The invention relates to an apparatus for locating a radiation source, which apparatus is a baffle arranged to attenuate the radiation detected by an circularly-sensing radiation detector. In addition, the invention also relates to a radiation detector, a system, and a method for locating a radiation source .

In field operations, there is known different kind of needs to determine the existence of a possible radiation source and es ^¬ pecially also to position its location relative to the observ ^¬ er. Using the applicant's radiation detector, available under the trade name RanidPro 200, the existence of a radiation source can be detected, but using it, however, it is not pos ^¬ sible to position the location of the source. In many cases, it is insufficient to simply know of the existence of a radia ^¬ tion source. In addition to that, there would be a need to lo- cate the radiation source, or at least determine its direc ^¬ tional information. I.e. information as to the direction in which the radiation source is located relative to the radia ^¬ tion detector and thus also to the observer. Examples of the aforementioned needs are frontier control and also various public events. In these it would be desirable to position a radiation source as quickly as possible in order to prevent criminal actions, or to minimize detriments. The search for the radiation source should also take place as in- conspicuously as possible, which makes demands on the imple ^¬ mentation of an apparatus suitable for field operations. The apparatus should be as compact as possible, light, and also portable. In addition, the apparatus should be easy to use, in order to permit the most inconspicuous searching and locating of the radiation source. Further, the operation of the appa- ratus or locating of the radiation source should not demand special expertise on the part of the operator of the appa ^¬ ratus . Locating a radiation source using an circularly-sensing radiation detector is known from South Korean patent application publication number KR20100069255. In it a baffle running around the radiation detector is used. The baffle prevents ra ^¬ diation reaching the detector from most of its field of view. In the baffle, there is a narrow gap relative to the entire length of its circumference, from which radiation reaches the detector without attenuation only from a precisely limited di ^¬ rection at a time. As the gap rotates along with the baffle around the detector, radiation reach the detector from this gap. On the basis of the radiation reaching the detector the direction of the radiation source relative to the detector can then be determined. Thus the direction of the radiation source is determined by utilizing the collimator principle. However, this implementation brings with it most of the aforementioned problems, in the form of, for example, the weight of the ar ^¬ rangement and thus its poor usability.

The invention is intended to create an apparatus, a radiation detector, a system, and a method for locating a radiation source, by means of which it is possible to easily, quickly, and inconspicuously locate a radiation source precisely, for example, relative to an observer. The characteristic features of the apparatus according to the invention are stated in Claim 1, of the radiation detector in claim 12, of the system in Claim 13, and of the method in Claim 15.

In the invention, a circularly-sensing radiation detector and a radiation-attenuating baffle arranged in connection with it, which belongs, for example, to the apparatus according to the invention, can be utilized in the invention. The baffle can also be integrated in the radiation detector itself. Using the baffle, the field of view surrounding the radiation detector can be attenuated direction-dependently . The radiation source can then be positioned from the attenuation caused by the baf ^¬ fle, i.e. on the basis of the attenuation. Thus, from the changes in the signal formed by the radiation detector, more specifically from the attenuation, it is possible to determine when the baffle is between the radiation detector and the radiation source and is attenuating the radiation reaching the radiation detector. If the signal weakens, or even vanishes, then the baffle is between the radiation detector and the radiation source. From this information it is possible to posi ^¬ tion the location of the radiation source relative to the ra ^¬ diation detector, because the position of the baffle around the radiation detector is determined and thus it is known in connection with the attenuation that has happened and been detected. In other words, the radiation source is then posi ^¬ tioned on the basis of the attenuation of the radiation.

According to one embodiment, the apparatus can be implemented, for example, in such a way that the apparatus includes a place arranged for the radiation detector, in which the radiation detector can be removably installed, and a baffle arranged to run around the place. The baffle includes an attenuating mate ^¬ rial, more generally one or several places creating attenua ^¬ tions, which are rotated on an orbit around the radiation de ^¬ tector using an actuator. The actuator can include a support, in which there is attenuating material, and a rotation device for rotating the support and thus also the attenuating material around the radiation detector. According to a second embodiment, the baffle can also be permanently attached to the ra ^¬ diation detector, thus forming a single package with it. The whole package can then rotate relative to an axis of rotation defined by the radiation detector, thus equally determining the direction of location of the radiation detector relative to the observer, more generally a set fixed point.

According to one embodiment, attenuating material is arranged in the support, more generally the baffle, for example, dis ^¬ cretely on different sides relative to the radiation detector, in order to create one or several attenuations in the radia ^¬ tion detected by the radiation detector. In addition, the attenuating material can then be fitted in a balanced way around the radiation detector. Besides this making the operation of the apparatus more balanced, it also improves the accuracy of the locating of the radiation source, according to one embodi ^¬ ment even, for example, of different radiation sources. The use of several baffles permits the optimal performance of the apparatus, for example, when locating different kinds of radi ^¬ ation sources. According to one embodiment, there can be more attenuating material in a specific direction than in other directions. The signal of the radiation detector is then attenu ^¬ ated more in one direction of the baffle than in other direc- tions. The invention permits a cost-effective, simple, and quick way to position a radiation source.

Yet another significant additional advantage, which the use of the invention also makes possible, is the detection of the ex- istence of a radiation source, which can be performed before it is positioned. Instead of the radiation detector being cov ^¬ ered by the baffle for most of its field of view, as happens precisely in the solution according to the prior art, by using an attenuator with a substantially smaller angle, according to the invention, and owing to that a completely contrary locat ^¬ ing method relative to the known prior art, the further ad ^¬ vantage is gained that the locating of the radiation source only needs to be done when necessary, i.e. only when the existence of a radiation source is detected. Thus using the same radiation detector, by which the positioning of the radiation source is also performed, it is possible to first perform only the detection, i.e. a search for the existence of a radiation source. Once the existence of a radiation source has been de ^¬ tected, only then is its locating initiated. Thus the locating of the radiation source, performed on the basis of attenua ^¬ tion, also permits the existence of the radiation source to be determined. By means of this two-stage method, savings are al ^¬ so made, for instance in the energy consumption of the system. Other additional advantages achieved by means of the invention are stated in the description portion and the characteristic features in the accompanying Claims.

In the following, the invention, which is not restricted to the embodiments described hereinafter, is described in greater detail with reference to the accompanying figures, in which

Figure 1 shows an example of the apparatus with the radiation detector being arranged in it,

Figure 2 shows the apparatus shown in Figure 1 with the radiation detector, seen at an angle from below, without the electronics compo ^¬ nent,

Figure 3 shows the apparatus without the radiation detector,

Figure 4 shows the apparatus with the jacket compo ^¬ nent removed,

Figure 5 shows a cross-section of the apparatus,

Figure 6 shows schematically a top view of a second example of the baffle,

Figure 7 shows schematically the measuring geometry using in the invention,

Figure 8 shows graphically the signal formed by the apparatus, when detecting a radiation source, Figure 9 shows graphically the signal formed in the case of the baffle according to Figure 6, when detecting a radiation source,

Figure 10 shows an embodiment of the system, in which the apparatus is utilized,

Figure 11 shows the graphical user interface of the application software belonging to the system, in two different situations,

Figure 12 shows the measuring principle for measuring the distance from the radiation source, and

Figure 13 shows an example of the measuring graphics when locating a radiation source from different locating points.

Figures 1 - 3 show an example of the apparatus 10 for locating a radiation source S. In Figures 1 and 2, a radiation detector D is situated in the apparatus 10 and in Figure 3 the appa ^¬ ratus 10 is shown in a stripped-down form and without the radiation detector D situated in it. In Figures 4 and 5 in turn the construction of the stripped-down apparatus 10 is shown with its casing opened in Figure 4 and in cross-section in Figure 5. The apparatus 10 according to the embodiment shown also includes a place 11 (Figures 3 - 5) for the radiation de ^¬ tector D (Figures 1, 2, and 5) . The radiation detector D can be removably installed in the place 11. In addition, the appa ^¬ ratus 10 also includes an orienter (Figures 4 and 5), which can now also be called a sight. The orienter is a baffle 12, which is arranged to affect the radiation R detected by the radiation detector D to be fitted in the place 11, in order to locate the radiation source S. More specifically in the case of the invention the affecting is the attenuation of the radiation R detected by the radiation detector D to be fitted in the place 11. It is also possible to speak of the shadowing of the radiation detector D taking place using the baffle 12 of the radiation R sent by the radiation source S position or di- rection-dependently . In addition, it is also possible to speak of the covering of the field of view 59 (Figure 7) of the ra ^¬ diation detector D mainly entirely on a laterally selected plane. The spatial angle covered by the baffle 12 is then ar- ranged to cover the radiation detector D when viewed from the radiation source S. Here position dependence means that the shadowing of the radiation detector D by the baffle 12 from the radiation source S depends on the position of the baffle 12 relative to the radiation detector D, more specifically the position of the baffle 12 around the radiation detector D, or even more specifically on its outer circumference. Direction- dependence means that the radiation detector D is made direc- tionally sensitive using the baffle 12. The radiation detector D can be circularly-sensing. It will then be insensitive to the input direction of the radiation R, nor will it be possible to determine the location of the radi ^¬ ation source S only from the radiation R detected by the radi ^¬ ation detector D. One example of the radiation detector D is the applicant's radiation detector marketed under the name Ra- nidPro 200. It then includes, as operational components, a multi-channel analyser 22 connected to a photomultiplier tube 23 and a connection interface 24. The photomultiplier tube 23 is connected to a crystalline substance 25, more generally to a radiation-sensitive substance, which is affected by radia ^¬ tion R and by means of which radiation R is detected. The crystalline substance 25 can be, for example, LaBr ₃ . More gen ^¬ erally, it is possible to speak of means belonging to the ra ^¬ diation detector D for detecting radiation R.

The radiation detector D can have the outer shape of an elongated tubular device, which detects radiation R from an area 360 degrees around. The outer diameter of the cylindrical ra ^¬ diation detector D used as an example can be, for example, 20 - 200 mm. For example, the outer diameter of the RanidPro 200 device is 80 mm and the diameter of the crystal detector 25 in it is 38 mm (1.5") . Using the radiation detector D according to the example ionizing radiation R can be detected in the energy range 30 keV - 10 MeV. It includes a carrying handle 66 arranged in the outer casing, thus making it a portable de ^¬ vice .

In the connector interface 24 there can be, for example, a da ^¬ ta-transfer interface 26 for connecting to a computer 54 (Fig- ure 10) or similar data-processing device and a connection to a power source/charger. In addition, the radiation detector D also includes the necessary electronics and a possible bat ^¬ tery. One example of an application for the apparatus 10 is locating a substance transmitting gamma radiation. However, it is generally possible to speak of locating a radiation source S transmitting ionizing radiation R. The ionizing radiation R can be, for example, radiation R caused by one or more radio ^¬ nuclides, i.e. the radiation source S can be an object con ^¬ taining radionuclides and the radiation R thus radionuclide radiation. In addition to radioactive substances, the radia ^¬ tion R can also come from devices producing ionizing radiation. Some examples of these are (continuously operating) x- ray tubes and particle accelerators. The detector D can be, for example, a spectrometer or a simple counter. The locating of neutron radiators is also possible using the apparatus 10 by means of a baffle, which attenuates neutron radiation (for example, boron or lithium) . In addition, the radiation detector D can be selected so that it is able to differentiate between gamma and neutron radiation (for example, plastic detectors and data collection in list mode) .

In the case of the embodiment shown of the apparatus 10, the place 11 for the radiation detector D is now formed by a space 27 with an opening arranged in the apparatus 10, in which the radiation detector D is to be removably installed. The radia ^¬ tion detector D is constantly in the place 11 and remains there firmly in the intended position relative to the baffle 12. The place 11 is now formed in principle by a cup, which has a bottom and a circumferential wall. On the bottom of the place 11 there can be a radiation absorbing cap 58. This pre ^¬ vents radiation R from reaching the radiation detector D at the end of that set against the bottom of the place 11. The diameter of the space 27 is arranged with the diameter of the radiation detector D in such a way that the radiation detector D is fitted tightly in the space 27. As the place 11 is simply a space 27 with an opening the radiation detector D can be quickly and easily placed in it and removed from it. Tools are not needed. The depth of the cup is arranged so that the radi- ation-detecting crystalline substance 25 is completely covered vertically by the baffle 12.

Figures 4 and 5 show an example of one way to implement the baffle 12 and the associated mechanism. The baffle 12 is ar- ranged to be removably installed around the radiation detector D between the radiation source S and the circularly-sensing radiation detector D, in order to cover the field of view 59 of the radiation detector D and in that way to locate the ra ^¬ diation source S relative to the radiation detector D on the basis of the attenuation created by the baffle 12. Thus, it is also possible to speak of the location of a radiation source S performed on the anti-collimator principle. Thus the baffle 12 is arranged to change its position/orientation relative to the radiation detector D and also the radiation source S in order to shade the radiation detector D from the radiation R transmitted by the radiation source S. The apparatus 10 can there ^¬ fore include, in addition, a position definer 13 for determining the direction of the shaded field of view 59 relative to the radiation detector D. Using the position definer 13 the position of the baffle 12 can be defined at least in connec- tion with the attenuation of the radiation R detected by the radiation detector D or even continuously relative to the ra ^¬ diation detector D and the radiation source S. Using the position definer 13 the orientation of the baffle 12 is determined when it is between the radiation source S and the radiation detector D. The definition takes place in the direction of a plane perpendicular to the elongated radiation detector D. In this way the location and position of the baffle 12 are deter ^¬ mined around the radiation detector D and thus also the loca- tion of the radiation source S around the radiation detector D relative to the location of the baffle 12. Thus the locating of the radiation source S can also be said to be the defini ^¬ tion of its direction of location relative to the radiation detector D.

By using the baffle 12 and more generally the apparatus 10, it is arranged to be formed one or more changes, more specifical ^¬ ly attenuations 14, 14.1 - 14.3, in the radiation R detected by the circularly-sensing radiation detector D. It is also possible to speak of one or more changes, more specifically attenuations in the radiation field 62 (Figure 10) surrounding the radiation detector D. The attenuations 14, 14.1 - 14.3 can be said to take place direction-sensitively or direction- dependently. An attenuation can be understood as a very small, but nevertheless detectable deviation or disturbance in the data produced by the radiation detector D. Attenuation of the radiation R is caused when the baffle 12 goes between the ra ^¬ diation detector D and the radiation source S. The position of the radiation source S around the radiation detector D is de- termined from the positions of the baffle 12 around the radia ^¬ tion detector D corresponding to the attenuations 14, 14.1 - 14.3. In the attenuations, the radiation R detected by the ra ^¬ diation detector D and thus also the signal formed from it no ^¬ ticeably weakens. When the radiation R and thus also the sig- nal weakens, then it is known that the attenuation part ar- ranged in the baffle 12 has gone in front of the radiation de ^¬ tector D relative to the radiation source S, i.e. between the attenuation part of the baffle 12 is located between the radi ^¬ ation detector D and the radiation source S. When the radiation R and thus also the signal again in turn strengthen, then it is known that the attenuation part of the baffle 12 has gone away from in front of the radiation source S. Due to this, the radiation detector D again "sees" the radiation source S, when the radiation R can reach the radiation detector D. Thus the detection of a change, more specifically an attenuation, reveals the direction of the location of the radiation source S relative to the radiation detector D. The good detection ability of the radiation detector D nevertheless remains nearly unchanged during the direction measure ^¬ ment. This is partly because the radiation detector D is cov ^¬ ered at one time over only a relatively small, but sufficient for location spatial angle relative to the radiation source S. Thus the locating of the radiation source S can be said to take place on the basis of attenuation.

The attenuation caused by the baffle 12 of the radiation R de ^¬ tected by the radiation detector D is thus arranged to change. For this purpose the baffle 12 includes attenuating material 16, 16.1 - 16.3 arranged to create one or more changes, more specifically attenuations 14, 14.1 - 14.3 in the radiation R detected by the radiation detector D now to be fitted in place 11. More generally, it is also possible to speak of attenua ^¬ tion parts, attenuation elements or attenuating points instead of attenuating material. The baffle 12 also includes an actua ^¬ tor 15 for removably placing the attenuating material 16, 16.1 - 16.3 between the radiation source S and the radiation detector D here to be fitted in place 11. The spatial angle covered by the baffle 12 then covers the radiation detector D, and preferably no more, when seen from the radiation source S. A constant track 17 is arranged in the apparatus 10 for the attenuating material 16, 16.1 - 16.3. By moving along the track 17 the place of the attenuating material 16, 16.1 - 16.3 can be changed constantly around the radiation detector D, or more generally relative to it, by means of its actuator 15. Thus by moving it along the track 17 the attenuating material 16, 16.1 - 16.3 can be aimed towards the radiation source S. The spatial angle covered by it then covers the part of the radiation detector D sensitive to radiation R, when seen from the radiation source S. The track 17 can also be called on orbit .

According to one embodiment, the actuator 15 includes a sup ^¬ port 18 and a rotation device 19. The attenuating material 16, 16.1 - 16.3 is then fitted to the support 18. The rotation de ^¬ vice 19 is, in turn, now arranged to move the support 18 in order to impart a rotating movement to the attenuating material 16, 16.1 - 16.3 around the radiation detector D. The rotating movement takes place constantly along the track 17, which is now formed using the support 18.

In the case according to the embodiment described, there is in the apparatus 10 a cup-like protective casing 28 in front of the baffle 12 and more particularly of the attenuating material 16. The place 11 for the radiation detector D is now also integrated in the casing 28. The casing 28 can then have a two-layer construction, which has an inner wall 28.1 and an outer wall 28.2 and a space 39 between them. The inner wall 28.1 now defines the cup, more generally the place 11 for the radiation detector D. The outer wall 28.2 forms an outer casing around the baffle 12. The support 18 of the baffle 12 and the attenuating material 16 arranged in it remain in the space 39 formed between the outer and inner walls 28.2, 28.1 belonging to the protective casing 28. The protective casing 28 is connected to the cover 30 of the electronics case 29 belonging to the apparatus 10. In the electronics case 29, an example of which is shown in Figure 1, is a circuit card 40, in which there are the electronic cir- cuits 20, 41, 42, such as the necessary memories and one or more processors, relating to the operations of the apparatus 10. In addition there can be a USB connector 43 connected to the circuit card 40, and a battery 44. The electronics case 29 can be, for example, a box-like structure. It can also form a base for the apparatus 10, by means of which the apparatus 10 and particularly the attenuating material 16 and the radiation detector D are put in a constant attitude in which locating of the radiation source S can be performed. Taking into account the embodiment shown, the elongated radiation detector D is then in a vertical attitude and it observes the environment sideways in the radial direction of the radiation detector D. In Figures 2 - 5 the apparatus 10 is shown without the elec ^¬ tronics case 29. On top of the cover 30 of the electronics case 29 is an adapt ^¬ er plate 31, in which there is a position sensor 32 belonging to the position definer 13. The position sensor 32 can be, for example, an opto-fork. The position sensor 32 now includes a sensor fork 33 arranged on the adapter plate 31. The baffle 12, more specifically the support 18 belonging to it, which rotates around the radiation detector D, is arranged to move through the sensor fork 33. The rotation takes place concentrically, i.e. coaxially. There is an edge protrusion 36 fit ^¬ ted to the outer circumference of the bottom 35 of the support 18, which now forms a hollow truncated cylindrical cup 34. There can be at least one opening 37 in the edge protrusion 36. By means of the electronics connected to the fork 33 the movement of the opening 37 through the fork 33 can be detect ^¬ ed. The opening 37 can be arranged in the circumferential di- rection of the cylindrical cup 34, for example in the centre of the attenuating material 16, which is arranged on the ex ^¬ ternal surface 38 of the cylindrical cup 34. It also possible to speak of a zero sensor, which is in the centre of the at ^¬ tenuating material 16 in its circumferential direction. With its aid and that of counting the steps of a stepper motor 45 the direction at the time of the attenuating material around the radiation detector D can be determined. If a linear or direct-current motor is used, a sensor based on reflection can be used.

In position definition, an angle sensor or angle encoder, for example, can be used in addition to/instead of an optical de ^¬ tector. Position definition can be a location detecting system or some other angle defined from a zero point. A sensor giving an absolute angle connected, for example, to the rotation shaft of the baffle 12 can also be used. It can be any angle sensor whatever.

Figures 2, 3, and 5 show one example of the rotation device 19. Now it is a stepper motor 45 attached by its body to the adapter plate 31. There is an opening in the centre of the adapter plate 31 for the shaft 46 of the stepper motor 45. At the end of the shaft 46 is an attachment plate 47, by which the shaft 46 is attached to the support 18 now belonging to the baffle 12, and more particularly to its base 35. By means of the stepper motor 45, the support 18, and thus also the at ^¬ tenuating material 16 attached to it, are made to rotate in a circle around the radiation detector D. In the embodiment described above, the baffle 12 includes only one attenuation element 16 covering the field of view 59 of the radiation detector D in the side direction. Figure 6 shows schematically a second example of the baffle 12, now seen from above. Here the baffle 12 includes attenuating material 16.1 - 16.3, again more generally, attenuating elements or attenuat- ing parts, fitted discretely on different sides of the baffle 12, i.e. also relative to the radiation detector D, in order to create two or more attenuations 14.1 - 14.3 in the radia ^¬ tion R detected by the radiation detector D. The locating of the radiation source S is facilitated by having more than one attenuation during a single revolution of the baffle 12. In addition, the attenuating material 16.1 - 16.3 can be arranged in a balanced way around the baffle 12 and thus also the radi ^¬ ation detector D. The balanced placing stabilizes the possible lack of balance caused by the attenuating material rotating around the radiation detector D. Because the attenuation material is only in some places in the support, it may make the support 18 unbalanced, particularly when using a thick attenuating material. In addition, a balanced placing also assists in the locating of the radiation source S. However, it should be noted that the operation of the apparatus 10 is not espe ^¬ cially unbalanced when using only one attenuating material. This is because the thickness of the baffle 12, more specifi ^¬ cally of the attenuating material can be relatively small.

According to one embodiment, an arrangement creating several attenuations per one revolution and arranging of balanced at ^¬ tenuation material 16.1 - 16.3 can be implemented in such a way that the sectoral attenuating materials 16.1 - 16.3 are attached to the support 18 at intervals of 120 degrees. Sector areas 48 without attenuation then remain between them. If the attenuating materials 16.1 - 16.3 are of the same material and surface area, then the ratio of the attenuations and also of the mass of the attenuating materials 16.1 - 16.3 can be, for example, 1:0.5:0.5. In other words, one of the attenuating materials 16.1 attenuates radiation R by a factor of one and the two other attenuating materials 16.2, 16.3 attenuate radiation R by a smaller factor than the attenuating material 16.1 attenuating by a factor of one. The thicknesses (d) of the at- tenuating materials 16.1 - 16.3 can then be in the same ratio (d, ½d, ½d) and the rotating movement of the baffle 12 will not cause vibrations in the apparatus 10 due to the effect of the movement of the centre of gravity of the attenuating mate ^¬ rial. The different attenuations bring also certainty and ac- curacy to locating. A single scanning, i.e. rotation of the baffle 12 brings two kinds of changes, more specifically at ^¬ tenuations 14.1 - 14.3, when the radiation source S is in the field of view of the radiation detector D. This is shown schematically in Figure 9. Because the radiation R attenuating ma- terial pieces 16.1 - 16.3 remain stationary in the support 18 relative to each other, and their positions in the support 18 are also known, it is then possible to determine the direction of the radiation source S by using the information of an angle calculator. Figure 4 shows only one piece of attenuating mate- rial 16.1. The position of the other two attenuating material pieces 16.2, 16.3 in the support 18 are shown by holes 49.

The attenuating material 16, 16.1 - 16.3 can be, for example, lead or wolfram. The lead pieces can be attached, for example, to a support 18 of plastic. On the other hand, the support 18 itself can also be of lead. Its jacket thickness and thus also its attenuation can change in a corresponding manner to that in the case of individual lead pieces. In the case of lead pieces, the thickness of the attenuating material in the radi- al direction of the radiation detector D can be, for example, 12 mm, and in the case of wolfram 7 mm. Depending on the embodiment and the material, the thickness of the attenuating material can be, for example, 1 - 20 mm. The shape, size, and mass of the baffle 12 and even more particularly of the atten- uating material 16, 16.1 - 16.3 can vary, as can the material. The baffle 12 can be constructed generically to attenuate all gamma radiation, or it can be dimensioned optimally according to the properties of the substance being sought. For example, when seeking americium, a very thin baffle (1 mm Pb) can be used. In practice, this has no effect on other radiators, such as, for example, cesium. For it, in turn, another optimal baffle could be dimensioned (6 mm Pb) at another location around the apparatus 10. According to yet another embodiment, the attenuating material in the same baffle 12 can also be of different substances (such as, for example, lead and boron-treated plas ^¬ tic/lithium) . The attenuating material will then be transparent to one type of radiation. In addition, the attenuation can be dimensioned according to the type (gamma radiation or neutron radiation) of the radiation-transmitting substance and/or the energy. It is then possible to use the same apparatus 10 to detect even several different types of radiation, on the basis of the attenuation. If there is lead on one side of the baffle 12 and boron on the other side, and the zero point is known, then in the case of gamma radiation the location direction of the radiation source S will be positioned in the at ^¬ tenuation direction shown by the lead and in the case of neu ^¬ tron radiation the location direction of the radiation source S will be positioned in the attenuation direction shown by the boron. In other words, the baffle 12 is then arranged to achieve by two or more attenuations 14, 14.1 - 14.3 to identi ^¬ fy the type of radiation source S and/or the energy, in addi ^¬ tion to locating.

In the embodiment described above, the baffle 12 rotates around the radiation detector D along a track 17 arranged for it. The invention can also be implemented in such a way that the baffle is fixed around the radiation detector D and then both of them are rotated around the vertical axis defined in the axial direction of the radiation detector D. When the direction in which the attenuation material of the baffle points at each time is known, the direction of the radiation source S can be determined when detecting the change indicating it in the data produced by the radiation detector D. The radiation source S is then in the direction in which the attenuating material covers the radiation detector D and attenuates, i.e. prevents the radiation R of the radiation source S from reaching the radiation detector D.

Figure 7 shows schematically the measurement geometry used in the invention and Figure 8 shows graphically the signal formed by the apparatus 10 when detecting a radiation source S. One example of a radiation source S is a gamma radiator, but, how- ever, one can speak more generally of ionizing radiation. The solution according to the invention is based on a relatively small baffle 12 and even more particularly on the use of at ^¬ tenuating material 16, 16.1 - 16.3 around the radiation detector D. By means of the attenuating material 16, 16.1 - 16.3 belonging to the baffle 12 the field of view (FOV) 59 of the radiation detector D against the radiation R can be covered. The scintillation-crystal material of the radiation detector D is then covered entirely in the vertical direction in a se ^¬ lected plane relative to the set direction. The radiation R can originate, for example, from a point-like radiation source S located relatively far from the radiation detector D (dis ^¬ tance >> 1 metre) . Owing to the solution according to the in ^¬ vention, in the search operations of the radiation source S the observation ability of the radiation detector D is not sacrificed when performing locating. This is because, owing to the invention, the radiation detector' s D field of view 59 is covered over only a narrow zone. In addition, the attenuator is not thick and thus massive. Figure 7 shows an example of the measurement geometry accord ^¬ ing to the invention. Using a cylindrical radiation detector D there is a similar response in all directions. In other words, it is a circularly-sensing detector in a static state. Thus it does not in itself distinguish the arrival direction of radia- tion R in any way, but only expresses the existence of a radi- ation source S in the detection area. The angular dependence of the detector can be measured and taken into account in analysis, but usually it is small, at least for large energies (> 100 keV) . The radiation source S is assumed to be far from the detector (> 1 metre) . In the following, the effect is ex ^¬ amined of a thin mask 16' ( A' ) around the detector on the signal produced by the cylindrical detector. The mask 16' can rotate around the detector along a track 17 arranged for it. Alternatively, the entire system can rotate, i.e. the mask 16' and in addition the radiation detector D. The mask 16' then does not move relative to the radiation detector D. In the present analysis, the mask 16' is ideal, i.e. it completely prevents gamma radiation from reaching the detector. In Figure 7, the inner curve AA' of the attenuating part covers exactly the diameter (2r) of a LaBr ₃ crystal, if the radiation S comes straight towards the detector D. Thus, in the case of optimal dimensioning the baffle 12 covers the cylindrical detector completely, but no more, if the radiation source S is far away. However, the curve AA' does not touch the sensitive part of the detector D, as there can be support and protective structures in between.

The arc length AA' of the mask 16', more generally the attenu ^¬ ating material 16.1 - 16.3, is

AA' = 2 ₀ R = 2R sirr r/R) (1) where R = the distance from the centre point of the radiation detector D to the attenuating material 16.1 - 16.3 and r = the radius of the radiation detector D.

The shape or shielding factor S (- _x ) is calculated, when the mask 16' moves from position AA' to position CC . When the mask 16' is in position AA' , the detector does not record the signal, i.e. S (- _x ) = 0, whereas the signal is saturated, i.e. S (-οίχ) = 1 for the mask 16' situated outside position AA' .

The shielding factor S (- _x ) has a geometric interpretation. It is the segment area (ZO'Z'Z), which is completely exposed to radiation normalized to a circle with unit radius (r ² = 1) . The height of the cylinder has no effect on the relative response. Calculation gives, when normalizing the maximum signal as one:

S (-oi _x ) = (1/π) [y - sin y cos y] (2) where cos y = (R/r) sin _x (3)

Here the circular segment area is equal to the circular sector area minus the area of the triangular part:

A = r ² /2 * [Θ - sin(6) ], where Θ = 2 y .

The following presents the results of measurements performed using a pilot apparatus. The ideal mask 16' was replaced by a macroscopic lead shield, which was 12 -mm thick. Using lead, the half-value thickness is 6 mm for cesium Cs-137 and 12 mm for cobalt Co-60. On this basis, the protection can be ex ^¬ pected to reduce the measured signals by a factor of four for cesium (Cs-137) and a factor of two for cobalt (Co-60), if the whole of the radiation detector's D field of view is covered.

In the measurement, a small cesium source Cs-137 (37 kBq) was used with the LaBr ₃ detector (1.5" x 1.5") . Data collection was performed using a backpack detector, and a RanidPro200 system (Environics Ltd) . The radiation sources were placed very close to the surface of the detector (12 mm), as otherwise the counts would have been too low for rapid initial testing of the new method.

Figure 8 shows the data given by the cesium source Cs-137 measured in steps at angle intervals and the prediction 14' given by a simple model (equation (2) above) . The ideal de ^¬ scriptor goes to zero, when the mask entirely covers the field of view of the detector, whereas the measured descriptor ex ^¬ presses a significant counter reading above background. The reason for this is that 12 mm of lead does not give complete protection. The radiation source was also not completely point-like and it therefore gives a wider response than the prediction 14' . A zero angle on the horizontal axis means com ^¬ pletely protection of the detector by the mask. The de- scriptors are not scaled to absolute units.

The measured data are directly proportional to the counting frequency. The results show that the response 14 has a shape that is similar to the prediction descriptor 14' given by the equation (2 ) .

The invention permits the simultaneous detection and locating of a radiation source S. The mask covers, for example, only 49 - 59 degrees of the full field of view (distance 0 mm and 12 mm from the surface of the radiation detector D) , which corresponds to 14 - 16 % cover. Broadly the cover can be, for example, 5 - 25 %. In reality the real observation ability dimin ^¬ ishes much less. Here two factors are of significance: (1) the mask reduces the background radiation, and (2) a large part ( 25 % for Cs-137) of the arriving radiation penetrates the mask. Thus the real observation reduction is less than 10 %. If even less disturbance is required, the mask should then be placed farther from the surface of the detector: with a dis ^¬ tance of 40 mm the observation ability is diminished by only 1 — 3 % . A system can be constructed in various ways, utilizing the ap ^¬ paratus 10 and also the radiation detector D as parts. The following describes at least three different manners of imple- mentation.

Manual implementation can be similar to the test arrangement described above. The radiation detector's D response is meas ^¬ ured from a few orientations (4 - 8), after which the counting produced by the detector can be exploited for locating. The data-collection program is then connected to a digital compass, in order to create automatic direction pointer to the end user. Locating can also be implemented mainly automatically. The mask can then rotate the whole time around the radiation de ^¬ tector D. The speed of rotation (K) of the mask can be, for example, 10 times the data-collection interval (T) , i.e. if the data-collection interval would be one second, the mask would make a full revolution around the detector in ten sec ^¬ onds. The higher the K/T ratio, the better the performance. An extreme solution here is list-mode data collection (each in ^¬ teraction event is time-stamped) . The speed of revolution can then be great (< 1 second) . An intermediate form of manual and automatic locating can be hand-driven locating. The apparatus 10 can then in other ways be according to the embodiment described, but without the rotation device 19. The support 18 is thus then rotated by hand. Figure 10 shows an example of a system 100 for locating a radiation source S and at the same time also an example of an application for the operation of the apparatus 10. The system 100 includes a radiation detector D, which is now circularly- sensing and the apparatus 10 similar to already described above. The apparatus 10 includes a baffle 12 arranged to act as a direction indicator arranged to affect, more particularly to attenuate the radiation R detected by the radiation detec ^¬ tor D, in order to locate the radiation source S on the basis of the attenuation. Thus the baffle 12 is arranged to shade the radiation detector D from the radiation R transmitted by the radiation source S. In addition the apparatus 10 according to the embodiment now also includes a place 11 for a circular ^¬ ly-sensing radiation detector D, in which it is preferably removably placed.

The system 100 further also includes one or more processor units 21, arranged to detect a change from the data formed by the radiation detector D, more particularly the attenuation 14, 14.1 - 14.3 in order to form information 51 - 53 concern- ing, for example, the direction of location of the located ra ^¬ diation source S relative to the observer. Thus, the processor unit 21 is arranged to detect from the data formed by the ra ^¬ diation detector D one or more attenuations 14, 14.1 - 14.3 appearing in the radiation R and to locate the radiation source S on the basis of the attenuation of the radiation R. The system 100 also includes a pointer device 50 arranged to display the information 51 - 53 formed by the processor unit 21. The processor unit 21 can be, for example, a portable computer 54, in which there is software for the radiation detector D and the locating performed from the data formed by it. The pointer device 50 or even the actual processor device can, in turn, be a mobile-communications device, a smart phone, a tab- let computer, or some similar portable or handheld device with output means, in which there can be a wireless local communi ^¬ cations functionality (for example, WLAN) . In the portable computer 54 there will then be a similar local communications functionality 61. The apparatus 10, the radiation detector D fitted to it, and the portable computer 54 fit easily inside, for example, a backpack 55 equipped with carrying means 67, i.e. make the system portable. Their combined weight is only a few kilogrammes. This allows the inconspicuous detection and locating of a radiation source S, more generally, radiation scouting .

In addition, the system can also include a position definer 13 for determining the direction of the baffle 12 around the ra ^¬ diation detector D. The position definer 13 can be part of the apparatus 10. The processor unit 21 is then arranged to detect a change from the data formed by the radiation detector D, more particularly the attenuation 14, 14.1 - 14.3, and also in addition the direction, where the attenuation is at a peak, of the baffle 12 determined by position definer 13, corresponding to the attenuation. The radiation source S is then in the direction shown by the greatest attenuation.

However, there is reason to note that the system 100 according to the invention can also be implemented without the position definer 13. The attenuating material 16 can then be arranged statically relative to the radiation detector D, thus covering its field of view 59. Then by rotating them both together the direction of the location of the radiation source S can be determined. When the detector D and the apparatus 10 are, for example, in a backpack, which is on the back of its carrier 56, and when the carrier knows the direction of the attenuat ^¬ ing material 16 (for example, between the radiation detector D and the carrier 56) , the carrier 56 can locate the radiation source S by turning around his own vertical axis. In the pre ^¬ sent arrangement, the radiation source S is then in front of the carrier 56, if the signal of the radiation detector D is attenuated when the attenuation material 16 is situated be ^¬ tween the radiation detector D and the radiation source S. The system 100 can include, for example, a compass 20 fitted to the apparatus 10 for determining the geographical direction and the GPS function 60 for determining the location. By combining the compass data with the other data the direction of the radiation source S relative to the observer 56 can also be transmitted to remote surveillance, for example, through a wireless data-transfer network 57.

Figure 11 shows two different situations and view examples us- ing the pointer device 50. It can now be, for example, a mobile station and more particularly its display. The left-hand part of Figure 11 shows a display, in which there is no radia ^¬ tion source S in the field of view of the radiation detector D. The user can then be shown a graphical indication (com- pletely green, 51) . The right-hand part of Figure 11 shows, for its part, a display, in which there is a radiation source S in the field of view of the radiation detector D. Its direc ^¬ tion can be expressed, for example by a red colour, or its hues 52, 53, 68 darkening in stages. The darker the red, the more certain it is that the radiation source S is in the di ^¬ rection shown by the hue in question. As locating and the associated calculation progresses, the sector area 53, 68 showing the direction of location of the radiation source S can further narrow and thus locating can become more precise. This can thus be implemented as a kind of real-time "radar dis ^¬ play". Other ways are a direction vector on a map base (for example outdoors) or an image connected to a web camera (for example, indoors) . The direction of the location of the radia ^¬ tion source S is then shown in the display by, for example, an arrow.

The invention further relates to a method for locating a radiation source S. In the method, the radiation source S trans ^¬ mitting radiation R is located using a circularly-sensing ra- diation detector D by affecting, more particularly by attenu- ating the radiation R detected by the circularly-sensing radiation detector D direction-dependently. The radiation source S is located on the basis of the attenuation of the radiation R detected by the radiation detector D. In the method, a small disturbance is caused in the radiation field when the baffle 12 is between the radiation detector D and the source S. The detection of this disturbance reveals the direction of the ra ^¬ diation source S. The baffle 12 itself can be designed in many different ways, but the principle is always the same.

According to one embodiment, before the locating of the radia ^¬ tion source S, by using the radiation detector D can be sought the radiation source S from its field of view 59. When the ex ^¬ istence of a radiation source S is detected, only then can lo ^¬ cating it be initiated. When performing it using the apparatus 10 the operation of the baffle 12 is initiated. Only then the baffle 12 and more particularly the attenuating material 16 begins to rotate coaxially around the radiation detector D, covering its field of view 59 by sector areas.

At first the basic direction can be determined, which fixes the set of co-ordinates and relative to which the locating is performed. The observer can stand stationary during the locat ^¬ ing. The measurement can be made, for example, at 20 - 30 de ^¬ gree rotation-angle intervals. Thus the locating of the radia ^¬ tion source S need not necessarily operate continuously. In other words, before locating the radiation source S the same radiation detector D can be used to seek the radiation source S from its field of view. Only when the radiation source S is found, the locating of the radiation source S is initiated as the joint operation of the baffle 12 and the radiation detec ^¬ tor D. This saves the system's power consumption and makes the radiation detector D more multi-purpose. When locating the radiation source S and the attenuating material 16 of the baffle 12 lands between the radiation detector D and the radiation source S, a detectable, for example, a peak-like change, more particularly an attenuation 14 is detected in the data collected by the radiation detector D. In the attenuation, the signal weakens locally. When it is deter ^¬ mined at which point in the outer circumference of the radia ^¬ tion detector D the attenuating material 16 was at the minimum of the attenuation 14, the location of the radiation source S can be determined to be in the direction that defined the location of the attenuating material 16 relative to the radia ^¬ tion detector D at the location of the relevant minimum. In other words, the radiation detector D and the attenuating material 16 then together define a straight line that points in the direction of the location of the radiation source S. When the attenuation to the radiation detector D caused by the baffle 12 is greatest, and the centre line of the attenuating ma ^¬ terial 16 is in the direction of the circumference of the ra ^¬ diation detector D, the axial centre point of the radiation detector D and also the radiation source S are on the same straight line. Thus the locating of the radiation source S can be said to take place on the basis of the attenuation of the radiation R, which is detected using the radiation detector D.

Next, an example of the implementation of the calculation of the system is explained. The collection time (dt) of the spec ^¬ trum can be, for example, 1 second. The time of rotation of the attenuating material 16 around the radiation detector D can be, for example, 5 - 20 seconds. The baffle 12 can rotate continuously. Its position can then be read at intervals of dt/10 seconds. The direction of the baffle 12 can be recorded timestamped in a separate add-on table in a database and linked to a co-ordinate-data table. Using the direction data of the baffle 12 and calculation data (counts) it is also pos- sible to interpolate the direction of the radiation source S, if it lies, for example, between two measurement points.

Locating can be carried out, for example, by binary search performed in sectors separately for each revolution of the baffle. In this, direction and counting data (cps, counts per second) are combined.

The division can be, for example, as follows:

6 x 60°

12 x 30°

24 x 15°

36 x 10°

72 x 5°

360 x 1°

Position 1 gives direction in the case of a weak signal, but it imprecision is greater. The other binnings are also calcu ^¬ lated and are utilized if statistics permit. From these it can be seen what the histogram formed from the data looks like seen from different directions. The direction of the source S can be calculated from the distribution of the binnings. It can be, for example, a simple search for a minimum or an adaptation to a calculated/measured shape. The direction can also be calculated from the raw data with the aid of data-fitting algorithms without binitization . A graphical presentation can be made of the calculation. If radiation libraries specific to each nuclide are recorded in the system, it will be possible, in addition to locating to identify the source S causing the radiation R, on a nuclide level.

The apparatus 10 itself can be controlled on the basis of the collected data. If, for example, a weak signal is received form a certain direction, the baffle 12 is directed to make long measurements precisely from the sector direction in ques ^¬ tion. If, for example, it seems that the source S is in the direction "60", the attenuating material of the baffle 12 would move slowly past this, but when the last part of the at ^¬ tenuating material of the baffle has passed 60 degrees, or (60 + x) degrees, the stepper motor could run the baffle 12 back to scan precisely this interesting area. It has been shown in pilot-stage tests that, owing to the invention, it is possible to determine the direction from the radiation detector D to the radiation source S with an accuracy of as much as a few degrees .

According to yet another embodiment, in the method the direc ^¬ tion of an unknown radiation source S can be determined, for example, from two (or more) places. The intersection of the vector directions then gives the location in (x,y) form. The locating of a radiation source S can also be performed in or ^¬ der to determine the distance from the radiation detector D to the radiation source S. If two measurements are made from dif ^¬ ferent places (two vectors), the source-detector distance can also be determined, even through the attenuation of the pho ^¬ tons might be asymmetrical. Thus the method is independent of different attenuations possibly appearing in different direc ^¬ tions. The locating of the source removes a great deal of vagueness from the activity analysis, because the uncertainty relating to the distance can be eliminated owing to the inven ^¬ tion .

Figure 12 shows the measurement principle for determining the distance x from the observation point 0 to the location point B of the radiation source S. The distance x can be determined in stages, for example, in such a way that 1) the base line OA defined by two different measurement points is defined, 2) the distance OA is measured, 3) the angles a and β are measured, and 4) the distance x is calculated using the equations γ = 180 - α - β and x = [sin(3) / sin(Y)] * d.

3D-locating is also possible. It takes place simply by rotat- ing the totality formed by the detector D and the apparatus 10 from a vertical position to a horizontal position, i.e. by 90 degrees. The vertical direction to the radiation source S is then defined after the azimuth. Figure 13 shows an example of the measurement graphics in locating a radiation source (Cs) from two different locating points (0 and B) . The curves 63 and 64 of the drawings of the set of polar co-ordinates depict the pulse frequency at a spe ^¬ cific energy interval (500 - 800 keV, default setup) . The source S is in the direction of the smaller pulse frequency. The curve 65 is the weighted mean value of the pulse frequen ^¬ cies calculated from the whole spectrum. It is calibrated in such a way that it corresponds to the dose rate in the air (microSv/h) at the location of the detector D. In addition, the graphics are implemented inversely to point straight to ^¬ wards the source S .

The shape of the attenuating material in the circumferential direction of the radiation detector D is such that it covers the detector D, and even more particularly its crystalline material 25 in the arrival direction of the radiation R. The left and right edges of the attenuating material can be sym ^¬ metrical (as in the case of the prototype of the apparatus) or asymmetrical. Additional conclusions can then be drawn on the direction and quality of the radiation. The edges can be cut radially, or the edge can be straight, relative to the direc ^¬ tion of the radiation source S. The thickness of the attenuat ^¬ ing material can also vary. However, it need not necessarily entirely stop the radiation arriving at the detector D, be- cause the location of the radiation source S can be determined from even a small disturbance in the arrival direction of the radiation R. In the prototype of the apparatus 10 there was 10-mm of lead and it operated well generically at all ener ^¬ gies. Americium (60 keV) stops entirely at such a baffle, but cesium and cobalt only partly, but nevertheless sufficiently for the location direction of the source S to be determined on its basis.

In the case of the embodiment described in connection with the RanidPro 200 radiation detector D, the length of the curve of the attenuating material can be about 54 mm in the outer edge of the baffle 12 and about 43 mm in the inner edge. The dis ^¬ tance from the outer surface of the RanidPro radiation detec ^¬ tor D to the inner surface of the attenuating material 16 is 9 mm. The coverage angle (i.e. examined relative to the centre point of the radiation detector D) of the attenuating material, more generally the individual attenuating component, can then be, for example, 40 - 60 degrees, more particularly 45 - 55 degrees, such as, for example, 50 degree.

Above, the baffle 12 is described as a kind of accessory to be attached to a radiation detector D (or vice versa) . In it, the baffle 12 was constructed outside the detector's D protective casing. The baffle property can also be integrated even di- rectly into the radiation detector D itself. Thus the inven ^¬ tion further also relates to a radiation detector D, which includes a radiation-sensitive substance 25 with electronics 22, 23 connected to it for measuring radiation R. The radiation- sensitive substance 25 is arranged to react in a circularly- sensing manner to the radiation R caused by a radiation source S. The electronics 22, 23 are connected to the radiation- sensitive substance 25 in order to detect radiation R. The ra ^¬ diation detector D then includes a baffle 12 arranged to af ^¬ fect, more particularly to attenuate the circularly-sensing detecting radiation detector D and now even more particularly, the radiation R detected by the radiation-sensitive substance 25 according to the invention, in order to locate the radiation source S on the basis of the attenuation of the radiation R.

In the embodiment integrated in the radiation detector D, the baffle could be very close to the surface of the crystalline substance 25 of the detector D, or even touch it. An implementation that is very light and small in size is then obtained, but, on the other hand, at the same time the directional accuracy diminishes, as does the detection ability. The baffle would then continuously cover 180 degrees of the diameter of the cylinder. Nevertheless, the precision of the bearing would still be reasonable, because the shape of the signal deter- mines the direction. Thus the basic idea according to the in ^¬ vention can be implemented in several different ways. A first bearing can be obtained very quickly using a small and light apparatus, in which the baffle is arranged very closely to the crystal itself.

In some applications the radiation detector can also be ex ^¬ tremely small, for example, 5 - 10-mm thick CdZnTe. A small, less than 1-cm ³ (10-g) baffle can then be placed around it and thus an excellent hand-driven apparatus can be obtained, which is, for example, the size of a mobile station. On the other hand, in permanent applications, for example, in frontier con ^¬ trol or in vehicles there can be a 5" Nal detector.

By covering a relatively small sector laterally of the field of view 59 of the relatively small radiation detector D data is easily obtained also on background radiation, from open sectors 48 of a larger field of view without an attenuating material, compared to the baffle. One use of the apparatus can be the determining beforehand of the angular dependence (anom- alies) of the natural background radiation, before an accident or deliberate act. This is important when securing, for in ^¬ stance, critical infrastructure, as the detection of changes in the radiation field allow the locating of the very weakest signals too. In addition, internal contamination (in the example, ¹³⁸ La) of the crystalline substance 25 (in the example LaBr ₃ ) will disturb the base line and, for example, the peak analysis of ⁶⁰ Co peaks. Owing to the invention, the use of a narrow covering and determination based on attenuations also permits good counter statistics. The crystal's internal con ^¬ tamination will then have no significant effect on the final result .