Portable radon detector

Abstract

The invention relates to the field of environment monitoring and analyzing instruments, and particularly discloses a portable radon detector which comprises a silicon photomultiplier sensor unit, a low-noise preamplifier unit, a comparator circuit and an STM32 main control module. By adopting the EQR-15 series silicon photomultiplier, the 300 [mu] m epoxy resin protective layer on the surface of the EQR-15 series silicon photomultiplier can directly emit light under the bombardment of alpha particles, the advantages of the integration of a photodiode and the high signal amplitude of a scintillator are integrated, and the detection sensitivity and the signal-to-noise ratio are remarkably improved while an independent scintillator is omitted. Aiming at weak current signals, a low-noise pre-amplification circuit with a TL084CDR operational amplifier as a core is designed, and a pulse shaping and emitter follower is arranged, so that the problems of signal amplification and interference resistance are effectively solved. The main control module realizes accurate capture and counting of alpha particle pulses through ADC sampling, hardware triggering and DMA storage in combination with a threshold self-adaption and baseline tracking algorithm.

Description

Technical Field

[0001] This invention belongs to the field of environmental monitoring and analysis instruments, specifically a portable radon detector. Background Technology

[0002] Radon is a naturally occurring radioactive inert gas, a product of the decay chain of uranium and radium, and is widely found in soil, rocks, and building materials. Due to its chemical inertness, radon can easily leach from the ground and diffuse into indoor environments through building gaps. Radon itself decays, releasing alpha particles, and its short-lived daughter particles (such as polonium-218 and polonium-214) also release high-energy alpha particles. Once these charged particles are inhaled, they cause continuous internal irradiation of lung cells, making it the second leading cause of lung cancer after smoking, and it has been classified as a Group 1 carcinogen by the World Health Organization. Therefore, accurate and convenient monitoring of radon concentrations in indoor and environmental environments is of great significance for protecting public health.

[0003] Currently, scintillator coupling is a mainstream method for radon concentration measurement based on alpha particle detection. The core principle of this method is that when alpha particles bombard a specific scintillator (such as ZnS(Ag)), they excite and de-excite it, producing fluorescence. This fluorescence is then captured by photosensitive devices such as photomultiplier tubes or silicon photomultiplier tubes and converted into electrical pulse signals for counting. Because alpha particles deposit high energy in the scintillator, the generated light signal is strong, and after photoelectric conversion, it can output a high-amplitude electrical signal, which is beneficial for subsequent processing and identification.

[0004] However, this scintillator coupling scheme has an inherent structural drawback: to efficiently transmit the weak fluorescence generated by the scintillator to the photosensitive surface of the photosensitive device, sophisticated optical packaging techniques must be employed, such as filling the space between the scintillator and the optical window with optical grease or using a mirror cavity. This optical guidance and coupling structure not only increases the fabrication complexity and cost of the detector but also fundamentally limits further miniaturization of the detector's physical size, creating a bottleneck in portable applications that prioritize thinness and lightness. Therefore, a novel detection scheme is urgently needed that can maintain high signal output performance while fundamentally simplifying the structure and achieving miniaturization. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a portable radon detector, which solves the problem that existing scintillator coupling schemes suffer from large detector size, complex manufacturing processes, and high costs due to their complex optical packaging structures, making it difficult to meet the requirements of portable applications.

[0006] A portable radon detector, comprising:

[0007] A silicon photomultiplier tube sensor unit is used to detect alpha particles released from radon decay and convert them into electrical signals.

[0008] A low-noise preamplifier unit is electrically connected to the silicon photomultiplier tube sensor unit and is used to amplify the electrical signal;

[0009] The comparator circuit, electrically connected to the low-noise preamplifier unit, is used to convert the amplified analog signal into a digital edge signal.

[0010] The main control module, electrically connected to the comparator circuit, is used to acquire, process, and count the digital edge signals to calculate the radon concentration.

[0011] Preferably, the silicon photomultiplier tube sensor unit uses an EQR-15 series silicon photomultiplier tube with an epoxy resin protective layer on its surface, which can emit light under alpha particle bombardment.

[0012] Preferably, the silicon photomultiplier tube sensor unit further includes a bias circuit for providing an adjustable DC reverse bias voltage in the range of 0V to 40V for the silicon photomultiplier tube.

[0013] Preferably, the operating bias voltage of the silicon photomultiplier tube is set to the voltage value corresponding to the flat region where its signal-to-noise ratio reaches or is close to its maximum value.

[0014] Preferably, the low-noise preamplifier unit includes:

[0015] The primary amplifier circuit uses a TL084CDR operational amplifier to amplify the weak current signal output by the silicon photomultiplier tube with low noise.

[0016] Pulse shaping and low-pass filtering circuits are used to shape the amplified signal and limit the noise bandwidth.

[0017] The emitter follower circuit uses a 2N2222NPN transistor to reduce the circuit's output impedance.

[0018] Preferably, the comparator circuit is a high-speed voltage comparator, configured with a threshold setting circuit for a programmable reference voltage, and includes a parallel filter capacitor and a positive feedback resistor to form a hysteresis comparator, thereby enhancing anti-interference capability.

[0019] Preferably, the main control module uses an STM32H503RBT6 microcontroller, which is configured for:

[0020] The analog pulse signal output by the comparator is sampled through the ADC channel;

[0021] The digital pulse output from the comparator is received via an external interrupt pin as the acquisition start signal;

[0022] Continuous sampling and storage of pulse data is performed using a DMA buffer.

[0023] Execute a threshold adaptive algorithm to periodically analyze noise levels and dynamically adjust the comparator threshold;

[0024] The baseline tracking algorithm is executed, and the baseline voltage is updated using an exponentially weighted average method to eliminate drift.

[0025] Preferably, the detector calibrates the radon concentration in the environment by the number of alpha particles detected per unit time.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] By using the EQR-15 series silicon photomultiplier tube with a 300μm thick epoxy resin protective layer as the core sensor, the characteristic of the protective layer being able to emit light directly under alpha particle bombardment is utilized. This gives it the integrated advantages of traditional photodiode solutions and the high signal amplitude output capability of scintillator solutions. As a result, the detector can still obtain a high amplitude electrical signal output while eliminating the need for a separate scintillator and its complex precision optical packaging structure. This fundamentally simplifies and miniaturizes the detector structure and significantly improves detection sensitivity and signal-to-noise ratio.

[0028] For the picoampere-level weak current signal output by SiPM, this invention designs a preamplifier circuit with the TL084CDR ultra-low noise operational amplifier as its core, supplemented by pulse shaping, low-pass filtering, and an emitter follower composed of 2N2222 transistors, together forming a high-performance, low-noise readout circuit. This circuit unit effectively solves the problems of amplification, shaping, and anti-interference of extremely weak signals, ensuring the integrity and reliability of the signal during transmission. Combined with the precise threshold triggering and hysteresis noise reduction design of the subsequent high-speed comparator circuit, it provides high-quality, high signal-to-noise ratio input for back-end signal processing.

[0029] Thanks to the powerful processing capabilities of the STM32H503RBT6 main control module, the system achieves intelligent signal acquisition and processing. By integrating hardware triggering, high-speed DMA data stream, threshold adaptive algorithm, and exponentially weighted average baseline tracking technology, the system can dynamically adapt to environmental noise fluctuations, accurately capture and count each effective alpha particle pulse, thereby achieving accurate, rapid, and stable monitoring of environmental radon concentration. Attached Figure Description

[0030] Figure 1 This is the output waveform of the SiPM;

[0031] Figure 2 The amplitude distribution of the alpha particle signal emitted by Am241;

[0032] Figure 3 This is a schematic diagram of an overall system based on silicon photomultiplier tube (Si-PM) and microcontroller technology.

[0033] Figure 4 This is a schematic diagram of a signal readout circuit. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] like Figures 1 to 4 As shown:

[0036] Example: A portable radon detector

[0037] This embodiment provides a portable radon detector based on silicon photomultiplier tube (SiPM) and microcontroller technology, aiming to achieve real-time monitoring of radon concentration with high sensitivity, low noise, and fast response.

[0038] The portable radon detector mainly includes: a silicon photomultiplier tube sensor unit, a low-noise preamplifier unit, a comparator circuit, and an STM32 main control module.

[0039] 1. Silicon photomultiplier tube sensor unit

[0040] This unit is the core sensing component of the detector, responsible for converting the alpha particles released from radon decay into electrical signals.

[0041] Sensor Selection and Characteristics: The EQR-15-11-6060D-S type silicon photomultiplier tube (SiPM) was selected as the alpha particle detection sensor. The specific performance parameters of this device are shown in the table below:

[0042] parameter symbol EQR-1511-6060D-S unit Breakdown voltage Terminal capacitor / Breakdown voltage temperature drift / Peak PDE Gain / Infinite element area /

[0043] Its structural parameters are shown in the table below:

[0044] parameter EQR-1511-6060D-S unit Chip size Effective area Effective pitch

[0045] This SiPM possesses high quantum efficiency, suitable junction capacitance, and excellent charge collection characteristics, enabling it to efficiently convert incident alpha particle energy into electrical signals. Its key innovation lies in the 300 μm thick epoxy resin protective layer covering the sensor surface. When bombarded by alpha particles with energy of approximately 5.5 MeV, this protective layer directly emits fluorescence, which is then captured by the underlying SiPM sensitive region. This eliminates the need for a separate scintillator component, achieving miniaturization and integration of the detector structure.

[0046] Bias circuit: Provides an adjustable DC reverse bias voltage for the SiPM. In this embodiment, a precision adjustable power supply circuit is used to adjust the bias voltage within the range of 0V to 40V.

[0047] Optimal operating point determination: The sensitive area of ​​the SiPM was irradiated with a standard alpha particle radiation source (such as Am-241), and the output signal was captured using a high-bandwidth digital oscilloscope. The signal-to-noise ratio (SNR) was calculated by analyzing the pulse amplitude and noise level under different bias voltages. A curve was plotted with the bias voltage on the x-axis and the SNR on the y-axis. Finally, the operating bias voltage of the SiPM was set to the voltage value corresponding to the flat region where the SNR curve reaches or is close to its maximum value, thereby optimizing sensor performance.

[0048] 2. Low-noise preamplifier unit

[0049] This unit is used to amplify and condition the weak picoampere-level current signal output by the SiPM.

[0050] Core Amplifying Device: Based on low-noise design principles, the TL084CDR precision operational amplifier is selected to construct the preamplifier circuit. Typical parameters of this op-amp are as follows:

[0051] parameter Typical value Input bias current (lb) Input resistance ( ) Gain-bandwidth product (GBW) Slew Rate Input offset current (Vos) Static current Power supply voltage range

[0052] This operational amplifier features ultra-low input bias current and extremely high input impedance, making it ideal for amplifying weak current signals from high-impedance sources. Its sufficient gain-bandwidth product and high slew rate ensure fast response and distortion-free operation of pulse signals.

[0053] Primary Amplification and Shaping: This circuit converts the transient current pulse output by the SiPM into a voltage signal and performs primary amplification. The amplification factor is set to 10 times to ensure that the output signal amplitude is ≥5mV. Simultaneously, the circuit performs appropriate pulse shaping on the amplified voltage pulse and integrates a low-pass filter to limit the noise bandwidth and improve the signal-to-noise ratio.

[0054] Impedance transformation: The amplified and shaped signal is connected to an emitter follower circuit composed of 2N2222NPN transistors. The emitter follower provides high input impedance and low output impedance, effectively reducing signal distortion and load effects during transmission to subsequent circuits.

[0055] 3. Comparator circuit

[0056] This unit is used to convert analog voltage pulses into digital signals for easy identification by the main control module.

[0057] Device selection: A high-speed voltage comparator was selected to ensure accurate response to transient pulses in the nanosecond to microsecond range.

[0058] Threshold triggering: A programmable reference voltage (i.e., threshold voltage) is generated through a precision adjustable resistor divider network and connected to the inverting input of the comparator. The shaped signal output from the preamplifier unit is connected to the non-inverting input of the comparator. When the signal amplitude exceeds the set threshold, the comparator outputs a clear digital edge signal (such as a transition from low to high).

[0059] Noise suppression design: A small-capacity filter capacitor is connected in parallel at the input of the comparator to suppress false triggering caused by high-frequency noise. At the same time, a positive feedback resistor is configured to form a hysteresis comparator (such as a Schmitt trigger), giving the circuit a certain interference immunity and preventing multiple false triggerings due to signal jitter near the threshold.

[0060] 4. STM32 main control module

[0061] This unit is the "brain" of the detector, responsible for the final processing and analysis of the signal and the calculation of radon concentration.

[0062] Core chip: The STM32H503RBT6 microcontroller is used as the main control chip, utilizing its high-performance ARM Cortex-M33 core, high-speed ADC and abundant timer / interrupt resources.

[0063] Signal acquisition and processing flow:

[0064] Hardware triggering and ADC sampling: The digital pulse output from the comparator is connected to the external interrupt pin of the STM32 as a start signal for data acquisition. Once triggered, the main control chip immediately starts its internal high-speed ADC to continuously sample the analog pulse signal from the preamplifier unit (before the comparator), dynamically configuring the sampling frequency to capture the complete pulse waveform.

[0065] Data storage: The sampled data is temporarily stored in a buffer using DMA (Direct Memory Access) technology, which greatly reduces CPU intervention overhead and ensures the real-time performance of the system under high-speed pulse sequences.

[0066] Threshold Adaptive: The microcontroller periodically analyzes the noise level of the collected data (such as calculating the RMS value) and dynamically adjusts the reference voltage of the hardware comparator (through the STM32's DAC output) and the software-identified threshold accordingly, enabling the system to adapt to fluctuations in environmental noise and maintain optimal detection sensitivity at all times.

[0067] Baseline tracking: The baseline voltage of the signal is updated in real time using an exponential weighted average method, which effectively eliminates baseline fluctuations caused by temperature drift and low-frequency noise, ensuring the accuracy of pulse amplitude measurement.

[0068] Counting and concentration calibration: The main control module counts the effective pulses, calculates the real-time radon concentration value in the environment based on the number of alpha particles detected per unit time and the pre-calibrated conversion coefficient, and outputs it through a display or communication interface.

[0069] The embodiments of the present invention are given for the purposes of illustration and description. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made by those skilled in the art to the above embodiments within the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A portable radon detector, characterized in that, include: A silicon photomultiplier tube sensor unit is used to detect alpha particles released from radon decay and convert them into electrical signals. A low-noise preamplifier unit is electrically connected to the silicon photomultiplier tube sensor unit and is used to amplify the electrical signal; The comparator circuit, electrically connected to the low-noise preamplifier unit, is used to convert the amplified analog signal into a digital edge signal. The main control module, electrically connected to the comparator circuit, is used to acquire, process, and count the digital edge signals to calculate the radon concentration.

2. The portable radon detector according to claim 1, characterized in that, The silicon photomultiplier tube sensor unit uses an EQR-15 series silicon photomultiplier tube with an epoxy resin protective layer on its surface, which can emit light under alpha particle bombardment.

3. The portable radon detector according to claim 2, characterized in that, The silicon photomultiplier tube sensor unit also includes a bias circuit for providing an adjustable DC reverse bias voltage in the range of 0V to 40V for the silicon photomultiplier tube.

4. The portable radon detector according to claim 2 or 3, characterized in that, The operating bias voltage of the silicon photomultiplier tube is set to the voltage value corresponding to the flat region where its signal-to-noise ratio reaches or is close to its maximum value.

5. The portable radon detector according to claim 1, characterized in that, The low-noise preamplifier unit includes: The primary amplifier circuit uses a TL084CDR operational amplifier to amplify the weak current signal output by the silicon photomultiplier tube with low noise. Pulse shaping and low-pass filtering circuits are used to shape the amplified signal and limit the noise bandwidth. The emitter follower circuit uses a 2N2222NPN transistor to reduce the circuit's output impedance.

6. The portable radon detector according to claim 1, characterized in that, The comparator circuit is a high-speed voltage comparator, equipped with a threshold setting circuit for a programmable reference voltage, and includes parallel filter capacitors and positive feedback resistors to form a hysteresis comparator, enhancing anti-interference capability.

7. The portable radon detector according to claim 1, characterized in that, The main control module uses an STM32H503RBT6 microcontroller, which is configured for: The analog pulse signal output by the comparator is sampled through the ADC channel; The digital pulse output from the comparator is received via an external interrupt pin as the acquisition start signal; Continuous sampling and storage of pulse data is performed using a DMA buffer. Execute a threshold adaptive algorithm to periodically analyze noise levels and dynamically adjust the comparator threshold; The baseline tracking algorithm is executed, and the baseline voltage is updated using an exponentially weighted average method to eliminate drift.

8. The portable radon detector according to any one of claims 1 to 7, characterized in that, The detector calibrates the radon concentration in the environment by detecting the number of alpha particles per unit time.

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