Abstract:
There are provided a gamma ray detecting apparatus, including: a secondary electron emitter causing a Compton scattering reaction with an incident gamma ray to emit secondary electrons in a progress direction of the gamma ray; a first radiation detector provided to be opposed to the secondary electron emitter with respect to an emission progress direction of the secondary electrons and detecting the position and transfer energy of the secondary electron; a second radiation detector provided to be opposed to the first radiation detector with respect to the emission progress direction of the secondary electron and detecting the position and the transfer energy of the secondary electron passing through the first radiation detector; a third radiation detector provided to be opposed to the second radiation detector with respect to the emission progress direction of the secondary electron and detecting residual energy of the secondary electron by absorbing the secondary electron passing through the second radiation detector; and a data processor having a coincidence circuit judging whether the secondary electrons simultaneously react in the first to third radiation detectors, and the data processor back traces trajectories of the secondary electrons detected by the first and second radiation detectors to detect the position of a ray source of the gamma ray, and a gamma ray detecting method.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a gamma ray detecting apparatus and a method for detecting a gamma ray using the same, and more particularly, to a gamma ray detecting apparatus and a method of detecting a gamma ray using the same capable of imaging location and distribution of ray sources of the gamma ray by reversely tracking a trace of a secondary electron generated in Compton scattering reaction of a gamma ray emitted from a gamma ray source or nuclear reaction. 
     2. Description of the Related Art 
     In general, in cancer treatment using a radiation, it is important to remove a cancer cell and prevent neighboring normal tissues from being damaged by locally transferring radiation energy to only a cancer tissue. Since a photon beam or an electron beam is used in conventional radiation treatment, it is difficult to limitedly apply a beam amount to the cancer tissue. 
     Meanwhile, in the case of cancer treatment using protons, the beam amount can concentrate on a desired portion and the damage of the neighboring normal tissues can be minimized due to a peculiar energy transfer characteristic called Bragg Peak. 
     However, up to now, a technology that accurately decides a Bragg Peak location in a patient&#39;s body in real time during treatment has not yet be provided, and as a result, a technology has held the limelight, which infers the Bragg Peak location through a distribution of a prompt gamma ray generated by a reaction between the protons and a target material. 
     In order to infer the Bragg Peak location, a gamma ray emission imaging device constituted by a focusing device and a position sensitive radiation detector is used and in the gamma ray emission imaging device, when the gamma ray emitted from a radiation source passes through the focusing device and thereafter, reacts in the position sensitive radiation detector, data generated at that time is acquired to image a distribution of the radiation source. 
     However, the existing gamma ray emission imaging device has various problems. In the existing gamma ray emission imaging device, since most gamma rays are removed by the focusing device, it is difficult to acquire high image sensitivity. Further, since the gamma ray is high in transmittance and low in reaction probability, it is difficult to expect high image sensitivity when the gamma ray is directly detected. In the conventional gamma ray emission imaging device, since image resolution and image sensitivity depend on a structure of the focusing device and have a conflicting characteristic to each other, there is a limit that the image resolution or image sensitivity cannot be independently improved. 
     Moreover, when energy of the gamma ray increases, the performance of the focusing device is rapidly degraded, and as a result, the image resolution is degraded. Therefore, the convention imaging device of the above scheme can be substantially applied to only a gamma ray of 1 MeV or less. 
     Further, since a target should be scanned while placing a measurement system measuring the gamma ray circularly or rotating the measurement system in order to acquire an image of the ray source emitting the gamma ray in a 3 dimension, there is a limit in minimizing the device and manufacturing cost is also high. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides a gamma ray detecting apparatus and a method for detecting a gamma ray using the same with which it is possible to indirectly detect location and distribution of a gamma ray source by using a secondary electron generated after a gamma ray is primarily converted into an electron, when a ray source of the gamma ray is detected. 
     An aspect of the present invention also provides a gamma ray detecting apparatus and a method for detecting a gamma ray using the same with which it is possible to enhance image resolution for a gamma ray source emitting a high-energy gamma ray and improve measurement efficiency. 
     An aspect of the present invention also provides a gamma ray detecting apparatus and a method for detecting a gamma ray using the same with which it is possible to three-dimensionally acquire location and distribution of a gamma ray source at a fixed position. 
     An aspect of the present invention also provides a gamma ray detecting apparatus and a method for detecting a gamma ray using the same with which it is possible to achieve a small size and a light weight of a device for acquiring an image of a gamma ray source. 
     According to an aspect of the present invention, there is provided a gamma ray detecting apparatus, including: a secondary electron emitter causing a Compton scattering reaction with an incident gamma ray to emit secondary electrons in a progress direction of the gamma ray; a first radiation detector provided to be opposed to the secondary electron emitter with respect to an emission progress direction of the secondary electrons and detecting the position and transfer energy of the secondary electron; a second radiation detector provided to be opposed to the first radiation detector with respect to the emission progress direction of the secondary electron and detecting the position and the transfer energy of the secondary electron passing through the first radiation detector; a third radiation detector provided to be opposed to the second radiation detector with respect to the emission progress direction of the secondary electron and detecting residual energy of the secondary electron by absorbing the secondary electron passing through the second radiation detector; and a data processor having a coincidence circuit judging whether the secondary electrons simultaneously react in the first to third radiation detectors, and the data processor back or reversely traces trajectories of the secondary electrons detected by the first and second radiation detectors to detect the position of a ray source of the gamma ray. 
     The first radiation detector or the second radiation detector may detect the positions of the plurality of secondary electrons, and the data processor may detect the ray source of the gamma ray from a cross point of lines connecting the positions of the secondary electrons. 
     The secondary electron emitter may be made of any one of liquefied helium, beryllium, and distilled water so that the secondary electron is emitted from the secondary electron emitter while maintaining a linear trajectory. 
     The first radiation detector or the second radiation detector may be made of a material having a low atomic number or a low density so as for the secondary electron emitted from the secondary electron emitter to maintain the linear trajectory while passing through the first radiation detector or the second radiation detector. 
     The first radiation detector or the second radiation detector may be formed in a double-sided silicon strip type. 
     An interval between the first and second radiation detectors may be larger than an interval between the second and third radiation detectors. That is, the interval between the first and second radiation detectors should be sufficiently large and the interval between the second and third radiation detectors is preferably minimized. 
     A thickness of the third radiation detector may be larger than a thickness of the first radiation detector or the second radiation detector. The third radiation detector is preferably sufficiently thick and the reason is that all secondary electrons and x-rays generated while the secondary electron is absorbed in the third radiation detector need to be absorbed of itself in order to accurately decide energy of the secondary electron that passes through the second radiation detector. 
     The gamma ray detecting apparatus may include an energy selector that sums up the energy of the secondary electrons detected by the first to third radiation detectors and judges whether the summed energy is included in a set reference energy range. It is possible to judge whether data detected by the selector may judge is effective data to acquire the position of the gamma ray source as a 3D image. 
     According to another aspect of the present invention, there is provided a gamma ray detecting method using the gamma ray detecting apparatus, including: (a) causing a Compton scattering reaction with the gamma ray incident in the secondary electron emitter and emitting the secondary electron in the same direction as a progress direction of the gamma ray; (b) detecting the position and transfer energy of the secondary electron at the time when the secondary electron passes through the first radiation detector; (c) detecting the position and transfer energy of the secondary electron at the time when the secondary electron passes through the second radiation detector; (d) detecting residual energy of the secondary electron at the time when the secondary electron is absorbed in the third radiation detector; (e) detecting data of the secondary electron detected simultaneously detected by the first to third radiation detectors by using the data processor; (f) detecting the position of a ray source of the gamma ray by back-tracing (or reversely tracing) a trajectory of the secondary electron detected by the first and second radiation detectors; and (g) acquiring as an image data included in a reference energy range in which the sum of the energy of the secondary electron detected by the first to third radiation detectors. 
     Step (b) may include measuring a position Pa 1  and Pb 1  where the plurality of secondary electrons passes through the first radiation detector and energy Ea 1  and energy Eb 1  transferred by the secondary electron at the time when the plurality of secondary electrons passes through the position Pa 1  and the position Pb 1 , and step (c) may include measuring a position Pa 2  and a position Pb 2  where the secondary electron passing through the first radiation detector passes through the second radiation detector and energy Ea 2  and energy Eb 2  transferred by the secondary electron at the time when the secondary electron passes through the positions Pa 2  and Pb 2 . 
     In step (f), a trajectory connecting the measured positions Pa 1  and Pa 2  and a trajectory connecting the positions Pb 1  and Pb 2  are back-projected to judge a point where both trajectories cross each other as the position of the ray source of the gamma ray. 
     In step (e), the data of the secondary electron simultaneously detected by the first to third radiation detectors may be selected by using a coincidence circuit. The reason is that a very thin detector is used as the first and second radiation detectors, a non-charged particle very rarely reacts with both detectors react with each other while two detecting and at the same time, a case in which a coincidence is satisfied is by a charged particle. 
     In step (e), the data included in a reference energy range (or sum energy windows) in which the sum of the energy of the secondary electron detected by the first to third radiation detectors is selected. 
     In step (e), the data included in respective reference energy ranges (or energy windows) in which the energy of the secondary electron transferred to the first and second radiation detectors may be selected. Since the data included in the reference energy range is selected as above, data included in base energy is regarded as an effective reaction and remnant may be effectively removed. 
     As described above, the gamma ray detecting apparatus and the gamma ray detecting method according to the present invention, since the position of a gamma ray source is indirectly detected by back-tracing an emission trajectory of a secondary electron generated in reaction with a gamma ray, detection efficiency can be increased and image resolution for a high-energy gamma ray source can be improved. 
     The gamma ray detecting apparatus and the gamma ray detecting method according to the present invention can image the position and the distribution of the gamma ray source in 3D at a fixed position and user convenience to use an apparatus can be increased by decreasing the size and weight of an apparatus for detecting the gamma ray source. 
     Since the gamma ray detecting apparatus and the gamma ray detecting method according to the present invention adopts an energy selector, the gamma ray detecting apparatus and the gamma ray detecting method can be minimize noise. 
     The gamma ray detecting apparatus and the gamma ray detecting method according to the present invention can be applied to imaging a radioactive isotope emitting a gamma ray having high energy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram schematically illustrating a gamma ray detecting apparatus according to an exemplary embodiment of the present invention; 
         FIG. 2  is a view schematically illustrating a gamma ray detecting apparatus according to an exemplary embodiment of the present invention; 
         FIG. 3  is a flowchart describing a method of detecting a gamma ray according to an exemplary embodiment of the present invention; and 
         FIG. 4  is a view illustrating a result acquired by experiment a beam path of proton beam by using a gamma detecting apparatus according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited or restricted to the exemplary embodiments. The same reference numerals denoted in the drawings are assigned to the same components. 
       FIG. 1  is a block diagram schematically illustrating a gamma ray detecting apparatus according to an exemplary embodiment of the present invention,  FIG. 2  is a view schematically illustrating a gamma ray detecting apparatus according to an exemplary embodiment of the present invention,  FIG. 3  is a flowchart describing a method of detecting a gamma ray according to an exemplary embodiment of the present invention, and  FIG. 4  is a view illustrating a result acquired by experiment a beam path of proton beam by using a gamma detecting apparatus according to an exemplary embodiment of the present invention. 
     Referring to  FIGS. 1 and 2 , a gamma ray detecting apparatus according to an exemplary embodiment of the present invention may include various devices capable of detecting a location of a ray source  50  of a gamma ray  55 , and a display device  180  displaying the location and distribution of the ray source  50  of the gamma ray  55  detected from each device with an image. 
     When the various devices capable of detecting the location of the gamma ray source  50  of the gamma ray  55  is described in more detail, the gamma ray  55  emitted from the gamma ray source  50  passes through a secondary electron emitter  120 . The secondary electron emitter  120  is formed by a material which reacts with the incident gamma ray  55  to generate secondary electrons  70 , and the gamma ray  55  generated from the ray source  50  of the gamma ray  55  causes a Compton scattering reaction to generate the secondary electrons  70 . 
     The secondary electron emitter  120  may be made of a material having a low atomic number which relatively causes the Compton scattering reaction well so that the secondary electrons  70  are more efficiently generated by the gamma ray  55  having high energy. Further, the secondary electron emitter  120  may be made of a material having a low atomic number and low density so that the generated secondary electrons  70  may be linearly emitted with little change of a trace in the secondary electron emitter  120 . For example, the secondary electron emitter  120  may be made of liquid helium, beryllium, distilled water, or the like, and of course, the secondary electron emitter  120  may be replaced with another material which may generate the secondary electrons  70  in the reaction with the gamma ray  55  other than the described materials. 
     Meanwhile, the secondary electrons  70  emitted from the secondary electron emitter  120  pass through a first radiation detector  130  which is provided to face the secondary electron emitter  120  in an emission progress direction of the secondary electrons  70  and detects the location of the secondary electrons  70  and transfer energy. Here, the transfer energy is energy of the secondary electrons  70  transferred to the first radiation detector  130 . 
     The first radiation detector  130  primarily determines a trace of the secondary electrons  70  emitted from the secondary electron emitter  120 , has a very small thickness for minimizing a trace change of the secondary electrons  70 , and may be made of a material having a low atomic number and low density. That is, the first radiation detector  130  is made of the material having a low atomic number and low density, and as a result, the trace of the secondary electrons  70  may maximally maintain a straight line while or after passing through the first radiation detector  130  and a change in linear trace may be minimized. 
     Meanwhile, the secondary electrons  70  passing through the first radiation detector  130  pass through a second radiation detector  140 . The second radiation detector  140  may be provided to face the first radiation detector  130  in the emission progress direction of the secondary electrons  70 , and detects the location and transfer energy of the secondary electrons  70  passing through the first radiation detector  130 . 
     The second radiation detector  140  has also a small thickness so as to minimize a change in linear trace while the secondary electrons  70  emitted from the first radiation detector  130  pass through a second radiation detector  140  and may be made of a material having a low atomic number and low density. The first and second radiation detectors  130  and  140  may be made of the same material, but may be made of different materials according to a condition of the invention. For example, the first radiation detector  130  and the second radiation detector  140  may be formed by a double-sided silicon stripe type. 
     The secondary electrons  70  emitted from the second radiation detector  140  are absorbed in a third radiation detector  150 . That is, the secondary electrons  70  pass through both the first radiation detector  130  and the second radiation detector  140 , and then are finally completely absorbed in the first radiation detector  130  and the second radiation detector  140  and stops. The third radiation detector  150  fully absorbs residue energy of the secondary electrons  70  emitted from the second radiation detector  140 , and as a result, the secondary electrons  70  stop in the third radiation detector  150  and the absorbed residue energy is measured, and a total energy selector may be applied below. 
     Here, the first radiation detector  130  and the second radiation detector  140  detect the location and the transfer energy of the secondary electrons  70 , while the third radiation detector  150  detects only the residue energy of the secondary electrons  70 . 
     In this case, a distance D 1  between the first and second radiation detectors  130  and  140  may be larger than a distance D 2  between the second and third radiation detectors  140  and  150 . As illustrated in  FIG. 2 , the distance D 1  between the first and second radiation detectors  130  and  140  may be separated by a sufficient distance so as to more accurately determine the linear trace of the secondary electrons  70  by reversely tracking the location of the secondary electrons  70  detected in the first and second radiation detectors  130  and  140 . 
     On the contrary, in order that the secondary electrons  70  passing through the second radiation detector  140  is all incident to the third radiation detector  150  to be completely absorbed, the distance D 2  between the second radiation detector  140  and the third radiation detector  150  may be minimized or smaller than the distance D 1  between the first radiation detector  130  and the second radiation detector  140 . As such, in order to more accurately measure the linear trace of the secondary electrons  70 , the distance D 1  between the first and second radiation detectors  130  and  140  needs to be sufficiently increased, and in order to efficiently measure or detect the secondary electron passing through the second radiation detector  140 , the distance D 2  between the second and third radiation detectors  140  and  150  may be minimized. 
     Further, a thickness T 3  of the third radiation detector  150  may be larger than thicknesses T 1  and T 2  of the first and second radiation detectors  130  and  140 . As described above, the third radiation detector  150  serves to determine energy of the secondary electrons  70  emitted from the second radiation detector  140 . While the secondary electrons  70  are finally completely absorbed in the third radiation detector  150 , another secondary electron and an X-ray are generated. Accordingly, in order to more accurately determine the energy of the secondary electrons  70  emitted from the second radiation detector  140 , the thickness T 3  of the third radiation detector  150  is sufficiently increased so as to absorb all secondary radiation generated while the secondary electrons  70  are absorbed in the third radiation detector  150  by themselves. 
     The thicknesses T 1  and T 2  of the first and second radiation detectors  130  and  140  may be formed as thinly as possible in order to minimize an effect on the trace of the secondary electrons  70 . In this case, the thicknesses T 1  and T 2  of the first and second radiation detectors  130  and  140  may be the same as each other like the exemplary embodiment of the present invention, but of course, may be different from each other. 
     Meanwhile, the gamma ray detecting apparatus  100  may include a data processor  160  having a coincidence counter circuit determining whether the secondary electrons  70  react in all of the first to third radiation detectors  130 ,  140 , and  150  in order to track the location of the gamma ray source  50 . 
     The data processor  160  acquires data of the secondary electrons  70  which coincidentally react by applying the coincidence counter circuit to the first to third radiation detectors  130 ,  140 , and  150  to decrease a background or increase a signal to noise ratio. 
     Further, the data processor  160  reversely tracks the trace of the secondary electrons  70  detected in the first and second radiation detectors  130  and  140  to detect the location of the ray source  50  of the gamma ray  55 . That is, the data processor  160  connect locations of a plurality of secondary electrons  70  detected in the first and second radiation detectors  130  and  140  with lines to detect locations where the lines cross each other. Cross points of the detected lines may be assumed as 3-dimensional locations of the gamma ray source  50 , and a plurality of lines is acquired, thereby 3-dimensionally imaging the distribution of the gamma ray source  50 . In other words, when the trace of the plurality of secondary electrons  70  is reversely projected, the location of the gamma ray source  50  may be 3-dimensionally imaged. As a result, the location of the gamma ray source  50  may be 3-dimensionally detected without moving the gamma ray detecting apparatus  100  according to the exemplary embodiment of the present invention. Accordingly, convenience of a user may be improved by decreasing the apparatus in size and weight. 
     Meanwhile, the gamma ray detecting apparatus  100  according to the exemplary embodiment of the present invention may further include an energy selector  170  which combines the energy of the secondary electrons  70  detected from the first to third radiation detectors  130 ,  140 , and  150  and determines whether the combined energy is included within a set reference energy range or sum energy windows. 
     The energy selector  170  may calculate total energy by combining the energy of the secondary electrons  70  detected from the first to third radiation detectors  130 ,  140 , and  150  in the data processor  160  and determine whether the calculated total energy is included in a predetermined energy region. The predetermined energy region and range is an energy region and range of the gamma ray  55  emitted from the gamma ray source  50  to be imaged by the user, and the energy region may be changed according to a condition required in the invention. 
     When the total energy acquired by combining all the energy detected from the first to third radiation detectors  130 ,  140 , and  150  in the energy selector  170  is included in the predetermined energy region, the data is determined as usable data, and may be used to track the location of the ray source  50  of the gamma ray  55 . Further, the energy transferred to the three detectors  130  to  150  by the energy selector  170  may improve the signal to noise ratio and decrease the background. The reason is that although the data is data satisfying coincidence counting by the coincidence counter circuit in accordance with data processing, when the energy transferred to the detectors is not included in the predetermined energy region, it may not be considered as effective reaction. If the total energy of the secondary electrons  70  detected from the energy selector  170  is not included in the predetermined energy region, the data are all removed to decrease the background and increase the signal to noise ratio. The energy selector  170  is provided, and as a result, data in the case where charged particles having different weights like protons may be removed from the effective data. 
     Here, in order to selectively detect only the secondary electrons  70 , separate independent energy selectors are used in the first and second radiation detectors  130  and  140 , and additionally, an energy selector  170  for determining whether the total energy acquired by combining all the energy transferred to the three radiation detectors  130 , 140 , and  150  is included in the predetermined energy region and range may be separately applied. 
     By the configuration, since the gamma ray source  50  is tracked by easily imaging the gamma ray source  50  emitting the high energy gamma ray  55  or distribution of nuclear reaction, detecting the location and the energy of the secondary electrons  70  generated from the secondary electron emitter  120 , and reversely tracking the trace of the detected secondary electrons  70 , the location of the gamma ray source  50  may be indirectly tracked and more accurately tracked with high efficiency. 
     Hereinafter, a method of measuring the gamma ray  55  according to an exemplary embodiment of the present invention will be described in more detail with reference to drawings. 
     Referring to  FIG. 3 , in the method of measuring the gamma ray  55  according to an exemplary embodiment of the present invention, the gamma ray  55  emitted from the gamma ray source  50  is incident to the secondary electron emitter  120 , the gamma ray incident to the secondary electron emitter  120  causes a Compton scattering reaction, and the secondary electrons  70  may be emitted in the same direction as an incident direction of the gamma ray  55  (S 310 ). 
     In this case, the gamma ray  55  emitted from the gamma ray source  50  may use the high energy gamma ray  55 . As such, the reason of preferring the high energy gamma ray  55  is that as the energy of the gamma ray  55  is increased, most of initial energy of the gamma ray  55  is transferred to the secondary electrons  70 , and most of the secondary electrons  70  receiving the energy of the gamma ray are emitted as it is in the same direction as a progress direction of the gamma ray  55 . For example, maximum transfer energy transferred to the secondary electrons  70  is 66.2% in the case of a 1 MeV gamma ray, and about 97.5% in the case of a 10 MeV gamma ray. 
     As described above, the emitted secondary electrons  70  pass through the first radiation detector  130  and the location and the transfer energy of the secondary electrons  70  are detected when the secondary electrons  70  pass through the first radiation detector  130  (S 320 ), and the location of the ray source  50  of the gamma ray  55  is detected by reversely tracking the trace of the secondary electrons  70  detected from the first and second radiation detectors  130  and  140  (S 360 ). 
     Here, the position where the plurality of secondary electrons  70  pass through the first radiation detector  130  and the transfer energy at this time are set as two points, and if two points are referred to as positions Pa 1  and Pb 1  and the transfer energy at each position is referred to as Ea 1  and Eb 1 , the positions of the plurality of secondary electrons and the transfer energy at each position may be detected (S 362 ). Meanwhile, in a method of detecting a gamma ray according to the exemplary embodiment of the present invention, a case where the position and the energy of the secondary electrons  70  are calculated with respect to the two points is described as an example, but three or more points are set, and a position and transfer energy at each point may be detected. 
     The secondary electrons  70  passing through the first radiation detector  130  pass through the second radiation detector  140 , and a position and transfer energy of the secondary electrons  70  when passing through the second radiation detector  140  may be detected (S 330 ). Even in this case, like the detecting of the position and the energy of the secondary electrons  70  in the first radiation detector  130  described above, if a plurality of positions passing through the second radiation detector  140  are referred to as Pa 2  and Pb 2  and transfer energy at each position is referred to as Ea 2  and Eb 2 , the positions of the plurality of secondary electrons and transfer energy at each position may be detected, respectively (S 363 ). 
     As such, the positions Pa 2  and Pb 2  and the energy Ea 2  and Eb 2  are detected, and while the secondary electrons  70  passing through the second radiation detector  140  is completely absorbed in the third radiation detector  150 , residue energy of the secondary electrons  70  may be detected (S 340 ). 
     The position Pa 1  and the position Pa 2  of the secondary electrons  70  measured in the first and second radiation detectors  130  and  140  are connected to each other in a trace or a line, and further, the position Pb 1  and the position Pb 2  are connected to each other in a trace or a line. The cross points are tracked by reversely projecting each connected trace (S 366 ), and it is determined that the gamma ray source  50  is positioned at the cross points of the lines by reversely tracking the trace of the secondary electrons  70 (S 368 ). 
     In this case, in the exemplary embodiment of the present invention, in order to 3-dimensionally determine the position of the gamma ray source  50 , an example in which the trace of the two secondary electrons  70  is reversely tracked is described, but the trace reversely tracked by selecting the position of the plurality of secondary electrons  70  is collected at one point to determine the position of the gamma ray source  50 . 
     In this case, it is determined whether a sum of the energy of the secondary electrons  70  detected from the first to third radiation detectors  130 ,  140 , and  150  is included in the predetermined reference energy range or sum energy windows (S 350 ), and an image is acquired by using only the data of the secondary electrons  70  included in the reference energy range (S 370 ). 
     Further, it is determined whether the energy of the secondary electrons  70  transferred to the first radiation detector  130  and the second radiation detector  140  is included in the predetermined reference energy range, and only the data of the secondary electrons  70  included in the reference energy range may be selected. 
     In the process of detecting the data, only the data, in which the reaction is caused at the same time in all of the three detectors by applying the coincidence counter circuit to the three radiation detectors, are recorded. In this case, since very thin detectors are used as the first and second radiation detectors  130  and  140 , a case where non-charged particles directly react with the two detectors at the same time is quire rare, and in the case of satisfying the coincidence counter, it is determined that nearly all are performed by charged particles. 
     Further, the total energy acquired by adding all the energy detected from the first to third radiation detectors  130 ,  140 , and  150  is applied to the energy selector  170 . The energy selector  170  means that even in the case of the data recorded by satisfying the coincidence counter in the data processor  160 , only when the data is within the energy range set by the user, the data is considered as the effective reaction, and the remaining data is removed. As a result, a case where other charged particles react may be effectively removed. 
     Hereinafter, a result of the beam path of the proton beam is examined by the apparatus and the method to examine accuracies of the gamma ray detecting apparatus and the gamma ray detecting method according to the exemplary embodiments of the present invention. 
       FIG. 4  illustrates a photograph and a graph acquired by experimenting the beam path and the position of the proton beam in a water phantom while irradiating the proton beam having treatment energy to the water phantom by using the gamma ray detecting apparatus and the gamma ray detecting method according to the exemplary embodiments of the present invention. That is, the proton reacts with the water phantom to generate a prompt gamma ray and a distribution of the prompt gamma ray is imaged by using trajectory tracing and coincidence of secondary electrons, an energy selector, a ray back-projection technique, and the like. The energy of the proton beam used at that time is 80, 150, 200 MeV. 
     The experiment is performed by changing the size of the water phantom for each energy by considering a spreading degree of the proton beam. Herein, the water phantom may serve as the secondary electron emitter  120 . The size of the water phantom is 2×2×30 cm 3  (80 Mev proton beam), 3×3×30 cm 3  (150 MeV proton beam), and 4×4×30 cm 3  (200 MeV proton beam) with respect to respective proton beams. 
     Referring to  FIG. 4 , a top photograph and a top graph, a second photograph and a second graph, and a bottom photograph and a bottom graph illustrate cases in which 80 MeV proton beam, 150 MeV proton beam, and 200 MeV proton beam are irradiated to the water phantom, respectively. 
     Further, in  FIG. 4 , a left (a) photograph shows the image of the distribution of the prompt gamma ray acquired by using the gamma ray detecting apparatus and the gamma ray detecting method according to the exemplary embodiments of the present invention and a right (b) photograph shows a pixel value (see a GEV image) acquired along a central axis of the corresponding image, a generation distribution of the prompt gamma ray in the water phantom (see prompt γ), and a distribution of a proton beam amount (see proton dose). 
     Herein, the graph marked with “prompt γ” in  FIG. 4(   b ) shows a distribution of the prompt gamma ray  55  generated by the proton beam and the graph marked with “GEV image” shows the pixel value of the image acquired by the gamma ray detecting apparatus  100  and the gamma ray detecting method of the present invention. 
     Referring to  FIG. 4 , it can be seen that the distribution of the prompt gamma ray  55  and data acquired by the gamma ray detecting apparatus  100  and the gamma ray detecting method of the present invention very accurately coincide with each other with an error of 1 mm or less. Therefore, it is possible to accurately infer the beam path of the proton beam in real time during the treatment or experiment using the proton beam. 
     The gamma ray detecting apparatus  100  and the gamma ray detecting method using the same described above may be applied to various fields such as nuclear medicine and molecular imaging for a medical purpose, an image device for a small animal, brain science, hydrography using a radiotracer, space physics, and the like, and when a high-energy gamma ray source is used, a more excellent image may be acquired. In particular, in a proton treatment facility, the gamma ray detecting apparatus  100  and the gamma ray detecting method using the same may be used in a device of deciding the beam path and position of the proton beam in real time during treatment or applied to a space gamma ray measuring and imaging apparatus for astrophysics such as a pulser or a supernova remnant research. 
     The specified matters and limited embodiments and drawings such as specific components in the embodiment of the present invention have been disclosed for illustrative purposes, but are not limited thereto, and those skilled in the art will appreciate that various modifications, additions and substitutions are possible from the disclosure in the art to which the present invention belongs. The spirit of the present invention is defined by the appended claims rather than by the description preceding them, and all changes and modifications that fall within metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the range of the spirit of the present invention. 
     The present invention can be applied to a medical field or a space gamma ray imaging field.