Flexible muon detector for inspecting an object

Abstract

A flexible muon detector for inspecting an object has a continuous scintillator film (102) for detecting incident muons by generating photons. Photomultipliers (104) are discretely distributed across

Description

Field of Invention The present invention relates to a flexible muon detector and its use for inspecting an object as well as a method of production thereof. This invention relates primarily to the field of muography / muon imaging / muon tomography / muon radiography. The present invention especially relates to multi-use of the flexible muon detector in inspecting the object. Background of the Invention Muon radiography is an imaging technique for inspecting properties of matter. A cosmic-ray muon passing through matter may be altered by the internal composition of the matter. By repeating muon radiography over time, the nature of any changes to the internal composition can be investigated, for example, changes in composition and density. Muography detectors are rigid and large-scale, which results in them not only being cumbersome and difficult to transport but also unsuitable for deployment around matter that has specific requirements as to shape and dimensions. In particular, cylindrical muon detector systems usually require multiple layers of fibres or bars and are complex to manufacture. There have been attempts to simplify the production of such cylindrical muon detector systems. A known cylindrical borehole detector for radiographic imaging with muons is disclosed in a non-patent publication “Cimmino et al., Scientific Reports 11, 17425 (2021)”. This cylindrical borehole detector was made with plastic scintillators of two different shapes: in the shape of an arc and in the shape of a bar, wherein the plastic scintillators are directly coupled to Silicon photomultipliers. The problem with this approach is that the production of such cylindrical borehole detector is still very complex, because it requires assembling two semicylinders, each composed of 32 bars and 128 arcs, for a total of 320 scintillator elements. It is often required to measure trajectories of incoming and outgoing muons from muon detectors to comprehend characteristics of an object. A high-resolution 3D MST (Muon Scattering Tomography) image of the object can be constructed using the measured trajectories. The 3D MST image has a high spatial resolution of up to approximately 1mm, which allows the internal composition of the object to be accurately characterised. However, a high-resolution 3D MST detector is not always necessary depending on the nature of the object under inspection. For example, it is not required to frequently deploy the MST detector for inspection of radioactive contents in a nuclear waste container because of the relatively long half-life of radioactive contents. It would be more cost-effective to deploy the MST detector only when it is likely that a change has occurred. Moreover, the high-resolution MST detector is not always easily accessible and sometimes it is impractical to deploy it frequently because human personnel are required to carry out the task, further increasing the logistical requirements for monitoring. Furthermore, it is required that the MST detector is placed around the object, or that the object is transported to the detector. The large dimensions of the MST detector or the object will make transportation difficult and cumbersome. This is complicated by the fact that objects under investigation may have significantly different shapes. Summary of invention It is desirable to have a flexible muon detector which is compact, portable and easy to manufacture at a low cost. It is also desirable that the flexible muon detector supports multiple uses tailored to a variety of inspection requirements. According to a first aspect of the present invention, there is provided a flexible muon detector for inspecting an object, the detector comprising: - a continuous scintillator film for detecting incident muons by generating photons in response to the incident muons; - a plurality of discrete photomultipliers discretely distributed across a face of the continuous scintillator film, which are configured to optically connect to the continuous scintillator film, wherein the plurality of discrete photomultipliers are arranged to detect the generated photons and generate corresponding electrical signals; and - flexible electronics electrically connected to the plurality of discrete photomultipliers so as to receive the generated electrical signals. Preferably, at least a portion of the continuous scintillator film is planar. Preferably, the continuous scintillator film is conformable to the object’s shape. Preferably, the continuous scintillator film is of a cylindrical shape. Preferably, the continuous scintillator film is configured to have a Swiss-roll structure. Preferably, the flexible muon detector is used as a vector muon detector configured to measure positions and directions of muons that have passed through the object from a plurality of different angles and have been scattered by the object. Alternatively, the flexible muon detector is used as a vectorless muon detector configured to measure positions, but not directions, of the muons that have passed through the object from a plurality of different angles and have been scattered by the object. Preferably, the flexible muon detector comprises an array of the flexible muon detectors configured to cooperate to connect together. Preferably, the plurality of discrete photomultipliers are discretely distributed in a regular pattern across the face of the continuous scintillator film. According to a second aspect of the present invention, there is provided a method of producing a flexible muon detector for inspecting an object, the method comprising: - providing a continuous scintillator film for detecting incident muons by generating photons in response to the incident muons; - providing a plurality of discrete photomultipliers discretely distributed across a face of the continuous scintillator film, and optically connecting the plurality of discrete photomultipliers to the continuous scintillator film, wherein the plurality of discrete photomultipliers are arranged to detect the generated photons and generate corresponding electrical signals; and - providing flexible electronics, and electrically connecting the flexible electronics to the plurality of discrete photomultipliers so as to receive the generated electrical signals. Preferably, the method further comprises changing the continuous scintillator film’s shape. Preferably, changing the continuous scintillator film’s shape comprises rolling the continuous scintillator film into a cylindrical shape. Alternatively, changing the continuous scintillator film’s shape comprises winding the continuous scintillator film into a Swiss-roll structure. Preferably, changing the continuous scintillator film’s shape comprises winding the continuous scintillator to surround the object, forming a flexible muon detector having the Swiss-roll structure. Preferably, the method further comprises discretely distributing the plurality of discrete photomultipliers in a regular pattern across the face of the continuous scintillator film. Brief description of drawings Embodiments of the present invention will now be described, by way of example only, with reference to the drawings, in which: Figure 1 illustrates, in schematic form, a cross-sectional view of a flexible muon detector, in accordance with an embodiment of the present invention. Figures 2a and 2b illustrate, in schematic form, application of the flexible muon detector of Figure 1 for inspecting an object, wherein the flexible muon detector is arranged below, and to a side of, the object. Figure 3a illustrates, in schematic form, a cross-sectional view of a flexible muon detector conformable to a portion of an object, in accordance with an embodiment of the present invention. Figure 3b illustrates, in schematic form, a cross-sectional view of a flexible muon detector conformable to a portion of an object, in accordance with another embodiment of the present invention. Figure 4a illustrates, in schematic form, a perspective view of a flexible muon detector of a cylindrical shape having a cross-sectional shape of circular cylinder, in accordance with an embodiment of the present invention. Figure 4b illustrates, in schematic form, a zoomed-in view of the cross section of Figure 4a. Figure 4c illustrates, in schematic form, a side elevation view of a flexible muon detector of a cylindrical shape having a cross-sectional shape of elliptic cylinder. Figure 5 illustrates, in schematic form, a cross-sectional view of a Muon Scattering Tomography (MST) detector comprising a plurality of the flexible muon detectors according an embodiment of the present invention. Figures 6a and 6b illustrate, in schematic form, a flexible muon detector of a cylindrical shape having multiple layers arranged from a single continuous scintillator film. Figure 7 is a flowchart of a method of producing a flexible muon detector, in accordance with an embodiment of the present invention. Description of embodiments In the Figures, elements labelled with reference numerals found in the preceding Figures represent the same elements as described for the respective preceding Figure. For example, feature 102 in Figure 4b corresponds to the same feature 102 as described with reference to Figure 1. Features described herein in the context of an embodiment may be provided separately or in any suitable combination with features described herein in the context of other embodiments. The flexible muon detector according to embodiments of the present invention is lightweight and more portable compared to a high-resolution 3D MST detector. The flexible muon detector according to embodiments of the present invention is conformable to the shape of an object under inspection, for example, conformable to the contour or curvature of at least a portion of the object. The flexible muon detector according to embodiments of the present invention can also be wrapped around the exterior of, or rolled to fit inside, a pipework or vessel. Being flexible, the flexible muon detector according to embodiments of the present invention is capable of inspecting objects having different shapes at a reduced cost. The flexible muon detector according to embodiments of the present invention can be of a wide range of length, width and depth dimensions, which may be customised to applications the detector is used for or upon request by end users. The flexible muon detector can be configured to cope with various inspection environments, for example, high pressure or temperature conditions. The skilled person would know how to customise the detector with appropriate components to satisfy such conditions. Advantageously, the flexible muon detector according to embodiments of the present invention can be embedded in structures permanently or for an extended period of time to provide continuous monitoring, which ensures the earliest possible detection of any changes in a cost-effective way. It is particularly relevant to objects for which maintaining active surveillance over a long period of time (e.g. a decade or more) is of critical importance. Therefore, in an example, the flexible muon detector may be at least partially embedded in a container body of a waste container containing radioactive nuclear waste to enable the detection of abnormalities in the waste container efficiently to maintain long-term safety. In another example, the flexible muon detector may be applied to inspect internal pipe integrity and functionality to detect structural defects such as cracks, fractures and corrosion hotspots. Figure 1 illustrates a flexible muon detector 100 for inspecting an object according to an embodiment of the present invention. The flexible muon detector comprise a continuous scintillator film 102 for detecting incident muons by generating photons in response to the incident muons. In an example, the continuous scintillator film is made of pure scintillator. In another example, the continuous scintillator film comprises an optically transparent substrate on which pure scintillator is deposited. In an example, the pure scintillator means a scintillator consisting of homogenous scintillation materials. In another example, the pure scintillator means a scintillator having scintillation materials uniformly distributed across length, width and depth dimensions of the continuous scintillator film. Scintillators can be liquid or gel, organic or inorganic (glass, single, crystal, etc.). In embodiments, the flexible muon detector comprises a plurality of discrete photomultipliers discretely distributed across a face of the continuous scintillator film, which are configured to optically connected to the continuous scintillator film. The plurality of discrete photomultipliers are arranged to detect the generated photons and generate corresponding electrical signals. In some embodiments, the plurality of discrete photomultipliers are detachably and optically connected to the continuous scintillator film. Referring to Figure 1, the flexible muon detector 100 comprises a plurality of discrete photomultipliers 104, which are configured to optically connect to the continuous scintillator film 102. The plurality of discrete photomultipliers 104 can be directly optically connected to the continuous scintillator film 102 or indirectly optically connected by means of optical couplers. The optical couplers may comprise any materials that allow incident light to pass through, for example, an optically transparent substance, optical gel wrapped in a reflective foil or optical fibres. The plurality of discrete photomultipliers 104 act together as a position-sensitive photon detector, which is capable of measuring positions of individual muons that pass through the object from a plurality of different angles and have been scattered by the object. Preferably, the plurality of discrete photomultipliers are silicon photomultipliers (SiPM) due to their low operating voltage, compactness, singlephoton sensitivity, temperature stability and low cost. In another example, the plurality of discrete photomultipliers 104 comprise solid-state photomultipliers made of other materials, for example, multi-pixel photon counters (MPPCs) and avalanche photo diodes (APDs). Referring to Figure 1, the plurality of discrete photomultipliers 104 are discretely distributed in a regular pattern across the face of the continuous scintillator film. To accurately determine emitted light collected by the plurality of discrete photomultipliers, a muon position may be determined from a signal-weighted position average of the surrounding photomultipliers. For example, when the flexible muon detector 100 is a flat-panel muon detector (as illustrated in Figure 2), a muon hitting at the centre point between four surrounding photomultipliers should create the same signal in all the four surrounding photomultipliers. The skilled person would understand that the more sparse the plurality of discrete photomultipliers distributed across the face of the continuous scintillator film are, the less optimal the spatial resolution of the detector when the detector is in use, e.g. having been flattened or rolled up. The regular pattern ensures that acceptable spatial resolution required for an inspection task can be achieved without sacrificing the flexibility of the detector. In an example, the plurality of discrete photomultipliers would be considered to be discretely distributed in a regular pattern across the face of the continuous scintillator film if the plurality of discrete photomultipliers cover at least 20% of, and are evenly distributed over, the entire total surface area of the continuous scintillator film. The skilled person would understand that the spatial resolution of the detector would depend on thickness of the continuous scintillator film. In embodiments, the flexible muon detector comprises flexible electronics for receiving the generated electrical signals, wherein the flexible electronics are configured to electrically connect to the plurality of discrete photomultipliers so as to receive the generated electrical signals from the plurality of discrete photomultipliers. In this example, flexible electronics refers to a flexible PCB (printed circuit board) populated with electronic components. In some embodiments, the plurality of discrete photomultipliers are detachably and electrically connected to the flexible electronics. Referring to Figure 1, the plurality of discrete photomultipliers 104 are electrically connected to flexible electronics 106. The flexible electronics 106 is thin and lightweight. In an example (not shown), the flexible muon detector 100 comprises a power supply electrically coupled to the flexible electronics. The flexible muon detector according to embodiments of the present invention support a multi-purpose inspection of an object, thereby the flexible muon detector is a multi-use flexible muon detector. The flexible muon detector comprises vector and vectorless configurations. In vectorless configurations, measurements from the detector are of positions, but not directions, of the muons that have passed through the object from a plurality of different angles and have been scattered by the object. In vector configurations, measurements from the detector are of positions and directions of the muons that have passed through the object from a plurality of different angles and have been scattered by the object and pass through two or more segments of scintillator film / flexible electronics (100 in Figure 1). According to an embodiment of the present invention, at least a portion of the continuous scintillator film of the flexible muon detector has a planar structure. Figure 2 illustrates the flexible muon detector 100 applied to inspect an object 202, in accordance with an embodiment of the present invention. In this example, the entire continuous scintillator film 102 is a coplanar flat-panel aligned with a horizontal plane of the object, thereby the flexible muon detector 100 is a flat-panel muon detector. Referring to Figure 2, the flexible muon detector 100 is configured with particular dimensions, wherein preferably its dimension along the x-axis 204 is at least equal to the width of the object 202 under inspection, and arranged in such a way that it can detect muons that have been scattered due to passing through the object 202 from a sufficiently wide range of angles. In use, the flexible muon detector is positioned at a location in close proximity to the object to ensure an optimal sensitivity of the detector with respect to the object. It will be understood by the person skilled in the art how to best deploy the detector. The flexible muon detector may be placed above the ground, in-ground or under the ground in close proximity to the object. As illustrated in Figure 2a, the flexible muon detector 100 is positioned below the object 202. As illustrated in Figure 2b, the flexible muon detector 100 is positioned at a side of the object 202. A two-dimensional (2D) radiographic projection of an object can be obtained using the flexible muon detector according embodiments of the present invention. The 2D radiographic projection is a convolution of signals from muons that have entered into the object from a plurality of different angles and some of which, for example 206, 208, 210, have been scattered or stopped by matter in the object 202. The 2D radiographic projection can be in a variety of forms. In an example, the 2D radiographic projection corresponds to raw muon detection data obtained directly from the flexible muon detector 200. In another example, the 2D radiographic projection refers to a 2D radiographic image produced from the muon detection data. According to another embodiment of the present invention, a plurality of flexible muon detectors are arranged in a detector assembly to inspect a large-scale object where the use of a single MST detector would be infeasible due to reasons of cost and scale. Measurements collected from individual detectors forming the detector assembly can then be combined to generate a 2D radiographic image of the entire large-scale object. According to an embodiment of the present invention, at least a portion of the flexible muon detector is conformable to the shape of an object. The shape of the object comprises the contour of the object, for example, contours representing boundaries of bumps and indentations of the surface of the object, which can be convex or concave shape. The flexible muon detector being conformable to different surfaces provide better muon coverage than coplanar configurations, making it possible to inspect objects of various shapes conveniently and efficiently. The better coverage ensures that muons coming from all angles can be detected, thus increasing accuracy of the measurements. Figure 3a illustrates a flexible muon detector 300 configured to conform to a portion of an object 302. In this example, opposing ends 304, 306 of the continuous scintillator film 102 are spaced apart. In another example, the flexible muon detector is conformable to the shape of an object to fully enclose at least a cross-sectional area of the object. In Figure 3b, the flexible muon detector 300 is configured to conform to the shape of the object 302 to fully enclose a cross-section area having a width 304 in a plane perpendicular to a horizontal plane of the object 302. According to an embodiment of the present invention, a flexible muon detector is in a cylindrical shape having a central longitudinal axis. Figure 4 illustrates a flexible muon detector of a cylindrical shape 400 comprising a single continuous scintillator film 402 forming a curved cylindrical surface. Opposing edges of the continuous scintillator film 402 are connected forming a seam 404. The flexible muon detector 400 of Figure 4a has a circular cross-sectional shape 406. Figure 4b illustrates (not to scale) a cross section of the detector 400 of Figure 4a in a horizontal plane. In Figure 4c, the flexible muon detector with a cylindrical shape 400 has an elliptical cross-sectional shape 408. In embodiments, the opposing edges of the continuous scintillator film may be secured relative to each other by means of one or more fasteners, which may be part of, or attached to, the flexible muon detector. The fasteners are not limited to exact arrangements and means as long as the fasteners support reusability and compactness of the detector. In another example (not shown), the flexible muon detector of a cylindrical shape comprises an array of the continuous scintillator films connected at corresponding edges of adjacent continuous scintillator films. Advantageously, the flexible muon detector according to embodiments of the present invention can be used in muon scattering tomography. In an example, a respective plurality of the flexible muon detectors may be arranged at opposing sides of an object under inspection, thus forming a vector muon detector which is capable of measuring positions and directions of muons that 1) have passed through the detector before traversing the object; and 2) have traversed the object (in which some of the muons have been scattered by the object) then have passed through the opposing detector. Figure 5 illustrates, in schematic form, a vector muon detector 500 comprising upper and lower muon detectors above 504 and below 510 an object 502, respectively. In this example, the upper 504 and lower 510 muon detectors comprise respective pairs of two planes of the flexible muon detectors 100. In another example, the upper 504 and lower 510 muon detectors comprise respective pairs of the flexible muon detectors 300. In yet another example, the upper 504 and lower 510 detectors correspond to the flexible muon detectors 400. Referring to Figure 5, the upper muon detector 504 is configured to measure the trajectories of incoming muons entering the object 502. The lower muon detector 510 is configured to measure the trajectories of outgoing muons scattered by the object 502. Each of the flexible muon detectors 100 can detect coordinates of the incoming and outgoing muons in two dimensions (e.g. x and y). With a known vertical separation 520 between the planes of the upper (504) and lower (510) muon detectors, a 3D trajectory can be calculated from the muon detection coordinates 522 (x1, y1) and 524 (x2, y2) for an incoming trajectory of a muon that has passed through the upper muon detector 504 before traversing the object 502, and 526 (x3, y3) and 528 (x4, y4) for an outgoing trajectory of the muon that has passed through the object 502 and has been scattered by the object 502. With this configuration, the structure and composition of the object 502 can be determined based on the scattering angle between incoming 516 and outgoing 518 muon tracks. According to an embodiment of the present invention, the flexible muon detector has a Swiss-roll structure such that neighbouring continuous scintillator films are separated by the flexible electronics. In an example, the flexible muon detector having the Swiss-roll structure is arranged from a single continuous scintillator film. In another example, the flexible muon detector having the Swiss-roll structure is arranged from an array of the continuous scintillator films connected at corresponding edges of adjacent continuous scintillator films. Figure 6a illustrates a flexible muon detector 600 having the Swiss-roll structure arranged from a single continuous scintillator film 102. Figure 6b illustrates a cross section of the detector 600 across plane A of Figure 6a. Segments 602, 604 of the continuous scintillator film 102 are separated by a segment 606 of the flexible electronics 106. To prevent crosstalk between layers of the Swiss-roll structure, in an example, the flexible electronics 106 is at least partially opaque. In another example, the flexible muon detector 600 comprises a light-absorbing film to prevent the crosstalk. As mentioned above, when the flexible muon detector is a flat-panel muon detector, a muon hitting at the centre point between four surrounding photomultipliers should create the same signal in all the four surrounding photomultipliers. When the continuous scintillator film is arranged in the Swiss-roll structure, the total internal reflection angle is warped and photon losses from the continuous scintillator film’s surfaces can occur. This leakage may then mean that for the flexible muon detector having the Swiss-roll structure a light absorbing thin film as part of the structure may be used to prevent leakage of photons from one layer of the detector into an adjacent layer of the detector. Referring to Figure 6a, the plurality of discrete photomultipliers 104 are discretely distributed across the face of the continuous scintillator film in a regular pattern, which becomes a corkscrew pattern wherein the plurality of discrete photomultipliers conform to the spiral wound near-cylindrical geometry of the flexible muon detector. In other examples (not shown), the Swiss-roll shape can be squashed to give an oval or more flattened shape, like a pain au chocolat. Similarly to the flexible muon detector 100 as illustrated in Figure 2, the flexible muon detector 300, 400, 600 can be positioned below, or at a side of, an object under inspection. Advantageously, the flexible muon detector 600 can be used in muon scattering tomography in a similar manner as illustrated in Figure 5 with respect to the flexible muon detector 100. In an example (not shown), a vector muon detector comprising a pair the flexible muon detectors 600 arranged respectively at opposing sides of the object under inspection, for measurements of positions and directions of muons before and after traversing the object. Alternatively, the flexible muon detector can be used in muon scattering tomography, wherein the continuous scintillator film is arranged in the Swiss-roll structure surrounding the object. In this configuration, both incoming muons before traversing the object, and outgoing muons which have passed through the object and have been scattered by the object, pass through a number of segments of the continuous scintillator film. The more segments of the continuous scintillator film incoming and outgoing muons pass through, the more accurate corresponding incoming and outgoing muon tracks can be reconstructed and more accurate structure and composition of the object can be determined. After the continuous scintillator film is arranged in the Swiss-roll structure, a particular configuration of overlapping layers of the flexible muon detector would determine relative positions of the plurality of discrete photomultipliers in the detector. This configuration can be calibrated and or modelled using detected muon traces. In an example, the relative positions of the plurality of discrete photomultipliers in layers of the Swiss-roll structure can be determined based on reference markers, for example, geometric shapes patterned on the flexible muon detector. Figure 7 illustrates a flowchart of a method of producing 700 a flexible muon detector, in accordance with an embodiment of the present invention. The method has the following steps. At step 702, a continuous scintillator film is provided. At step 704, a plurality of discrete photomultipliers are provided. This step comprises optically connecting the plurality of discrete photomultipliers to the continuous scintillator film. This step further comprises discretely distributing the plurality of discrete photomultipliers across a face of the continuous scintillator film. At step 706, flexible electronics is provided, wherein the plurality of discrete photomultipliers are electrically coupled to the flexible electronics. The method further comprises changing the continuous scintillator film’s shape to produce a flexible muon detector. Changing the continuous scintillator film’s shape may comprise bending, folding, flexing or rolling the continuous scintillator film. In an example, a flexible muon detector of a curved shape is formed by conforming the detector to a portion of the object’s shape. In another example, a flexible muon detector of a cylindrical shape is formed by rolling the continuous scintillator film into a cylinder. In yet another example, a flexible muon detector of a cylindrical shape is formed by wrapping the continuous scintillator film around the object to form a Swiss-roll structure.

Claims

1. A flexible muon detector for inspecting an object, the detector comprising:- a continuous scintillator film for detecting incident muons by generating photons in response to the incident muons;- a plurality of discrete photomultipliers discretely distributed across a face of the continuous scintillator film, which are configured to optically connect to the continuous scintillator film, wherein the plurality of discrete photomultipliers are arranged to detect the generated photons and generate corresponding electrical signals; and- flexible electronics electrically connected to the plurality of discrete photomultipliers so as to receive the generated electrical signals.

2. The flexible muon detector of claim 1, wherein at least a portion of the continuous scintillator film is planar.

3. The flexible muon detector of claim 1, wherein the continuous scintillator film is conformable to the object’s shape.

4. The flexible muon detector of claim 1, wherein the continuous scintillator film is of a cylindrical shape.

5. The flexible muon detector of claim 1, wherein the continuous scintillator film is configured to have a Swiss-roll structure.

6. Use of the flexible muon detector of claims 1 to 5 as a vector muon detector configured to measure positions and directions of muons that have passed through the object from a plurality of different angles and have been scattered by the object.

7. Use of the flexible muon detector of claims 1 to 3 as a vectorless muon detector configured to measure positions, but not directions, of the muons that have passed through the object from a plurality of different angles and have been scattered by the object.

8. The flexible muon detector of any preceding claim, comprising an array of the flexible muon detectors configured to cooperate to connect together.

9. The flexible muon detector of any preceding claim, wherein the plurality of discrete photomultipliers are discretely distributed in a regular pattern across the face of the continuous scintillator film.

10. A method of producing a flexible muon detector for inspecting an object, the method comprising:- providing a continuous scintillator film for detecting incident muons by generating photons in response to the incident muons;- providing a plurality of discrete photomultipliers discretely distributed across a face of the continuous scintillator film, and optically connecting the plurality of discrete photomultipliers to the continuous scintillator film, wherein the plurality of discrete photomultipliers are arranged to detect the generated photons and generate corresponding electrical signals; and- providing flexible electronics, and electrically connecting the flexible electronics to the plurality of discrete photomultipliers so as to receive the generated electrical signals.

11. The method of claim 10, further comprising changing the continuous scintillator film’s shape.

12. The method of claim 11, wherein changing the continuous scintillator film’s shape comprises rolling the continuous scintillator film into a cylindrical shape.

13. The method of claim 11, wherein changing the continuous scintillator film’s shape comprises winding the continuous scintillator film into a Swiss-roll structure.

14. The method of claim 13, wherein changing the continuous scintillator film’s shape comprises winding the continuous scintillator to surround the object, forming a flexible muon detector having the Swiss-roll structure.

15. The method of any of claims 10 to 14, further comprising discretely distributing the plurality of discrete photomultipliers in a regular pattern across the face of the continuous scintillator film.

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