the following describes embodiments of the present invention . x - rays in the embodiment correspond to radiation in the present invention . an fpd is the abbreviation of a flat panel detector . the following firstly describes an x - ray apparatus 1 according to embodiment 1 . here , the configuration of embodiment 1 adopts an improvement over a conventional manual mode . the x - ray apparatus 1 images a standing subject m . as illustrated in fig1 , the x - ray apparatus 1 includes a strut 2 extending vertically from the floor , an x - ray tube 3 emitting x - rays , an fpd 4 supported on the strut 2 , and a suspending holder 7 extending vertically and held on the ceiling . the suspending holder 7 suspendingly holds the x - ray tube 3 . the x - ray tube 3 corresponds to the radiation source in the present invention . the fpd 4 corresponds to the detecting means in the present invention . a collimator 3 a is provided for restricting an area of x - rays emitted from the x - ray tube 3 . an operator adjusts a leaf of the collimator 3 a , and correspondingly an emission area of x - rays becomes larger or smaller . the fpd 4 is slidable vertically relative to the strut 2 . the suspending holder 7 is also expandable vertically . a position of the x - ray tube 3 in a vertical direction is variable with expansion of the suspending holder 7 . an fpd moving mechanism 15 between the above elements 2 and 4 moves the fpd 4 vertically relative to the strut 2 . consequently , the vertical direction is a moving direction m of the x - ray tube 3 and the fpd 4 . an fpd movement controller 16 controls movement of the fpd moving mechanism 15 . the fpd 4 can detect x - rays passing through the subject m . the following describes movement of the x - ray tube 3 . the x - ray tube 3 is moved by an x - ray tube moving mechanism 13 provided in the suspending holder 7 . an x - ray tube movement controller 14 controls the x - ray tube moving mechanism 13 . the x - ray tube moving mechanism 13 moves the x - ray tube 3 ( 1 ) in the vertical direction ( moving direction m ), ( 2 ) in directions approaching and away from the fpd 4 , and ( 3 ) in a horizontal direction s orthogonal to an emission direction from the x - ray tube 3 to the fpd 4 ( orthogonal direction n : in fig1 , a plane - passing direction , a body - side direction of the subject m ). the suspending holder 7 expands and contracts when the x - ray tube 3 is moved in the vertical direction . here , the emission direction , the moving direction , and the orthogonal direction n are each orthogonal to one another . an x - ray tube rotating mechanism 21 rotates the x - ray tube 3 . the x - ray tube rotating mechanism 21 has a rotary axis around which the x - ray tube 3 is rotated . the rotary axis is orthogonal to the central axis of x - ray beams from the x - ray tube 3 and the vertical direction . moreover , the rotary axis passes a focus of the x - ray tube 3 . an x - ray tube rotation controller 22 controls the x - ray tube rotating mechanism 21 . an x - ray tube controller 6 controls a tube voltage and a tube current of the x - ray tube 3 and an irradiation time of x - rays . the x - ray tube controller 6 controls the x - ray tube 3 so as to output radiation with a given tube current , a tube voltage , and a pulse width . parameters , such as the tube current , are stored in a storing unit 37 . the x - ray tube controller 6 corresponds to the radiation source controller in the present invention . the storing unit 37 corresponds to the storing means in the present invention . the fpd 4 has a detecting surface 4 a detecting x - rays ( see fig1 ). the detecting surface 4 a is disposed in the x - ray apparatus 1 while erecting in the vertical direction . this achieves effective radiography to the standing subject m . the detecting surface 4 a faces to an x - ray emitting hole of the x - ray tube 3 . in other words , the detecting surface 4 a is disposed along a plane formed by two directions , i . e ., the orthogonal direction n and the moving direction m . the detecting surface 4 a is rectangular , one side thereof corresponding to the orthogonal direction n and the other side orthogonal to the one side corresponding to the moving direction m . an image generating unit 11 constructs detection data outputted from the fpd 4 to generate an original image p 0 with a projection image of the subject m appearing therein . the image generating unit 11 generates a plurality of images in accordance with detection signals every x - ray emission in series performed plural times to the subject m , the detection signals each being outputted from the fpd 4 . the image generating unit 11 corresponds to the image generator in the present invention . the x - ray apparatus 1 of embodiment 1 can perform so - called long - length radiography . in the radiography , a plurality of original images p 0 is combined to generate one large image . here , the x - ray apparatus 1 performs radiography three times while a relative positional relationship between the x - ray tube 3 and the fpd 4 is maintained . see fig2 . that is , first radiography is performed when the x - ray tube 3 and the fpd 4 are located in a position denoted by dashed - dotted lines . second radiography is performed when the x - ray tube 3 and the fpd 4 are located in a position denoted by dotted line . third radiography is performed when the x - ray tube 3 and the fpd 4 are located in a position denoted by solid lines . the original images p 01 taken through the first , the second and the third radiographies are denoted by signs p 0 a , p 0 b , and p 0 c , respectively , for differentiation . as illustrated in fig3 , a long - length image generating unit 12 combines the original images p 0 a , p 0 b , p 0 c having different sites of the subject m appearing therein to generate one long image p 1 . that is , the long - length image generating unit 12 combines a series of images taken while the subject m is moved relative to the fpd 4 . the long - length image generating unit 12 corresponds to the long - length image generating means in the present invention . an operation switch 38 inputs various instructions by the operator . the operator can provide the activation instruction of the x - ray tube 3 and the x - ray emission instruction via the operation switch 38 . the operation switch 38 is a dual - position switch . the first position is used for inputting the activation instruction of the x - ray tube 3 by the operator . the second position is used for inputting the x - ray emission instruction by the operator . in this manner , the operation switch 38 inputs the activation instruction of the x - ray tube 3 in a rest state by the operator , and inputs the x - ray emission by the operator to the activated x - ray tube 3 . the operation switch 38 corresponds to the emission instruction input means and the activation instruction input means in the present invention . if the operator inputs the activation instruction of the x - ray tube 3 , the x - ray tube controller 6 initiates an activation of the x - ray tube 3 in a rest state . here , the rest state of the x - ray tube 3 represents a condition in which a filament in the x - ray tube 3 that ejects electrons is kept at low temperatures . moreover , a state in which the activation of the x - ray tube 3 completes represents a condition in which the filament is kept at high temperatures . the x - ray tube 3 allows the x - ray emission only in the condition in which the activation is completed . the x - ray tube 3 is changed to its rest state after one - time x - ray emission . a timing determining unit 17 , a difference time calculating unit 18 , and a notifying unit 36 are the most characteristic feature in embodiment 1 , and detailed description thereof is to be made later . the notifying unit 36 corresponds to the notifying means in the present invention . the difference time calculating unit 18 corresponds to the difference time calculating means in the present invention . the most characteristic feature in embodiment 1 is that the operator can provide the activation instruction of the x - ray tube 3 at an appropriate timing in embodiment 1 . the following firstly describes how the long - length radiography is performed in embodiment 1 . fig4 ( a ), 4 ( b ) illustrate on the upper thereof a timing chart of performing the long - length radiography with the x - ray apparatus 1 according to embodiment 1 . an upper sequence indicates a state of the x - ray tube 3 , and a lower sequence indicates a state of the fpd 4 . in the upper of fig4 ( a ), 4 ( b ) , the original images p 0 a , p 0 b , and p 0 c illustrated in fig3 are taken in this order . the following describes in detail the radiography above . prior to activation of the long - length radiography , the x - ray tube 3 is in a rest state . accordingly , the x - ray tube 3 cannot emit x - rays under this state . then , the operator provides the activation instruction of the x - ray tube 3 via the operation switch 38 . the x - ray tube controller 6 controls the x - ray tube 3 so as to be activated immediately after receipt of the instruction from the operator . however , it takes some time from the activation of the x - ray tube 3 to complete the activation . the time period is referred to as an activation time period . after the activation time period has elapsed , the operator provides the emission instruction via the operation switch 38 . then , the x - ray tube controller 6 provides the x - ray emission instruction to the x - ray tube 3 , and correspondingly the x - ray tube 3 emits x - rays . the x - rays are incident through the subject m on the fpd 4 . the fpd 4 detects the x - rays , and transmits a detection signal to the image generating unit 11 . in this manner , a first original image p 0 a is generated . after completion of the x - ray emission , the x - ray tube 3 is brought back into a rest state where the temperature of the filament in the x - ray tube 3 decreases . here , the fpd 4 requires some time for subsequent detection of x - rays after one - time detection of x - rays passing through the subject m . when x - rays are emitted continuously regardless of such the state , a generated image may contain a false image . although the detection signal has already been transmitted to the image generating unit 11 , an residual image of the subject m does not completely disappear and remains on the fpd 4 immediately after being subjected to incident x - rays . such a residual image disappears by itself after some time has elapsed from the incidence of the x - rays . when radiography is performed before the residual image on the fpd 4 disappears , the residual image upon anterior radiography may be superimposed on an image generated upon posterior radiography . consequently , radiography should be delayed for successive imaging until the fpd 4 having detected x - rays one time allows detection of x - rays again . a time period during which the fpd 4 cannot detect x - rays is referred to as a non - detectable time period . when radiography is performed in the non - detectable time period of the fpd 4 , the false image mentioned above may appear in the image to be generated . after the original image p 0 a is generated , the operator provides the activation instruction of the x - ray tube 3 via the operation switch 38 . then , the instruction by the operator is transmitted to the x - ray tube controller 6 . the x - ray tube controller 6 activates the x - ray tube 3 changed into a rest state . after the activation time period has elapsed , the operator provides the emission instruction via the operation switch 38 . at this time , the non - detectable time period of the fpd 4 has already ended , and accordingly no false image appears in the original image p 0 b . in this manner , a second original image p 0 b is generated . after completing the x - ray emission , the x - ray tube 3 is brought back into a rest state where the temperature of the filament in the x - ray tube 3 decreases . simultaneously , the fpd 4 enters into the non - detectable time period . after the original image p 0 b is generated , the operator provides the activation instruction of the x - ray tube 3 via the operation switch 38 . then the x - ray tube controller 6 controls the x - ray tube 3 in a rest state so as to be activated again . after the activation time period has elapsed , the operator provides the emission instruction via the operation switch 38 . at this time , the non - detectable time period of the fpd 4 has already ended . accordingly , no false image appears in the original image p 0 c to be generated . in this manner , a third original image p 0 c is generated . as noted above , the operator provides the activation instruction of the x - ray tube 3 at an appropriate timing . consequently , activation of the x - ray tube 3 and restore of the fpd 4 under a non - detectable state overlap each other sequentially . this causes a shorter interval of x - ray emission by the operator than that in the conventional manual mode that activates the x - ray tube 3 after the fpd 4 is restored . consequently , embodiment 1 can obtain an image with a high resolution and with no false image appearing therein despite the shortened interval of x - ray emission . here , the operator allows providing the activation instruction to the x - ray tube 3 at an appropriate timing since the x - ray apparatus 1 notifies the operator as to the timing to activate the x - ray tube 3 via the notifying unit 36 . accordingly , the operator can perform appropriate radiography as illustrated on the upper of fig4 by merely providing the instruction in accordance with the notification from the x - ray apparatus 1 . fig4 ( b ) illustrates a timing chart indicating a timing of notification to the operator from the x - ray apparatus 1 . the x - ray apparatus 1 performs the notification via the notifying unit 36 to activate the x - ray tube 3 during the non - detectable time period of the fpd 4 after the x - ray emission . in addition , the x - ray apparatus 1 performs notification via the notifying unit 36 that x - ray emission is performable when the activation of the x - ray tube 3 completes . such time conforms to time when the non - detectable time period of the fpd 4 ends in the second and third radiography . in embodiment 1 , radiography of the original image p 0 is performed three times . accordingly , notification to activate the x - ray tube 3 is provided two times , and notification that x - ray emission is performable is provided three times . here , the first activation of the x - ray tube 3 merely means activation of the long - length radiography , and thus is any timing that the operator can determine optionally . consequently , there is no need to provide notification to activate the x - ray tube 3 in the first radiography . for specific operation of the notifying unit 36 , it is conceivable to display contents of the notification on a monitor of the notifying unit 36 . moreover , the notifying unit 36 may be formed by a speaker , and the contents of the notification may be transmitted to the operator with sounds . as noted above , the notifying unit 36 allows notification to the operator by the visible display or the sounds . the following describes how to determine a timing of notification . the timing determining unit 17 in fig1 determines a timing of notification . fig5 ( a ), 5 ( b ) illustrate operations of notification to activate the x - ray tube 3 by the timing determining unit 17 . that is , the timing determining unit 17 is in a standby state until given time period t 1 has elapsed from completion of the x - ray emission for radiography . thereafter , the timing determining unit 17 controls the notifying unit 36 so as to provide display indicating activation of the x - ray tube 3 . fig5 ( a ) illustrates a timing chart when the given time period t 1 has not elapsed from the completion of the x - ray emission . at this time , the timing determining unit 17 never controls the notifying unit 36 so as to providing the display noted above . the timing determining unit 17 corresponds to the determining means in the present invention . fig5 ( b ) illustrates the right time thereof when the given time period t 1 has elapsed from the completion of the x - ray emission . at this time , the timing determining unit 17 controls the notifying unit 36 as to providing the above display . correspondingly , the notifying unit 36 provides the display to the operator to activate the x - ray tube 3 , and accordingly , the operator provides the activation instruction of the x - ray tube 3 via the operation switch 38 to the x - ray apparatus 1 . as noted above , the timing determining unit 17 determines that the timing to activate the x - ray tube 3 in a rest state has arrived after the difference time elapsed from the x - ray emission when the operator provides the emission instruction to the operation switch 38 . here , the time after the given time period t 1 has elapsed from the completion of the x - ray emission is in the middle of the non - detectable time period of the fpd 4 , as illustrated in fig5 ( b ) . the x - ray tube 3 activates before the non - detectable time period of the fpd 4 ends . accordingly , the time when the activation of the x - ray tube 3 completes conforms to the time when detection by the fpd 4 is performable . the difference time calculating unit 18 concretely determines the given time period t 1 necessary for operation of the timing determining unit 17 . the difference time calculating unit 18 calculates the given time period t 1 from a time width of the activation time period of the x - ray tube 3 determined in advance and a time width of the non - detectable time period of the fpd 4 also determined in advance . that is , the difference time calculating unit 18 calculates the given time period t 1 by subtracting a time period representing a length of the activation time period of the x - ray tube 3 from a time period representing a length of the non - detectable time period . in other words , the difference time calculating unit 18 calculates difference time as a difference obtained by subtracting the time width of the activation time period of the x - ray tube 3 from the time width of the non - detectable time period of the fpd 4 . specifically , the time width of the non - detectable time period of the fpd 4 is around 5 seconds , and the time width of the activation time period of the x - ray tube 3 is around 1 second . the given time period t 1 calculated by the difference time calculating unit 18 is a time period representing how the non - detectable time period of the fpd 4 is longer than the activation time period of the x - ray tube 3 , as illustrated in fig6 . the given time period t 1 also represents suspended time for activating the x - ray tube 3 from completion of the x - ray emission so as for the completion of the activation of the x - ray tube 3 to conform to end of the non - detectable time period of the fpd 4 . a storing unit 37 stores set values of the given time period t 1 . the timing determining unit 17 reads out one of the set values as necessary from the storing unit 37 for operation . the following summarizes the above operation . that is , after receiving the x - ray emission instruction ( emission instruction ) via the operation switch 38 , the notifying unit 36 notifies the operator that the timing has arrived to provide the instruction via the operation switch 38 in accordance with the determination by the timing determining unit 17 . fig7 illustrates operation of the timing determining unit 17 when the notifying unit 36 notifies the operator that the x - ray emission is performable . see fig4 ( b ) . that is , the timing determining unit 17 provides the activation instruction of the x - ray tube 3 to the operator , and correspondingly the x - ray tube 3 is in a standby state until a given time period t 2 has elapsed from the activation of the x - ray tube 3 . then the timing determining unit 17 controls the notifying unit 36 as to providing display indicating that the x - ray emission is performable after the give time period t 2 has elapsed from the activation of the x - ray tube 3 . accordingly , the notifying unit 36 notifies the operator of the performable x - ray emission . then , the operator correspondingly provides an instruction to emit x - rays via the operation switch 38 to the x - ray apparatus 1 . the time after the given time period t 2 has elapsed from the time when the operator provides the activation instruction of the x - ray tube 3 is also time when the activation of the x - ray tube 3 completes , and the non - detectable time period of the fpd 4 ends . here , the given time period t 2 is set so as to have the time width of the activation time period of the x - ray tube 3 . the storing unit 37 stores set values of the given time period t 2 . the timing determining unit 17 reads out one of the set values as necessary from the storing unit 37 for operation . the timing determining unit 17 receives information on control of the x - ray tube 3 sequentially from the x - ray tube controller 6 . the timing determining unit 17 determines time when the x - ray emission completes and time when the activation instruction of the x - ray tube 3 is provided from the information received from the x - ray tube controller 6 . the following describes an effect by the timing determining unit 17 configured as mentioned above . fig8 illustrates a conventional configuration . in the conventional configuration , an instruction to activate the x - ray tube 3 is displayed at time when the non - detectable time period of the fpd 4 ends . accordingly , the operator activates the x - ray tube 3 after the non - detectable time period of the fpd 4 ends . the following is revealed from comparison between fig8 and the upper of fig4 illustrating embodiment 1 . that is , in embodiment 1 , the fpd 4 that does not allow detection of x - rays is restored simultaneously with the activation of the x - ray tube 3 . in contrast to this , in the configuration illustrated in fig8 , the operations are performed in series . as noted above , embodiment 1 achieves shorter time necessary for the posterior x - ray emission after the anterior x - ray emission than that in the conventional manual mode . the following describes other elements of the x - ray apparatus 1 . the storing unit 37 stores various parameters , such as an incidence area to be mentioned later and an imaging distance , used for x - ray radiography in association with types of radiography . as illustrated in fig1 , the x - ray apparatus 1 includes a main controller 41 controlling en bloc the components 6 , 14 , 16 , 11 , 18 , and 22 . the main controller 41 has a cpu , and provides each unit executing various programs . the above components may be divided into arithmetic units that perform their functions . a display unit 39 is provided for displaying the long image p 1 obtained through radiography . the storing unit 37 stores the time width of the activation time period required for activating the x - ray tube 3 , and the time width of the non - detectable time period required until posterior x - ray detection is performable after the one - time x - ray detection by the fpd 4 . the following describes how the long - length radiography is actually performed . in embodiment 1 , when the x - ray apparatus 1 performs long - length radiography , the operator provides the activation instruction of the x - ray tube 3 and the x - ray emission instruction at the timings as described in fig4 . the x - ray tube controller 6 controls the x - ray tube 3 in accordance with the instructions . as illustrated in the upper of fig4 , the x - ray tube 3 and the fpd 4 are moved immediately after the x - ray emission completes . the movement has already been described with fig2 . that is , the x - ray tube 3 and the fpd 4 located at the positions denoted by dashed - dotted lines in fig2 are moved to the positions denoted by dotted line after x - ray emission for taking an original image p 0 a , and then an original image p 0 b is obtained . then after the x - ray emission for taking the original image p 0 b , the x - ray tube 3 and the fpd 4 in the positions denoted by dotted lines are moved to the positions denoted by solid lines , whereby an original image p 0 c is obtained . the obtained original images p 0 a , p 0 b , and p 0 c are transmitted to the long - length image generating unit 12 . the long - length image generating unit 12 combines the original images p 0 a , p 0 b , and p 0 c to generate a long image p 1 . the display unit 39 displays the generated long image p 1 , whereby the long - length radiography completes . as noted above , with the x - ray apparatus according to embodiment 1 , successive imaging is performable while the timing to activate the x - ray tube 3 in a rest state is acquired appropriately . that is , with the configuration of embodiment 1 , the difference time is calculated by subtracting the time width of the activation time period from the time width of the non - detectable time period , and the time after the difference time has elapsed from the x - ray emission is determined as a timing to activate the x - ray tube 3 . here , the time width of the non - detectable time period is a time width from when the fpd 4 detects x - rays one time to when posterior x - ray detection is performable . the time width of the activation time period is a time width from activation to completion of the activation of the x - ray tube 3 . the x - ray tube 3 activates at the timing with embodiment 1 , whereby end of the non - detectable time period of the detector conforms to end of the time period for activating the x - ray tube 3 . this allows rapid successive imaging while the activation of the radiation source and preparation of the detector are performed simultaneously . in other words , embodiment 1 achieves shorter time necessary for posterior emission of x - rays after the anterior emission of x - rays than that in the conventional manual mode . as noted above , notification of the timing determined by the determining unit 17 is provided to the operator , whereby the operator allows activating the x - ray tube 3 at an appropriate timing only in accordance with the notification . the x - ray tube controller 6 is provided so as to cause the x - ray tube 3 to perform the activation instruction in accordance with the determination by the timing determining unit 17 . this allows activating the x - ray tube 3 at an appropriate timing under automatic control regardless of the instruction by the operator . the following describes an x - ray apparatus 1 according to embodiment 2 . the x - ray apparatus 1 according to embodiment 2 is similar to embodiment 1 in its configuration . accordingly , description about the configuration of embodiment 2 common to that of embodiment 1 is to be omitted . the configuration of embodiment 2 is improvement of the conventional automatic mode . embodiment 2 differs from embodiment 1 in that long - length radiography for the second and subsequent times is performed automatically . that is , the x - ray apparatus 1 in embodiment 2 allows successive radiography of a plurality of images by merely one - time instruction to activate the x - ray tube 3 and one - time instruction to emit x - rays by an operator . fig9 ( a ), 9 ( b ) illustrate a timing chart illustrating performance of long - length radiography with the x - ray apparatus 1 of embodiment 2 . an upper sequence 9 ( a ) of the drawing indicates a state of the x - ray tube 3 , and a lower sequence ( 9 b ) indicates a state of the fpd 4 . in the upper portions of fig9 ( a ), 9 ( b ) , the original images p 0 a , p 0 b , and p 0 c illustrated in fig3 are taken in this order . the following described in detail the radiography above . prior to activation of the long - length radiography , the x - ray tube 3 is in a rest state . accordingly , the x - ray tube 3 cannot emit x - rays under this state . then , the operator provides the activation instruction of the x - ray tube 3 via the operation switch 38 . the x - ray tube controller 6 controls the x - ray tube 3 so as to be activated immediately after receipt of the instruction from the operator . after the activation time period elapsed , the operator provides the emission instruction via the operation switch 38 . then , the x - ray tube controller 6 provides the x - ray emission instruction to the x - ray tube 3 , and correspondingly the x - ray tube 3 emits x - rays . the x - rays are incident through the subject m on the fpd 4 . the fpd 4 detects the x - rays , and transmits a detection signal to the image generating unit 11 . in this manner , a first original image p 0 a is generated . after completing of the x - ray emission , the x - ray tube 3 is brought back into a rest state where the temperature of the filament in the x - ray tube 3 decreases . after the original image p 0 a is generated , the x - ray tube controller 6 activates again the x - ray tube 3 changed into a rest state . after the activation time period elapsed , the x - ray tube controller 6 provides the x - ray emission instruction to the x - ray tube 3 , at this time , the non - detectable time period of the fpd 4 has already ended , and accordingly no false image appears in the original image p 0 b . in this manner , a second original image p 0 b is generated . after completion of x - ray emission , the x - ray tube 3 is brought back into a rest state where the temperature of the filament in the x - ray tube 3 decreases . simultaneously , the fpd 4 enters into the non - detectable time period . after the original image p 0 b is generated , the x - ray tube controller 6 causes the x - ray tube 3 to provide the activation instruction . then the x - ray tube 3 in a rest state is activated again . after the activation time period elapsed , the x - ray tube controller 6 provides the x - ray emission instruction to the x - ray tube 3 . at this time , the non - detectable time period of the fpd 4 has already ended . accordingly , no false image appears in the original image p 0 c to be generated . in this manner , a third original image p 0 c is generated . as noted above , the x - ray tube controller 6 provides the activation instruction of the x - ray tube 3 at an appropriate timing , whereby rapid successive imaging is performable as before without activating the x - ray tube 3 all the time . consequently , embodiment 2 allows performing radiography of an image having high resolution and with no false image appearing therein under suppressed degradation of the x - ray tube 3 . here , the x - ray tube controller 6 allows providing the activation instruction of the x - ray tube 3 at an appropriate timing since the timing determining unit 17 provides notification of a timing to activate the x - ray tube 3 to the x - ray tube controller 6 . the x - ray tube controller 6 allows performing appropriate radiography as illustrated in the upper of fig9 by merely providing the instruction to the x - ray tube 3 in accordance with the notification from the timing determining unit 17 . in other words , the x - ray tube controller 6 provides the activation instruction to the x - ray tube 3 in accordance with the determination by the timing determining unit 17 after the emission instruction via the operation switch 38 . fig9 ( a ), 9 ( b ) illustrate a timing chart indicating a timing of notification to the x - ray tube 3 by the x - ray tube controller 6 . the x - ray tube controller 6 activates the x - ray tube 3 via the timing determining unit 17 after the x - ray emission and in the middle of the non - detectable time period of the fpd 4 . in addition , the x - ray tube controller 6 causes the x - ray tube 3 to emit x - rays via the timing determining unit 17 at the time when the activation of the x - ray tube 3 is completed . such time conforms to time when the non - detectable time period of the fpd 4 ends in the second and third radiography . in embodiment 2 , radiography of the original image p 0 is performed three times . accordingly , notification to activate the x - ray tube 3 is provided two times , and notification that x - ray emission is performable is provided three times . here , the first activation of the x - ray tube 3 is performed through the operator &# 39 ; s instruction . consequently , there is no need for the timing determining unit 17 to provide notification to activate the x - ray tube 3 in the first radiography . fig1 ( a ), 10 ( b ) illustrate operations of the timing determining unit 17 at the timing of activating the x - ray tube 3 according to embodiment 2 . see the lower of fig9 ( a ), 9 ( b ) . the operation of the timing determining unit 17 is almost equal to that of embodiment 1 described with fig5 . specifically , fig1 ( a ) illustrates a timing chart when given time period t 1 has not elapses from the completion of the x - ray emission . at this time , the timing determining unit 17 never controls the notifying unit 36 to provide the display noted above . fig1 ( b ) illustrates a timing when the given time period t 1 has elapsed from the completion of the x - ray emission . at this time , the timing determining unit 17 provides the notification to the x - ray tube controller 6 to activate the x - ray tube 3 . here , the time after the given time period t 1 has elapsed from the completion of the x - ray emission is in the middle of the non - detectable time period of the fpd 4 , as illustrated in fig1 ( b ) . the x - ray tube 3 activates before the non - detectable time period of the fpd 4 ends . accordingly , the time when the activation of the x - ray tube 3 completes conforms to the time when detection by the fpd 4 is performable . the end of the time periods conforms to each other in the same manner as that in embodiment 1 . the difference time calculating unit 18 calculates the given time in the same manner as that in embodiment 1 described with fig7 , and thus description thereof is to be omitted . the given time period t 1 calculated by the difference time calculating unit 18 is a time period representing how the non - detectable time period of the fpd 4 is longer than the activation time period of the x - ray tube 3 . the given time period t 1 also represents delay time of activating the x - ray tube 3 from completion of the x - ray emission so as for the completion of the activation of the x - ray tube 3 to conform to end of the non - detectable time of the fpd 4 . the storing unit 37 stores set values of the given time period t 1 . the timing determining unit 17 reads one of the set values as necessary from the storing unit 37 for operation . fig1 illustrates operation of the timing determining unit 17 when the x - ray tube controller 6 causes the x - ray tube 3 to emit x - rays . see fig9 ( b ) . that is , the timing determining unit 17 is in a standby state until a given time period t 2 elapses from activation of the x - ray tube 3 by the x - ray tube controller 6 . then the timing determining unit 17 provides notification of emitting x - rays to the x - ray tube controller 6 after the given time period t 2 has elapsed from the activation of the x - ray tube 3 . correspondingly , the x - ray tube controller 6 causes the x - ray tube 3 to emit x - rays . the time after the given time period t 2 has elapsed from the time of providing the activation instruction of the x - ray tube 3 is also time when the activation of the x - ray tube 3 completes , and the non - detectable time period of the fpd 4 ends . here , the given time period t 2 is set so as to have the time width of the activation time period of the x - ray tube 3 determined in advance . the storing unit 37 stores set values of the given time period t 2 . the timing determining unit 17 reads one of the set values as necessary from the storing unit 37 for operation . the notifying unit 36 may operate in association with the timing determining unit 17 . that is , the timing determining unit 17 may notify the operator via the notifying unit 36 that the x - ray emission is performable before radiography of the original image p 0 . in this case , the timing determining unit 17 activates operation from the time when the x - ray tube 3 activates activation in accordance with the activation instruction of the x - ray tube 3 via the operation switch 38 by the operator . specifically , the timing determining unit 17 controls the notifying unit 36 so as to provide display indicating that the x - ray emission is performable after the given time period t 2 has elapsed from the time . see fig9 ( b ) . consequently , rapid and accurate long - length radiography is performable with only the emission instruction by the operator in accordance with the notification . the timing determining unit 17 receives information on control of the x - ray tube 3 sequentially from the x - ray tube controller 6 . the timing determining unit 17 determines time when the x - ray emission completes and time when the activation instruction of the x - ray tube 3 is provided from the information received from the x - ray tube controller 6 . the following describes an effect by the timing determining unit 17 configured as mentioned above . fig1 illustrates a conventional configuration . the following is revealed from comparison between fig1 and fig9 ( a ) illustrating embodiment 2 . that is , in embodiment 2 , the x - ray tube 3 is in a rest state during x - ray emission . in contrast to this , in the conventional automatic mode in fig1 , the x - ray tube 3 is always in an activated state once the successive imaging is activated . accordingly , in the conventional automatic mode , the filament in the x - ray tube 3 is always kept at high temperatures , causing ready damages on the filament . as noted above , embodiment 1 achieves a longer life of the x - ray tube 3 than in the conventional type . the other configuration of the x - ray apparatus 1 in embodiment 2 is equal to that in embodiment 1 , and thus description thereof is to be omitted . the following describes how the long - length radiography is actually performed . in embodiment 2 , when the x - ray apparatus 1 performs long - length radiography , the operator provides the activation instruction of the x - ray tube 3 and the emission instruction at the timings as described in fig9 . the x - ray tube controller 6 controls the x - ray tube 3 in accordance with the instructions . as illustrated in fig9 ( a ) , the x - ray tube 3 and the fpd 4 are moved immediately after the x - ray emission completes . the movement has already been described with fig2 . that is , the x - ray tube 3 and the fpd 4 located at the positions denoted by dashed - dotted lines in fig2 are moved to the positions denoted by dotted line after x - ray emission for taking an original image p 0 a , and then an original image p 0 b is obtained . then after the x - ray emission for taking the original image p 0 b , the x - ray tube 3 and the fpd 4 in the positions denoted by dotted lines are moved to the positions denoted by solid lines , whereby an original image p 0 c is obtained . the obtained original images p 0 a , p 0 b , and p 0 c are transmitted to the long - length image generating unit 12 . the long - length image generating unit 12 combines the original images p 0 a , p 0 b , and p 0 c to generate a long image p 1 . the display unit 39 displays the generated long image p 1 , whereby the long - length radiography completes . as noted above , with the x - ray apparatus according to embodiment 1 , successive imaging is performable while the timing to activate the x - ray tube 3 in a rest state is acquired appropriately . that is , with the configuration of embodiment 2 , the difference time is calculated by subtracting the time width of the activation time period from the time width of the non - detectable time period , and the time after the difference time has elapsed from the x - ray emission is determined as a timing to activate the x - ray tube 3 . here , the time width of the non - detectable time period is a time width from when the fpd 4 detects x - rays one time to when posterior x - ray detection is performable . the time width of the activation time period is a time width from activate to completion of activation of the x - ray tube 3 . the x - ray tube 3 is activated at the timing with embodiment 2 , whereby end of the non - detectable time period of the detector conforms to end of the time period for activating the x - ray tube 3 . this ensures rapid successive imaging while the activation of the x - ray tube 3 and preparation of the detector are performed simultaneously . moreover , in embodiment 2 , the x - ray tube 3 is in a rest state during x - ray emission . in contrast to this , in the conventional automatic type in fig1 , the x - ray tube 3 is activated all the time once the successive imaging is activated . in other words , in the conventional automatic mode , the filament in the x - ray tube 3 is always kept at high temperatures , causing readily damages on the filament . as noted above , embodiment 2 achieves a longer life of the x - ray tube 3 than that in the conventional type . the present invention is not limited to the above embodiments , but may be modified as under . ( 1 ) in addition to the configurations mentioned above , the notifying unit 36 may count down the timing before the difference time elapses when the emission instruction is provided through the operation switch 38 . in this case , the given time period t 1 as a standby time from completion of the x - ray emission should be shortened by time required for the count down . the notifying unit 36 provides notification that the timing for the timing determining unit 17 has arrived through the count down , whereby the operator can provide the instructions more easily . any time point within a time period after the given time period t 1 has elapsed from the x - ray emission is selectable as a timing to activate the count down . consequently , the time period of the countdown should not be longer than the given time period t 1 . ( 2 ) moreover , the notifying unit 36 may notify the operator of the instruction after given time delay from the timing provided by the timing determining unit 17 . this ensures a sufficient rest time of the x - ray tube 3 . ( 3 ) the embodiments of the present invention are not limited to the feature that the x - ray tube 3 is moved along with the fpd 4 during the long - length radiography . alternatively , the embodiments are applicable to the feature that the x - ray tube 3 inclines relative to the movement of the fpd 4 . ( 4 ) the embodiments of the present invention are not imitatively applicable to the long - length radiography . alternatively , the embodiments are applicable to radiography in which successive imaging is performed to the subject m while the x - ray tube 3 and the fpd 4 are not moved . ( 5 ) a function of switching between the manual mode in embodiment 1 and the automatic mode in embodiment 2 through operator &# 39 ; s decision may be added to the embodiments of the present invention . as noted above , the above invention is suitable in medical fields . it will be further understood that the enclosed devices , systems , apparatus , module , and means herein , it will be expressly understood that the phrase ‘ means ’ in the specification does not create a ‘ means for ’ presumption , and any presumption is expressly rebutted here stating that unless expressed in an exact ‘ means for ’ language there is no assertion of § 112 ¶ 6 presumption within the lexicography of the applicant , the structure noted herein would include the understood structure , processors , processing boards , memory and other electronic devices discussed herein to achieve the stated function and not external to this disclosure . having described at least one of the preferred embodiments of the present invention with reference to the accompanying drawings , it will be apparent to those skills that the invention is not limited to those precise embodiments , and that various modifications and variations can be made in the presently disclosed system without departing from the scope or spirit of the invention . thus , it is intended that the present disclosure cover modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents .
according to this radiography device , by taking images in rapid succession while appropriately obtaining the timing for which an x - ray tube in a rest state should be activated , rapid successive imaging and protection of a radioactive source can both be achieved . that is , in the configuration of the present invention , a time difference is calculated , obtained by subtracting a temporal width of an activation period from a temporal width of an undetectable period , and the time after the time difference has elapsed from the time at which an x - ray is irradiated is determined as the timing for activating the x - ray tube . the temporal width of an undetectable period is the temporal width between the time at which an fpd detects an x - ray once and the time at which the following x - ray can be detected , and the temporal width of an activation period is the temporal width between the start of activation of the x - ray tube to the completion of activation . thus , while simultaneously activating the x - ray tube and preparing the detector , images can be taken in rapid succession without excessive burden on the x - ray tube and the life of the x - ray tube can be extended .