JPS60119431A - Method of determining no leakage and application for usage of electron tube filled with non-negative gas - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for determining whether a gas-filled electron tube is suitable for use in its operating mode, and in particular to a method for determining whether a gas-filled electron tube During the sequence, a leak in the electron tube placed near the radiation source to ionize the gas! The present invention relates to a method for detecting ``L.''.

When a gas-filled electron tube, such as an ionization chamber, is subjected to ionizing radiation, the incident radiation interacts with the gas, liberating electrons from the gas atoms and leaving positively charged gas ions. The charge is swept out of the gas by a sweeping electric field applied between the anode and cathode electrodes in the ionization chamber, electrons moving to the anode and positive ions moving to the cathode. The charge moving within the ionization chamber causes the current to flow to the external circuit. To ensure the desired current saturation characteristics for the ionization chamber, it is necessary to fill the ionization chamber with pure gas. . A major quality control issue associated with the manufacture of ionization chambers is evaluating the condition of the fill gas after the ionization chamber is removed from the evacuation system that fills the ionization chamber with the fill gas. Also, when the ionization chamber is installed in a working device such as an operating nuclear reactor, the quality of the gas in the ionization chamber is periodically checked to ensure that the ionization chamber is functioning properly. It is desirable to be able to do so.

If a leak occurs and air, oxygen or other negative gas enters the ionization chamber, the performance of the ionization chamber will be adversely affected. Seven methods used in the prior art to detect leaks are to include a small amount of helium in the fill gas. If helium escapes from the ionization chamber, standard leak testing methods are followed. In the unfortunate event that a leak occurs, the helium will rapidly dissipate from the ionization chamber, so that after a short period of time it will disappear and the leak can no longer be detected. Therefore, this leak detection method is
The ionization chamber can only be used for a relatively short period of time after it has been manufactured.

It is known that applying a relatively low frequency alternating voltage between the electrodes of an ionization chamber causes a current to flow through the ionized gas of the ionization chamber.

The magnitude of this current corresponds to the degree of ionization of the filling gas of the ionization chamber and thus to the amount of radiation flux incident on the ionization chamber. The current in the ionization chamber also provides information about the state of the gas fill, which is used in the present invention to detect tube or electron tube leaks.

As the alternating voltage applied across the ionized gas within the ionization chamber increases toward its peak value, electrons and positive gas ions are pulled apart by the electric field. As the electrons move toward the positive electrode, the current through the ionization chamber increases rapidly, forming a spike at the leading edge of each half-cycle of the current waveform. Spikes are undesirable for AO operation in ionization chambers, and methods have been developed to eliminate them. For example, Davi
``The A-0 ionization chamber is simple and reliable'' by Roberts L.
ucleontcs) Published in /96/ issue)
Pages 3-SS describe seven methods for including negative gases such as air or oxygen in the fill gas.

The presence of negative gas eliminates the spike as free electrons released by the incident radiation attach themselves to form heavy anions before being collected by the rising voltage. Therefore, the fast initial electron focusing at the anode is eliminated.

Rather than requiring spikes to be removed, the invention uses the information provided by spikes rC in a novel method for detecting leakage in gas-filled electron tubes.

It is an object of this invention to provide a method for detecting leaks in gas-filled electron tubes that can be performed during standard factory acceptance testing.

A further object of the invention is to improve the quality of the gas when the gas-filled electron tube is installed in an operating device, especially when the electron tube is an ionization chamber installed in an operating nuclear reactor. It is an object of the present invention to provide a method for detecting leakage n'l of a gas-filled electron tube, which can be used to confirm the leakage n'l of a gas-filled electron tube.

Another object of the present invention is to provide a leak detection method that does not require special substances such as helium for the fill gas.

Yet another object of the invention is to provide a method for detecting leakage in a gas-filled electron tube that can be performed remotely.

The above and other objects are achieved in accordance with the present invention, which provides a novel method for determining whether an electron tube filled with a non-negative gas is leak-free and suitable for use. This method involves exposing the electron tube to radiation to ionize the gas inside, and applying an alternating current voltage across the anode and cathode electrodes of the electron tube to generate a current passing therethrough, with spikes at the leading edge of the current waveform. Detects the current waveform, which indicates that gas has not leaked from the electron tube, and indicates that a leak has occurred if there is no spike. I try to use it in that mode of operation.

The invention applies only to gas-filled electron tubes with non-negative gases as filling gas.

The presence of a spike at the leading edge of the transmitted waveform within such an electron tube is an indication that the electron tube is not leaking. If a leak occurs and air, a negative gas, seeps into the electron tube, applying an alternating voltage across the electrodes of the electron tube will cause a current to be transmitted through those electrodes with no spikes at the -1'1 edge. Become so. If air is present within the electron tube, this causes the electrons to recombine before being collected at the anode as a result of the increased voltage, as discussed above. As a matter of fact, the absence of spikes is evidence of impure gas fill and indicates that there is probably a leak in the electron tube.

In practicing the invention, it is generally necessary to remove the reactive components of the current transmitted by the gas-filled electron tube in order to detect spikes in the front of the current waveform. That is, the ionization chamber is filled with gas such as -nf? 'The electron tube has an inherent capacitive reactance that exists whether or not the ionization chamber is irradiated. The component of the transmitted current due to the capacitive reactance of the ionization chamber tends to swamp the current resulting from the ionization of the gas.

Several methods are useful for removing the reactive components of the electron tube current. One such method, described in the article by Roberts, is to divide a given alternating current voltage into a voltage component that is approximately equal in magnitude and opposite in phase. One voltage component is applied to the electron tube and the other is applied to a variable impedance device which generates a current equal and opposite to the capacitive component through the electron tube, thereby reducing the capacitive component through the electron tube. To disable.

It is preferable that the capacitance adjustment be performed when the electron tube is not receiving radiation. When the ionization chamber is exposed to radiation and an alternating voltage is applied across the ionization chamber, the component of the electron tube current that is not nullified is the portion of the current carried by the ionized gas in the ionization chamber. Once the dead part of the electron tube current is removed, the spikes are clearly visible on the cathode tube. The transmitted signal is suitably amplified and, according to the invention, the signal is used as an indication of the level of radiation incident on the ionization chamber and as an indication of whether the ionization chamber has leakage. Ru.

Ionization chambers for use in conjunction with nuclear reactors can be tested for gas quality according to the novel method of this invention as a standard part of a neutron sensitivity acceptance test.

This test method can be applied even while the device is installed in an operating nuclear reactor, as long as ionizing radiation is present and ionizes the charge gas.

The method according to the invention is not limited to ionization chambers, but with suitable circuitry can detect leaks in proportional counters, spark gaps, fission ionization chambers, and other gas filling devices that do not contain negative gases. Used to get 扛.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a test circuit used to detect all leaks in gas-filled electronic devices using electronic spike observation techniques in accordance with the method of the present invention. The pulse signal generator/generates a test signal consisting of an alternating current test voltage which may have a sinusoidal or rectangular waveform with a frequency on the order of 60-70 hertz and a voltage magnitude of /volts.

This signal is passed through a phase splitter (5 splitter) which produces two voltage signals approximately equal in magnitude and opposite in phase.
er) and given to the inverter 3.

The phase splitter/inverter 3 may be, for example, a phase splitter transformer (phase sp'l) in a manner well known in the art.
Itting trausfor+ner) or may be implemented by a push-pull amplifier. One of the output signals 3a from the phase splitter/inverter 3 is applied across the anode and cathode electrodes of the gas filling device whose gas quality is being inspected, that is, the impedance of the gas filling device 5 having a capacitive reactance component. Spread. The inverted output signal 3b of the phase splitter and inverter 3 is supplied by a variable impedance device containing a balanced capacitor as shown in the paper by Roberts.
is applied across r or other suitable circuit to adjust and obtain n to approximate the reactance exhibited by the gas filling device 5. The current 1a passing through the variable impedance device 7 and the current 1t passing through the gas filling device S are combined and amplified by an operational amplifier, and the combined and amplified signal is sent to a cathode ray tube (C).
RT) // or other optical indicating or detecting device;
The combined output signal is then monitored.

First, the variable impedance device @7 has a current 1a of
The capacitive reactance of the gas filling device 5 adjusts the portion of the current 1t passing through the gas filling device S until it is completely nullified. Preferably, this disabling process is carried out when the gas filling device S is not exposed to radiation and therefore the gas within it is in a stable non-ionized state. In such a state, the electric current transmitted by the gas filling device 5 is entirely due to its capacitive reactance, and the reactive current of the electron tube or tube can be determined by visual observation of when a reactive signal occurs on the CRT. , balance. The impedance of the variable impedance device, which is inactive when the gas filling device is not irradiated, is maintained while the gas filling device j is exposed to radiation from the radiation source /3.

Alternatively, if the capacitive reactance of the gas filling device 5 is known, the variable impedance device can be set to that known capacitive reactance either before or during irradiation of the gas filling device 5. It is possible to

The incident radiation ionizes the gas in the gas filling device j, causing the current rt to increase. The electrons and positive gas ions in the electron tube, across which the applied alternating voltage increases towards the peak value of the applied voltage, are separated by the resulting electric field. Since the gas filling device 5 contains only non-negative gas, the electrons move rapidly towards the positive electrode, creating a spike at the leading edge of the generated current waveform. The reactive portion is clearly visible on the cathode ray tube because it is presented and nullified by a variable impedance device.Alternatively, the output of the amplifier can be fed into a conventional spike detection circuit that detects the presence or absence of that current spike. It's okay.

The electron tube is then used in its operating mode, e.g. to measure radiation or to operate as a spark gap, only if a spike is present in the front of the current waveform. If a spark or spark is not detected, appropriate corrective action is taken, such as repairing or discarding the tube. FIG. 21 shows that the gas filling device 5 contains pure non-negative gas. It shows the waveform displayed on the cathode ray tube when the screen is on. If there is no leakage and only non-negative gas is contained in the electron tube, spikes is and are present on the waveform displayed on the cathode ray tube. If this occurs, air will enter and clean the inside of the device, eliminating the electronic spikes at the leading edge of the transmitted waveform displayed on the cathode ray tube. The reason is that before the free electrons reach the anode electrode of the gas filling device S,
This is because the free electrons released by the radiation that ionizes gold recombine to form heavy anions. This fast initial electron focusing at the anode does not occur in the presence of dirty negative gas, thus removing spikes from the leading edge of the transmitted waveform. This is shown in the zb diagram, where the electron spikes are not present due to air pollution.

The ionization density required to perform electron spike detection depends on how well the capacitive component of the electron tube current is nullified. For example, the model WL-6,377 ionization chamber made by Westinghouse Electric Corporation has a neutron sensitivity of approximately 7 x 7 (f" amps/nv and -
// It has a gamma sensitivity of approximately λ×/θ ampere/R/hr. Here, nv is the unit neutron flux at 7 cm of neutrons for 7 seconds, and R represents the roentgen. If, for example, b l! has a magnitude of /volt rms! II
WL where the IH2 signal has /G Opf capacity fikk
- If it is supplied to the ionization chamber of A3ri7, then what? ,
! Peak currents on the order of x10-A/Ve will occur. Assuming that /chi invalidity is obtained, ri, 5×/θ−
``Ampere peak 6θHz background (bac
kgground) signal will be present. For a good reading such as signal-to-noise ratio 100: /, tJ
It would require a radiation current of X/θ amps peak. Using the sensitivity of the ionization chamber of WL-6377, this is! , θX10'nv radiation level, or gamma radiation of 3.5×/03R/Hr. Improvements in circuit sensitivity result in
This would allow for a lower ratio of radiation to bias signal. The variable impedance device 7 is designed to cover a relatively wide range of radiation detectors in use.
It would be preferable to be able to cover the entire company from GooP to GooP. A device with a larger capacity will require a suitably larger variable capacity.

Various non-negative gases may be used as fill gases in the electron tube chambers tested by the method of the present invention. N.Ho
A pure mixture of is an example of such a non-negative gas.

This method is particularly useful when associated with DO-operated ionization chambers used to monitor radiation near an operating nuclear reactor. The circuit of Figure 1 periodically provides an AC test signal for leakage testing to the ionization chamber while it is installed in an operating nuclear reactor, and the ionization chamber is working properly. It's used to make sure of the tsunami. The novel method according to the invention can also be carried out according to the invention as a standard factory acceptance test immediately after the gas filling device has been filled with non-negative gas. Similarly, the test circuit described in connection with FIG. away from the electron tube
It can be done anywhere.

The leakage detection method according to the invention is a simple and inexpensive method for checking the quality of the gas in a gas filling device and ensuring its proper functioning.

Furthermore, since there is no need to add special additives such as helium to the fill gas to complete leak detection tests, such additives disappear due to leakage, which can then be observed by attentive personnel. There is no danger of not being able to do so.

It will be understood that the detailed description of the invention is susceptible to various modifications, changes and applications. The same is intended to be interpreted within the meaning and scope of the equivalents in the claims fl-fl.

[Brief explanation of drawings]

FIG. 7 is a block circuit diagram illustrating a test circuit for carrying out a method according to an embodiment of the present invention, FIGS.
FIG. 0 is a waveform diagram showing the current output waveform generated by the circuit of FIG. In the figure, / is a pulse signal generator, 3 is a phase splitter/inverter, 5 is a gas filling device (electron tube), 7 is a variable impedance device, // is a cathode ray tube (CRT), and /3 is a radiation source.

Claims (1)

[Claims] In order to fully determine whether an electron tube filled with a non-negative gas having an anode and a cathode electrode is leak-free and suitable for use, the electron tube is exposed to radiation and the gas inside the tube is applying a full alternating current voltage between the electrodes of the electron tube to generate a current through the electron tube having a magnitude corresponding to the intensity of the radiation; For example, detecting the current waveform indicates that the gas is not leaking from the electron tube, and the absence of a spike indicates that a leak has occurred; A method for determining whether an electron tube filled with a non-negative gas is leak-free and suitable for use, comprising: using an electron tube in its operating mode;