Patent Application: US-201715446569-A

Abstract:
this invention presents a new device to produce images of the gamma field , specially designed for circumstances requiring high efficiency and fast response imaging , by applying the concept of image extraction within a given field of view , through the combination of efficient gamma radiation detectors . each detector is located inside a shielding , with an area of the detector with no shielding to enter the incident gamma radiation detector with a plurality of angles in relation to the normal outgoing central axis to the surface of the detector through the unshielded area , where that central axis is divergent in relation to the outgoing central axes of neighboring detectors .

Description:
before proceeding to a detailed description , we can see that the creation described is not limited to the use as a detector type for a specific use , and that although the present description is shown and described as applied as a radiation monitor for fixed positions , it can be implemented in a variety of applications and sizes in different geometries and mechanical solutions , using different types of gamma detectors , for fixed or mobile applications , in order to create images of the gamma field . the present invention presents a device capable of obtaining gamma images with high efficiency and within short periods of time , with a concept for the creation of the gamma image that can adapted to the sensitivity , speed and resolution needs of various uses . it applies a concept that is compatible with the intrinsic physical properties of the fields of gamma photons and the need to create an image at very high speed . fig1 is a simplified diagram of the two classical gamma camera options , on the left a gamma camera with telescope collimator ( 10 ), formed by a plurality of parallel collimators ( 11 ) which select the direction of gamma incident on the gamma sensor ( 12 ), position - sensitive , from the sources ( 14 ) schematically displayed in the figure as a thick line ( 16 ), while the photons schematically shown in the figure as lines ( 17 ), ( 18 ) and ( 19 ) cannot reach the gamma sensor ( 12 ). in this type of detectors , the image of the gamma field generated by the gamma sensor ( 12 ) can never have a higher spatial resolution than the resolution that can be obtained on the collimation degree that can be achieved with a telescope collimator . on the right side of the same figure , we see a gamma camera with a pin - hole collimator ( 20 ), composed of the position - sensitive gamma detector ( 22 ), which detects the incident gamma originating from the source ( 23 ), these photons are shown schematically as line ( 24 ), while the photons schematically shown in fig1 , such as lines ( 25 ), ( 26 ) and ( 27 ) cannot reach the gamma sensor ( 22 ), and therefore do not contribute to the image of the gamma field . the two types of gamma cameras displayed in fig1 generate the image from the collimation of outgoing gamma ( 16 ) ( 17 ) ( 18 ) and ( 19 ), and ( 24 ) ( 25 ) ( 26 ) and ( 27 ) from sources ( 14 ) and ( 23 ), which is why they generate the image by rejecting the gamma which do not go through collimators ( 17 ) ( 18 ) ( 19 ) ( 25 ) ( 26 ) and ( 27 ), and not those which can go through ( 16 ) and ( 24 ). that is to say that the higher resolution will always take a higher collimation , and therefore lower efficiency in the measurement process , which is why the measurement time will be higher depending on the desired spatial resolution for the image . the imaging concept of gamma cameras is , in some aspects , similar to the type of systems used by optical cameras and the view of the human eye and the eyes of other animals , as outlined in fig2 . in that system , rays from the focus ( 50 ) ( 52 ), when going through the lens of the eye ( 60 ) are deflected by the refraction index and curvature radius of the lens of the eye ( 60 ), and so they change paths ( 62 ) and ( 64 ), to be finally measured by the retina located on the back of the eye ( 70 ). in the concept of human eye and optical cameras , when the object is fully in focus , the image has its maximum definition . but current gamma cameras cannot use the same concept of the lens , since the gamma radiation does not have a behavior similar to that of light when it goes through a medium with a different refraction index , but rather makes compton , photoelectric and pair creation interactions ( the latter for energies above the minimum energy required to create an electron - positron pair ). the gamma field penetrates the medium continuously , depending on the cross section , generating a spatial distribution , which is also continuous , of outgoing secondary photons , with a plurality of output angles for the compton interaction , and 2 opposite gamma photons from pairs creation . that is to say , it interacts with a plurality of positions , with a plurality of output angles , which is why it is not possible to achieve an effect similar to the lens of the eye ( 60 ) or optical cameras , because in the latter , the lens allows ( when in focus ) all light coming from a single external point to the view device incident on the lens to project towards the retina of the eye , also on one same spot . therefore , to build an image , gamma camera devices , with their collimator concepts , generate the image so that each position of gamma sensors ( 12 ) and ( 22 ), receives one only incoming radiation path . this concept is essentially slow , since the photons &# 39 ; count rate under real , everyday conditions will be very low , except in places with a very high rate of radiation , since the image has been generated by collimating directions , i . e ., rejecting a significant fraction of the photons available in the gamma field . this is why these cameras are slow , and for many applications they require a very long time to acquire an image . another way to acquire an image , or in this case to make a map , since the image is obtained to be overlapped with a map or image of the land , is to use gamma detectors for geophysical studies , which are also used to locate lost gamma sources or to know the distribution of gamma radiation after an accident . these detectors are formed by a single non - collimated sensor , which in the most common commercial forms are similar to those outlined in fig3 . the diagram example of fig3 displays a gamma detector for geophysical surveys consisting of four prismatic scintillators ( 110 ) ( 112 ) ( 114 ) ( 116 ), as a typical example , a sodium iodide activated with thallium , 16 inches by 4 inches by 4 inches , with an approximate volume of detection of 4 liters . that crystal issues its light through the bottom face of the figure , to a photomultiplier ( 120 ) ( 122 ) ( 124 ) ( 126 ) for each detector . the signals are processed with the electronics , which acquires the signals from the four detectors and combines them to obtain a single spectrum on pulses height corresponding to the full detector , i . e ., acquired by the four detectors which are part of the detector assembly . these detectors have fields of view oriented towards the direction ( 130 ) of fig3 , with a lobe response with a side aperture of about 50 degrees approximately in relation to the regular direction of the detector , generated because at greater angles , the geometric detection efficiency is significantly lower . these detectors are used to acquire an image or map of the radiation by placing them on an aerial vehicle with the detection face looking downwards , flying in a trajectory with a regular pattern of equidistant air lines , in order to cover the entire area to be measured . the time of acquisition of an image is very long because although the detector is very sensitive , the resulting spatial resolution is low . then , in order to measure with a higher resolution , it has to fly at low heights , but as the lateral area covered during the flight decreases , more flights have to be carried out to cover the same area , which increases the measurement time even more . considering the limitations of the various types of gamma cameras and geophysical gamma detectors , another concept is proposed to obtain the image of a gamma field , which makes use of the property that gamma fields are inherently diffuse , since when you move a gamma detector for small distances , the rate count and energy spectrum does not change significantly in open places . measurements in laboratory and confined spaces , with samples close to the detector or a shielding are very sensitive to position , but outside of this specific situation , gamma fields , both in its angular and energy dependence , vary very slightly with position . the proposed device uses this property of gamma in relatively open spaces to carry apply another method to capture the image of the gamma field . taking a plurality of detectors for one same device , as outlined in fig4 , for illustration purposes only , with three schematic gamma detectors ( 200 ) ( 202 ) ( 204 ), each detector is located inside a shielding close to the sensor ( 210 ) ( 212 ) ( 214 ), or in contact with it , which does not cover the face of the sensor ( 220 ) ( 222 ) ( 224 ). each detector assembly — shielding , like units ( 200 ) and ( 210 ), ( 202 ) and ( 212 ), ( 204 ) and ( 214 ), form a complete unit of measurement , or gamma sensor , with its own electronics and processing . each gamma sensor presents a response to the path of the incident gamma radiation with lobar form ( 230 ) ( 232 ) ( 234 ) in relation to the central axis of each sensor ( 240 ) ( 242 ) ( 244 ), since when the radiation separates from the central axis , the shielding and the decrease of the geometric efficiency reduce the response of the gamma sensor in the proposed device . the axes of view ( 240 ) ( 242 ) ( 244 ) of each lobe diverge in relation to the center ( 250 ) the image of the radiation is obtained from the fact that each gamma sensor , as well as its central axes ( 240 ) ( 242 ) ( 244 ) have an angle , ( 252 ) and ( 254 ), in relation to the axis of view of the neighboring lobe , each gamma sensor then sustains a certain area of view ( 260 ) ( 262 ) and ( 264 ) with respect to the center ( 250 ). as in most practical cases , the gamma field in a point has a slight angle variation , and is similar to the gamma field by moving the point to a short distance ; for such cases the plurality of angles measured by a detector is similar to the same plurality of angles measured by another detector if the position of the second detector is close to the first detector . for these cases , the proposed device then measures the angular response of the gamma field at one point by measuring different pluralities of angles facing different directions simultaneously at nearby positions . it is clear that if we place a small shielding as that in fig4 , lobes ( 230 ) ( 232 ) and ( 234 ) of each detector may overlap , as shown schematically in fig4 , so that there may be gamma rays coming from an area of view that can be detected in the neighboring detector . since the measurement lobes of each gamma sensor can be completely characterized , and as precisely as desired , the overlapping between neighboring lobes can be considered fully known , which is why it can be mathematically calculated , based on the counts rate of each detector ( 200 ) ( 202 ) and ( 204 ), the counts rate which incident on each detector from its area of view ( 260 ) ( 262 ) ( 264 ) only , subtracting the contribution of gamma from neighboring areas . unlike gamma cameras , each sensor receives a plurality of incoming paths of incident gamma radiation , and as the gamma sensor can be sufficiently large and efficient for many practical applications , the measurement statistics is high and there can be a very short time from one gamma image to the next . in fig4 , a divergence has been considered in relation to a center ( 250 ), but different three - dimensional arrangements of gamma sensors and detection lobes may diverge in relation to a center , or several centers , or an axis , or several axes , or combinations thereof , depending on the suitability for the different uses . in an alternative of the device , as that schematically shown in fig5 , each shielding ( 270 ) ( 272 ) ( 274 ) has additional side divergent screens ( 275 ) ( 277 ) ( 279 ) of shielding material for gamma radiation , outside the face exposed to the detection lobe ( 280 ) ( 282 ) and ( 284 ), so as to reduce the overlapping between neighboring lobes and simplifying the treatment of signals to the detector output . this side screens are quite lightweight , because the thicknesses may be relatively small , because the gamma have oblique incidence on its surface , the paths have to penetrate a shield length significantly greater than the thickness of the screen to reach the detector . the alternative for the device in fig5 also includes , with respect to fig4 , internal divergent screens ( 285 ) ( 287 ) and ( 289 ) to external side divergent screens ( 275 ) ( 277 ) and ( 279 ), also composed of shielding material for gamma radiation , and divergent with respect to the central axes ( 290 ) ( 292 ) and ( 294 ), but with an equal or smaller angle of divergence as compared to the angle of the external divergent screen ( 275 ) ( 277 ) and ( 279 ), to not significantly decrease the response to the gamma from the same area of view , and strongly reduce detection form areas of view from neighboring sensors . this other alternative reduces the overlapping of lobes ( 295 ) ( 297 ) ( 299 ) among neighbors and simplifies the treatment of signals of each detector . if the use , weight , size of the device and the count rate allow this type of external and internal screens to reduce the contribution of detection from areas of view of neighboring sensors , the contribution of neighbors in terms of count rates becomes statistically irrelevant , and the counts rate of each gamma sensor correlates directly to the area of view only , without mathematical corrections of neighboring contributions . fig6 shows the section of an alternative shape for a gamma sensor proposed to be used in the device mentioned , composed of half cylindrical scintillator ( 300 ), and a photodiode ( 310 ), with preamp electronics ( 320 ) next to the photodiode ( 310 ). the half scintillator is surrounded by a shielding ( 330 ), and preceded , on the direction of the incoming radiation , by a side screen ( 340 ) composed of shielding material . since the detector is a cylindrical section detector , it is convenient for this side screen to have a conic section , while to achieve a decrease in the influence of neighboring lobes , it has two internal screens , ( 350 ) and ( 360 ), also made of shielding material , which , like with cylindrical screens , shall preferably have conic section . fig7 shows an alternative to a small device , consisting of an arrangement of gamma sensors as those in fig6 , forming a gamma view camera consisting of 5 horizontal and 3 vertical elements , with a side aperture of about 25 degrees and a vertical aperture about 15 degrees in relation to the central axis . it is clear then that various mechanical dispositions , on a sphere , on a plane or on different surfaces spatially arranged , various mechanical solutions of gamma sensors that use the concept of the sensors in fig4 and 5 , will produce images of the gamma field , provided that the detection lobes are divergent in relation to a center , axis or combination of one or more of these . when due to the desired sensitivity large gamma detectors are used , such as scintillator crystals for geophysical prospection or search for radioactive sources , as the detectors in fig3 , the crystals are as efficient to the energies of gamma of greatest interest , which can be considered to almost completely absorb the incident radiation , that is to say , only a small fraction of the incoming radiation comes out to a detector , and then for outgoing radiation , the detector complies with conditions similar to a shielding . then in this case , on the proposed device , each neighboring detector can be considered as the side shielding of the other detectors , provided the detectors are placed at the lower distance from one another . then , for this application we can leave aside the shielding surrounding the detector and build the proposed device without side shielding . likewise , we can leave aside the front shielding and internal and side screens to reduce the overlapping between the neighboring detection lobes and maximize sensitivity , using the naturally cosine detection lobe as the detection lobe , which is generated when the direction of the incident gamma deviates from the norm to the center of a flat face detector . an alternative to the design of the proposed device is displayed in fig8 , which consists of four prismatic scintillators with trapezoidal section ( 370 ) ( 272 ) ( 374 ) and ( 378 ), together , joined by their oblique sides and optically coupled with photomultipliers ( 380 ) ( 382 ) ( 384 ) and ( 386 ). it is suitable for geophysical measurements or aerial search for radioactive sources , with the advantage that it allows acquisition of a gamma image by subdividing the measurement or image in about four different angles of view covering about 180 degrees , which allows to quadruple resolution , with an even greater aperture , since it increases efficiency in relation to classical detectors , by separating for large angles with respect to the norm to the detector . the use of large sodium iodide crystal can be very expensive , and even more so if the crystal section is not square or rectangular or cylindrical , and a trapezoidal section is required . this is why a construction alternative for the device in fig8 may be specifically appropriate to be used with plastic scintillators , low - cost for large sizes . in this case , it is not possible to perform a spectrometry by pulse height of the photopeak , but it is possible to perform a spectrometry through deconvolution of compton spectra , and in this case regain the capacity to analyze the incident photon energy spectrum , or analyze only the count rate within a certain region of the spectrum of pulse height . an alternative to the concept in fig8 can be seen in fig9 , with a slight decrease in efficiency but with a cost reduction , is obtained by using square section detectors , as shown by detectors ( 390 ) and ( 392 ) joining them through the side of the internal vertex ( 394 ). since part of the side shielding is lost , it is convenient to add a thin plate of shielding between the detectors in the space between two neighboring detectors , as seen in plate ( 396 ), for a lightweight and efficient design also using divergent internal side panels , as we can see in plates ( 397 ) and ( 398 ). an example of practical application for commercial use of the proposed device used as an area monitor can be seen in fig1 , where we can see a half - height section of a set of 4 gamma detectors ( 400 ) ( 402 ) ( 404 ) and ( 406 ), inside a shielding ( 410 ) which includes external and internal side deflectors ( 420 ) ( 422 ), ( 430 ) ( 432 ), applied , for instance , as those for the detector ( 400 ), so that each single sensor only significantly receives incident radiation from the southern lobe of its own angular sector . the section in fig8 can be seen in fig1 , which contains a diagram showing that for this type of device , when it is in front of the area of view , the screens design allows the radiation from a gamma source ( 500 ) to be detected only by the detector that is within its area of view , such as paths ( 510 ) ( 512 ) and ( 514 ), and not for paths ( 520 ) ( 522 ) and ( 524 ). in this practical example , as shown in fig1 , the gamma detectors in fig1 and 11 are small scintillators ( 600 ), typically sized 10 mm × 10 mm × 40 mm , clear type , such as sodium iodide or cesium iodide , or plastic , or liquid scintillators , which have a photodiode ( 610 ) on one side , which is highly sensitive to visible radiation in light emission wavelengths of the scintillator , with the signal processed by a preamplifier and amplifier schematically contained inside the electronic box ( 620 ) of the same detector . in this case , the gamma sensor is used receiving the incident radiation through the side face ( 630 ), with an efficiency superior to that of a geiger counter of similar size , but at comparatively similar costs , taking into consideration the low costs of this type of components , both crystal and plastic . in this practical example , the full sensor can be seen in fig1 , where we can see the shielding ( 700 ), the face of the gamma sensor ( 710 ) facing the person looking at the figure , and the lower electronics box ( 720 ). in this example , the total length of the device ( 730 ) is about 12 cm , and the total width ( 740 ) is about 10 centimeters , weighing approximately 1 to 2 kg , including the lead shielding and even less for tungsten . in the case of fig1 , the detector measures the gamma field with a field of view of 180 degrees , and is suitable to be placed on a wall , under a roof , or in aerial or ground vehicles . this type of example of application of the proposed device is very useful , since as gamma fields are naturally diffuse and have little dependence with height , it is of great practical interest to make a very quick measurement of the incident radiation , only measuring its angular dependence , since as it is a device generating a high - speed gamma image it can operate in real time within 1 second or less . when using sodium iodide or cesium iodide crystals , this example of application can be also used to make a spectrometry of the signal coming from each detector . due to the low cost and size of this example of application , the benefits of the device proposed as an example of application can be improved with a low additional investment , overlapping the gamma count rates of southern lobes of measurement with an image obtained with an optical camera with the same field of view that the device proposed , so as to correlate the variations of the rate of radiation of each southern lobe with the objects moving in front of the sensor , taking advantage of the fact that the proposed device , because it is highly efficient , allows to produce the gamma image within 1 second or less . in this application example , one - dimensional and in real - time , and within the same cost range as geiger monitors , the presented 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