Method for reducing dark current influence of photomultiplier

Abstract

The invention relates to the technical field of photoelectricity, in particular to a method for reducing influence of dark current of a photomultiplier, which comprises the following steps of: connecting an anode of the photomultiplier with a constant current source for counteracting the dark current; when the positive electrode of the photomultiplier has pulse output, the positive electrode of the photomultiplier realizes output through an integrating circuit; and when the anode of the photomultiplier has no pulse output, the anode of the photomultiplier is grounded. Compared with the prior art, the device is simple in structure and convenient to operate, the constant current source is arranged to offset dark current, meanwhile, the dynode of the photomultiplier is used for controlling the single-pole double-throw analog switch, then the dark current cannot flow into the integrating circuit when the anode of the photomultiplier has no pulse output, the contribution rate of the dark current to the integrating result is reduced, and the integration accuracy is improved. The problem that the dark current has great influence on the measurement result is solved.

Description

Technical Field

[0001] The invention relates to the field of optoelectronic technology, and in particular to a method for reducing the influence of dark current of a photomultiplier tube. Background Art

[0002] The photomultiplier tube will also have a tiny current when there is no light, which is called dark current. The dark current of the photomultiplier tube is generally several nA to more than ten nA, but when using the integration method to measure the radiation field of low dose rate, the integral value of the pulse current per second is also in the order of nA, and the dark current will have a greater impact on the measurement results. Summary of the invention

[0003] The object of the present invention is to provide a method for reducing the influence of dark current of a photomultiplier tube.

[0004] The technical solution is as follows:

[0005] The present invention proposes a method for reducing the influence of dark current of a photomultiplier tube, wherein the anode of the photomultiplier tube is connected to a constant current source for offsetting the dark current; when the anode of the photomultiplier tube has a pulse output, the anode of the photomultiplier tube is output through an integration circuit; when the anode of the photomultiplier tube has no pulse output, the anode of the photomultiplier tube is grounded.

[0006] Furthermore, the constant current source is realized by connecting the anode of the photomultiplier tube to a positive voltage source via an adjustable resistor R1.

[0007] Furthermore, when the anode of the photomultiplier tube has no pulse output, a fixed resistor R2 is provided on the grounding circuit of the anode of the photomultiplier tube.

[0008] Furthermore, a single-pole double-throw analog switch is used to control the connection between the anode of the photomultiplier tube and the integration circuit or the ground.

[0009] Furthermore, the control signal of the single-pole double-throw analog switch is output by the dynode of the photomultiplier tube.

[0010] Furthermore, the pulse signal output by the dynode of the photomultiplier tube is input into the amplifier circuit through the DC blocking capacitor C1, and then the pulse output by the amplifier circuit is input into the comparator. After the threshold of the comparator is triggered, the comparator outputs a high level to trigger the monostable circuit to output a square wave signal to control the connection of the single-pole double-throw analog switch.

[0011] Compared with the prior art, the present invention has a simple structure and is easy to operate. A constant current source is set to offset the dark current, and the dynode of the photomultiplier tube is used to control the single-pole double-throw analog switch, so that the dark current will not flow into the integration circuit when there is no pulse output from the anode of the photomultiplier tube, thereby reducing the contribution rate of the dark current to the integration result, and solving the problem that the dark current has a great influence on the measurement result.

[0012] Instruction Manual

[0013] Figure 1 This is a circuit structure block diagram of the present invention.

[0014] Figure 2 It is a schematic diagram of the amplification circuit structure.

[0015] Figure 3 This is a schematic diagram of the monostable circuit structure.

[0016] Figure 4 This is a schematic diagram of the integration circuit structure. DETAILED DESCRIPTION

[0017] The technical scheme of the present invention is further described below in conjunction with specific examples. It should be understood that the following examples are only exemplary descriptions and explanations of the present invention, and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0018] See also Figure 1 and Figure 2 In one embodiment of the present invention, a method for reducing the influence of dark current of a photomultiplier tube is provided, wherein the anode of the photomultiplier tube is connected to a constant current source for offsetting the dark current; when the anode of the photomultiplier tube has a pulse output, the anode of the photomultiplier tube is output through an integration circuit; when the anode of the photomultiplier tube has no pulse output, the connection between the photomultiplier tube and the integration circuit is disconnected, and the anode of the photomultiplier tube is grounded; when the anode of the photomultiplier tube has a pulse output, dark current also exists, and at this time, the dark current is usually negligible compared with the pulse current, but it still has some influence on a small number of pulse current signals with relatively small amplitudes, and the constant current source can further reduce this influence; when there is no pulse output from the anode of the photomultiplier tube, the connection between the anode of the photomultiplier tube and the integration circuit is disconnected, so that when the anode of the photomultiplier tube has no pulse output, the dark current will not flow into the integration circuit when the anode of the photomultiplier tube has no pulse output, thereby reducing the contribution rate of the dark current to the integration result.

[0019] Please continue reading Figure 1 In one embodiment, the constant current source is realized by connecting the anode of the photomultiplier tube to a positive voltage source via an adjustable resistor R1; and the adjustable resistor R1 is adjusted to offset the dark current to the maximum extent.

[0020] Please continue reading Figure 1 In one embodiment, when the anode of the photomultiplier tube has no pulse output, a fixed resistor R2 is set on the grounding circuit of the anode of the photomultiplier tube to ensure that the anode voltage of the photomultiplier tube is normal after the integration circuit is disconnected from the anode of the photomultiplier tube.

[0021] Please continue reading Figure 1 In one embodiment, a single-pole double-throw analog switch is used to control the connection between the anode of the photomultiplier tube and the integration circuit or the ground.

[0022] In the above embodiment, when the anode of the photomultiplier tube has no pulse output, the connection between the photomultiplier tube and the integration circuit is disconnected, and the anode of the photomultiplier tube is grounded to ensure that the high voltage output by the anode of the photomultiplier tube will not damage the single-pole double-throw analog switch.

[0023] Please continue reading Figure 1 In the above embodiment, the control signal of the single-pole double-throw analog switch is output by the dynode of the photomultiplier tube; the single-pole double-throw analog switch is controlled by the dynode of the photomultiplier tube instead of using the anode of the photomultiplier tube to control the single-pole double-throw analog switch, so as not to generate additional shunt to the anode of the photomultiplier tube, and to ensure that the circuit flowing out of the photomultiplier tube flows into the integration circuit; if the anode of the photomultiplier tube is used to control the single-pole double-throw analog switch, a part of the current flowing out of the anode of the photomultiplier tube will flow into the circuit used for control, thereby causing the current flowing into the integration circuit to be smaller than the actual current output by the anode of the photomultiplier tube, which will deteriorate the linearity of the instrument; and the gain of the photomultiplier tube is related to the total high voltage of the voltage divider circuit, and the current taken out from the dynode of the photomultiplier tube will not cause the total voltage of the voltage divider circuit to change, so the current taken out from the dynode of the photomultiplier tube will not change the gain of the photomultiplier tube, and the output current of the anode of the photomultiplier tube will not be affected.

[0024] Please continue reading Figure 1-Figure 4 In the above embodiment, the pulse signal output by the dynode of the photomultiplier tube is input into the amplifier circuit through the DC blocking capacitor C1, and then the pulse output by the amplifier circuit is input into the comparator. After the threshold of the comparator is triggered, the comparator outputs a high level to trigger the monostable circuit to output a square wave signal with a fixed width, so as to control the single-pole double-throw analog switch to disconnect from the integration circuit (C and S1) and turn to ground (C and S2).

[0025] In one embodiment, a photomultiplier tube model CR125 produced by Hamamatsu is used, and the maximum dark current is 10nA. After being improved by the method of the present invention, the current detected by the actual integration circuit is about 0.3nA, which further proves that the method of the present invention reduces the influence of the dark current to a negligible level.

[0026] Working principle: When the anode of the photomultiplier tube has a pulse output, the adjustable resistor R1 is adjusted to offset the dark current to the maximum extent. When the anode of the photomultiplier tube has no pulse output, the connection between the photomultiplier tube and the integration circuit is disconnected, and the anode of the photomultiplier tube is grounded so that the dark current does not flow into the integration circuit, thereby reducing the contribution rate of the dark current to the integration result.

[0027] Although the specific implementation modes of the present invention are described above, those skilled in the art should understand that the specific implementation modes described are only illustrative and are not intended to limit the scope of the present invention. Any modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for reducing the influence of dark current of a photomultiplier tube, characterized in that: The anode of the photomultiplier tube is connected to a constant current source for offsetting dark current; when the anode of the photomultiplier tube has pulse output, the anode of the photomultiplier tube is output through an integration circuit; when the anode of the photomultiplier tube has no pulse output, the anode of the photomultiplier tube is grounded.

2. The method for reducing the influence of dark current of a photomultiplier tube according to claim 1, characterized in that: The constant current source is realized by connecting the anode of the photomultiplier tube to a positive voltage source via an adjustable resistor R1.

3. The method for reducing the influence of dark current of a photomultiplier tube according to claim 1, characterized in that: When the anode of the photomultiplier tube has no pulse output, a fixed resistor R2 is arranged on the grounding circuit of the anode of the photomultiplier tube.

4. The method for reducing the influence of dark current of a photomultiplier tube according to claim 1, characterized in that: The anode of the photomultiplier tube is controlled to be connected to the integration circuit or the ground through a single-pole double-throw analog switch.

5. A method for reducing the influence of photomultiplier tube current according to claim 4, characterized in that: The control signal of the single-pole double-throw analog switch is output by the dynode of the photomultiplier tube.

6. A method for reducing the influence of photomultiplier tube current according to claim 5, characterized in that: The pulse signal output by the dynode of the photomultiplier tube is input into the amplifier circuit through the DC blocking capacitor C1, and then the pulse output by the amplifier circuit is input into the comparator. After the threshold of the comparator is triggered, the comparator outputs a high level to trigger the monostable circuit to output a square wave signal to control the connection of the single-pole double-throw analog switch.

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