Container for radiation detector and detector apparatus

Abstract

Described herein is a container (1) for a radiation detector (2), comprising a cover (4) made of electrically insulating, non-abrasive, non-rigid and elastically deformable material. Said cover (4) is fixed to a housing portion (3) configured to house the radiation detector (2), so as to protect it from impurities by forming an airtight chamber (5).

Description

[0001] CONTAINER FOR RADIATION DETECTOR AND DETECTOR APPARATUS

[0002] DESCRIPTION

[0003] TECHNICAL FIELD

[0004] The present invention relates to the field of radiation detectors, more particularly to containers for such detectors.

[0005] BACKGROUND ART

[0006] Hyperpure -germanium gamma-radiation (HPGe) detectors are known in the art, which are protected from external agents by means of containers fitted with a metal cover, where they are kept in a vacuum or inert atmosphere. Detector containers of this kind are described in documents US5604349, US5646407 and US10107923.

[0007] In brief, the above-mentioned known detector apparatuses consist of a detector operating within a container equipped with a rigid cover having a closing flange. Said closing flange is provided with an access for depressurisation and inert atmosphere intake, and an access for housing an electric feedthrough whereto a getter is applied.

[0008] The Applicant observed that such detector containers suffer from some drawbacks, which will be discussed below.

[0009] A problem concerns geometric efficiency. Detectors are typically assembled side by side as close as possible to each other in order to reduce the so-called dead zone between them, i.e. insensitive gaps that are not covered by detectors. This is useful to maximise the angular coverage of the detector apparatuses. According to the prior art, this dead zone cannot be reduced to zero because of the rigid metal cover and the free space necessary to avoid that the cover might trigger a short-circuit in the electric contacts. Since dead-zone space is not sensitive to incident radiation, the detector’s geometric efficiency decreases.

[0010] Another limitation relates to detection quality. Containers according to the above- mentioned prior art attenuate by absorption and deviate by scattering the incident beam, and, upon excitation of their cores, emit decay gamma rays, which increase the background radiation in the detector. These undesired effects translate into a reduction in the quality of the measured energy spectra and contamination of the same with undesired spurious backgrounds. The Applicant observes that such phenomena are greatly dependent on the thickness of the rigid cover in use. They also depend on the material of the cover. Document US10107923 describes the use of alloys of magnesium, aluminium, titanium or manganese. Such alloys are composed of atoms with many electrons (12, 13, 22, 25, respectively) and have a high density (1.7 g / cm3, 2.7 g / cm3, 4.5 g / cm3, 7.2 g / cm3, respectively). These characteristics increase the probability that a photon (or another particle of the incident radiation capable of producing secondary radiation) will interact with the cover. Moreover, since the detector’s surface houses electric contacts, the Applicant observes that the prior-art container must also include a spacer made of electrically insulating material (e.g. ceramic or polyimide) separating it from the contacts. Just like the cover, this material contributes to the above-mentioned effects that reduce the quality of the detection.

[0011] As concerns the subsequent signal analysis, the Applicant observes that the geometry and thickness of prior-art containers, insulating spacers and gaps between the cover and the detector are not homogeneous with respect to the detector’s shape. Furthermore, the materials of the spacer and of the cover are not homogeneous as well. These differences make the calculations and simulations (e.g. carried out by using Monte Carlo methods) that are necessary for correctly analysing the data produced by prior-art detection apparatuses more complex and less accurate.

[0012] In prior-art detector apparatuses, the Applicant also noticed some problems related to the assembly process. As previously mentioned in relation to geometric efficiency, the electric contacts connected to the prior-art detector have to be electrically insulated from each other to prevent short-circuits and allow the detector to operate properly. The prior- art cover is electrically conductive, and is insulated by leaving a free space between the contacts and the inner surface of the container. Due to the above-mentioned issues related to geometric efficiency, the free space must preferably be as small as possible (typically a few tenths of a millimetre). This results in the assembly process being quite difficult because, when the detector is inserted in the rigid cover, it may happen that, the available space being very narrow, the detector will scrape against the cover, so that the continuity of the electric contacts may be jeopardised and the surface of the detector may be damaged, since it includes delicate components of nanometric thickness.

[0013] The Applicant also noticed a problem related to the closing flange employed in the above-mentioned known containers. The signals coming from the electric contacts of the detector are brought outside the container by means of electric feedthroughs going through the closing flange. Such electric feedthroughs are welded onto bores formed in the closing flange, which is coupled to a counter-flange of the rigid cover. In more detail, the Applicant observes that, for the welding operation to be executed correctly, the closing flange should be made of stainless steel, because the external necks of all standard electric feedthroughs are made of such material. Moreover, the counter-flange of the rigid cover should also be made of the same material as the closing flange (i.e. stainless steel) to avoid sealing problems. Sealing problems may arise, in fact, when two different materials are used, because of different roughness and hardness of the contact surfaces or different thermal expansion coefficients, which may lead to significant misalignments when the apparatus is in operation (typically, these detectors are assembled at room temperature and then operate at cryogenic temperatures). However, the rigid cover of the known containers discussed herein cannot be made of stainless steel because this material absorbs gamma rays, thus essentially preventing them from interacting with the detector. The Applicant noticed that, if the closing flange were made from the same material as the rigid cover (i.e. aluminium, titanium, magnesium or manganese alloy), problems would arise when welding the electric feedthroughs. On the other hand, a cover made of stainless steel would solve the welding problems, but sealing problems would then arise.

[0014] As concerns the positioning of the detector in the container, the Applicant observes that the detector needs to be held in position in its seat, whatever the installation direction (relative to the force of gravity), by means of a thrust mechanism (e.g. a spring or a threaded support having a known load) located in the rear part of the detector, which pushes the detector against the insulating spacer and the rigid cover. The Applicant noticed that this mechanism has some drawbacks. In the first place, such a mechanism exerts thrust through an insulating support used to prevent contact with the rear part of the detector, which has been subjected to a delicate passivation treatment. Therefore, mounting this component to the thrust mechanism is quite a difficult task, with a high risk of damaging the detector in the very part thereof which has said delicate passivation treatment. In the second place, in the front part of the detector the electric contacts need to be insulated from the rigid metal cover, as previously described herein. As a consequence, between the inner surface of the cover and the electric contacts an insulating spacer is interposed, which leads to the above-mentioned signal distortion.

[0015] The Applicant also observes that the prior-art container has a cover that, being rigid and closely adhering to the detector, is typically custom-designed, implying higher production times and costs. Furthermore, the technology of semiconductor detectors is constantly evolving, and existing systems are often updated with more modern detectors having different geometries. Therefore, the prior-art container is seldom suitable for housing a newly updated detector.

[0016] SUMMARY OF THE INVENTION

[0017] The present invention tackles the problem of providing a container for a radiation detector which can be used as an alternative to those currently known in the art, and which solves, at least partly, the above-described problems suffered by the prior art. According to one aspect, the present invention relates to a container for a detector as set out in claim 1 and in accordance with some preferred embodiments thereof as described in claims 2-13. According to another aspect, the present invention relates to a detector apparatus as set out in claim 14 and in accordance with some preferred embodiments thereof as described in claims 15-16.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be described in detail below, by way of non-limiting example, with reference to the accompanying Figure 1, which shows a cross-sectional view of a radiation detector apparatus comprising a container made in accordance with one exemplary embodiment of the present invention.

[0020] DETAILED DESCRIPTION

[0021] Figure 1 shows a sectional view of a detector apparatus 100 according to a particular embodiment. The detector apparatus 100 comprises a container 1, in which a radiation detector 2 is arranged.

[0022] In particular, the radiation detector 2 is suitable for detecting radiations such as y rays or X rays. According to other embodiments, the radiation detector 2 may be designed to detect high-energy corpuscular radiation, e.g. cosmic muons.

[0023] In addition, the detector 2 operates in a vacuum and / or in an inert atmosphere, i.e. a chemically inactive environment created in the container 1. In order to make an inertatmosphere chamber, it is necessary to create a vacuum and then fill the chamber with an inert gas (typically high-purity argon), i.e. a gas not reacting chemically with it or with its contents.

[0024] It should also be noted that, for particular applications, the detector apparatus 100 will have to operate at cryogenic temperatures, i.e. temperatures below 120 K (-153.15 °C). Therefore, the detector 2 may be of a type suitable to withstand such temperatures.

[0025] In particular, the detector 2 is of the type capable of outputting electric signals or light pulses, the characteristics of which are dependent on the radiation hitting it. For example, the detector 2 is of the type operating according to one of the following effects: photoelectric effect, Compton effect, pair production.

[0026] Furthermore, the detector 2 is, for example, a semiconductor detector. According to a preferred embodiment, the semiconductor detector 2 is a germanium (Ge) detector, in particular hyperpure germanium (HPGe) detector. Silicon (Si), cadmium-zinc telluride (CZT), gallium arsenide (GaAs) or cadmium telluride (CdTe) detectors may be used as well.

[0027] It should be noted that the detector 2 made of hyperpure germanium can be used for detecting y rays, and hence for high-resolution y spectroscopy. The hyperpure germanium detector 2 can be designed with volumes on the order of one cubic centimetre and completely depleted of charge carriers with bias voltages on the order of one kV. The hyperpure germanium detector 2 has high density and atomic number, which lead to high efficiency in detecting y radiation. Moreover, the hyperpure germanium detector 2 has high energy resolution, on the order of one part per thousand, at typical energies of use (on the order of one MeV).

[0028] In an embodiment which is alternative to the use of semiconductors, the detector 2 is a scintillation detector made of, for example: bismuth germanate (BGO), caesium iodide (CsI), lanthanum bromide (LaBr), or CLYC.

[0029] In particular, the detector apparatus 100 can be used in the fields of research (e.g. gamma-ray spectroscopy, nuclear research), inspection (e.g. detection of radioactive metals at borders, anti-terrorism), medicine (e.g. diagnostics, dosimetry, nuclear medicine, imaging). Other applications may include: protection against radiation, environmental monitoring, non-destructive testing of materials, industrial production control, and space research.

[0030] The container 1 includes a housing portion 3 and a cover 4. The cover 4 is fixed to the housing portion 3 so as to form a chamber 5, in which the detector 2 is arranged. It is in this chamber 5 that a vacuum or an inert atmosphere is created.

[0031] The container 1, including both the cover 4 and the housing portion 3, performs the function of protecting the detector 2 from any impurities (including moisture) that may be present in the environment where it will operate.

[0032] The cover 4 is made of electrically insulating, non-abrasive, non-rigid and elastically deformable material. In particular, the cover 4 is manually deformable and, once mounted, assumes a shape substantially similar to that of the detector. Moreover, the cover 4 may be made of a material that maintains its structural strength even at cryogenic temperatures.

[0033] For example, said material is a polymer, in particular an elastomer such as polyisoprene or poly-dimethylsil oxane (PDMS). These materials offer the advantage of maintaining good structural strength even at cryogenic temperatures, so long as such temperatures are reached gradually, and the application is static.

[0034] Other polymers that may be used in order to facilitate the installation of the cover 4 are heat-shrinkable ones (e.g. polyethylene), the adaptation of which to the detector’s geometry is facilitated by heating.

[0035] According to a particular embodiment, the cover 4 may be pre-formed to match the geometry of the detector 2 before being mounted to the housing 3.

[0036] According to one embodiment, the cover 4 has a thickness on the order of hundredths of a millimetre, typically ranging between 0.01 mm and 0.10 mm and may be shaped, depending on the geometry of the detector 2, as a cylinder, a parallelepiped, or other geometric solids.

[0037] The housing portion 3 is a rigid body made up of several sub-portions, and is provided with fixing devices adapted to act upon a peripheral region (i.e. the edges) of the cover 4 to fasten it to the housing portion. In particular, the cover 4 is so arranged that a part thereof is in direct contact with at least one wall of the detector 2, while its outer edges are anchored to the housing portion 3 by the fixing devices 3. It should be noted that, even after a vacuum has been created in the chamber 5, the cover 4 will adhere, at least partially, also to the side walls of the detector 2.

[0038] In accordance with the example shown in Figure 1, the housing portion 3 comprises a base or flange 6, such as a metal plate (preferably made of stainless steel) having, for example, a circular shape, and delimiting the chamber 5 at the bottom (with reference to the illustrative orientation shown in Figure 1).

[0039] In the illustrated example, the base 6 comprises through-bores 8 for electric conductors 9 intended to connect the detector 2 to an external conditioning device (frontend electronics), not shown in the drawing. Advantageously, the base 6 also acts as a removable closing flange of the container 1.

[0040] In particular, the base 6 is also provided with two bores. An access bore 18 permits depressurising the chamber 5 (and possibly admitting inert atmosphere), and is typically closed by a valve. A passage bore 21 permits inserting an electric feedthrough whereto a getter is applied to assist vacuum formation and conservation.

[0041] The housing portion 3 is also provided with an annular flange 7 lying on top of and secured to the base 6 at the latter’s outer edges. The annular flange 7, which delimits the chamber 5 laterally, may advantageously be made of the same material used for the base

[0042] 6.

[0043] For example, the flange 7 is fixed to the base 6 by means of first clamping screws 16 that go through respective threaded holes formed in the base 6 and in the annular flange

[0044] 7. A gasket 10, e.g. arranged in an annular seat formed in the base 6 under the flange 7, ensures an airtight mechanical coupling between the base 6 and the flange 7.

[0045] Furthermore, according to the example illustrated herein, the housing portion 3 comprises a fixing flange 19 (annular in shape and preferably made of the same material as the flange 7) adapted to press the edge of the cover 4 against a wall of the flange 7 under the action of second fixing screws 17. The fixing flange 19 is just one possible example of a means for fastening the cover 4 to the flange 7. As an alternative to the use of the fixing flange 19, the cover 4 may be directly fixed to the flange 7 by gluing or vulcanisation.

[0046] In addition, the housing portion 3 may comprise a support structure 11 arranged inside the chamber 5 to support the detector 2 and hold it in a fixed position. For example, said support structure 11 comprises a rigid support made of electrically insulating material 12, on which the detector 2 directly rests, arranged on a prop 13 resting on an inner wall of the base 6. Said support structure 11 may also be non-height-adjustable.

[0047] The cover 4 is so positioned as to close the chamber 5 at the front and at the sides, and has, in the example of Figure 1, its outer edge inserted between the flange 7 and the fixing flange 19. It should be noted that, according to some illustrative embodiments, the chamber 5, closed by an individual cover 4, may house more than one radiation detectors 2, forming a so-called cluster detector.

[0048] The detector 100 comprises also electric contacts 20 disposed in contact with the outer walls of the detector 2 and also in contact with an inner face of the cover 4. Such electric contacts 20 are connected to the electric conductors 9.

[0049] The above-described container 1 offers numerous advantages over the prior art.

[0050] One advantage is geometric efficiency. The cover 4 can be constructed, as described, with a reduced thickness (e.g. on the order of hundredths of a millimetre) and in such a way as to be in contact with a large portion of the walls of the detector 2. This makes it possible to arrange multiple detectors (e.g. the components of an array) side by side, thereby improving geometric efficiency.

[0051] Another advantage is related to detection quality. For several reasons, the container considerably reduces the attenuation and scattering of the incident radiation beam, as well as background radiation. Being electrically insulating, the cover 4 does not require, unlike the prior art, the insertion of any spacers between the front part of the detector and the cover itself. Moreover, as already remarked, the cover 4 may have, in both its front part and lateral part, a thickness on the order of hundredths of a millimetre, which is more than ten times less than the thickness of the rigid metal cover according to the prior art. It should be noted that the cover 4 may be made from polymers, the density of which is on the order of tenths of a gramme per cubic centimetre, i.e. ten times less than that of the metals used for making the rigid cover according to the prior art. All this keeps detection quality high.

[0052] Another advantage concerns the subsequent analysis of the electric signal provided by the detector. By using the cover 4 it is possible to coat almost the entire surface (front and rear) of the detector 2 with one same material of homogeneous thickness (without any spacers in between), and this makes for less complex and more accurate calculations and simulations (e.g. carried out using the Monte Carlo methods).

[0053] The container 1 offers some advantages also as far as installation is concerned, since the cover 4, which is made of non-abrasive material, can be simply and safely laid directly on the contacts 20 of the detector 2, to which it will adhere perfectly, thus being also useful to hold them in place.

[0054] It should be noted that another advantage consists of the possibility of using the same material (e.g. stainless steel) for the base 6, for the flange 7, and for the optional fixing flange 19. These solutions can prevent problems that would otherwise arise if different materials (having different roughness, hardness and expansion coefficients) were placed in contact with each other, e.g. imperfect sealing of the chamber 5.

[0055] Furthermore, the cover 4 is made of a non-rigid material which can elastically deform, pressing on the detector 2 and holding it in place, thus avoiding the need for using a thrust mechanism on the detector. In addition, since this material is electrically insulating, it can be made to press directly onto the front part of the detector 2 without requiring the interposition of a spacer.

[0056] It should also be noted that, as a further advantage, the cover 4 can be easily adapted to detectors having different dimensions and geometries.

[0057] List of references identifying the components of Figure 1 detector apparatus 100 container 1 radiation detector 2 housing portion 3 cover 4 chamber 5 base 6 flange 7 through-bores 8 electric conductors 9 gasket 10 support structure 11 rigid support 12 prop 13 first clamping screws 16 second clamping screws 17 first bore for vacuum pump access / inert gas intake 18 fixing flange 19 electric contacts 20 second bore for getter feedthrough 21

Claims

CLAIMS1. Container (1) for a radiation detector (2), comprising: a housing portion (3) configured to house the radiation detector (2); a cover (4) fixed to the housing portion (3) so as to protect the detector (2) from impurities, the cover (4) and the housing portion (3) forming an airtight inner chamber (5), wherein: said cover (4) is made of an electrically insulating, non-abrasive, non-rigid and elastically deformable material.

2. Container (1) according to claim 1, wherein the material of the cover (4) is a polymer.

3. Container (1) according to claim 2, wherein the material of the cover (4) is an elastomer.

4. Container (1) according to claim 3, wherein the material of the cover (4) is selected from: poly-isoprene, poly-dimethylsiloxane.

5. Container (1) according to claim 2, wherein the material of the cover (4) is a heat- shrinkable material.

6. Container (1) according to claim 1, wherein the cover (4) has a homogeneous thickness ranging between 0.01 mm and 0.10 mm.

7. Container (1) according to claim 1, wherein the airtight inner chamber (5) is configured for creating an inert atmosphere or a high vacuum.

8. Container (1) according to claim 1, wherein the housing portion (3) comprises: a base (6) intended to support the detector (2); a flange (7) mechanically coupled to the base (6), and to which a peripheral region of the cover (4) is fixed; a sealing gasket (10) interposed between the base (6) and the flange (7).

9. Container (1) according to claim 8, wherein the peripheral region of the cover (4) is fixed to the flange (7) by vulcanisation or gluing.

10. Container (1) according to claim 8, wherein the housing portion (3) further comprises a fixing flange (19) mechanically coupled to the flange (7), wherein the peripheral region of the cover (4) is interposed between the flange (7) and the fixing flange (19), and is fixed to the flange(7) by mechanical compression by means of clamping screws (17).

11. Container (1) according to claim 8, wherein the housing portion (3) further comprises: a support structure (11) positioned on the base (6) inside the chamber (5); said support structure (11) comprising a rigid support made of electrically insulating material (12), on which the detector (2) directly rests.

12. Container (1) according to claim 1, wherein said housing portion (3) comprises a first bore (18) for depressurising the chamber (5) and / or a second bore (21) for inserting a getter feedthrough.

13. Container (1) according to claim 1, wherein said housing portion (3) comprises bores(8) for electric conductors (9) .

14. Detector apparatus (100) comprising: a radiation detector (2); a container (1) defined by at least one of the preceding claims, and in which the detector (2) is arranged.

15. Detector apparatus (100) according to claim 14, wherein said detector (2) is made of a semiconductor material selected from the group including: germanium, hyperpure germanium, silicon, cadmium-zinc telluride, gallium arsenide, cadmium telluride.

16. Detector apparatus (100) according to claim 14, wherein said detector (2) is made of a scintillator material.

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