System of modular energy threshold detectors for monitoring soil density and / or permeability

Abstract

The present invention relates to a modular energy threshold muon detector (101 ) for monitoring soil density and / or permeability comprising at least two muon passage position detection modules (5), each muon passage position detection module (5) comprising a pair of scintillating elements (9) consisting of two segmented plates (9) placed one on top of the other, each segmented plate (9) comprising a plurality of scintillating bars (8) positioned in such a way that the scintillating bars (8) of one of the two segmented plates (9) are rotated by 90° with respect to the scintillating bars (8) of the other plate (9), each scintillating bar (8) comprising at least one silicon photomultiplier (21 ) positioned at an end face (71 ) of said scintillating bar (8), an outer casing (1 ) adapted to contain said at least two muon passage position detection modules (5), arrangement means configured to arrange said at least two muon passage position detection modules (5) in respective positions selectable from a plurality of positions inside said outer casing (1 ). The present invention also relates to a system for monitoring soil density and / or permeability.

Description

[0001] System of modular energy threshold detectors for monitoring soil density and / or permeability

[0002] The present invention relates to a system of modular energy threshold detectors for monitoring soil density and / or permeability. In particular, the present invention relates to a system of modular energy threshold muon detectors.

[0003] Particle physics has by now reached a state of maturity such as to enable it to be applied outside the laboratory and allow for answering the question as to how it can actually help man in everyday life.

[0004] As is well known, cosmic rays are a natural source of muons, highly penetrating particles which can pass through kilometres of earth and can thus be used in a similar manner to how X-rays are used in the medical field to carry out a ’’muography” of various layers of material, with the sole limit of using a natural particle source with a limited number of muons available per day. In fact, the muons of cosmic rays are a natural source of highly penetrating particles, which are capable of passing through hundreds of metres of material, based on their energy, but have the disadvantage of being available in nature in a limited number.

[0005] In particular, muon tomography techniques can be used to: identify veins of heavy metals, aquifers, petroleum, uranium, in the defence sector to monitor soil permeability after rainfall and thus prevent the possibility of landslides.

[0006] A series of problems have been identified, to which highly penetrating particles such as muons, naturally produced in cosmic rays by the interaction of protons with atoms of the Earth’s atmosphere, can provide an operational solution.

[0007] In mining techniques, core sampling systems are used to identify possible sites with the presence of material of interest such as to start an extraction activity. An analysis of the chemical properties of the earth extracted with core sampling, to maximum depths of two kilometres, makes it possible to provide a prediction of the presence of interesting material in the surrounding area. This is then followed by a series of narrow or wide diameter core sampling operations to predict the entity of the usable volume, but without a precise definition of the real dimensions of the volume under examination. “Muon radiography” or muography, analogous to X-ray radiography at scales of distance a thousand times greater, allows these difficulties to be overcome. It is in fact capable of providing two-dimensional mapping of the density of the volume under examination, by comparing the number of muons detected by a single sensor with the number of muons expected in the event that no volume of material with a density differing from that of the surrounding earth is present. Based on the simultaneous analyses of two-dimensional images obtained from different angles, i.e. from different sensors positioned in different geographical points, it is possible to obtain a reconstruction of the complete three-dimensional image. The technique in question has been presented in international patent applications no. W02007084149 and no. W02009065213, together with drilling of holes for installation.

[0008] Furthermore, with the same technique it is possible to identify heavy metals, such as gold, silver, and uranium, which form subsurface deposits, or natural gas bubbles, underground air, or else deposits of liquids such as petroleum, or even groundwater aquifers, as presented in international patent application no. WO2021038129.

[0009] The majority of the current techniques used to carry out muography of e.g. volcanoes, pyramids (recently the Pyramid of Giza), or small objects on the scale of a metre, exploit gas technologies such as proportional chambers, resistive plate chambers, and drift tubes, such as are illustrated, for example, in international patent applications no. WO2021038129, no. WO2022087729, and no. W02009065213.

[0010] Gas detectors revealed to be the first allies of muon detection for decades, albeit with many disadvantages. Indeed, they show effects such as aging and internal gas leaks, and thus require frequent dedicated maintenance, as well as a delicate treatment of the mechanical construction of the detectors themselves. Furthermore, they must be filled with mixtures of gases that are highly polluting, or rare, or both. One example is noble gases and fluoride, with fluctuations in their market availability and costs.

[0011] In order to overcome these difficulties, in international patent applications no. W020201 98885, no. WO2021038129 and no. WO2020237369 it was shown that scintillator-based detectors and silicon photomultiplier sensors can effectively remedy the problem of using harmful and rare gases. Such detectors also have a very compact size and are thus suitable for use in boreholes such as those presented in international patent application no. W02009065213.

[0012] Nevertheless, such detectors suffer from the same physical problem as all the others, namely multiple scattering in the overlying material the muons must pass through to reach the detector itself. When muons pass through a dense material, they are in fact diverted by interaction with the material itself. The detectors are able to detect muons up to very low muon energies. But they have very limited abilities to measure their energy. In fact, the effects of multiple scattering depend on the energy of the muons.

[0013] It follows that this limits the ability of the detector and image reconstruction software to be sensitive to the real dimensions of any volume of interest present in the material through which the muons pass.

[0014] Therefore, this technique does not allow the real dimensions of the volume under examination to be defined with precision.

[0015] In the specific sector, there thus exists the need for a system of detectors for monitoring soil density and / or permeability capable of overcoming the problems of the systems present in the prior art.

[0016] This need is satisfied by the system according to the present invention, which offers, moreover, further advantages that will become clear below.

[0017] The solution according to the present invention fits into this context; it aims to implement soil density analyses and three-dimensional image reconstruction techniques to enable a complete mapping of the subsurface in the presence of deposits of liquids, gases, and heavy metals, with densities differing from those of the surrounding earth, through the use of modular energy threshold detectors with planar geometry, a compact size and variable configuration - to enable an optimal adaptation to operating conditions, in particular by allowing variable energy thresholds to be defined - and with thickness proportions and an area such as to ensure the detection of muons in a cone having a wide angle with respect to the direction orthogonal to a two-dimensional direction of extension of said modular detectors.

[0018] These and other results are achieved according to the present invention by proposing a system of modular energy threshold detectors for monitoring soil density and / or permeability, wherein the modular detectors use a plurality of modules adapted to be arranged inside an outer casing by means of respective arrangement means. The distribution of the various modules may differ between the various embodiments, as described below. This distribution may depend, for example, on the size of the detector and thus on the size of the resulting modules. In particular, this distribution may be adapted to the size of the boreholes, which generally have diameters ranging between 25 cm and 30 cm. Therefore, given the small size of the boreholes, the modularity of said detector makes it possible to have a compact detector adaptable to different configurations. Furthermore, installability and maintenance are further reasons for having different module configurations.

[0019] Additionally, the modularity of said detector allows the modules to be arranged in variable positions, also very close together, thus enabling the detector itself to detect muons with larger angles. By way of example, considering that a scintillator bar has a thickness of about 0.5 cm, the modular detector is capable of detecting muons with a maximum angle of incidence of 76° with respect to the line perpendicular to the substantially two-dimensional surface of extension of the modular detector.

[0020] The aim of the present invention is thus to provide a system which makes it possible to overcome the limits of the systems according to the prior art and to achieve the technical results previously described.

[0021] In particular, the system of modular detectors according to the present invention makes it possible to select the muon energies and thus carry out an analysis of the flux of muons as a function of energy and thereby reduce the uncertainty deriving from multiple scattering. In fact, the angle induced by the multiple scattering decreases as the energy of the muons increases.

[0022] A further aim of the invention is that said system can be produced at substantially low costs, both as regards the production costs and as regards the operating costs.

[0023] A further aim of the invention is to provide an analysis of soil permeability and to provide a tool for preventing the landslide phenomenon, a system for identifying deposits, mineral deposits, and gas and liquid deposits, and for identifying the dimensions of the volumes under examination.

[0024] Yet another aim of the invention is to propose a system that is simple safe and reliable.

[0025] Therefore, a specific object of the present invention is a modular energy threshold muon detector for monitoring soil density and / or permeability, comprising at least two muon passage position detection modules, each muon passage position detection module comprising a pair of scintillating elements consisting of two segmented plates placed one on top of the other, each segmented plate comprising a plurality of scintillating bars positioned in such a way that the scintillating bars of one of the two segmented plates are rotated by 90° with respect to the scintillating bars of the other segmented plate, each scintillating bar comprising at least one silicon photomultiplier positioned at an end face of said scintillating bar, an outer casing adapted to contain said at least two muon passage position detection modules, arrangement means configured to arrange said at least two muon passage position detection modules in respective positions selectable from a plurality of positions inside said outer casing.

[0026] In particular, according to the present invention, said modular detector can further comprise at least one muon energy absorber module arranged above said at least two muon passage position detection modules, said at least one muon energy absorber module being adapted to be arranged inside said outer casing by means of respective arrangement means.

[0027] Furthermore, according to the present invention, said modular detector can further comprise a muon detection module arranged above said at least one muon energy absorber module, said muon detection module being adapted to be arranged inside said outer casing by means of respective arrangement means.

[0028] Additionally, according to the present invention, said modular detector can further comprise at least one muon energy absorber module arranged between said at least two muon passage position detection modules, said at least one muon energy absorber module being adapted to be arranged inside said outer casing by means of respective arrangement means.

[0029] In particular, according to the present invention, said modular detector can further comprise at least one muon selection module adapted to be arranged inside said outer casing, by means of respective arrangement means, below said at least two muon passage position detection modules, each muon selection module comprising at least one muon energy absorber module and one muon detection module positioned below said at least one muon energy absorber module.

[0030] Again according to the present invention, each muon detection module can be a pair of scintillating elements or a scintillating plate comprising at least one silicon photomultiplier positioned on an end face of said scintillating plate.

[0031] Furthermore, according to the present invention, said muon energy absorber module can be a layer of absorbent material with a thickness comprised between 1 cm and 3 cm.

[0032] Furthermore, according to the present invention, said scintillating plate and each scintillating bar of each segmented plate may comprise a reflective layer applied on all the faces thereof with the exception of one end face.

[0033] In particular, according to the present invention, said muon energy absorber module can be made of an absorbent high atomic number material, preferably steel, lead or tungsten. Said materials provide the best cost-benefit ratio.

[0034] Additionally, according to the present invention, said outer casing can be made of a high atomic number material, preferably steel.

[0035] Again according to the present invention, said at least one photomultiplier can be mounted on a printed circuit, said printed circuit comprising a signal amplifier, a threshold comparator, an analogue to digital converter, at least one connector for the power supply and a temperature sensor.

[0036] A further object of the present invention is a system for monitoring soil density and / or permeability, characterised in that it comprises at least one modular detector, which selects muons by means of energy thresholds in order to mitigate the effects of multiple scattering, with different configurations, planar geometry, and thickness proportions and an area which are sufficient to ensure the detection of muons in a cone having a wide angle with respect to the direction perpendicular to the substantially two-dimensional direction of extension of the modular detector.

[0037] In particular, according to the present invention, said system may comprise at least two modular detectors and a communication network adapted to connect said at least two modular detectors.

[0038] The present invention will now be described by way of non-limiting illustration according to a preferred embodiment thereof, with particular reference to the figures of the appended drawings, wherein:

[0039] - figure 1 shows a schematic view of a modular detector of the system according to a first embodiment of the present invention,

[0040] - figures 2a-2b show a perspective view of the scintillating bars of the modular detector in figure 1 ,

[0041] - figure 3 shows a perspective view of the scintillating plate of the modular detector in figure 1 ,

[0042] - figure 4 shows a schematic view of a printed circuit where silicon photomultipliers according to the present invention are installed,

[0043] - figure 5 shows an example of an event wherein a muon passes through the system according to a second embodiment of the present invention, and - figure 6 shows an example of an event wherein a muon passes through the system according to a third embodiment of the present invention.

[0044] The description below will be focused on a system of detectors for monitoring soil density and / or permeability, but it is clearly evident that the same must not be considered limited to this specific use.

[0045] Making reference preliminarily to figure 1 , a system of detectors for monitoring soil density and / or permeability comprises at least one energy threshold modular detector 101. Said modular detector 101 has a planar geometry, i.e. it extends substantially over a two-dimensional surface.

[0046] In particular, said system can be used in an array or stand-alone mode, as a single detector for use at different subsurface depths, up to 600 m (and optimised for a depth of 400 m), reachable by means of core drilling, with diameters comprised between 25 cm and 30 cm. Given the small size of the boreholes, said modular detector 101 must be configured as a compact detector.

[0047] In further embodiments, not shown, the modular detector according to the present invention can be installed in already formed mines, without having to rely on the use of core drilling, in order to scan the surrounding volume.

[0048] In the case of an array of detectors, said system comprises a communication network between the various detectors.

[0049] In particular, said modular detector 101 is a detector of muons, i.e. particles produced in cosmic rays, capable of passing through large layers of material. Said modular detector 101 is adapted to be used in underground environments.

[0050] Said modular detector 101 , also referred to by the name HIVE hereinafter in the present description, comprises an outer casing 1. Preferably, said outer casing 1 comprises panels made of steel or another high atomic number material a few millimetres thick for the absorption of environmental radiation, in order to suppress the background radiation which could be confused with the signal of muons. In fact, the natural radiation in the surrounding volume of earth does not possess sufficient energy to be reconstructed by the detector.

[0051] Furthermore, in the embodiment shown by way of example with reference to figure 1 , said modular detector 101 comprises, proceeding from top to bottom, a muon detection module consisting of a scintillating plate 10, three muon passage position detection modules 5 and three muon energy absorber modules 2.

[0052] Furthermore, each muon energy absorber module 2 has a thickness necessary for the measurement of energy. Preferably, each muon energy absorber module 2 has a thickness comprised between 1 cm and 3 cm. The objective of the choice of thickness is to select particles penetrating with a given energy, while at the same time maintaining compact dimensions. In particular, it is possible to associate the thickness of each muon energy absorber module with a threshold energy, every thickness defining a “jump” in energy.

[0053] Upon the passage through a given thickness of each muon energy absorber module an amount of energy is lost, which depends on the density of the material and its thickness. In particular, the energy loss is calculated by multiplying the density of the material (g / cm3) by the energy loss of muons as minimum ionising particles (MIPs), which is equal to 2MeV / gcrrr2

[0054] The density of steel, used for example as the absorbent material, is 7.8gcrrr3and the energy loss of muons as minimum ionising particles is 2 MeV / (gcrrr2), hence the typical energy loss for a muon energy absorber module made of steel is 15.6MeV per centimetre of muon energy absorber module passed through.

[0055] In particular, said absorbent material can be steel, lead, tungsten or another high atomic number material. These materials provide the best cost-benefit ratio.

[0056] Therefore, said muon energy absorber module is capable of implementing different energy thresholds by acting on two levels, through both the thickness of the material and its density, and is adapted to the specifications of the geophysical situation under examination.

[0057] In the case of a muon energy absorber module made of lead, there is an energy loss of 22.7MeV per cm of absorbent material passed through, considering that the density of lead is equal to 11 .34gcrrr3.

[0058] In the case of a muon energy absorber module made of tungsten, there is an energy loss of 38.6MeV per cm of absorbent material, considering that the density of tungsten is equal to 19.3gcrrr3.

[0059] It follows, therefore, that it is possible to create an energy threshold ranging from 15.6MeV (in the case of steel with 1 cm of absorbent material) to over 110MeV (in the case of tungsten with 3cm of absorbent material), also considering the angle of incidence of the muons. In fact, muons that pass through the detector at an angle with respect to the direction perpendicular to the substantially two-dimensional surface of extension of the modular detector pass through larger layers of material compared to the nominal thickness of the absorbent layer. Furthermore, in one embodiment, not shown, said muon energy absorber module 2 can be positioned in a housing, for example a housing of a thickness equal to 3cm. In this manner, each housing can contain muon energy absorber modules having a thickness of 1 to 3cm. In particular, thanks to the system’s modularity, a muon energy absorber module can be added or subtracted without having to act on the structure of the detector itself. In particular, the thickness of 3cm is itself a balance that is reached between the maximum angle of incidence of the muons the detector is capable of detecting, and the usable energy threshold required to implement this solution. In fact, for simple geometric reasons, as the maximum thickness of the muon energy absorber module increases, the maximum angle of incidence of the muons, that is, their “lever arm”, decreases. It is also necessary to implement a jump in energy of several dozen MeV, in order to select muons with energy that is sufficient to mitigate the effects of multiple scattering, thereby ensuring that the detector in question has a technological superiority such as to reach maximum depths of 600m in the earth.

[0060] Therefore, in a preferred embodiment, said modular detector 101 comprises alternating muon energy absorber modules 2 and segmented plates 9, so that the muon can lose energy in the muon energy absorber module 2. In particular, if the muon does not manage to reach the subsequent scintillator layer, it means that it would not have had enough energy to pass through the muon energy absorber module, and thus acts as an energy threshold detector, providing a measurement of the energy of the muon with a granularity given by the thickness of the muon energy absorber module, thereby improving the resolution, due to multiple scattering, with respect to the volume of any material of interest, and ensuring the possibility of reaching depths of 600m in the earth with precision as to the real dimensions of the possible deposits in the earth, as well as creating a valid alternative to existing core sampling and chemical analysis techniques.

[0061] In fact, when passing through the material, the muons of cosmic rays undergo the effects of the physical phenomenon known in particle physics as “multiple scattering”, that is, the muons are deflected randomly by the atoms of the material passed through. In the passage to 600m of depth, the effect of multiple scattering would be preponderant, but the effect depends on the energy of the muon when it enters the detector. The threshold of energy introduced into the absorber layer with planar geometry serves to ensure the successful selection of an energy sufficient to mitigate the effects of multiple scattering. Byway of example, a depth of 200m would account for a precision of the order of 30% with respect to the real dimensions of a possible deposit or vein, without having access to the energy of the muons. By selecting the energy of the muons, it is possible to reach a precision of the order of 5% with respect to the systematic uncertainty arising from the analysis of multiple scattering.

[0062] In particular, making reference to figures 2a and 2b, each muon passage position detection module 5 comprises a pair of scintillating elements 9 consisting of two segmented plates 9 placed one on top of the other. In particular, each segmented plate 9 is made up of a plurality of scintillating bars 8, individually shielded and glued together to form said segmented plate 9. Each scintillating bar 8 consists of a bar of scintillating material coated by a reflective layer 6 on all its faces, with the exception of an end face 71 . In particular, the scintillating material is an organic polymer with a dopant enabling the production of scintillation light upon the passage of charged particles. As it uses scintillating materials instead of gases, the modular detector 101 does not require any substantial maintenance, being able to operate for long periods (potentially years) continuously.

[0063] A silicon photomultiplier 21 (SiPM) is applied at the end face 71 , not coated by a reflective layer 6, so that the light produced by the scintillating material is conveyed to it.

[0064] In particular, each segmented plate 9 comprises a number of scintillating bars 8 comprised between 20 and 50, depending on the usable dimensions it is desired to use for an application. Preferably, each segmented plate 9 comprises twentyeight scintillating bars 8.

[0065] In particular, in the modular detector 101 , each pair of scintillating elements 9, or segmented plates 9, consists of two segmented plates 9 placed one on top of the other with an orientation such that the scintillating bars 8 of one of the two segmented plates 9 are rotated by 90° with respect to the scintillating bars 8 of the other.

[0066] In fact, each segmented plate 9 comprises a plurality of photomultipliers 21 , adapted to capture the scintillation light produced in the plate itself. However, being composed of a plurality of scintillating bars 8, all having the same orientation, a single segmented plate 9 allows only one item of spatial information to be identified. By arranging the second segmented plate 9 of each pair with the respective scintillating bars 8 rotated by 90°, it is possible to identify a second item of spatial information.

[0067] Finally, a number of second scintillating elements 9 can be stacked to obtain a number of energy measurements. Consequently, it is possible to obtain the first point (x,y,z) of a particle trace. A trace is composed of a number of points and consequently also comprises angular information. Therefore, the device behaves like an energy threshold device, i.e. if the muon does not reach the subsequent module, it means that it did not have sufficient energy to get there. However, the muon has in any case created points in the previous modules, and it is possible to reconstruct a trace with the available points, thereby also obtaining the energy range of that muon.

[0068] Furthermore, making reference to figure 3, said scintillating plate 10 consists of a single plate of scintillating material, on all the faces of which a reflective layer 6 is applied, with the exception of a portion 72 of a lateral face of the plate of scintillating material, where a silicon photomultiplier 21 (SiPM) is applied, so that the light produced is conveyed to it.

[0069] Figure 5 shows an example of a typical event in the system according to the present invention. In particular, a muon 11 passes through the modular detector 101 obliquely, with a travel path from top to bottom (atmospheric muon), and passes through the various modules of the modular detector 101 .

[0070] In particular, making reference to the embodiment shown in figures 1 and 5, said modular detector 101 comprises a muon detection module consisting of a scintillating plate 10. Said muon detection module is used to provide a rapid measurement of the passage of muons, taking on the function of a trigger of the detection system, and to simplify discrimination from the background noise.

[0071] Alternatively, making reference to the embodiment shown in figure 6, said detector 191 further comprises a muon selection module arranged inside said outer casing by means of respective arrangement means (not shown), below said two muon passage position detection modules 5.

[0072] In particular, again making reference to the embodiment shown in figure 6, each muon selection module comprises a muon energy absorber module 2 and a muon detection module positioned below said muon energy absorber module 2. More particularly, said muon detection module is a scintillating plate 10. In this case, the triggering of the detection system is obtained from an analysis of the temporal coincidence of the signal of the silicon photomultipliers 21 of the other scintillating elements of said muon passage position detection modules 5. In fact, two scintillating layers with a coinciding signal can generate a signal that triggers the data acquisition system, and thus the scintillating plate 10 takes on the function of an energy-based trigger, i.e. it detects the passage of the muon, and thus detects that the muon had sufficient energy to pass through the muon energy absorber module before it.

[0073] Furthermore, the energy filter effect due to the absorbent materials is shown in the embodiment in figure 6. In fact, a high energy muon passes through all the moduli, whereas a muon having insufficient energy is absorbed without passing through the last module.

[0074] In further embodiments, not shown, other configurations can be obtained by changing the order of the modules.

[0075] Again making reference to the embodiment shown in figure 6, the modular detector 101 comprises a main printed circuit 201 connected by cables to said printed circuits 19.

[0076] Said main printed circuit 201 comprises a conditioning section for conditioning the signals coming from the silicon photomultipliers 21 , the high-voltage power supplies for the silicon photomultipliers 21 , analogue to digital converters for monitoring voltages, a field programmable gate array (FPGA), an inertial measurement unit composed of a magnetometer, accelerometer and gyroscope, and an ethernet connector for the power supply and data transmission.

[0077] Making reference to the embodiment shown in figure 4, the silicon photomultipliers are installed in groups on different printed circuits 19 to simplify the wiring towards the main printed circuit. In particular, in the embodiment shown in figure 4, a printed circuit 19 comprises four photomultipliers 21. Furthermore, a printed circuit 19 comprises a signal amplifier, a threshold comparator, a digital to analogue converter to set the threshold and a temperature sensor 22 to monitor the status of the photomultipliers 21. Furthermore, every printed circuit 19 has a connector for the power supply 20 and a connector for carrying the signals 23 towards the main printed circuit.

[0078] Preferably, said photomultipliers 21 are multipixel photodiode arrays. In particular, their operation requires a bias power supply of a few dozen Volts, the generator of which is present on the main printed circuit 201 . The signal of every photomultiplier 21 is amplified and digitised by means of a threshold comparator 22. The digitised signal is read and processed by the FPGA. The FPGA continuously reads the status of all the photomultipliers 21 at a frequency defined by the user. When there is a signal coming from the scintillating plate 10, the measurements performed in the last period, of a length defined by the user, are saved as a possible candidate event for reconstruction. The FPGA has a microprocessor that allows part of the reconstruction to be carried out directly on the apparatus and offers an interface towards the outside via the ethernet standard. The collected data are saved in the apparatus and can be sent to a central surface processor via the ethernet connection. The central processor enables the reconstruction algorithm to be executed in real time by aggregating the data coming from all the systems according to the present invention. The reconstruction can be carried out at a later time based on the saved data.

[0079] Additionally, said system comprises at least one battery to enable the system to operate without an external power supply. Furthermore, said system can contain a storage device for recording the measurements performed.

[0080] The system according to the present invention can also be used as a system with properties analogous to those of underground GPS, i.e. where the GPS cannot be exploited. If a muon passes through a detector of the array, if an entity below that system also carries another muon detector, and if the same muon passes through that detector, one will be able to identify the position of the entity with precision constrained by the effect of multiple scattering. This system would be proposed as an alternative to GPS where its use is not possible, and is thus of interest in the defence sector and in the self-driving vehicle sector. A wide area system would further serve to monitor the structure overlying a tunnel, as shown in international patent no. W02020198885, but the present technology improves the response compared to the uncertainties of multiple scattering.

[0081] Additionally, said system may comprise a software system for reconstructing two-dimensional and three-dimensional images for the identification of volumes of material of interest. In particular, said image reconstruction software enables the reconstruction of particle traces based on the signals, using the Kalman filter technique, so as then to carry out a density analysis on the volumes of earth analysed, identify the two-dimensional dimensions of the volumes of material of interest over the angle direction of the muons detected by the detector, then combined for the three-dimensional reconstruction of the final image of the dimensions of the volumes of material of interest.

[0082] Depending on the deployment modes, said HIVE modular detector takes on different configurations, with which respective names reflecting its different application modes have been associated for the sake of simplicity of illustration:

[0083] - geoMINE: in the geoMINE configuration, HIVE is proposed as a stand-alone detector, at depths of less than 50 metres; in this mode HIVE is proposed as a system for monitoring soil permeability following rainfall; thus HIVE is proposed as a system for preventing landslides on soils where rainwater can permeate; it can also be used in proximity to precipices or cliffs to monitor the creation of landslides;

[0084] - MEGA: HIVE can be used for wide area applications, with 250x250x5 cm3modules, to monitor the average density in the layers overlying tunnels; it is conceived for the identification of: overlying groundwater aquifers, air bubbles and gas reserves;

[0085] - muGPS: HIVE can be used in an array mode, i.e. with HIVE detectors positioned at a depth of about 50, 100 or 150 metres, to detect the passage of muons; another HIVE detector can be carried by another entity, e.g. a person, a worker, or a mobile object, into the layers below the previously installed HIVE array; in this case the passage of a particle into the last module, together with the passage of the same particle in the array, enables a unique positioning of the underlying mobile object or entity; this application is conceived in the defence sector, for monitoring underground tunnels, and in the sector of self-driving vehicles, where a GPS solution cannot be applied due to signal unavailability;

[0086] - MINE: in the array mode, HIVE detectors are placed in columns, where two or three HIVEs are placed at a depth of 100 or 150 metres, up to a maximum of 600 metres, bearing in mind that the number of muons per day decreases by a factor of 10 every 150 metres. This means that every measurement at 150 metre intervals of depth takes ten times longer than the measurement at 150 metres less depth, given that the flow decreases with increases in depth and not vice versa. In particular, the less deep the detector is, the more muons will be available per day. This application of HIVE is conceived for the identification of veins of heavy metals, e.g. deposits of gold, lead, uranium and silver; it is sensitive, moreover, to the presence of gas bubbles, e.g. methane or air; it is further capable of identifying aquifers and deposits of petroleum and liquids in general. HIVE is thus capable of identifying variations in density compared to the average density of the surrounding earth, information that is made available by analysing the earth extracted by core drilling during the installation of the HIVE detectors themselves.

[0087] The present invention has been described by way of non-limiting illustration according to preferred embodiments thereof, but it is understood that variations and / or modifications may be introduced by the person skilled in the art without going outside the relevant scope of protection as defined by the appended claims.

Claims

CLAIMS1 ) A modular energy threshold muon detector (101 ) for monitoring soil density and / or permeability, comprising at least two muon passage position detection modules (5), each muon passage position detection module (5) comprising a pair of scintillating elements (9) consisting of two segmented plates (9) placed one on top of the other, each segmented plate (9) comprising a plurality of scintillating bars (8) positioned in such a way that the scintillating bars (8) of one of the two segmented plates (9) are rotated by 90° with respect to the scintillating bars (8) of the other segmented plate (9), each scintillating bar (8) comprising at least one silicon photomultiplier (21 ) positioned at an end face (71 ) of said scintillating bar (8), an outer casing (1 ) adapted to contain said at least two muon passage position detection modules (5), arrangement means configured to arrange said at least two muon passage position detection modules (5) in respective positions selectable from a plurality of positions inside said outer casing (1 ).2) The modular detector (101 ) according to the preceding claim, characterised in that it further comprises at least one muon energy absorber module (2) arranged above said at least two muon passage position detection modules (5), said at least one muon energy absorber module (2) being adapted to be arranged inside said outer casing (1 ) by means of respective arrangement means.3) The modular detector (101 ) according to the preceding claim, characterised in that it further comprises a muon detection module positioned above said at least one muon energy absorber module (2), said muon detection module being adapted to be arranged inside said outer casing (1 ) by means of respective arrangement means.4) The modular detector (101 ) according to any one of the preceding claims, characterised in that it further comprises at least one muon energy absorber module (2) arranged between said at least two muon passage position detection modules (5), said at least one muon energy absorber module (2) being adapted to be arranged inside said outer casing (1 ) by means of respective arrangement means.5) The modular detector (101 ) according to any one of the preceding claims, characterised in that it further comprises at least one muon selection module adapted to be arranged inside said outer casing (1 ) by means of respectivearrangement means, below said at least two muon passage position detection modules (5), each muon selection module comprising at least one muon energy absorber module (2) and one muon detection module positioned below said at least one muon energy absorber module (2).6) The modular detector (101 ) according to any one of claims 3-5, characterised in that each muon detection module is a pair of scintillating elements (9) or a scintillating plate (10) comprising at least one silicon photomultiplier (21 ) positioned at an end face (72) of said scintillating plate (10).7) The modular detector (101 ) according to any one of claims 2-6, wherein said muon energy absorber module (2) is a layer of absorbent material with a thickness comprised between 1 cm and 3 cm.8) The modular detector (101 ) according to claim 1 or 6-7, characterised in that said scintillating plate (10) and / or each scintillating bar (8) of each segmented plate (9) comprise a reflective layer (6) applied on all the faces thereof with the exception of an end face (72, 71 ).9) The modular detector (101 ) according to any one of claims 2-8, characterised in that said muon energy absorber module is made of a high atomic number absorbent material.10) The modular detector (101 ) according to the preceding claim, wherein said muon energy absorber module is made of steel, lead or tungsten.11 ) The modular detector (101 ) according to any one of the preceding claims, characterised in that said outer casing (1 ) is made of a high atomic number material, preferably steel.12) The modular detector (101 ) according to any one of the preceding claims, characterised in that said at least one photomultiplier (21 ) is mounted on a printed circuit (19), said printed circuit (19) comprising a signal amplifier, a threshold comparator, an analogue to digital converter, at least one connector for the power supply (20) and a temperature sensor (22).13) A system for monitoring soil density and / or permeability, characterised in that it comprises at least one modular detector (101 ) according to any one of claims 1 -12.14) The system according to the preceding claim, characterised in that it comprises at least two modular detectors (101 ) and a communication network adapted to connect said at least two modular detectors (101 ).

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