generally, an alarm sounds when neutrons exceed ~0.2 cps = 12 cpm), but various sources are well separated in the corresponding region. Therefore, this algorithm is effective for low neutron counts and is compatible with the background. At present, it can be said that the neutron beam alarm constitutes a condition that is too sufficient for correctly recognizing the source. For example, in the case of a U source, it can be seen how well the algorithm correctly identifies the source, including those made at Seibersdorf containing HEU (90% U-235).

[0077] It is also possible to observe the positions of the two measurements with AmLi placed between the Cf-252 box and the U box.

[0078] To make the behavior of the algorithm using different sources clearer, Figure 11 shows the results obtained using no shielding material and only sources with neutron counts > 8 cpm.

[0079] From this chart, the regions of the plane occupied by different sources are clear. Based on these data, the regions are defined with a confidence level (CL) = 100%.

[0080] In the following charts, under the same conditions, Figure 12 shows a Pu radiation source divided into side A and side B of CBNM (the gamma-ray emission amounts are different between side A and B because the shielding of the ENEA-radiation source housing is thinner). Figure 13 shows Pu radiation sources with different enrichments of Pu-239 (Seibersdorf).

[0081] From the chart of Figure 13, considering that there is no shielding and external masking radiation source, it can be seen that the positions of Pu with different enrichments are clearly defined.

[0082] Figures 14, 15, and 16 show various measurements while always maintaining the neutron number > 8 cpm (0.133 cps) using shielding of only Pb (5 cm), only PE (2 cm to 10 cm), and Pb + PE (Pb: 5 cm, PE: 2 cm to 10 cm), respectively.

[0083] From these charts, the expected behavior is verified. That is, the presence of Pb, unlike polyethylene, shifts the measurement towards the region with less R C .

[0084] Finally, Figure 17 shows the case where there is a gamma-ray source in addition to the neutron source (blue is Cf-252, orange is Pu). In the case of Cf-252, it can be seen how the points move in the plane according to the energy of the gamma-ray source used as masking (in addition to the relative dose). As the dose by the masking gamma-ray source increases, the points instead move to the region with larger R C . (The multiplicity of the range increases). In this way, a region for identifying the presence of masking is defined.

[0085] Referring to the attached Figure 18, a portable device for recognizing a radiation source is generally indicated by 1. A radiation source Rad that emits both n neutrons and gamma γ-rays is schematically shown.

[0086] In a preferred embodiment, the portable device 1 includes a type II detector 3 consisting of a cylindrical cell of an organic liquid scintillator. In another embodiment, the detector 3 is of the type that uses xylene as an organic solvent, i.e., the EJ 309 model of Eljen Technology, which has innovative characteristics such as low flammability and low toxicity and is suitable for use on a commercial scale.

[0087] The sensor is coupled to a photomultiplier tube or SiPm reader 4, e.g., model H12700 of Hamamatsu Photonics, and is connected to a miniaturized power supply circuit 6 that supplies the high voltage required for the correct operation of the photomultiplier tube 4.

[0088] The detector 3 can detect both the light pulses generated by the interaction with neutrons (an interaction known as "n-p scattering") and the interaction with gamma rays (an interaction known as "Compton scattering").

[0089] The high-speed type digitizer circuit 5 is adapted to convert the light pulses into digital signals and analyze and process them on the fly via a programmable integrated digital processor 9, e.g., an FPGA ("Field Programmable Gate Array").

[0090] The portable device 1 also includes a type I detector 3-bis consisting of a cylindrical cell of an organic crystal scintillator. In a variant of the preferred embodiment, the sensor 3-bis is of the type that uses a cerium bromide (CeBr3) crystal lattice, i.e., the CeBr3 model by Scionix-Holland, which has a high ability to distinguish gamma γ radiation with close energies (this characteristic is called detector resolution, and the better the resolution, the higher the ability to distinguish two gamma γ with close energies).

[0091] The sensor 3-bis is coupled to a photomultiplier tube or SiPm reader 4-bis and is connected to a small power supply circuit 6-bis that supplies the high voltage required for its correct operation.

[0092] Sensor 3-bis can only detect the optical pulses generated by the interaction with gamma rays γ, and its sensitivity to neutron n rays is close to zero. Sensor 3-bis interacts with gamma rays not only through the interaction known as "Compton scattering" (similar to Sensor 3), but also through the interaction known as "photoelectric effect". Due to this effect, the total energy of gamma γ rays is released in a single interaction, and the detector can record the total energy of gamma in one shot. Since each radiation source Rad has characteristic gamma rays γ (with different energies respectively), by collecting all the energies of each gamma ray, the radiation source Rad can be accurately recognized (like a fingerprint) in a single measurement performed by Sensor 3-bis.

[0093] The optical pulses (fingerprints) collected by Sensor 3-bis are converted into digital signals by a high-speed type digitizer circuit 5-bis and analyzed and processed in-line via a programmable integrated digital circuit 9, for example, an FPGA (Field Programmable Gate Array).

[0094] Device 1 also embeds a graphic user interface (GUI) 7 and a control panel 8 to exchange information and data between Device 1 and its user.

[0095] All components of Device 1 have dimensions and weights suitable for the carrying and operation of a single user.

[0096] The programmable integrated circuit 9 may also function as the internal memory of Device 1, where a data processing program containing a plurality of instructions for executing the method according to the present invention is loaded. By said method, when the program is executed from the portable device 1, the radiation source Rad can be recognized.

Claims

1. A method for identifying a radiation source, comprising: - Detecting a gamma-ray emitting source from the radiation source using a gamma-ray spectroscopy type I detector; - Detecting, from the radiation source, a plurality of impulses related to respective neutron emissions and gamma-ray emissions using a gamma-ray / neutron type II detector; - Identifying a first impulse related to neutron emission among the plurality of impulses and a second impulse related to gamma-ray emission among the plurality of impulses, the step of identifying the first impulse and the second impulse including calculating a respective total integral value Ltot for each impulse; including: - The first number n of the first impulse ｎ and the second number n of the second impulse γ and determining steps - The first average value E of the total integrated value Ltot ｎ and the second average value E γ are steps of calculating, where E ｎ is calculated by the following formula (1), and E γ is calculated by the following formula (2), steps and ・par ｘ = n γ / n ｎ and par ｙ = E γ / E ｎ a step of calculating ・ Data par ｘ , par ｙ , identifying whether the radiation source is a neutron source or a gamma ray source by - When the radiation source is the neutron source, performing identification of the gamma-ray source detected by the type I detector by spectroscopy; - When both gamma-rays and neutrons are detected, double-checking the identification; - Detecting a masking state of neutrons in the presence of gamma-rays, performed by merging the result of the identification of the type I detector and the result of the identification of the type II detector; - Detecting and identifying a gamma-ray source and a neutron source in the presence of a moderator and / or a shielding material using the type II detector; further including: 【Number 1】 【Number 2】

2. The step of detecting a gamma-ray emitting source from the radiation source using a gamma-ray spectroscopy type I detector includes: a first identification spectrum Spec1; a background as a reference spectrum; a second identification spectrum Spec2 = Spec1 - Background; The method according to claim 1, including obtaining.

3. The step of detecting a gamma-ray emitting source from the radiation source using a gamma-ray / neutron type II detector includes: a third identification spectrum Spec3; a fourth identification spectrum Spec4; a background as a reference spectrum; The method according to any one of claims 1 to 2, including obtaining.

4. The step of detecting a gamma-ray emitting source from the radiation source using a gamma-ray spectroscopy type I detector includes: searching for gamma-ray peaks on the second identification spectrum spec2; verifying the spec2 peaks; verifying the spec1 peaks; searching for further peaks; calculating integral values within the region of interest; searching for multiplets; eliminating possibly overlapping peaks; Identification of Compton edge and backscattering peak, Identification of gamma-ray source, Identification of minor source, The method according to any one of claims 2 to 3, comprising:

5. Merging the results of the identification of the type I detector with the results of the identification of the type II detector, Verification of AmLi source, Determination of masking conditions for neutron source, Estimation of concentration The method according to any one of claims 1 to 4, comprising:

6. The method according to any one of claims 1 to 5, wherein the type I detector uses a cerium bromide (CeBr ３ ) crystal lattice.

7. The method according to any one of claims 1 to 6, wherein the type II detector uses xylene as an organic solvent.

8. A method for identifying a radiation source, comprising: - Detecting a gamma-ray emission source from the radiation source with a gamma-ray spectroscopy type I detector; - Detecting a plurality of impulses related to respective neutron emissions and gamma-ray emissions from the radiation source with a thermal neutron type III detector; - Identifying a first impulse related to neutron emission among the plurality of impulses and a second impulse related to gamma-ray emission among the plurality of impulses, the step of identifying the first impulse and the second impulse including calculating a total integral value Ltot of each impulse for each impulse; including - Determining a first number nn of the first impulse and a second number nγ of the second impulse; - Calculating a first average value En and a second average value Eγ of the total integral value Ltot, where En is calculated by the following formula (1) and Eγ is calculated by the following formula (2); - Calculating par x = nγ / nn and par y = Eγ / En; - Identifying whether the radiation source is a neutron source or a gamma-ray source based on the data par x, par y; - When the radiation source is the neutron source, performing identification of the gamma-ray source detected by the type I detector by spectroscopy; - When both gamma-rays and neutrons are detected, double-checking the identification; - Detecting a masking state of neutrons in the presence of gamma-rays, which is performed by merging the results of the identification of the type I detector with the results of the identification of the type III detector. - A step of detecting and identifying a gamma-ray source and a neutron source when a moderator and / or a shielding material is present by the type III detector; A method further comprising. [Number 3] 【Number 4】 **Claim 9**: A method for identifying a radiation source, - A step of detecting a gamma-ray emitting source from the radiation source with a gamma-ray / neutron type II detector; - A step of detecting, from the radiation source, a plurality of impulses related to respective neutron emissions and gamma-ray emissions with a thermal neutron type III detector; - A step of identifying a first impulse related to neutron emission among the plurality of impulses and a second impulse related to gamma-ray emission among the plurality of impulses, wherein the step of identifying the first impulse and the second impulse includes calculating a total integral value Ltot of each impulse for each impulse; Including, - A step of determining a first number nn of the first impulses and a second number nγ of the second impulses; - A step of calculating a first average value En and a second average value Eγ of the total integral value Ltot, where En is calculated by the following formula (1) and Eγ is calculated by the following formula (2); - A step of calculating par x = nγ / nn and par y = Eγ / En; - A step of identifying whether the radiation source is a neutron source or a gamma-ray source based on the data par x, par y; - When the radiation source is the neutron source, a step of performing identification of the gamma-ray source detected by the type II detector by spectroscopy; - A step of double-checking the identification when both gamma-rays and neutrons are detected; - A step of detecting a masking state of neutrons in the presence of gamma-rays, which is performed by merging the identification result of the type II detector and the identification result of the type III detector; - A step of detecting and identifying a gamma-ray source and a neutron source when a moderator and / or a shielding material is present by the type III detector; A method further comprising. 【Number 5】 【Number 6】 **Claim 10** A device for identifying a radiation source, A gamma-ray / neutron type II detector (3); A first photomultiplier tube or SiPM reader (4) associated with the gamma-ray / neutron type II detector (3); A first digitizer circuit (5) associated with the first photomultiplier tube (4) and adapted to convert optical pulses into digital signals, A first power supply circuit (6) associated with the first photomultiplier tube (4), A gamma-ray spectroscopy type I detector (3-bis), A second photomultiplier tube or SiPM reader (4-bis) associated with the gamma-ray spectroscopy type I detector (3-bis), A second digitizer circuit (5-bis) associated with the second photomultiplier tube (4-bis) and adapted to convert optical pulses into digital signals, A second power supply circuit (6-bis) associated with the second photomultiplier tube (4-bis), A programmable digital processor (9) associated with the first and second photomultiplier tubes (4, 4-bis), A user interface, GUI (7), A control panel (8) for exchanging information and data with the user, Comprising, The programmable digital processor (9) is programmed to have a plurality of instructions for executing the method according to any one of claims 1 to 9, a device.

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