JPH0518071B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an output dose measuring device for a radiation generating device having a pulsed radiation source.

[Conventional technology]

FIG. 5 explains a general dosimetry device for a radiation generating device having a pulsed radiation source, and a
1 shows its block diagram, and b shows a waveform diagram of signals of each part of the block and input/output signals. In the figure, 1
2 is a radiation generating section that generates pulsed radiation triggered by a pulse signal from a pulse oscillator 5 whose pulse repetition frequency can be controlled by an external volume VR ₁ ; An ionization chamber is used for detection; 3 is a preamplifier that converts the ionization current of the ionization chamber into a voltage; 4 is a voltage inverting amplifier equipped with a gain adjustment volume VR ₂ that amplifies the output voltage; and 5 is a pulse oscillator.

Next, the operation will be explained. external volume
The output pulse v _T of the pulse oscillator 5 whose pulse repetition frequency can be controlled by VR ₁
(See Figure 5b) provides a trigger for each pulsed power drive necessary to generate pulsed radiation. The pulsed radiation generated by this trigger pulse passes through the ionization chamber 2 and passes through the radiation generating section 1.
The light is emitted from the opening 1a and is irradiated onto the object to be irradiated.

Therefore, the ionization chamber 2 is provided to measure the amount of radiation generated by detecting the amount of ionizing current ionized in a certain volume by utilizing the ionization effect of radiation in the atmosphere. The current I ₀ has a pulse current waveform I ₀ synchronized with the trigger of the pulse oscillator 5 as shown in FIG. 5b. Then, the preamplifier 3 converts the pulse current I ₀ into a voltage v ₀ (see Figure 5b), and at the same time connects an impedance with a certain C ₁ R ₁ time constant to the feedback loop. The current signal I ₀ is converted into a smoothed voltage signal, and the relationship between the input and output signals of this preamplifier 3 is as follows.

τ _w : Ionizing current pulse width τ _R : Pulse repetition frequency I _p : Ionizing current peak value v ₀ Output voltage of preamplifier 3 v _0ave : Output average voltage of preamplifier 3 Δv ₀ : Ripple voltage of preamplifier 3 p-p v _0ave ≒ −R ₁ I _p τ _w ／τ _R ……(1) Δv ₀ ≒τ _R ／R ₁ C ₁ v _0ave ……(2) (However, τ _w ≪τ _R , τ _R ≪R ₁ C ₁ ) The voltage inverting amplifier 4 that has obtained the above output voltage v ₀ amplifies the output voltage of the preamplifier 3 and can change the degree of amplification by varying the gain adjustment volume VR ₂ . _A becomes as shown in equation (3).

v _A = −R ₃ /R ₂ v ₀ ...(3) (However, R ₃ is the value of the feedback resistor, R ₂ is the resistance value of the gain adjustment volume VR ₂ ) This output voltage v _A is the radiation output dose The output dose is detected as a monitor signal and is also used as a feedback signal for the automatic output dose control circuit.

[Problem that the invention seeks to solve]

However, in the conventional device as shown in FIG. 5, the ripple component Δv ₀ is not completely removed because the output pulse current signal of the ionization chamber 2 is smoothed using the preamplifier 3 and the CR integration circuit and converted into a DC signal. , the pulse repetition period τ _R is the ionizing current pulse width τw
When it becomes larger than , the ripple component Δv ₀ becomes large, which increases the vibration of the output dose monitor signal and causes poor controllability of the output dose rate automatic control circuit. On the other hand, if the time constant C ₁ R ₁ of the preamplifier 3 is increased in order to reduce the ripple component Δv ₀ , there are disadvantages such as vibration of the meter that detects the monitor signal and poor response of the control circuit. .

This invention was made to solve the above-mentioned problems, and by converting the output pulse current signal of the ionization chamber 2 into a DC voltage signal with no ripples between each pulse signal, ripples can be eliminated. The object of the present invention is to obtain a device that can eliminate vibrations in the output dose monitor signal itself and improve the response and controllability of the output dose rate automatic control circuit.

[Means for solving problems]

The output dose measuring device for a radiation generating device according to the present invention converts the pulsed ionizing current waveform of the radiation generating device into a voltage waveform and uses a voltage frequency converter (hereinafter referred to as V/
It is called an F converter. ) to perform frequency conversion,
At the same time as the first integration counter integrates the pulse interval time of the pulsed ionizing current converted into a voltage waveform, the second integration counter integrates the value of the first integration counter and the value of the second integration counter. is divided by a division circuit, and the output signal of this division circuit is used as a radiation output dose monitor signal.

[Effect]

In the V/F converter and integration counter of the present invention, a pulsed ionizing current signal is obtained by calculating the time integral value of the pulsed ionizing current waveform and dividing the above time integral value by the time of each pulse interval using a division circuit. is converted into an average voltage signal for each pulse interval, resulting in a monitor signal that does not contain ripple components.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 and 2 are the same as the explanation of the prior art, so the explanation will be omitted. 9 is a trigger oscillator corresponding to the pulse oscillator 5 of the prior art. 4a is a current-voltage converter that converts the output pulse current signal of the ionization chamber 2 into a voltage signal;
5a connected to the output is a V/F converter that converts the voltage signal into a frequency, and 6 is a first V/F converter that integrates the pulse signal output from the V/F converter 5a.
, and 7 is this first integration counter 6.
a first latch circuit for holding the integrated value of 8
is a first D/A converter that converts the digital output signal of the first latch circuit 7 into an analog signal. 10 is a monostable multivibrator driven in synchronization with the radiation generation trigger of trigger oscillator 9; 11 is a reference oscillator for pulse interval time counting; and 12 connected to the output of this reference oscillator 11 is a second integration Counter 13 is a delay circuit connected to the reset input of second integration counter 12. 14 is a second latch circuit that holds the output of the second integration counter 12 at every pulse interval, and the output of this second latch circuit 14 is
It is connected to a second D/A converter 15 that converts the time integration value obtained by the integration counter 12 into an analog value. 16 is an analog division circuit.

Next, the operation of the above embodiment will be explained with reference to FIGS. 2 and 3. Similar to the explanation of the conventional output dose measuring device, the radiation generating device is driven by the trigger signal of the trigger oscillator 9, and the pulsed ionizing current I _{0 (t)} outputted in synchronization with the trigger period is transferred to the current-voltage converter 4a. and the output is v(t)
(See Figure 3) voltage is generated. Current at this time
The relationship between I ₀ (t) and voltage v(t) is as shown in equation (4).

v ₀ (t)=R ₁ I ₀ (t) ...(4) The pulse voltage waveform v ₀ (t) generated here is V/F
The converter 5a converts the frequency into a pulse signal (see FIG. 3) with a repetition frequency proportional to the input voltage. This pulse signal is integrated by a first integration counter 6. Further, the output reset pulse of the monostable multivibrator 10 is applied to the reset input of the first integration counter 6 via the delay circuit 13, and the output of v(t) is applied to the first integration counter 6 at every trigger pulse interval of the trigger oscillator 9. Integration of the frequency-converted pulse signals is performed. At this time, the integrated value of the first integrating counter 6 is held in the first latch circuit 7 immediately before the first integrating counter 6 is reset (see FIG. 3). When a rectangular voltage signal as shown in FIG. 2 is converted by a V/F converter with a conversion ratio of C (Hz/V) and integrated by a counter, the integrated value of one pulse becomes as shown in equation (5).

Σv ₀ =C∫〓 ^w ₀₀ (t)dt ...(5) =CfwVp The digital output value latched in the latch circuit 7 is converted into an analog signal by the first D/A converter 8, and the numerator of the divider circuit 16 This is a side input.

Next, the operation of the pulse interval time counting circuit will be explained. The reference oscillator 11 is always in oscillation operation. A second integration counter 12 is connected to the output of the reference oscillator 11 and integrates the output pulses of the reference oscillator 11 until the reset signal of the monostable multivibrator 10 is output (see FIG. 3). This integrated value is held in the second latch circuit 14 immediately before the second integrating counter 12 is reset by the output pulse of the monostable multivibrator 10 as described above, and this latch output digital signal is the pulse interval time value. The signal is converted into an analog signal by the D/A converter 15 (see FIG. 3). In the case of the rectangular voltage signal shown in FIG. 2, if the oscillation frequency of the reference oscillator 11 is f, the pulse interval time is expressed by equation (6).

T=τ _R f ...(6) The analog output signal of the second D/A converter 15 becomes the denominator side input of the divider circuit 16, and the output signal of the divider circuit 16 is expressed by equation (5), (6 ) can be derived from equation (7).

When f = C, Σv ₀ /T = τ _w V _p /τ _R = v _0ave ...(7) In other words, this equation (7) shows that the pulse ionization current signal is v
_0ave τ _w V _p /τ _R = τ _w R ₁ I ₀ /τ _R This shows that the signal has been converted into a DC signal calculated by 0ave τ w V p /τ R = τ w R 1 I 0 /τ R.

FIG. 4 shows an example of a modification of the above embodiment. 1
The functions of 7 and 9 to 14 are the same as in the previous embodiment, except that 15 is a digital input interface section and 16a is a microcomputer system. This microcomputer 16a inputs the pulse waveform integral value of the first latch circuit 7 and the pulse interval time of the second latch circuit 14 as digital signals, performs division, and outputs the result via the digital output interface 17. By outputting to the D/A converter 18, the same functions as in the previous embodiment can be achieved.

〔Effect of the invention〕

As described above, this invention makes it possible to convert the integral value of a pulsed ionizing current signal output at any repetition frequency into a DC signal obtained by dividing the integral value by the time until the next pulse. CR of
To configure a radiation output dose measuring device that does not generate ripple components unlike a method using an integrating circuit, has a quick response from a control circuit, and is not affected by the pulse repetition frequency of a pulsed ionizing current signal. becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a block diagram illustrating an embodiment of the output dose measuring device of the radiation generating device of the present invention;
Figure 2 is a pulse waveform diagram explaining the relationship between the pulse width and pulse repetition frequency of the voltage-converted pulsed ionizing current signal, Figure 3 is an operation waveform diagram showing the relationship between the output signals of each part in Figure 1, and Figure 4. 5 is a block diagram showing another embodiment of the present invention, and FIGS. 5a and 5b are block diagrams showing a conventional radiation generating apparatus and explanatory waveform diagrams showing input and output signals for each block. In the figure, 1 is a radiation generating part, 2 is an ionization chamber,
4a is a current-voltage converter, 6 is a first integration counter, 7 is a first latch circuit, 10 is a monostable multivibrator, 11 is a reference oscillator, 12 is a second integration counter, and 14 is a second latch circuit. , 16 is a division circuit.

Claims (1)

[Claims] 1. In a radiation generator that generates pulsed radiation to irradiate an irradiated object, a detection means for detecting the pulsed output dose, a current-voltage converter for converting the current detected by the detection means into voltage, and the output of this converter. voltage frequency converter, which converts voltage to frequency;
A first integration counter that integrates the output pulses of this voltage frequency converter for each pulsed output dose, a first latch circuit that latches this integrated value, and a pulse of a predetermined width based on the reference pulse signal of the radiation generator. a second integration counter that integrates the output pulses of the reference oscillator at every output pulse interval of the monostable multivibrator; A radiation generating device comprising: a second latch circuit that holds based on the output; and a division circuit that divides the output signal of the second latch circuit and the output signal of the first latch circuit. Output dosimetry device.