FI129251B - An apparatus for detecting radiation - Google Patents

Abstract

An apparatus for detecting radiation comprises a radiation converter (101), a photodetector (102), and a light guide (103) for conducting photons emitted by the radiation converter. The radiation converter is a layer in contact with a first Surface (105) of the light guide and the photodetector is attached to an opposite side of the light guide. A convex second surface (106) of the light guide receives the photons from the radiation converter and has a reflective coating (104) reflecting the photons backwards to the radiation converter that, in turn, reflects the photons to the photodetector. As the photons are reflected back-and-forth in the above-mentioned way, the photons can be directed to a small area even if the light guide is short in a direction (z) perpendicular to the first surface of the light guide.

Description

An apparatus for detecting radiation Field of the disclosure The disclosure relates generally to radiation detection.

More particularly, the disclosure relates to an apparatus for detecting radiation such as e.g. gamma rays, X-rays, neutrons, alpha particles, beta particles, and/or other electrically charged or neutral particles.

Background In many cases, there is a need to detect and measure radiation for example to ensure safety of people, analyze materials, and for many other purposes, too.

The radiation to be detected may comprise for example gamma rays, X-rays, neutrons, alpha particles, beta particles, and/or other electrically charged or neutral particles.

Radiation can be detected using radiation detectors such as for example a Geiger counter, an ionization chamber, a scintillation detector, a neutron detector, and so forth.

In a scintillation detector, energy of incoming radiation is at least partly converted into photons that are, in turn, detected with a photodetector which produces electric output signals indicative of the detected photons.

The electric output signals of the photodetector are processed with an appropriate processing system to produce output data suitable for an application under consideration. - 20 Organic and inorganic scintillator materials offer a platform for fabricating radiation O detectors which can be tailored for different applications.

For specifying a detector N design, there are typically many aspects to define such as for example: i) © characteristics of radiation to be detected such as e.g. type, energy, and expected z flux, ii) mechanical constraints such as e.g. limitations of size and/or shape, so 25 mechanical stresses, and a need for mechanical flexibility, iii) electrical constraints E related to e.g. powering and signal read-out, iv) functional reguirements such as e.g.

D reguired detector efficiency, sensitivity, and radiation hardness, v) background N conditions such as e.g. radiation background and electric noise, and vi) operating environment-related aspects such as e.g. available cooling and variations in temperature, humidity, and atmospheric pressure.

Furthermore, in detector design,

it is advantageous to provide for an efficient signal extraction.

In case of scintillating detectors, it is a well-known practice to use different types and geometries of light guides and/or light concentrators to maximize the number of photons arriving at a photodetector which can be either a photomultiplier tube PMT or a semiconductor- based photodetector such as e.g. a PIN diode, an avalanche P/N diode APD, or a silicon photomultiplier SIPM.

The light guides/light concentrators enable larger detector areas to be read out by a photodetector with a small active surface area.

As discussed above, there are numerous aspects to be considered when constructing an apparatus for detecting radiation.

Furthermore, the apparatus for detecting radiation should be as cost-effective as possible.

To improve the possibilities to fulfil the numerous aspects of the kind described above, there is still a need for new ways to construct apparatuses for detecting radiation.

Publication EP3306352 describes a radioactive contamination inspection apparatus that comprises a plastic scintillator, a light receiving element, a light guide configured to allow scintillation light emitted from the plastic scintillator to reach the light receiving element, a light shielding housing including an incidence window, and a thin film layer structure provided between the incidence window provided in the light shielding housing and the plastic scintillator, and including a protective film, a light shielding film, and a reflective film in the stated order from the incidence window side.

A side surface of the light guide is made up of a diffused reflection surface.

The reflective film is disposed with an air layer placed between the reflective film and the plastic scintillator.

A surface of the reflective film, which faces the plastic S scintillator, is made up of a specular reflection surface. 5 Publication WO2018211578 describes a radiation detector that comprises: a S 25 detector case which has an opening portion, a reflector which is attached to the = opening portion, a plastic scintillator which is disposed inside of the detector case 2 with a clearance from the reflector, a light guide into which fluorescence emitted 3 from the plastic scintillator enters, a photo multiplier tube at which the fluorescence > having passed through the light guide enters, and a pre amplifier which converts an output of the photo multiplier tube into a current pulse.

The plastic scintillator or the light guide has a soaked layer of ammonia which is formed on a surface thereof.

This radiation detector is improved in the chemical resistance to the process fluid which includes a corrosive gas.

Publication EP1016881 describes a radiation detecting apparatus where an alpha ray and a beta ray are transmitted through a light shielding film, but an incident light is shielded.

A first light is emitted from a first scintillator by the alpha ray transmitted through the light shielding film.

The first scintillator has an emission center wavelength based on the alpha ray.

A second light is emitted in a second scintillator by the beta ray transmitted through the light shielding film.

The second scintillator has an emission center wavelength based on the beta ray.

The first and second lights are detected by two photodetectors, respectively.

The first emission center wavelength and the second emission center wavelength are different from each other.

Publication US5241180 describes a radiation detection device that comprises a scintillator having an upper scintillator body section and a lower scintillator body section.

The upper section forms an arcuate-shaped cap through which the incident radiation enters the scintillator, and the lower section has sidewalls disposed at a selected taper angle with respect to the longitudinal axis of the scintillator body and an optically transmissive window disposed opposite the cap of the upper section such that optical photons can pass from the scintillator to a photodetector coupled to the window.

An optically diffusing reflective layer is disposed over the sidewalls and the cap.

The sidewalls typically have a positive taper angle, being closer to one another near the optically transmissive window and farther from one another near S the cap.

The arcuate shape of the cap typically conforms to the arc of a circle K. centered on the optically transmissive window.

The selected taper angle of the 2 25 sidewalls and the radius of the arc of the cap are chosen to cause light photons 7 generated within the scintillator body to be reflected from the sidewalls toward the E cap and reflected from the cap towards the optically transmissive window, or 3 reflected directly to the optically transmissive window for sidewalls having a negative 3 taper angle, such that the photons are focused on the window and strike the window N 30 at an angle greater than the critical angle for the scintillator-to-photodetector interface.

Publication US2003122083 describes a photodiode detector array that comprises a layer of intrinsic semiconductor material having a first doped layer on a first surface of a first conductivity type and an array of photodiodes having respective doped regions on a second surface of an opposite conductivity type.

Electrical contacts on the second surface respectively contact the doped regions and convey electrical signal therefrom.

Conductors extend from the electrical contacts to convey the electrical signals to output terminals of the array.

A scintillator is optically coupled to the layer of the intrinsic semiconductor material at the first surface thereof and can be pixelated with individual scintillator elements aligned with and corresponding to the doped regions of the photodiode.

The photodiode detector array can be mounted to a rigid printed wiring board or to a flat bottom wall surface of the scintillator.

Publication US2009296087 describes a concave cell for collecting radiated light.

The concave cell comprises a body with a concave surface and a flat surface opposite thereto, and a reflective surface coupled to the body to cover the concave surface.

The reflective surface comprises an opening and a photo detector operatively coupled thereto.

Publication US2011068273 describes a radiation-detection device.

The radiation- detection device includes a scintillation crystal and an avalanche photodiode.

The surface of the scintillation crystal is coated with a high-reflection layer.

When ionizing radiation irradiates the scintillation crystal, the crystal emits luminescence which passes through or is reflected by the high-reflection layer at least once within the scintillation crystal before it is received by the avalanche photodiode, generating a S detection signal. 5 Summary 3 I 25 The following presents a simplified summary to provide a basic understanding of a © some aspects of various invention embodiments.

The summary is not an extensive O overview of the invention.

It is neither intended to identify key or critical elements of 2 the invention nor to delineate the scope of the invention.

The following summary N merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention.

In this document, the word “geometric” when used as a prefix means a geometric concept that is not necessarily a part of any physical object. The geometric concept can be for example a geometric point, a straight or curved geometric line, a geometric plane, a non-planar geometric surface, a geometric space, or any other 5 geometric entity that is zero, one, two, or three dimensional.

In accordance with the invention, there is provided a new apparatus for detecting radiation such as e.g. gamma rays, X-rays, neutrons, alpha particles, beta particles, and/or other electrically charged or neutral particles. An apparatus according to the invention comprises: - a radiation converter comprising one or more conversion materials for converting radiation at least partly to photons, the one or more conversion materials comprising at least one scintillation material for producing the photons, - a photodetector for detecting the photons, and - a light guide for conducting the photons emitted by the radiation converter, the light guide comprising a first surface on a first side of the light guide and a convex second surface on a second side of the light guide opposite to the first side of the light guide.

The radiation converter constitutes a layer that is parallel and in mechanical contact with the first surface of the light guide, and the photodetector is attached to the light N guide on the second side of the light guide so that the second surface of the light N guide extends from an outer periphery of the photodetector towards an outer S periphery of the light guide. The second surface of the light guide has a reflective S coating for reflecting the photons backwards towards the radiation converter and the E 25 radiation converter is arranged to reflect the photons arriving from the second 3 surface so that the photons are focused to the photodetector.

LO = As the photons are reflected in the above-mentioned way back-and-forth within the N light guide, the photons can be directed to a small area even if the light guide is short in a direction perpendicular to the first surface of the light guide. Therefore, an active surface of the photodetector can be small compared to a radiation reception area of the radiation converter without a need for a long light guide between the radiation converter and the photodetector. Exemplifying and non-limiting embodiments are described in accompanied dependent claims.

Various exemplifying and non-limiting embodiments both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying and non- limiting embodiments when read in conjunction with the accompanying drawings. The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of un-recited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality. Brief description of the figures Exemplifying and non-limiting embodiments and their advantages are explained in greater detail below in the sense of examples and with reference to the accompanying drawings, in which: figures 1a, 1b, and 1c illustrate an apparatus according to an exemplifying and non- limiting embodiment for detecting radiation, N 20 figure 2 illustrates an apparatus according to another exemplifying and non-limiting . embodiment for detecting radiation,

O S figures 3a and 3b illustrate an apparatus according to an exemplifying and non- E limiting embodiment for detecting radiation, and

LO O figures 4 and 5 illustrate details of apparatuses according to exemplifying and non- > 25 limiting embodiments for detecting radiation.

N In the accompanying drawings, an underlined reference number is employed to represent an item over which the underlined number is positioned. A non-underlined reference number relates to an item identified by a line linking the non-underlined number to the item. When a reference number is non-underlined and accompanied by an associated arrow not in contact with any item, the non-underlined reference number is used to identify a general item towards which the arrow is pointing. When areference number is non-underlined and accompanied by an associated arrow in contact with an item, the non-underlined reference number is used to identify a surface of the item. Description of exemplifying and non-limiting embodiments The specific examples provided in the description below should not be construed as limiting the scope and/or the applicability of the accompanied claims. All lists and groups of examples provided in the description are not exhaustive unless otherwise explicitly stated. Figure 1a shows a section view of an apparatus 100 according to an exemplifying and non-limiting embodiment for detecting radiation. Figure 1b shows a front view of the apparatus, and figure 1c shows a back view of the apparatus. The section shown in figure 1a has been taken along a line A-A shown in figures 1b and 1c. The section plane is parallel with the yz-plane of a coordinate system 199. The apparatus 100 comprises a radiation converter 101 that comprises one or more conversion materials for converting incoming radiation at least partly to photons. The one or more conversion materials comprise at least one scintillation material for producing the photons. In figure 1a, the incoming radiation is depicted with wavy line arrows N and some of the photons are depicted with dashed line arrows.

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N N The apparatus 100 comprises a photo-detector 102 for detecting the photons O produced by the radiation converter 101. The photo-detector 102 can be for example I 25 a semiconductor-based photodetector such as e.g. a silicon photomultiplier “SiPM” a © a PIN diode, or an avalanche P/N diode “APD”. A PIN-diode is a diode with a wide, O undoped intrinsic semiconductor region between a P-type semiconductor region 2 and an N-type semiconductor region. The photodetector 102 comprises wirings for N powering and signal read-out. The wirings are not shown in figures 1a-1c.

The apparatus 100 further comprises a light guide 103 for conducting the photons emitted by the radiation converter 101. The light guide 103 can be made of for example transparent polymer.

In many cases, an acrylic based polymer is advantageous but there are also other materials which can be used as the material of the light guide 103, e.g. polyvinyl toluene “PVT”, acrylonitrile butadiene styrene “ABS”, polycarbonate “PC”, polystyrene “PS”, and non-polymers such as e.g. glass, optical silicone, and crystals of other inorganic materials.

The diameter D of the light guide 103 can be, for example but not necessarily, in the range from 10 mm to 100 mm.

In many applications, the diameter can be for example but not necessarily about 30 mm.

The light guide 103 comprises a first surface 105 on a first side of the light guide 103 and a convex second surface 106 on a second side of the light guide opposite to the first side of the light guide.

As shown in figure 1a, the radiation converter 101 constitutes a layer that is parallel and in mechanical contact with the first surface 105 of the light guide 103, and the photodetector 102 is attached to the light guide 103 on the second side of the light guide so that the second surface 106 of the light guide extends from the outer periphery of the photodetector 102 towards the outer periphery of the light guide 103. In this exemplifying case, the light guide 103 has a cavity for the photodetector 102 as it is shown in figure 1a.

The second surface 106 of the light guide has a reflective coating 104 for reflecting the photons backwards towards the radiation converter 101, and the radiation converter 101 is arranged to reflect the photons arriving from the second surface 106 so that the photons are — focused to the photodetector 102. The reflective coating 104 may comprise for S example silver, aluminum, and/or white pigment material e.g. titanium oxide.

As the 5 25 photons are reflected in the above-mentioned way back-and-forth within the light 3 guide 103, the photons can be directed to a small area even if the light guide 103 is E short in the z-direction of the coordinate system 199. Therefore, the active surface 10 of the photodetector 102 can be small compared to the radiation reception area of 3 the radiation converter 101 without a need for a long light guide between the > 30 radiation converter 101 and the photodetector 102. The length L of the apparatus 100 in the z-direction of the coordinate system 199 can be for example from 15 % to 30 % of the diameter D of the light guide 103. The apparatus 100 can be manufactured e.g. in such a way that the three components: the radiation converter 101, the light guide 103, and the photodetector 102 are integrated using e.g. ultraviolet curable acrylic leading to good optical couplings between these components and to good mechanical stability.

In the exemplifying apparatus 100 shown in figures 1a-1c, the radiation converter 101 is a layer on top of the first surface 105 of the light guide 103. It is however also possible that a spatial area of the light guide 103 extending a given distance, e.g. 1 mm, from the first surface 105 towards the second surface 106 and the photodetector 102 has one or more integrated conversion materials and thus the above-mentioned spatial area of the light guide constitutes the radiation converter that is parallel and in mechanical contact with the first surface 105 of the light guide

103. For example, the above-mentioned spatial area of the light guide may comprise particles of the one or more conversion materials so that the particles are mixed with the material of the light guide. An exemplifying case of the kind described above is — illustrated in figure 4 where one of the particles is denoted with a reference 425. In an apparatus according to an exemplifying and non-limiting embodiment, the above-mentioned radiation converter 101 comprises one or more organic scintillator materials such as for example polyethylene napthalate “PEN”, polyethylene terepthalate “PET”, polyvinyltoluene "PVT containing napthalate, and/or polystyrene “PS” containing napthalate. Organic scintillator materials are typically low atomic number materials, i.e. low-Z materials, with densities in the range of about 1 g/cm3. Most of the organic scintillators are doped, and there is a wide choice S of signal photon wavelengths. However, e.g. polyethylene napthalate “PEN” is an K. intrinsic scintillator, and there is no need for activation components, leading to a 3 25 highly competitive pricing of the scintillator material. The organic scintillator I materials are relatively radiation hard. For example, polyethylene napthalate “PEN” E has excellent radiation hardness, up to 1 MGy/year. The radiation to be detected E may comprise for example gamma rays, X-rays, neutrons, alpha particles, beta > particles, and/or other electrically charged or neutral particles. The scintillation N 30 material is selected based on the type or types of the radiation to be detected. Information about plastic scintillators fabricated by a polymerization reaction are presented e.g. by Cheol Ho Lee, et al.: Characteristics of Plastic Scintillators

Fabricated by a Polymerization Reaction, Department of Nuclear Engineering, Hanyang University, 222 Wangsimni-ro, Seongdong-gu, Seoul 04763, South Korea, Nuclear Engineering and Technology 49, 2017, pp. 592-597. In an apparatus according to an exemplifying and non-limiting embodiment, the radiation converter 101 comprises one or more inorganic scintillation material such as for example Gadolinium Aluminum Gallium Garnet "GAGG”, Gd;Al,Gaz0;., doped with cerium Ce, cesium iodide Csl, sodium iodide containing thallium Nal:T, lithium iodide Lil, Cadmium telluride CdTe, cadmium zinc telluride CdZnTe, zinc sulfide containing thallium ZnS:T, and/or zinc selenium containing thallium ZnSe: T. In an apparatus according to an exemplifying and non-limiting embodiment, the radiation converter 101 comprises one or more primary conversion materials for emitting charged particles in response to the incoming radiation and one or more scintillation materials for producing photons in response to the charged particles emitted by the one or more primary conversion materials. The primary conversion materials may comprise for example Boron isotope-10 for detecting neutrons, Lithium isotope-6 for detecting neutrons, Gadolium natural or enriched with isotope- 157 for detecting neutrons, tungsten for detecting gamma radiation and beta radiation, lead for detecting gamma radiation and beta radiation, iron for detecting gamma radiation and beta radiation, copper for detecting gamma radiation and beta radiation, zinc sulfide ZnS for detecting charged particles having a mass at least a mass of a proton, and/or zinc selenium ZnSe for detecting charged particles having a mass at least a mass of a proton.

O N In an apparatus according to an exemplifying and non-limiting embodiment, the S radiation converter 101 comprises support material arranged to mechanically S 25 support the one or more conversion materials including the at least one scintillation E material. The support material can be at least partially optically transparent. The 3 support material can be e.g. suitable polymer. Particles of the one or more O conversion materials can be for example mixed with the support material for > example so that the particles are uniformly distributed within the volume of the support material. It is also possible that the one or more conversion materials are e.g. printed on a surface of a membrane made of suitable support material. In an apparatus according to an exemplifying and non-limiting embodiment, the radiation converter 101 comprises a stack of membranes made of one or more support materials and the one or more conversion materials are on surfaces of the membranes. The membranes are stacked in the z-direction of the coordinate system

199. An exemplifying case of the kind described above is illustrated in figure 5 where the membranes are denoted with references 521 and 522 and the one or more conversion materials are denoted with references 523 and 524. In the exemplifying apparatus 100 illustrated in figures 1a-1c, the first surface 105 of the light guide 103 is planar. The second surface 106 of the light guide 103 can be for example paraboloidal for reflecting light arriving along the negative z-direction of the coordinate system 199 towards a focal point. In figure 1a, the focal point is depicted as a crossing point of dash-and-dot lines and denoted with a reference

120. The photons are however directed to the photodetector 102 as they are reflected off the radiation converter 101 as illustrated in figure 1a with the aid of dashed lines. It is however also possible that the first and/or second surfaces of the light guide have shapes other than the above-mentioned. In other words, the first surface is not necessarily planar, and/or the second surface is not necessarily paraboloidal, but the second surface can be e.g. hyperboloidal or spherical as well. Suitable shapes of the first and second surfaces of the light guide for directing the photons to the photodetector 102 can be found for example with the aid of beam- optical simulations. In the exemplifying apparatus 100 illustrated in figures 1a-1c, the radiation converter N 101 comprises one or more materials capable of reflecting the photons as illustrated . in figure 1a with the aid of the dashed lines. Figure 2 shows a section view of an 3 25 apparatus 200 according to another exemplifying and non-limiting embodiment for I detecting radiation. The apparatus 200 shown in figure 2 is otherwise like the E apparatus 100 shown in figures 1a-1c but a front surface of the radiation converter 3 201, which is facing away from the photodetector 102, comprises a coating 207 that 3 is penetrable by incoming radiation and capable of reflecting photons arriving from N 30 the second surface 106 so that the photons are focused to the photodetector 102 as illustrated in figure 2 with the aid of dashed lines. The coating 207 may comprise e.g. silver, aluminum, and/or white pigment material.

Figure 3a shows a section view of an apparatus 300 according to an exemplifying and non-limiting embodiment for detecting radiation. Figure 3b shows a back view of the apparatus 300. The section shown in figure 3a has been taken along a line A-A shown in figure 3b so that the section plane is parallel with the yz-plane of a coordinate system 399. The apparatus 300 comprises a radiation converter 301 comprising one or more conversion materials for converting radiation at least partly to photons. In this exemplifying case, the radiation converter 301 is a plate-like element and the apparatus comprises a plurality of light guides attached to the radiation converter 301 so that first surfaces of the light guides are attached to a first side of the radiation converter 301. In figure 3a, three of the light guides are denoted with references 303a, 303b, and 303c. Figure 3b shows also a light guide 303d. The apparatus 300 comprises a plurality of photodetectors attached to the light guides. In figure 3a, three of the photodetectors are denoted with references 302a, 302b, and 302c. Figure 3b shows also a photodetector 302d. As shown in figure 3b, the — first surface of each light guide has substantially the shape of a regular hexagon when seen along the geometric optical axis of the light guide under consideration i.e. along the z-axis of the coordinate system 399. In figure 3a, the first surface of the light guide 303a is denoted with a reference 305. The hexagonal shape is advantageous as it provides a coverage without significant gaps between adjacent ones of the light guides. It is also possible that there are separate radiation converters in conjunction with the light guides. Furthermore, it is also possible that each of the light guides comprises integrated one or more conversion materials in the vicinity of the first surface of the light guide under consideration, e.g. particles of N the one or more conversion materials mixed with the material of the light guide.

N 5 25 Powering and signal read-out of the apparatuses 100, 200, and 300 illustrated in 3 figures 1a-1c, in figure 2, and in figures 3a and 3b can be carried out with a E processing system connected to wirings of an apparatus under consideration. The 10 processing system may comprise for example driver circuits, analogue-to-digital 3 converters, and one or more digital processing circuits. Each digital processing > 30 circuit can be a programmable processor circuit provided with appropriate software, a dedicated hardware processor such as for example an application specific integrated circuit “ASIC”, or a configurable hardware processor such as for example a field programmable gate array “FPGA”. Furthermore, the processing system may comprise one or more memory circuits each of which can be for example a Random- Access Memory “RAM” circuit. The specific examples provided in the description given above should not be construed as limiting the scope and/or the applicability of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.

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Claims (17)

What is claimed is:

1. An apparatus (100, 200, 300) for detecting radiation, the apparatus comprising: - a radiation converter (101, 201, 301) comprising one or more conversion materials for converting radiation at least partly to photons, the one or more conversion materials comprising at least one scintillation material for producing the photons, - a photodetector (102, 302a-302d) for detecting the photons, and - a light guide (103, 303a-303d) for conducting the photons emitted by the radiation converter, the light guide comprising a first surface (105, 305) on a first side of the light guide and a convex second surface (106) on a second side of the light guide opposite to the first side of the light guide, wherein the radiation converter constitutes a layer parallel and in mechanical contact with the first surface of the light guide, and the photodetector is attached to the light guide on the second side of the light guide, characterized in that the second surface of the light guide has a reflective coating (104) for reflecting the photons backwards towards the radiation converter and the radiation converter is arranged to reflect the photons arriving from the second surface so that the photons are focused to the photodetector, the second surface of the light guide extending from an outer periphery of the photodetector towards an outer periphery of the light N guide. & N

2. An apparatus according to claim 1, wherein the first surface (105) of the light © guide is planar. = -

3. An apparatus (200) according to claim 1 or 2, wherein a front surface of the 3 25 radiation converter (201) facing away from the photodetector comprises a coating 3 (207) penetrable by the radiation and suitable for reflecting the photons arriving from S the second surface so that the photons are focused to the photodetector.

4. An apparatus (300) according to any of claims 1-3, wherein the first surface (305) of the light guide has substantially a shape of a regular hexagon when seen along a geometric optical axis of the light guide.

5. An apparatus according to any of claims 1-4, wherein the photodetector is a silicon photomultiplier.

6. An apparatus according to any of claims 1-5, wherein the light guide is made of one of the following: acrylic plastic, polycarbonate, optical silicone, glass.

7. An apparatus according to any of claims 1-6, wherein the reflective coating of the second surface of the light guide comprises at least one of the following: silver, aluminum, white pigment material.

8. An apparatus according to any of claims 1-7, wherein the conversion materials comprise primary conversion material for emitting charged particles in response to the radiation and the at least one scintillation material is suitable for producing the photons in response to the charged particles.

9. An apparatus according to claim 8, wherein the primary conversion material comprises at least one of the following: Boron isotope-10 for detecting neutrons, Lithium isotope-6 for detecting neutrons, Gadolium natural or enriched with isotope- 157 for detecting neutrons, tungsten for detecting gamma radiation and beta radiation, lead for detecting gamma radiation and beta radiation, iron for detecting gamma radiation and beta radiation, copper for detecting gamma radiation and beta N radiation, zinc sulfide ZnS for detecting charged particles having a mass at least a N mass of a proton, zinc selenium ZnSe for detecting charged particles having a mass 3 at least a mass of a proton.

O =E 10. An apparatus according to any of claims 1-9, wherein the at least one o 25 scintillation material comprises at least one organic scintillation material.

D O 11. An apparatus according to claim 10, wherein the at least one organic S scintillation material comprises at least one of the following: polyethylene napthalate PEN, polyethylene terepthalate PET, polystyrene PS containing napthalate, polyvinyltoluene PVT containing napthalate.

12. An apparatus according to any of claims 1-11, wherein the at least one scintillation material comprises at least one inorganic scintillation material.

13. An apparatus according to claim 12, wherein the at least one inorganic scintillation material comprises at least one of the following: Gadolinium Aluminum Gallium Garnet GAGG doped with cerium, cesium iodide Csl, sodium iodide containing thallium Nal:T, lithium iodide Lil, Cadmium telluride CdTe, cadmium zinc telluride CdZnTe, zinc sulfide containing thallium ZnS:T, zinc selenium containing thallium ZnSe: T.

14. An apparatus according to any of claims 1-13, wherein particles of the one or more conversion materials are mixed with support material of the radiation converter.

15. An apparatus according to any of claims 1-13, wherein the radiation converter comprises a stack of membranes (521, 522) made of one or more support materials and the one or more conversion materials are on surfaces of the membranes.

16. An apparatus according to any of claims 1-13, wherein the radiation converter comprises particles (425) of the one or more conversion materials mixed with material of the light guide within a spatial area of the light guide extending from the first surface of the light guide a distance towards the second side of the light guide.

17. An apparatus according to any of claims 1-16, wherein the light guide is one of two or more light guides (303a-303d) and the photodetector is one of two or more N photodetectors (302a-302d), the first surfaces of the light guides being attached to

O N a first side of the radiation converter (301) and each of the photodetectors being

NN <Q attached to the second side of a corresponding one of the light guides.

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