Low-intensity alpha particle detection device ionization chamber with electric current pulse amplifier

Abstract

The invention relates to radiation detection and analysis devices, in particular, to portable alpha particle sensors adapted for the identification and quantification of radioactive decay products - alpha particles. The proposed low-intensity alpha particle detection device ionization chamber with an electric current pulse amplifier contains an electrode placed in the ionization chamber with zero potential and a protective ring placed around the electrode. The electric current pulse amplifier is placed inside the ionization chamber with the possibility of being electrically connected to a power source, as well as with the possibility of being electrically connected to a processor for supplying an amplified electric current pulse to the processor. This design allows avoiding interference caused by an external electric field without additional shielding of the amplifier.

Description

[0001] Low-intensity alpha particle detection device ionization chamber with electric current pulse amplifier

[0002] Technical Field

[0003]

[0001] The invention relates to radiation detection and analysis devices, in particular, to portable alpha particle sensors adapted for the identification and quantification of radioactive decay products - alpha particles.

[0004] Prior Art

[0005]

[0002] Alpha particles are a type of ionizing radiation. They are the nuclei of helium atoms that are released as a result of certain radioactive decay processes. Several sensor technologies are used to detect and measure them, such as ionization chambers, scintillation and semiconductor detectors. These devices are used to detect and analyze radioactive sources. Typically, alpha particle detectors are stationary and require an external power source, which limits their use in remote or difficult-to-access locations.

[0006]

[0003] The use of ionization chambers to detect alpha particles and measure the intensity of radiation is a well-known principle in nuclear physics and radiation detection technology. The principle of operation of an ionization chamber is based on the ionization of a gas, which occurs when alpha particles are present in the chamber. This process produces pairs of electrons and positively charged ions, which can be detected and recorded as an electrical signal, allowing to measure the intensity of the radiation.

[0007]

[0004] To reduce the effect of the electric field on the sensitive elements of the measuring device or the measurement results, various means are used, such as electrostatic shielding or filtering and grounding.

[0008]

[0005] One of the effective solutions to reduce the effects of electric fields is the use of a guard ring. Such a ring helps to reduce or eliminate interference that can arise from unwanted capacitive interactions, as well as reduce leakage currents that can affect the accuracy of measurements. Traditionally, a guard ring is placed around an electrode or other sensitive components and can be electrically connected to a potential that is similar to or equal to the zero potential of the device being measured. Thus, it acts as a protective barrier that stabilizes the electric field and helps to ensure more accurate measurements, especially in weak signal conditions.

[0009]

[0006] In some known alpha particle detection devices, a sensitive high-impedance amplifier is used. In these alpha particle detection devices, the electrode in the ionization chamber is electrically connected to the high-impedance amplifier. The amplifier must be shielded to avoid interference from external electric fields. Therefore, the electrode via an insulator and an additional protective ring in the ionization chamber is connected to the sensitive high-impedance amplifier [Fig. 1).

[0010]

[0007] There is a known alpha particle detection device [1], wherein the reduction of the influence of the electric field is solved by using a double-probe structure ionization chamber and a differential amplifier, as well as a guard ring. The ionization chamber uses a main probe that detects ionization charges caused by alpha particles, and an auxiliary probe that detects external noise. The signals of the auxiliary probe and the main probe are amplified in separate preamplifiers, then the differential amplifier subtracts the noise signals, allowing to obtain a clean alpha particle detection signal. The guard ring is placed around the main probe, outside the second ionization chamber. The known device uses two electric current pulse amplifiers that are electrically connected to both probes and are located outside the ionization chamber. This structure eliminates the influence of electrical noise and improves the signal-to-noise ratio, thereby increasing the accuracy of the detector.

[0011]

[0008] A device for measuring radon and thoron using an ionization chamber is known [2]. In this device, the issue of reducing the influence of the electric field is solved by using two probes: a main and an auxiliary probe; a differential amplifier that receives signals from both probes and allows the calculation of noise entering the probes; as well as a protective ring that is placed around the main probe outside the ionization chamber to absorb leakage currents that may occur between the ionization chamber and the main probe. This device also uses two electric current pulse amplifiers that are electrically connected to both probes and are located outside the ionization chamber.

[0012]

[0009] There is known an alpha particle counter [3] comprising a gas-filled chamber having a sample region; an anode disposed in the chamber to collect charges in the chamber; a preamplifier connected to the anode to receive the charge collected thereon; a voltage source configured to, in use, apply a bias to the anode such that, whenever an ionization track is generated by an alpha particle passing through the gas within the chamber, the electrons in the track are collected by the anode and are received by the preamplifier to cause the preamplifier to produce an anode output signal pulse associated with the alpha particle; the chamber and the anode are configured such that ionization tracks emanating from different surfaces of the counter produce characteristically different anode output signal pulses; and a primary pulse feature analyzer configured to: measure the one or more features of an anode output signal pulse that differ depending on the pulse's surface of emanation; and determine, based on the measurement of the one or more features of the anode output signal pulse, the surface within the chamber from which the ionization track generated by the alpha particle emanated.

[0013]

[0010] There is also known a portable rugged alpha particle counter [4] comprising a housing, a first electrode having an aperture open to ambient air and carried by the housing, insulation means between the first electrode and the housing, a wire screen cover for the first electrode aperture opposite the housing, a second electrode carried by the housing and disposed adjacent to the first electrode, a field effect transistor within the housing and having respective emitter, collector and base terminals, a first battery connected between the first electrode and the housing providing a negative bias on the first electrode with respect to the second electrode, a second battery connected between the housing and the collector terminal of the field effect transistor, a dropping resistor between the housing and the emitter of the field effect transistor, an attenuating resistor between the base terminal and the housing, means for connecting the base terminal and the second electrode, an external count analyzer, and a means for connecting the count analyzer to the junction of the dropping resistor and the emitter terminal of the field effect transistor, whereby the transistor operates as an emitter follower amplifier producing single voltage pulses for each energetic alpha particle which enters the first electrode through the wire screen and loses its energy by ionization of the ambient air within the first electrode.

[0014] Disclosure of the Invention

[0015]

[0011] The aim of the invention is to eliminate the shortcomings of the known solutions and to offer a low-intensity alpha particle detection device ionization chamber with an electric current pulse amplifier design that would effectively avoid interference caused by an external electric field.

[0016]

[0012] The stated objective is achieved by the proposed design of a low-intensity alpha particle detection device ionization chamber with an electric current pulse amplifier, containing an electrode placed in the ionization chamber with zero potential and a protective ring placed around the electrode; wherein the electric current pulse amplifier is placed inside the ionization chamber. A supply voltage is supplied to the electric current pulse amplifier through the wall of the ionization chamber, and an already amplified signal is discharged from the said amplifier, which can be supplied to the processor for processing the received signal.

[0017]

[0013] The solution described in this patent document relates to a device for detecting low-intensity alpha particles and a low-intensity alpha particle detection device ionization chamber, which are described in detail in International Patent Application No. W02024232748 [5]. The content of the said International Patent Application is hereby fully incorporated into the description of this invention by a reference.

[0018] Brief Description of Drawings

[0019]

[0014] Fig. 1 - the prior art ionization chamber design with external [shielded) electric amplifier;

[0020] Fig. 2 - the proposed low-intensity alpha particle detection device ionization chamber design with electric current pulse amplifier;

[0021] Fig. 3 - one variant of the spatial structure of the device;

[0022] Fig. 4 - an example of electrical circuit of the electrode and amplifier together with passive elements;

[0023] Fig. 5 - a diagram illustrating the voltage signal present in the device at the moment when the device records a voltage pulse resulting from alpha decay.

[0024]

[0015] The proposed low-intensity alpha particle detection device ionization chamber 1 with an electric current pulse amplifier 3 - Fig. 2, containing an electrode 2 placed in the ionization chamber 1 with zero potential and a protective ring 4 placed around the electrode 2. Furthermore, the electric current pulse amplifier 3 is placed inside the ionization chamber 1 with the possibility of being electrically connected to a power source 6, as well as with the possibility of being electrically connected to a processor MCU for supplying the amplified electric current pulse to the processor MCU. This design allows avoiding interference caused by an external electric field without additional shielding of the amplifier.

[0025]

[0016] In contrast the prior art solution illustrated in Fig. 1, in the proposed solution the electric current pulse amplifier 3 is placed inside the ionization chamber 1 with the possibility of electrical connection to the power source 6, and is also connected with the possibility of electrical connection to the MCU processor for supplying an amplified electric current pulse for the MCU processor. Furthermore, unlike the prior art solution illustrated in Fig. 1, in the proposed solution (Figs. 2-4), the electric current pulse amplifier 3 is used without shielding 5.

[0026]

[0017] Fig. 3 shows the spatial structure of one embodiment of the invention. The device comprises an ionization chamber 1 and a printed circuit board consisting of an upper conductive layer 7, a lower layer 8, between which there is a dielectric 10. Essentially, an electrode 2 and an electric current pulse amplifier 3 together with passive elements are arranged in the center of the ionization chamber 1. An example of their possible electrical connection is shown in Fig. 4. Around the electric current pulse amplifier 3 and the passive elements there is a protective ring 4 at 0 V electric potential 4, which conducts leakage currents from the upper conductive layer 7. The ionization chamber 1, which is electrically conductive (e.g. made of metal or conductive plastic), is electrically connected to the upper conductive layer 7 of the printed circuit board by screws or soldering. A chamber voltage in the range of +40 V to +200 V is connected to the upper conductive layer 7, which creates an electrostatic field between the ionization chamber 1 and the electrode 2. The electric current pulse amplifier 3 is located inside the ionization chamber 1, which ensures its resistance to the influence of an external electric field, for example, caused by the alternating voltage of the power supply. The output OUT of the electric current pulse amplifier 3 and its supply voltage +3V are output through the lower layer 8 of the printed circuit board, the electrical potential of which is 0 V. The device contains a 10 GΩ resistor, which is electrically connected to the supply voltage +3V and the non-inverting input of the current pulse amplifier 3.

[0027]

[0018] Air together with radon gas can flow into the ionization chamber 1 through the openings 9. When the radon gas atoms undergo radioactive decay, alpha particles are produced, which ionize some of the air molecules in the chamber. Since there is an electric field between the walls of the ionization chamber 1 and the electrode 2, a shortterm small current pulse flows to the electrode 2, wherein said pulse is generated by the ionized air molecules being accelerated in the electric field and temporarily ensuring the electrical conductivity of the environment. The design of the electrode 2 and the electric current pulse amplifier 3 is characterized by the electric capacitance, which is formed by the sum of the input capacitances of the electrode 2 and the electric current pulse amplifier 3. The small current pulse charges this capacitance. The electric current pulse amplifier 3 amplifies the voltage at its input. Since in the specific embodiment of the invention the sum of the input capacitances of the electrode 2 and the electric current pulse amplifier 3 is in the range between 2 and 4 pF and the input resistance of the resistor is 10 GΩ, the pulse width is large enough to use electric current pulse amplifiers 3 with a current consumption in the range of 1-10 pA. When the device is powered by batteries a surprisingly long operating time of the device can be achieved.

[0028]

[0019] According to the preferred embodiment of the invention, the device may additionally comprise an integrating circuit 12, which is designed to return a signal from the output of the electric current pulse amplifier 3 back to its input [Fig. 4). The said integrating circuit 12 ensures filtering of the voltage signal caused by mechanical vibrations of the device, which is characterized by a resistor and capacitor [RC] circuit time constant of 20-50 ms. In the provided example of the implementation of the invention, a 10 MΩ resistance is used and the overall design of the device is characterized by a capacitance between 2 and 4 pF, which means a 20 to 40 ms RC circuit time constant.

[0029]

[0020] The time diagram of the OUT pulse output of the electric current pulse amplifier 3 of the proposed device during the radioactive decay of radon is shown in Fig. 5. When counting the visible pulses per unit of time, information about the concentration of radon gas in the air can be obtained. According to another embodiment of the invention, the OUT pulse duration of the electric current pulse amplifier 3 is selected in the range between 200 and 250 ms, which determines the maximum frequency of the resolved pulses.

[0021] Practical experiments show that, using an ionization chamber 1 with a volume of 0.13 L, the proposed device can measure radon radioactive decay events in air up to 4000 Bq / m³, which is approximately 20 times higher than the recommendations set by the World Health Organization for residential premises. This value corresponds to approximately 50 pulses per minute. According to the preferred embodiment of the invention, the ionization chamber 1 can be selected with a volume of 0.05 to 0.5 liters.

[0030]

[0022] The proposed solution surprisingly provides the possibility of effectively eliminating interference caused by external electric fields and allows the creation of a relatively simple, portable low-intensity alpha particle detection device. The nominal values of the electrical components used allow to provide a long operating time of the device when powered by batteries. The selected electrical circuit ensures filtering of unwanted effects caused by mechanical vibrations.

[0031] References

[0032] 1. W02017034158 Al.

[0033] 2. W02020130317 Al.

[0034] 3. EP1419397 Bl.

[0035] 4. US5059803 A.

[0036] 5. W02024232748A1.

Claims

Claims1. An ionization chamber (1) of a low-intensity alpha particle detection device with an electric current pulse amplifier (3), comprising an electrode (2) with zero potential placed in the ionization chamber (1) and a protective ring (4) placed around the electrode (2), characterized in that the electric current pulse amplifier (3) is placed inside the ionization chamber (1) with the possibility of being electrically connected to a power source (6), as well as with the possibility of being electrically connected to a processor MCU for supplying the amplified electric current pulse to the processor MCU.

2. The device according to claim 1, characterized by an electric current pulse amplifier (3), the current consumption of which is in the range between 1 and 10 pA.

3. The device according to claim 1, characterized in that an additional integrating circuit (12) with a resistor and capacitor (RC) time constant of 20 to 50 ms is arranged in the feedback loop of the electric current pulse amplifier (3).

4. The device according to claim 1, characterized in that the duration of the output OUT pulse of the electric current pulse amplifier (3) is selected within the range between 200 and 250 ms.

5. The device according to claim 1, characterized in that the ionization chamber (1) is selected with a volume of 0.05 to 0.5 liters.

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