CN109283570B - Method for measuring drift velocity of electrons in gas with external electric field - Google Patents
Method for measuring drift velocity of electrons in gas with external electric field Download PDFInfo
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- CN109283570B CN109283570B CN201811289037.5A CN201811289037A CN109283570B CN 109283570 B CN109283570 B CN 109283570B CN 201811289037 A CN201811289037 A CN 201811289037A CN 109283570 B CN109283570 B CN 109283570B
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Abstract
In the field of nuclear radiation detection such as gas ionizing radiation detection and ion mobility spectrometry, the drift velocity of electrons is an important factor for determining the time response performance, and has a decisive influence on the radiation measurement result. The research on the drift velocity of electrons in gas is a precondition for improving the time response performance of the ionizing radiation detector and optimizing the design of the detector, and has important significance for promoting the development of gas electronics and gas ionizing radiation detection technology; the method is a method for measuring the drift velocity of electrons in gas with an external electric field based on the design of a screen grid ionization chamber detector, heavy particles such as alpha particles and the like are incident in a manner that a collimator close to a cathode is parallel to the plane of the cathode, the drift velocity of the electrons under different electric field conditions of different component gases can be measured, and an effective way is provided for measuring the drift velocity of the electrons.
Description
Technical Field
The invention relates to the technical field of radiation detection, in particular to a method for measuring the drift velocity of electrons in gas with an external electric field.
Background
In the field of nuclear radiation detection such as gas ionizing radiation detection and ion mobility spectrometry, the drift velocity of electrons is an important factor for determining the time response performance, and has a decisive influence on the radiation measurement result. The research on the drift velocity of electrons in gas is a precondition for improving the time response performance of the ionizing radiation detector and optimizing the design of the detector, and has important significance for promoting the development of gas electronics and gas ionizing radiation detection technology.
At present, the research on the drift velocity of electrons and ions in gas is mainly carried out by means of experimental measurement or simulation calculation, and the common methods are as follows: drift tube measurement, gas electron multiplier measurement, high pressure gas-filled ionization chamber measurement, and monte carlo simulation.
Disclosure of Invention
In order to support the research in the aspect of ionizing radiation detection technology, the invention aims to provide a method for measuring the drift velocity of electrons in gas with an external electric field, because an anode signal induced by electrons in a screen grid ionization chamber is shielded by a grid, a time difference delta t exists between the anode signal and a cathode signal when the anode signal is generated; the method of the invention utilizes the characteristic that the electrons do not induce signals at the anode in the process of drifting between the cathode and the grid, and measures and calculates the electron drifting speed according to the distance D between the cathode and the grid and the time difference delta t generated by the signals.
A method of measuring the drift velocity of electrons in a gas having an applied electric field, the method comprising the steps of:
the method comprises the steps of firstly, building a screen grid ionization chamber detection device, wherein an ionization chamber main body is cylindrical by taking stainless steel as a material, energized stainless steel circular rings are respectively connected to positions close to the upper surface and the lower surface in a cavity and serve as a cathode and an anode to carry out ion detection, a grounding stainless steel circular ring capable of carrying out position adjustment is connected between the cathode and the anode and serves as a grid to shield anode signals, and a region between the cathode and the grid is a gas ionization occasion;
secondly, measuring the distance D between the cathode and the grid of the screen grid ionization chamber;
thirdly, introducing specific component gas to be measured into the cavity of the screen grid ionization chamber;
fourthly, collimators are arranged in parallel close to the cathode electroplate to screen the incident angles of charged particles, the initial velocity direction of the charged particles is ensured to be vertical to the direction of an external electric field when the charged particles are injected into the ionization chamber, meanwhile, the flight of the incident charged particles in the ionization chamber has the collimation characteristic, the experiment is carried out by limiting and selecting the charged particles with larger mass number in the aspect of the selection of the charged particles, such as α particles and other heavy particles, the motion trail of the charged particles in the ionization chamber is approximately not subjected to longitudinal displacement, electrons generated by ionization in the transverse motion process are considered to drift from the cathode position to the anode, the source intensity A of a radioactive source generating the charged particles cannot be too strong, and the limitation A is that the source intensity A is too strong<105Bq。
Fifthly, after the charged particles enter the ionization chamber, gas ionization is caused to generate positive ions and free electrons, the positive ions induce signals on the cathode at the moment of generation, the free electrons are shielded by the grid electrode and need to drift through the grid electrode to induce signals on the anode, and time difference delta t exists between the generation time of the signals of the cathode and the anode; the generated signals are subjected to amplification discrimination and time-amplitude conversion through a preamplifier, a discriminator and a TDC time-digital converter, and time data delta t is obtained on a recorder;
sixthly, according to the data obtained by the measurement in the second step and the fifth step, the formula is used
The electron drift velocity v is calculated.
Compared with the prior art, the method has the following advantages:
the method is a method for measuring the electron drift velocity in the gas with an external electric field based on the design of a screen grid ionization chamber, can measure the electron drift velocity of gases with different components by simply injecting heavy particles such as alpha particles and the like, and provides an effective way for measuring the electron drift velocity.
Drawings
FIG. 1 is a schematic diagram of a screen grid ionization chamber test system.
Fig. 2 is a schematic diagram illustrating the principle of a screen ionization chamber.
Detailed description of the invention
As shown in fig. 1, the screen grid ionization chamber test system can obtain mutually independent cathode and anode detection signals of the screen grid ionization chamber, and obtain a time difference Δ t generated by the cathode and anode signals. Fig. 2 is a schematic illustration of a screen ionization chamber.
With the components of Ar and CO2(90%/10%) gas with pressure of 1atm for example, cathode and anode voltages are set to-800V and 300V respectively, and the following are examples of measuring the electron drift velocity of the gas by a screen ionization chamber:
firstly, measuring the distance D between the cathode and the grid of a screen grid ionization chamber to be 70 mm;
secondly, introducing Ar and CO to be measured into the cavity of the screen grid ionization chamber2(90%/10%) gas at a pressure of 1 atm;
third, select241An Am- α source generates charged particles, the charged particles are injected into α particles in parallel by a collimator close to a cathode electric plate, the initial velocity direction of the α particles is ensured to be vertical to the direction of an external electric field, and electrons generated by ionization in the transverse movement process drift from a cathode to an anode;
fourthly, measuring to obtain the time difference delta t of the signals generated by the cathode and the anode to be 9.47 mu s;
fifthly, analyzing according to the data obtained by the measurement in the first step and the fourth step, and obtaining the data through a formula
The electron drift velocity v is calculated to be 7391.8 m/s.
Claims (4)
1. A method of measuring the drift velocity of electrons in a gas having an applied electric field, comprising the steps of:
step (1): the method comprises the following steps of building a screen grid ionization chamber, wherein a main body of the screen grid ionization chamber is cylindrical and is made of stainless steel, energized stainless steel rings are respectively connected to positions close to the upper surface and the lower surface in a cavity and serve as a cathode and an anode to perform ion detection, a grounding stainless steel ring capable of performing position adjustment is connected between the cathode and the anode and serves as a grid to shield anode signals, and the region between the cathode and the grid is the place where gas ionization occurs;
step (2): measuring the distance D between the cathode and the grid of the screen grid ionization chamber;
and (3): introducing specific component gas to be measured into the cavity of the screen grid ionization chamber;
and (4): a collimator is arranged in parallel close to the cathode electric plate, the incident angle of charged particles is screened, and the initial velocity direction of the charged particles is ensured to be vertical to the direction of an external electric field when the charged particles are irradiated into the screen grid ionization chamber;
and (5): charged particles enter a screen grid ionization chamber to cause gas ionization to generate positive ions and free electrons, the positive ions induce cathode signals on a cathode at the moment of generation, the free electrons are shielded by a grid electrode and need to drift through the grid electrode to induce anode signals on an anode, and a time difference delta t exists between the generation of the cathode signals and the generation of the anode signals; the cathode signal and the anode signal respectively pass through a preamplifier, a discriminator and a TDC time-digital converter in turn to carry out amplification discrimination and time-amplitude conversion, and a time difference delta t is obtained on a recorder;
and (6): according to the data obtained by the measurement in the step (2) and the step (5), the formula is used
The electron drift velocity v is calculated.
2. A method of measuring the drift velocity of electrons in a gas having an applied electric field according to claim 1, wherein: the charged particles incident in the step (4) have a collimation characteristic in the flight in the screen grid ionization chamber, and the heavy charged particles are limited and selected in the aspect of selection of the charged particles for experiment, the moving tracks of the charged particles in the ionization chamber are approximately not subjected to longitudinal displacement, and electrons generated by ionization in the transverse moving process are considered to drift from the cathode position to the anode.
3. A method of measuring the drift velocity of electrons in a gas having an applied electric field according to claim 2, wherein: the heavy charged particles are alpha particles.
4. A method of measuring the drift velocity of electrons in a gas having an applied electric field according to claim 1, wherein: the source intensity of the radioactive source generating the charged particles, A, must not be too strong, defining A<105Bq。
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