TECHNICAL FIELD OF THE INVENTION

The invention relates to a detector for detecting neutrons and X- and/or gamma ray photons, as well as also a method for manufacturing said detector. In addition, the invention relates to an imaging apparatus for providing an image of an object to be imaged by using at least one of said detectors.

BACKGROUND OF THE INVENTION

Detectors are known from the prior art for detecting, tracking, and/or identifying photons, ionizing particles, or neutrons. In order to register neutrons, the detector should be provided with neutron reactive material to interact with neutrons and to produce ionizing radiation reaction products, such as a-particles or conversion electrons. The ionizing radiation reaction products can then be determined e.g. by semiconducting elements where the ionizing radiation reaction products generate electrical charges proportional to the energy of the ionizing radiation reaction products.

The neutron detectors are typically designed to be minimally sensitive to X-ray or gamma ray photons. This is because most of the neutron sources or reactions are accompanied by a gamma or X-ray background radiation which interacts with the semiconductor material of the detectors and thereby tend to disturb the neutron measurement, which is an undesired effect especially in connection with the neutron imaging. Thus the prior art neutron detectors should be sensitive for detecting the neutrons but at the same time "transparent" for the background gammas and/or X-rays.

Detectors for detecting X-ray or gamma ray photons are minimally sensitive to neutrons, because neutrons do not interact with the semiconductor materials. Several imaging apparatuses using the prior art detectors are able to register either neutrons or X-ray / gamma ray photons, but not both simultaneously. Accordingly, these imaging apparatuses are blind to certain features or structures of the object to be imaged, and only limited image data can be gathered. For example, all features of an object comprising e.g. both metals (or other high Z materials) and e.g. plastics (or other low Z materials) cannot be imaged, since neutrons will preferentially interact with the low Z materials, whereas X-ray or gamma ray photons will interact preferentially with the high Z materials. Thus, when using X-ray or gamma ray photons, only portions having high Z materials can be detected such as metals, and vice versa, when using neutrons only portions having low Z materials such as plastics can be detected.

Only few detectors that are able to measure both neutrons and X-ray / gamma ray photons are known from prior art. For example, US 8,022,369 and US 8,263,940 disclose a detector which includes a neutron converter, a thin semiconductor element and a thick semiconductor element. Since these detectors are able to detect neutrons as well as X-ray and gamma photons, they are suitable for use in imaging apparatuses. However, there are important drawbacks relating to these prior art detectors, namely in aligning and calibrating two or more physically separate semiconductor elements. To fulfil these requirements tend to be a challenging task, and adds to the manufacturing costs.

SUMMARY OF THE INVENTION An object of the invention is to alleviate and eliminate the problems relating to the known prior art. Especially the object of the invention is to provide a detector, which can be used for detecting both neutrons as well as X- and gamma ray photons and thereby use said detector e.g. for imaging objects consisting of different materials. In addition an object of the invention is to provide said detector so that signals of possible undesired background X- and/or gamma ray photons can be ignored in order to further improve e.g. the X-ray or gamma rejection ratio of the detector when used as a neutron detector. The object of the invention can be achieved by the features of independent claims. The invention relates to a detector for detecting neutrons and X- and gamma ray photons according to claim 1 and to system for detecting neutrons and X- and gamma ray photons according to claim 15. In addition the invention relates to an imaging apparatus using said detector according to claim 16, as well as a method for manufacturing the detector according to claim 17.

Accordingly, the detector of the present invention comprises a single semiconductor element, which is a high resistivity material, such as n type or p type Si wafer (Silicon), GaAs (gallium arsenide) or CdTe (cadmium telluride) wafer or SOI (Silicon On Insulator) wafer. The whole single semiconductor element is of same material. The single semiconductor element is electrically divided into two portions, namely a first portion and a second portion, which is preferably thicker than said first portion. As an example the first portion is typically within a range of only about 1 -30 μιη and the second portion is typically within a range of 100 pm up to 5 mm. It is to be known that said two portions are still portions of said single semiconductor element and thus not physically separate parts.

The thickness of the first portion depends for example on the neutron converter material used in the detector, and what kinds of ionizing radiation reaction products are generated in the interaction of the neutrons with the neutron converter material, as well as on the material of the semiconductor element, i.e. on the material of the first portion. For example if the neutron converter material is boron, the generated ionizing radiation reaction products are able to travel about 5 μιτι in silicon at maximum, whereupon the thickness of 5 μιτι for the first depletion layer is optimum. When the neutron converter material is lithium, tritons are generated, which travel about 40 μιτι in silicon, whereas conversion electrons generated by gadolinium can travel about 30 μιτι. It is to be noted that if the X-ray or gamma sensitivity of the first portion should be very low, one appropriate neutron converter material is boron, whereupon the first depletion layer might be very thin, such as about 5-10 μιτι, which is suitable for the ionizing radiation reaction products generated in boron. Another parameter when determining the thickness of the first depletion layer is capacitance formed between the layers, namely the thinner the first layer the bigger is the capacitance and thus poorer the signal to noise ratio. According to an embodiment of the invention a detector for neutrons and X- and gamma ray photons comprises a single semiconductor element, which is advantageously a high resistivity material, preferably selected from a group comprising: n type or p type Si wafer (silicon), GaAs (gallium arsenide) or Cd or SOI (Silicon On Insulator) wafer. Most advantageously the whole single semiconductor element is a monolithic semiconductor element and of same material. The single semiconductor element is defined by two depletion layers, namely a first depletion layer and a second depletion layer.

According to an example the second depletion layer is thicker, such as one or two orders thicker than said first one. As an example, thickness of the first depletion layer is configured according to an exemplary embodiment to be so thin that it is practically insensitive to said photons but at the same time effective to interact with said ionizing radiation reaction products of neutrons, such as a-particles, and is advantageously in the range of 1-100 μιτι, more advantageously 1-50 μιτι, and most advantageously 1-10 μιτι. In addition as an example thickness of the second depletion layer of said semiconductor element is according to an exemplary embodiment thicker than the thickness of said first depletion layer, and is advantageously 100 μιτι - 5 mm, more advantageously 200 μιτι - 5 mm, and most advantageously 300 μιτι - 1 mm. However it is to be noted that the invention is not limited to these examples but also other configurations may be applied.

According to an example, the first depletion layer is implemented electrically, such as e.g. by electrodes or by doping (introducing the acceptor and/or donors into semiconductor, may be implemented e.g. by diffusion or ion implanting as an example), on a first portion of said semiconductor element so that said first depletion layer defines said first portion of said single semiconductor material. According to an embodiment said first depletion layer is essentially transparent for X-ray and gamma ray photons, which may be achieved for example by the thickness of said first layer.

The second depletion layer is implemented electrically, such as e.g. by electrodes or by doping ( introducing the acceptor and/or donors into semiconductor, may be implemented e.g. by diffusion or ion implanting as an example), on a second portion of said semiconductor element so that said second depletion layer defines said second portion of said single semiconductor material. According to an embodiment said second depletion layer is configured to interact with the X-ray and gamma ray photons. This may be achieved via its thickness whereupon the interaction probability is much higher and proportional to the thickness.

The detector comprises, when to be used for detecting neutrons, also a layer (typically in the range of 1 -10 μιτι) of neutron reactive material in/on or connection with the first portion (or first side) of said semiconductor element for interacting with neutrons incident thereon to be detected. The neutron converter material used with the detector may be for example: enriched boron ¹⁰ B, lithium ⁶ Li, gadolinium ¹⁵⁵ Gd, ¹⁵⁷ Gd, or natural Gd, cadmium ^{1 13} Cd, cadmium telluride (CdTe), cadmium zinc telluride (CdZnTe), or composite materials based on boron nitride (BN), boron carbide ( ⁴ BC), boron oxide (B2O3), gadolinium oxide (Gd2Os) or lithium fluoride (LiF) deposited e.g. on top of or inside the first side of the semiconductor element to capture neutrons.

When neutrons interact with the neutron reactive material they release ionizing radiation reaction products, such as a-particles accompanied by X-ray or gamma ray photons responsive to interactions with the incident neutrons. According to an embodiment the first depletion layer is configured to interact with said ionizing radiation reaction products (e.g. a-particles) and generate electrical charges proportional to the energy of said ionizing radiation reaction products responsive to interactions with said incident neutrons. The charges are then collected by charge collecting means or regions. The X-ray or gamma ray photons interact advantageously with the second depletion layer, whereupon said second depletion layer is configured to provide electrical charges proportional to the energy of said photons responsive to interaction of said photons with said second depletion layer. The charges are then collected from said second depletion layer by charge collecting means or regions. The X-ray or gamma ray photons might originate from the interactions of the neutrons with said neutron converter material or they might as well be background photons. In addition, especially in connection with imaging purposes the X-ray or gamma ray photons may be produced by corresponding X-ray or gamma ray source.

The produced charges are advantageously collected by the charge collecting means or regions and corresponding electrodes arranged in connection with an appropriate portion of the semiconductor element. The charge collecting regions may be implemented by doping or ion implanting regions into the portions of the semiconductor element, whereupon the charges are collected from that regions defined by the doping or ion implanting. Sometimes these regions from where the charges are collected are called also as pixels. The electrodes are then electrically coupled with said charge collecting regions in order to gather said charges collected by the charge collecting regions. The electrodes function as electrical contacts between the charge collecting regions and the signal readout electronics. It is to be noted that each portions or layers of the semiconductor element may comprise dedicated charge collecting regions and electrodes. The invention relates also to a method for manufacturing the detector with a single semiconductor element described in this document, where the single semiconductor element comprises said first portion and second portion. In the method neutron reactive material, if needed, is arranged in/on or connection with the first portion of said semiconductor element by applying a surface deposition method, such as ion implantation, laser ablation, atomic layer deposition (ALD), photolithography or sputtering technique, as an example. In addition an electrically implemented depletion layer is arranged on the first portion of said semiconductor element to interact with ionization reaction products as well as a second depletion layer to interact with X-ray and gamma-ray photons. Also the charge collecting means or regions are arranged (e.g. doped, ion implanted, by ALD or the like) in connection with said first portion and/or said second portion of said semiconductor element to collect charges generated in said portions proportional to the energy of said interactions, as discussed elsewhere in this document.

In addition, the invention relates to an imaging apparatus using any detector described in this document, whereupon the imaging apparatus is capable of imaging features of objects consisting of different materials, like metals and plastics. The imaging apparatus, whether it is for scanning purposes or imaging still or video images, may comprise one or more detectors for interacting with X- ray and gamma-ray photons, as is described elsewhere in this document. In addition the imaging apparatus may also comprise any other suitable and appropriate signal readout and processing electronics, as well as control electronics for controlling the readout process of the detectors and image formation processes.

The detector according to embodiments of the invention offers clear advantages over several prior art detectors, such as simultaneously and independently detecting both, X-rays / gamma rays and neutrons. Again when the first depletion layer responds to neutrons but not to X-rays / gamma rays and the second depletion layer detects X-rays / gamma rays but is transparent to neutrons, the neutrons and photons do not disturb each other's detection. The detector structure, in addition, has two distinct benefits in comparison to the state of the art. In imaging applications simultaneous acquisition of neutron and X- ray / gamma ray images of the same object reveals complementary details of the object both in the "low" and "high" contrast region. In detection of low intensity neutron radiation present in high gamma backgrounds the X- and gamma ray sensitive portion can be used for background detection and subtraction to further improve the X-ray / gamma-ray rejection ratio of the neutron detector. Moreover, since the detector according to the invention utilises a single monolithic semiconductor element for both X-ray / gamma ray and neutron detections, the focusing, as well as alignment and calibration of the detector, is straightforward when compared the devices which have number of different separate semiconductor elements coupled with each others. The above also decreases the overall manufacturing costs.

BRIEF DESCRIPTION OF THE DRAWINGS

Next embodiments will be described in greater detail with reference to exemplary embodiments in accordance with the accompanying drawings, in which:

Figures 1-2 illustrate an exemplary detector for detecting neutrons as well as X- ray and gamma ray photons according to an advantageous embodiment of the invention;

Figure 3 illustrates an exemplary detector with edge doping added to the sides of the detector to extend the active region to the physical chip periphery according to an advantageous embodiment of the invention;

Figure 4 illustrates (top view) an exemplary detector for detecting, neutrons as well as X-ray and gamma ray photons according to an advantageous embodiment of the invention;

Figure 5 illustrates an exemplary detector with simulated electric field lines between the p and n pixels (like doped or ion implanted areas) on the front side according to an advantageous embodiment of the invention;

Figure 6 illustrates an exemplary detector with 3D trenches for enhanced neutron detection efficiency according to an advantageous embodiment of the invention;

Figure 7 illustrates an exemplary detector with connections for signal readout electronic according to an advantageous embodiment of the invention; Figure 8 illustrates an exemplary detector with signal readout electronic according to an advantageous embodiment of the invention; and

Figure 9 illustrates an exemplary detector with bond elements and grooves arranged on the semiconductor element surface and filled with neutron reactive material according to a, possibly advantageous, embodiment of the invention.

DETAILED DESCRIPTION Figures 1-9 illustrate an exemplary detector 100 for detecting both neutrons as well as X-ray and gamma ray photons according to an advantageous embodiment of the invention. According to an exemplary embodiment the detector can be realised with a double sided planar process on a single high resistivity monolithic semiconductor element 101 , such as n type silicon wafer, for example, which is electrically divided to a first depletion layer 101 a and a second depletion layer 101 b as described elsewhere in this document. The first depletion layer 101 a is advantageously implemented electrically on the first side (Fig. 1 ) of said semiconductor element 101 to define said first portion 101 a, and second depletion layer 101 b on the second side (Fig. 2) of said semiconductor element 101 to define said second depletion portion 101 b on the second side (Fig. 1 ) of the same single semiconductor element 101 . The detector 100 can be designed as a single channel device for simple detection of the presence of radiation, or alternatively in more complex multi-channel such as pixel (as described in figures) or strip configurations for imaging applications, for example.

The dividing may be implemented e.g. by doping, such as is illustrated in connection e.g. with Figures 1 , 2 and 3, where, as an example, p or p+ region or pool may be provided into/onto the surface of n-type element with n+ pixels, for example, whereupon the element comprises two depletion layers (and non- depletion layer between said two depletion layers).

According to another embodiment the dividing may also be implemented e.g. by electrodes or alternating doped n+ and p+ contacts in the first side of the semiconductor element 101 , and a uniform n+ region in the other side of the element, for example, whereupon there is one depletion layer and the charges are guided by the electric field so that charges generated in the vicinity of the first side are guided from the region between the n+ and p+ contacts, and the charges generated in the deeper region are guided into the other side of the semiconductor element. However it is to be noted that these examples for dividing the semiconductor element to depletion layer(s) are only examples and that the invention is not limited to those but also other techniques can also be used for the same purpose.

In addition, the detector comprises neutron reactive material 106 (shown e.g. in Figures 3 and 8) in, on and/or in connection with the first portion 101 a or first side of said semiconductor element 101 for interacting with neutrons incident thereon to be detected and to release ionizing radiation reaction products (e.g. a-particles) responsive to interactions with said incident neutrons.

The first portion 101 a is configured to interact with said ionizing radiation reaction products or secondary radiation (a-particles or conversion electrons) following the neutron capture with the neutron reactive material, and provide electrical charges (e ^" ) proportional to the energy of said ionizing radiation reaction products responsive to interactions with said incident neutrons.

The second portion 101 b of said semiconductor element is configured to interact with the X- and gamma ray photons and provide electrical charges (e ^" ) proportional to the energy of said photons responsive to interactions with said photons.

The first 101 a and/or second 101 b portions of the semiconductor element 100 comprises advantageously plurality of charge collecting regions 102, 104, coupled with electrodes, so that the electrical charges generated in the corresponding portion of the semiconductor element are collected by the nearest charge collecting region, whereupon the location of the generated electrical charge can be determined based on the location of the charge collecting region and/or electrode(s) coupled with said charge collecting region and collecting said electrical charges.

According to an embodiment the charge collecting regions are doped in/on the first depletion layer and in/on the second depletion layer of said semiconductor element and isolated from each other by so called floating stops 105, which are advantageously doped regions configured to prevent charge flow between the adjacent charge collecting regions. According to an embodiment the first side of the detector comprises n+ charge collecting regions (i.e. pixels) 102 doped in the p+ type well, square or circular ring 103. The second side of the detector comprises n+ charge collecting regions (i.e. pixels) 104 electrically isolated with the floating p+ stops 105. An alternative realisation of the detector 100 is manufactured on a high resistivity p type semiconductor (e.g. silicon wafer), where the p+ charge collecting regions (pixel) and n+ charge collecting regions (e.g. in a strip form) are arranged on the first side of the detector and p+ charge collecting regions (pixels) with n+ isolation to prevent charge flow between the adjacent charge collecting regions on the second side.

The charge collecting regions 102, 104 are configured to collect said electrical charges a) from the first depletion layer 101 a (with regions 102) and b) from said second depletion layer 101 b of said semiconductor element 101 (with regions 104) and thereby to provide electrically readable signal proportional to said collected electrical charges. Electrical charges collected from the first depletion layer 101 a are responsive to interactions with the neutrons and electrical charges collected from the second depletion layer 101 b are responsive to interactions with X- and gamma ray photons. Thus the second portion 101 b of the detector 100 is responsive only to signals induced by X-ray and gamma ray photons.

The thickness of the first depletion layer 101 a of the first side p+n+ junctions is according to an exemplary embodiment very thin compared to the second depletion layer and thus the first side of the detector 100 is practically insensitive X-ray and gamma ray photons. However, the first side depletion layer 101 a (implemented e.g. by p+ well 103 doping) is advantageously made thick enough to stop all neutron induced secondary particles. The thickness of the first depletion layer 101 a is advantageously in the range of 1 -100 μητι, more advantageously 1 - 50 μιτι, and most advantageously 1 -10 m depending for example of the material of neutron converter and thereby of the induced secondary particles. The second depletion layer of said semiconductor element is according to an exemplary embodiment much thicker than said first depletion layer, and is advantageously in the range 100 m - 5 mm, more advantageously 200 m - 5 mm, and most advantageously 300 μιτι - 1 mm, for example. Anyway when selecting the thickness of said first and second depletion layers, the second depletion layer is typically at least as thick or clearly thicker than said first depletion layer as discussed elsewhere in this document.

Figure 3 illustrates an exemplary detector 100 with depletion layer 107 added to the edge sides of the semiconductor element 101 to extend the active region to the physical semiconductor element periphery according to an advantageous embodiment of the invention. The depletion layer 107 may also be implemented electrically, e.g. by doping. The vertically doped layer 107 (advantageously same type (n+ or p+) as the charge colleting regions) at the edge region of the semiconductor element 101 between said first and second portions of said semiconductor element is configured to prevent the depletion layer 101 a from reaching the diced semiconductor element edge and thus prohibit excessive leakage current generation. In addition, despite the possible thick depletion layer 101 b of the second portion 101 b of the detector, the depletion layer 107 prevents blind regions at the edge region of the semiconductor element where the charges cannot otherwise be gathered -namely the thicker the second portion the deeper the blind region from the edge side.

The depletion layer 107 at the edge region offers clear advantage over the known detectors, because now the full depletion is possible all over the semiconductor element 101 . Eliminating the dead region at the semiconductor element or chip periphery will enable side to side arrangements of individual detector chips 100 to cover e.g. larger continuous imaging regions. Figure 4 illustrates a top view of an exemplary detector 100 for detecting both neutrons as well as X-ray and/or gamma ray photons according to an advantageous embodiment of the invention, where the p+ type region (like strip or well) 103 is doped on the n type element 101 and where the n+ type charge collecting regions (i.e. pixels) 102 are doped on the p+ type region 103. The readout electronics, e.g. CMOS circuit, can then be connected, such as bump bonded to the electrodes. The X-ray / gamma ray induced signals created in the second portion 101 b of the detector 100 ("backside" in the Figure 4 and thus not shown) can be collected by a similar CMOS circuit connected to the second side charge collecting regions (104) that the first side charge collecting regions (102).

Figure 5 illustrates an exemplary detector 100 with simulated electric field lines 501 between the p and n implemented (e.g. doped) charge collecting regions (i.e. pixels) on the first side 101 a of the semiconductor element 101 according to an advantageous embodiment of the invention, where the first depletion layer 101 a implemented by the electric field of said electrodes can be clearly seen. Figure 5 illustrates an alternative embodiment of the invention in which the first neutron sensitive and the second X-ray sensitive region of the detector are created and separated by a special charge collecting region arrangement on the surface of the first region. In this configuration both n+ and p+ charge collecting regions are processed at the surface of the first side and a lateral electric field is applied between the n+ and the p+ regions. Signal charge that is generated at the surface of the element will be collected by these n+ and p+ regions while signal charge that is created deeper in the semiconductor crystal element 101 will be drifted to the back side charge collecting region. Short range secondary particles will induce charge within the lateral surface field region only and will thus be detected at the front (first) side of the semiconductor element. The probability of X- or gamma ray interaction in the lateral field region at the first side of the detector is low and hence most of the X- and gamma rays entering the detector will be detected at the back (second) side of the element 101 .

Figure 6 illustrates an exemplary detector 100 with 3D trenches 108 for enhanced neutron detection efficiency according to an advantageous embodiment of the invention. The neutron reactive material 106 typically forms a few μιτι layer, as is described in figure 3, but also other configurations can be implemented, such as complex way comprising figure of sawtooth-like or other 3D structures like pores, pillars, channels, grooves and/or other cavities, which are filled with the neutron reactive material. In addition neutron reactive material 106 can be applied on, inside and/or in the connection with the structure of the semiconductor element 101 and advantageously in the portion nearest to said charge collecting regions (like pixels and/or electrodes) 102 to interact with neutrons to be detected and release ionizing radiation reaction products into the first portion 101 a.

According to an embodiment the neutron reactive material 106 is arranged between the first portion 101 a and readout electronics 109 electrically coupled with electrodes of said first portion 101 a, on the same surface of said first portion 101 a as the charge collecting regions 102, within said electrode structures electrically coupled with said charge collecting regions and/or on the surface of said readout electronics (as is described in connection with Figures 3, 6, 8, 9).

According to an embodiment the neutron reactive material 106 may also be arranged as clusters on and/or in the surface of the first portion of the semiconductor element, and/or between the readout electronics and the first portion of the semiconductor element.

The planar configuration of the neutron sensitive part 106 of the detector gives a maximum neutron detection efficiency of typically only 5-10 % depending on the choice of the neutron conversion material. To increase the neutron detection efficiency the 3D structures can be etched in the region between the charge collecting region implantations. The depth of the trenches, wells or other structures has to be adjusted to the thickness of the p+ region (like a well) 103 so as to prevent the secondary radiation from penetrating into the n type semiconductor element 101 . The surface of the 3D structures can be coated with a neutron conversion material, e.g., by atomic layer deposition (ALD). Figure 7 illustrates an exemplary detector 100 with connections for signal readout electronics 109 according to an advantageous embodiment of the invention, where the signal readout electronics can be implemented e.g. by CMOS ASIC signal readout circuits 109. The signal readout electronics can either be pulse counting and energy sensitive or charge integrating circuits for intensity recording. In a single channel configuration the first side 101 a and the second side 101 b of the detector 100 can be connected to discrete preamplifiers, e.g. by wire bonding (as is described in Figure 7). In a multichannel strip-type detector configuration the strip-type electrodes can be wire bonded to integrated preamp inputs of an ASIC signal readout electronics.

Figure 8 illustrates an exemplary detector 100 according to an advantageous embodiment of the invention, where the signal readout electronics 109 is "bump"- bonded via "bump"-elements 1 10a, 1 10b, such as "bump"-balls, with the electrodes of first 101 a and also second 101 b portions of the semiconducting element 101 . The "bump"-balls 1 10a connecting the signal readout electronics 109 with the electrodes of the first portion 101 a, possibly advantageously, comprises neutron reactive material 106 in order to still increase the efficiency of the detector to detect neutrons. However it is to be noted that the readout electronics 109 may also be coupled with said electrodes in other ways than "bump"-elements.

Especially it can be seen from the Figure 8 that the neutrons can interact with the neutron reactive material 106 arranged both between the semiconductor element 101 and the signal readout electronics 109, as well as also neutron reactive material 106 inside the bonding elements, such as "bump"-balls 1 10a or the like. In addition the neutron reactive material 106 may be arranged also on the surface (e.g. as clusters) of the signal readout electronics being connection with the first portion 101 a of the semiconducting element 101 and/or implanted inside said the first portion 101 a. It should be however noted that the detector 100 may comprise own signal readout electronics 109 for reading the charges generated by the second portion of the semiconducting element 101 . According to an embodiment the detector may be coupled with a coincidence or triggering means 1 12 for providing a time window during which the detector is adapted to detect said photon 1 1 1 in the second portion 101 b. The starting point of the time window may be triggered e.g. the signal produced by the charge collecting regions (e.g. pixels) 102 of the first portion 101 a of the detector. The signal may be responsive to interactions with the incident neutrons (or their ionization products), and because the neutron conversion generates also the gamma photon 1 1 1 , it can then be detected by the second portion 101 b charge collecting regions 104within the triggered time window when the gamma photon 1 1 1 is interacting with said second portion 101 b.

According to an embodiment the detector 100, such as the detector 100 described in Figure 8, is configured to determine a position and energy of the interaction of the incident neutron for example by measuring electrical charges 1 13 produced by the a-particle (or other ionization reaction products) in the interaction with the first portion 101 a. In addition the position and energy of the neutron conversion photon 1 1 1 interacting with the second portion 101 b can be measured via the corresponding charge collecting regions (via e.g. electrode(s)) 104 coupled with the second portion, and thereby determine the angle of the incident photon in relation to said detector.

Thus, based on the above, the detector 100 may be configured to

a) determine the signal provided with the second portion 101 b of the detector 100 and being responsive to interactions of X-ray or gamma ray photon, either direct or neutron conversion photon,

b) check whether there was, within a predetermined time window, provided a signal with energy greater than a predetermined threshold energy level with the first portion 101 a of the detector, and

c) if there was detected the signal in step b) with energy greater than the predetermined threshold energy level, the both signals were responsive to interactions with said incident neutrons, and d) if there was not detected the signal in step b) with energy greater than the predetermined threshold energy level, the signal provided with the second portion 101 b of the detector was responsive to interactions with background X-ray or gamma ray photons, whereupon the detector 100 is configured to subtract or ignore said background X-ray or gamma ray photon signal in order to further improve for example the X-ray or gamma rejection ratio of the detector 100 when used as a neutron detector. For this purpose the detector 100 (or arrangement utilising said detector) is advantageously provided with a registering means 1 16 as well as with suitable memory and data processing means (not shown).

Figure 9 illustrates an exemplary detector 100 (or its first side) with bond elements 1 10a (like bump bond elements) and grooves 1 17 arranged on the first surface of the semiconductor element 101 and filled with neutron reactive material 106 according to a, possibly advantageous, embodiment of the invention.

It is to be noted that according to a, possibly advantageous, embodiment of the invention the "bump-balls" 1 10a or the like electrically conductive means used for "bump" bonding the electrodes coupled with the charge collecting regions 102 of the first portion 101 a of the detector 100 to the signal readout electronics 109 comprises also neutron reactive material 106, which still makes the neutron detection much more effective since the neutrons may also interact with the neutron reactive material inside and/or on the surface of the bonding elements, such as "bump-balls" 1 10a. Also the grooves 1 17 may be filled with neutron reactive material 106, as well as also spaces between the bump-pad regions, and/or between the read-out electronics and bump-bonding elements. The grooves 1 17 may be provided on the semiconductor element for example by dicing or etching. The detector according to embodiments of the invention can be manufactured, e.g., utilizing a conventional planar process on high resistivity n-type silicon wafers or other semiconductor elements. The simple layout configuration of the detector with one signal readout channel on the back or second side of the detector (X- / gamma ray detection side) can be realized, as an example, with a single sided process for example: the back side of the semiconductor element (i.e. wafer) does not need photolithography patterning but is heavily doped with phosphor ions to form a uniform n+ region for X- and gamma ray signal readout and to prevent over depletion. The first (front) side (neutron detection side) process may start with a deep p implantation (boron ions) to form the p region (e.g. a well type). Photolithography can be used to limit the region (e.g. well) dimensions from reaching the semiconductor element edges. Following the p region (e.g. well) implantation a shallow n+ doping is implemented at the surface of the p region (e.g. the well). The doping density of the p region is preferably chosen so as to yield an appropriate depletion region width (typically 10 μιτι, not however limiting to this only) at the contact potential without applying an external voltage. The n+ doping can be in the shape of a pad or it can be patterned (with photolithography) as a mesh, fork or similar shape. The front side can also be processed as a multichannel detector by patterning the n+ doping to separate regions, pixels, strips or similar shapes. To ensure good electrical contacts to the n and p regions of the detector aluminum may be sputtered on both sides of the detector wafer and patterned along the shapes of the doped regions. The front side can also be processed without the p region (or the well). In this case alternating p+ and n+ dopings are implanted on the front side. Signal charges created close to the front surface of the detector will be collected by the horizontal field between the front side p+ and n+ dopings. Signal charges created deeper in the detector bulk will be collected by the vertical field between the front side p+ dopings and the back side n+ doping.

Finally the neutron conversion layer, like a thin film neutron conversion layer, is implemented on the top side of the detector by evaporation, sputtering, atomic layer deposition or another suitable method. Contact openings are etched through the neutron conversion layer to enable electrical contacts to the detector metal electrodes through wire or "bump" bonds or similar means. The first depletion region at the first side and the second depletion region extending from the second side to the semiconductor element )e.g. silicon) are formed by grounding the p region (or alternatively the p+ contacts) and by connecting a positive voltage at the n+ regions.

If a multichannel detector is requested also on the back side a double sided planar process is advantageously used. The back side is then also patterned by photolithography. The patterned n+ contacts on the back side are separated by floating p+ barrier regions. Front and back side alignment can be done mechanically or more accurately by infrared alignment.

The neutron capture region at the first side of the detector can be increased by implementing grooves or trenches at the first (front) side of the semiconductor element between the n+ dopings by chemical or ion etching.

To minimize the dead regions at the semiconductor element periphery a heavy n+ doping can be implemented at the vertical surface of the element edges. This n+ doping will prohibit the thick side depletion region from reaching the element edge and causing an extensive increase in the detector leakage current. A minimum dead region at the element periphery is an advantage when tiling individual detector elements side to side to form larger detection regions.

The invention has been explained above with reference to the aforementioned embodiments, and several advantages of the invention have been demonstrated. It is clear that the invention is not only restricted to these embodiments, but comprises all possible embodiments within the spirit and scope of the inventive thought and the following patent claims. Especially it is to be noted that some of the functional features or means of the detector illustrated in Figures above can be outsourced for example to a larger unit, such as imaging apparatus utilising plurality of the detectors described in Figures. For example the imaging apparatus or the like utilizing said detector(s) may comprise said coincidence or triggering means 1 12, as well as the registering means 1 16, memory means and data processing means.