Development of a method for fast radiation measurement as a solution to signal pile-up by measuring the rising slope of the signal waveform

Development of a method for fast radiation measurement as a solution to signal pile-up by measuring the rising slope of the signal waveform | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Development of a method for fast radiation measurement as a solution to signal pile-up by measuring the rising slope of the signal waveform Seung-Jae Lee, Cheol-Ha Baek This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7448685/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Detection systems based on photon counting utilize a system that makes use of a dedicated application specific integrated circuit (ASIC) for very fast radiation measurement. However, even with a high-speed system, the signal pile-up phenomenon still occurs. In this study, a general-purpose method that can measure radiation very fast, and can measure radiation lost due to pile-up was developed. This method determines the energy by analyzing the signal waveform, and by converting the rising slope of the signal into energy. Analysis of the slope, instead of measuring the entire waveform, enables the measurement time to be greatly reduced, and by measuring the rising slope, each individual radiation signal can be separated and measured even in signals where pile-up occurred. This method, which eliminates the need for a dedicated ASIC, can be applied to existing systems. In addition, this method is expected to enable a very efficient detection system to be developed because the loss of photon counting can be minimized in high radiation fields. photon counting pile up signal waveform slope detector Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Ⅰ. Introduction X-ray photon counting detectors are used in various systems for medical and materials analysis [ 1 ]. To individually detect a large number of incident photons, a very fast detection speed is required. For this purpose, application specific integrated circuit (ASIC) type photon counting detectors have been developed and used in dedicated systems [ 2 – 8 ]. However, even when ASIC type detectors with fast detection speeds are used, X-ray signal pile-up occurs. Attempts to solve this problem have led to the development of pile-up removal methods [ 9 – 11 ]. In this paper, we propose a general photon counting acquisition method for implementation in a photon counting detector. In general, a radiation detection system collects the electrical signal that is generated when it collects incident photons to measure the energy of the radiation. These measurements are typically conducted by using one of the following two methods: the first method stores the peak value of the waveform of the output signal and the second method conducts the measurement by integrating the signal waveform. The method that measures the peak value by analyzing the waveform of the signal generates a trigger signal to obtain information about the peak value. The method that involves integration of the waveform of the signal collects the signals by adding up all the signal sizes from the time at which the signal magnitude is detected to have reached a certain level. Systems based on the ASIC type signal measurement method utilize the latter of these two methods; that is, measurement by integrating the waveform of the generated signal. In this study, a method was devised to enable fast signal collection by modifying the aforementioned method that relies on signal waveform integration. The magnitude of a signal varies depending on the energy of the incident radiation. However, although analysis of the signal waveform of the detection system can confirm that the signal magnitude depends on the energy of the radiation, the time at which the peak value appears is the same for all signals [ 12 ]. Figure 1 shows the waveform of the signal measured using the Hamamatsu SiPM S13360-3075CS model. As is confirmed in Fig. 1 , the magnitude of the signal is different for all signals, but the time at which the peak value of the signal appears is the same for all signals. In other words, the time taken from the moment the signal is generated until it reaches the peak signal is the same. As the amount of radiation energy changes, the magnitude of the signal changes, but the time to reach the peak value is the same; thus, it is confirmed that the slope of the signal reaching the maximum value from the minimum value varies depending on the radiation energy. By analyzing this process to reach the signal magnitude, we inferred that the radiation energy can be measured by determining the slope of the waveform. Measurement of the signal size at two points for conversion into the slope to shorten the signal measurement time is expected to represent the entire radiation signal. To verify this assumption, we conducted a basic experiment using the data acquisition system developed by the ARALE Laboratory Co., Ltd. Based on these data, we developed a method to clearly measure the radiation energy, even from pile-up signals, by measuring the slope. This method enables signal loss due to pile-up to be reduced, and the maximum number of radiation signals that can be measured in the same period of time can be increased as a result of the fast measurement time. In addition, fast signal measurement is foreseen to be possible by implementing our proposed method in a system that can be used universally without the need for a fast signal-processing circuit. Ⅱ. Materials and Methods 1. Detector system configuration The radiation energy was derived by measuring the slope of the signal rise by using the data acquisition system of ARALE Laboratory Co., Ltd. as the signal measurement system [13]. This system was developed for use in a small gamma camera and was used in this study to measure the signal using a scintillator. The waveform of the signal generated by the radiation was acquired with a light sensor, the S13361-3050AE-08 model of Hamamatsu (Fig. 2), which consists of an 8 ´ 8 array of 3 mm ´ 3 mm multi-pixel photon counter (MPPC) pixels [14]. The signals generated from the 64 MPPC pixels are reduced to four channels of signals, X+, X-, Y+, and Y-, through a symmetric charge division circuit. The signals of each channel are converted into digital signals through the analog-to-digital converter (ADC) through the four-channel transimpedance amplifier and the ADC driver circuit, and then transmitted to a computer through the network to store the data. The ADC was the TI ADS5296A model with 100 megasamples per second (MSPS) of 10-bit resolution [15]. The analog waveform generated by a gamma-ray event was quantized once every 10 ns through the ADC, and this value was designed to be continuously stored in the field programmable gate array (FPGA) register up to 400 times so that data for the entire waveform could be collected. The waveform data stored in the FPGA was transferred to the dual core ARM, generated as a single universal datagram protocol (UDP) packet, and then transferred to the computer via Ethernet. Fig. 3 shows internal data acquisition system in the small gamma camera 2. Experimental setup The collimator of the gamma camera and the existing scintillator block were removed, and a single-pixel scintillator was combined with the light sensor. Fig. 4 shows the equipment for data collection using the scintillator and Na-22 radiation source placed on the light sensor of the gamma camera. The single-pixel scintillator was a gadolinium aluminium gallium garnet (GAGG) scintillator measuring 3 mm ´ 3 mm ´ 5 mm. The GAGG scintillator has a high density of 6.3 g/cm 3 , which is effective for detecting high-energy radiation, and has an excellent light yield (50,000 photons/MeV), which offers outstanding energy resolution [16]. In addition, as it does not generate background radiation, it does not affect the energy of the radiation to be measured, thus enables only the signal of the corresponding radiation to be measured. The GAGG scintillator and light sensor were combined to configure a detector, and the signal was measured using the Na-22 radiation source. The detection system is connected to a cable that supplies 20 V direct current (DC) power, and an Ethernet cable for transmitting both input data for controlling the data acquisition system and output data consisting of the detected gamma-ray waveform to a computer. 3. Data acquisition The signals generated by the Na-22 radiation source were acquired using the configured detector with the gamma camera. The signal waveform for each gamma-ray event was acquired using the MAETEL ver. 1.42 software. The data for the 4 channels can be acquired from one signal. The data of these 4 channels is a signal in which the signal of each 64 MPPC pixel channel of X+, X-, Y+, Y- is reduced to 4 channels, and the addition of the signals of each of the 4 channels can be expressed as one detected gamma-ray energy. Analysis of the characteristics of the signal of each channel reveals that the rising time and peak value of the signals are all the same. This means that changes in the measured energy would change the rising slope, which means that the signals can be converted into energy by measuring the rising slope. Based thereupon, the energy spectrum was constructed by measuring the rising slope of the signal generated by measuring the Na-22 radiation source. This energy spectrum was then compared and evaluated with the energy spectrum constructed by measuring all values of the signal. The method that entails measuring the slope through the signal waveform is illustrated in Fig. 5. A signal of which the magnitude exceeds the threshold is set to be collected. Using three clocks, the first signal value is collected at the time on the first clock, and the second signal value is collected at the time on the second clock. After that, by connecting to the ground at the third clock and initializing the generated signal value, this signal sampling process allows radiation measurement with only 3 clocks. Even if a low-speed ADC is used, sufficiently fast radiation measurement is possible. In addition, this method can prevent coefficient loss due to signal pile-up. Ⅲ. Results and Discussion Counting the photons of X-rays and measuring the energy of radiation in very strong radiation fields requires a very fast measurement system. For this purpose, existing systems are designed to perform fast measurement by using a dedicated ASIC, which is designed to fit the system to be used. However, even in these systems, signal pile-up occurs when a very large amount of radiation is incident. This inspired us to develop a signal measurement method to address the problem of signal pile-up for use in existing general-purpose systems. When a radiation signal is generated, the slope of the waveform produced by the signal quickly rises before levelling off at the peak, where after the slope of the waveform decreases more gradually. Considering that the rising time in the same measurement system is the same for all the signals regardless of the energy of the radiation being measured, we devised a method for measuring the energy of radiation by assuming that the rising slope depends on the energy of the radiation and this was confirmed through experiments. Figure 6 shows the waveform of the signal of the Na-22 radiation source measured for each channel using the data acquisition system of ARALE Laboratory Co., Ltd. Because the measured energy for each channel is different, the height of the waveform is different for each channel. However, the time points where the peak values ​​appear are all the same. Here, the rising slope can be measured for conversion into radiation energy. The slope was calculated from the 49th to the 50th sampling values ​​from the point where the signal waveform was stored. Figure 7 shows the energy spectrum of the Na-22 radiation source. More specifically, Fig. 7 (a) shows the entire energy spectrum of all the signal waveforms that were measured, and Fig. 7 (b) shows the part of the energy spectrum that was constructed by measuring the slope. The photopeak area of ​​the energy spectrum in (b), which was not produced by measuring the signal waveform, is clearly shifted to the left. This means that the total amount of energy that was measured was smaller. The energy spectrum has photopeaks of 511 keV and 1275 keV. The energy resolution is 7.9% in (a) and 17.7% in (b), which indicates that it is preferable to measure all the signal waveforms. It takes about 200 ns to measure all the signal shapes, whereas only 30 ns is needed to measure the slope. In other words, the signal can be measured very quickly. Our experiments confirmed that signals can be measured within several tens of nanoseconds even if the system is not equipped with a dedicated ASIC. The proposed method of determining the radiation energy by measuring the slope can largely prevent signal pile-up by employing fast signal measurement, although signal pile-up would still be possible when a very large amount of radiation is incident for a very short time. However, by measuring the slope, measurement is possible as illustrated in Fig. 8 , which enables the pile-up signal to be separated and the radiation energy to be measured. That is, the second signal in Fig. 8 is in a form that can appear due to the incident radiation during the process of decreasing the first signal, and by designing the slope measurement such that it is collected when the signal rises, it is considered possible to separate the pile-up signal for measurement. Ⅳ. Conclusion ARALE Laboratory Co., Ltd. developed a method to resolve the phenomenon of signal pile-up that can occur when a very large amount of radiation is incident on a gamma camera in a very short period of time. A very fast measurement system is therefore required to count the photons of X-rays. Towards this goal, fast signal measurement systems equipped with dedicated ASIC systems have been developed. Because these systems are developed exclusively, they can only be used in the system in question, and their development and production is expensive. This led us to develop a method that can be used in general-purpose systems and that require minimal changes to existing systems and the operating method. When a radiation signal is generated, the slope of the generated waveform increases sharply before levelling off until the peak value is reached, after which the slope of the waveform declines more slowly. Even if the energy of the radiation differs, the point at which the peak value appears is the same. In other words, after confirming that the energy of the radiation can be measured by measuring the rising slope of the signal, the possibility was confirmed through experiments. After measuring the signal size at the two points in the rising part of the waveform of the generated signal, the difference was accumulated to form a radiation energy spectrum. In other words, the experiments confirmed that conversion into radiation energy was possible by measuring the slope of the signal. Compared to the measurement of the signals of all waveforms, the energy resolution is lower, but the measurement time is greatly shortened. In fact, the measurement time is shortened from 200 ns to 30 ns, thus a very fast measurement time can be achieved. This time was measured with an ADC with a speed of 100 MSPS, and is expected to be shortened even further by using a faster ADC. This shortened measurement time can prevent signal pile-up, and even if signal pile-up was to occur, the piled up signal could be separated and measured by measuring the point at which the signal waveform starts rising. This method is sufficiently applicable to existing systems, and a very fast measurement time is expected to be achievable even with a relatively low-speed ADC. In addition, since a sufficiently fast measurement time can be secured even without developing a dedicated system, the development of a highly efficient system that could achieve a very fast measurement time at a very low cost is foreseen to be possible. Declarations Author Contribution S.-J.L. designed and performed the experiments, collected and analyzed the data, and prepared the initial draft of the manuscript. C.-H.B. conceived the study, supervised the research, and contributed to interpretation of the results. S.-J.L. and C.-H.B. wrote the main manuscript text together. All authors reviewed and approved the final manuscript. ACKNOWLEDGMENTS This work was conducted during the sabbatical year of Dongseo University in 2025. References K. Shimazoe, D. Kim, M. Hamdan, Y. Kobayashi, K. Kamada, M. Yoshino, Y. Shoji, K. Sakamoto, F. Acerbi, and A. Gola, Comms. Eng., 3 , 167 (2024). P. Otfinowski, G. W. Deptuch, and P. Maj, J. Instrum., 15 , C01016 (2020). R. Ballabriga, J. Alozy, G. Blaj, M. Campbell, M. Fiederle, E. Frojdh, E. H. M. Heijne, X. Llopart, M. Pichotka, S. Procz, L. Tlustos and W. Wong, J. Instrum., 8 , C02016 (2013). T. Poikela, J. Plosila, T. Westerlund, M. Campbell, M. De Gaspari, X. Llopart, V. Gromov, R. Kluit, M. van Beuzekom. F. Zappon, V. Zivkovic, C. Brezina, K. Desch, Y. Fu and A. Kruth, J. Instrum., 9 , C05013 (2014). R. Bellazzini, G. Spandre, A. Brez, M. Minuti, M. Pinchera and P. Mozzo, J. Instrum., 8 , C02028 (2013). H-S. Kim, S-W. Han, J-H. Yang, S. Kim, Y. Kim, S. Kim, D-K. Yoon, J-S. Lee, J-C. Park, Y. Sung, S-D. Lee, S-T. Ryu, G-H. Cho, IEEE J. Solid-State Circuits, 48 , 541 (2013). R. Dinapoli, A. Bergamaschi, B. Henrich, R. Horisberger, I. Johnson, A. Mozzanica, E. Schmid, B. Schmitt, A. Schreiber, X. Shi, G. Theidel, Nucl. Instrum. Methods Phys. Res. A, 650 , 79 (2011). P. Grybos, P. Kmon, P. Maj, R. Szczygiel, IEEE Trans. Nucl. Sci., 63 , 1155 (2016). D. Lee, K. Park, K. T. Lim, G. Cho, Nucl. Instrum. Methods Phys. Res. A, 856 , 36 (2017). M. Lee, D. Lee, E. Ko, K. Park, J. Kim, K. Ko, M. Sharma, G. Cho, Nucl. Eng. Technol., 52 , 1029 (2020). K. Treb, J. Radtke, W. S. Culberson, K. Li, Phys. Med. Biol., 68 , 155003 (2023). S. Gómez, D. Sánchez, J. Mauricio, E. Picatoste, A. Sanuy, A. Sanmukh, M. Ribó and D. Gascón, Electronics, 10 , 961 (2021). Compact Gamma Camera data acquisition system, ALARE Laboratory Web. https://www.aralelab.com/index.html#section-02 MPPC array, Hamamatsu Web. https://www.hamamatsu.com/content/dam/hamamatsu-photonics/sites/documents/99_SALES_LIBRARY/ssd/s13361-3050_series_kapd1054e.pdf ADS5296A, Texas Instruments Web. https://www.ti.com/lit/ds/symlink/ads5296a.pdf GAGG scintillator, Epic-Crystal Web. https://www.epic-crystal.com/data/upload/20240409/6614a154ea168.pdf Additional Declarations No competing interests reported. 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This confirms that the waveforms of all signals require the same amount of time to reach their peak values (as indicated by the vertical white line).\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7448685/v1/4b75def7f0ce10989ca5cec3.jpeg"},{"id":91420005,"identity":"258dc52d-c72f-4606-b654-2539ee383fe3","added_by":"auto","created_at":"2025-09-16 10:07:41","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":963789,"visible":true,"origin":"","legend":"\u003cp\u003eLight sensor (model S13361-3050AE-08 from Hamamatsu) used to measure radiation energy through the slope of the signal. (a) 8 ´ 8 array of SiPMs, (b) Connector for connecting to the data acquisition system.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7448685/v1/cfa634f175c1f69640f9b0ae.jpeg"},{"id":91421273,"identity":"83bff4de-16b9-46e4-8971-1ec99992699f","added_by":"auto","created_at":"2025-09-16 10:15:41","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1497943,"visible":true,"origin":"","legend":"\u003cp\u003eData acquisition system that has been explored in this study to acquire signals generated from the light sensor. (a) 4-channel analog front-end circuit, (b) power distribution circuit with SiPM bias voltage supply, (c) 16-channel ADC circuit, (d) SoC FPGA-based digital signal processing circuit, and (e) symmetric charge division circuit for the SiPM array\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7448685/v1/046c5229d9b067bf8a451545.png"},{"id":91420007,"identity":"945c22ac-01c7-4fc4-bdb4-b4846423478e","added_by":"auto","created_at":"2025-09-16 10:07:41","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":313741,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental setup for radiation energy measurement. (a) The scintillator and light sensor are configured as a single detector module and connected to a data acquisition system, (b) data acquisition using a Na-22 radiation source.\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7448685/v1/20a6e494bf99ff67bb67fe2d.jpeg"},{"id":91420006,"identity":"4b541461-38d9-4232-8c7d-c6c502c39a95","added_by":"auto","created_at":"2025-09-16 10:07:41","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":45381,"visible":true,"origin":"","legend":"\u003cp\u003eThe process of measuring slope through a signal waveform. The slope can be measured by sampling from the first and second clocks, respectively.\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7448685/v1/80e04542c9f9b6eeb6012557.jpeg"},{"id":91421270,"identity":"d1ba8f31-29d5-474e-b8c8-6da8243a0959","added_by":"auto","created_at":"2025-09-16 10:15:41","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":106245,"visible":true,"origin":"","legend":"\u003cp\u003eSignal waveforms of the Na-22 radioactive source measured for each channel using the data acquisition system of the ARALE Laboratory.\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7448685/v1/2bcaa61a2612fd0a0f549683.jpeg"},{"id":91420011,"identity":"2098d01b-cb87-41bd-bb78-7ee38f76d713","added_by":"auto","created_at":"2025-09-16 10:07:41","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":125207,"visible":true,"origin":"","legend":"\u003cp\u003eEnergy spectrum of the Na-22 radiation source displayed using the data acquisition. (a) Energy spectrum constructed by measuring all the waveforms of the signal, (b) Energy spectrum constructed by measuring the slope.\u003c/p\u003e","description":"","filename":"floatimage7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7448685/v1/8cb4795a0338ce72b2eab6e6.jpeg"},{"id":91420009,"identity":"dafcc1ab-743f-40ae-96cf-6638724725c0","added_by":"auto","created_at":"2025-09-16 10:07:41","extension":"jpeg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":61051,"visible":true,"origin":"","legend":"\u003cp\u003eThe process of separating and measuring each signal from a signal waveform that may appear to be the result of signal pile-up.\u003c/p\u003e","description":"","filename":"floatimage8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7448685/v1/49ade81a63c4a0adca416809.jpeg"},{"id":105827694,"identity":"205572b2-d1e8-4644-9fb9-704ce92cd970","added_by":"auto","created_at":"2026-03-31 14:13:52","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3602363,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7448685/v1/b79ef402-0c50-4e4f-a28f-f82de1c6b17b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Development of a method for fast radiation measurement as a solution to signal pile-up by measuring the rising slope of the signal waveform","fulltext":[{"header":"Ⅰ. Introduction","content":"\u003cp\u003eX-ray photon counting detectors are used in various systems for medical and materials analysis [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. To individually detect a large number of incident photons, a very fast detection speed is required. For this purpose, application specific integrated circuit (ASIC) type photon counting detectors have been developed and used in dedicated systems [\u003cspan additionalcitationids=\"CR3 CR4 CR5 CR6 CR7\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. However, even when ASIC type detectors with fast detection speeds are used, X-ray signal pile-up occurs. Attempts to solve this problem have led to the development of pile-up removal methods [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn this paper, we propose a general photon counting acquisition method for implementation in a photon counting detector. In general, a radiation detection system collects the electrical signal that is generated when it collects incident photons to measure the energy of the radiation. These measurements are typically conducted by using one of the following two methods: the first method stores the peak value of the waveform of the output signal and the second method conducts the measurement by integrating the signal waveform. The method that measures the peak value by analyzing the waveform of the signal generates a trigger signal to obtain information about the peak value. The method that involves integration of the waveform of the signal collects the signals by adding up all the signal sizes from the time at which the signal magnitude is detected to have reached a certain level. Systems based on the ASIC type signal measurement method utilize the latter of these two methods; that is, measurement by integrating the waveform of the generated signal. In this study, a method was devised to enable fast signal collection by modifying the aforementioned method that relies on signal waveform integration. The magnitude of a signal varies depending on the energy of the incident radiation. However, although analysis of the signal waveform of the detection system can confirm that the signal magnitude depends on the energy of the radiation, the time at which the peak value appears is the same for all signals [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the waveform of the signal measured using the Hamamatsu SiPM S13360-3075CS model. As is confirmed in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, the magnitude of the signal is different for all signals, but the time at which the peak value of the signal appears is the same for all signals. In other words, the time taken from the moment the signal is generated until it reaches the peak signal is the same. As the amount of radiation energy changes, the magnitude of the signal changes, but the time to reach the peak value is the same; thus, it is confirmed that the slope of the signal reaching the maximum value from the minimum value varies depending on the radiation energy. By analyzing this process to reach the signal magnitude, we inferred that the radiation energy can be measured by determining the slope of the waveform. Measurement of the signal size at two points for conversion into the slope to shorten the signal measurement time is expected to represent the entire radiation signal. To verify this assumption, we conducted a basic experiment using the data acquisition system developed by the ARALE Laboratory Co., Ltd. Based on these data, we developed a method to clearly measure the radiation energy, even from pile-up signals, by measuring the slope. This method enables signal loss due to pile-up to be reduced, and the maximum number of radiation signals that can be measured in the same period of time can be increased as a result of the fast measurement time. In addition, fast signal measurement is foreseen to be possible by implementing our proposed method in a system that can be used universally without the need for a fast signal-processing circuit.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Ⅱ. Materials and Methods","content":"\u003cp\u003e1.\u0026nbsp; \u0026nbsp;\u0026nbsp;Detector system configuration\u003c/p\u003e\n\u003cp\u003eThe radiation energy was derived by measuring the slope of the signal rise by using the data acquisition system of ARALE Laboratory Co., Ltd. as the signal measurement system [13]. This system was developed for use in a small gamma camera and was used in this study to measure the signal using a scintillator. The waveform of the signal generated by the radiation was acquired with a light sensor, the S13361-3050AE-08 model of Hamamatsu (Fig. 2), which consists of an 8\u0026nbsp;\u0026acute;\u0026nbsp;8 array of 3 mm\u0026nbsp;\u0026acute;\u0026nbsp;3 mm multi-pixel photon counter (MPPC) pixels [14]. The signals generated from the 64 MPPC pixels are reduced to four channels of signals, X+, X-, Y+, and Y-, through a symmetric charge division circuit. The signals of each channel are converted into digital signals through the analog-to-digital converter (ADC) through the four-channel transimpedance amplifier and the ADC driver circuit, and then transmitted to a computer through the network to store the data.\u003c/p\u003e\n\u003cp\u003eThe ADC was the TI ADS5296A model with 100 megasamples per second (MSPS) of 10-bit resolution [15]. The analog waveform generated by a gamma-ray event was quantized once every 10 ns through the ADC, and this value was designed to be continuously stored in the field programmable gate array (FPGA) register up to 400 times so that data for the entire waveform could be collected. The waveform data stored in the FPGA was transferred to the dual core ARM, generated as a single universal datagram protocol (UDP) packet, and then transferred to the computer via Ethernet. Fig. 3 shows internal data acquisition system in the small gamma camera\u003c/p\u003e\n\u003cp\u003e2.\u0026nbsp; \u0026nbsp;\u0026nbsp;Experimental setup\u003c/p\u003e\n\u003cp\u003eThe collimator of the gamma camera and the existing scintillator block were removed, and a single-pixel scintillator was combined with the light sensor. Fig. 4 shows the equipment for data collection using the scintillator and Na-22 radiation source placed on the light sensor of the gamma camera. The single-pixel scintillator was a gadolinium aluminium gallium garnet (GAGG) scintillator measuring 3 mm\u0026nbsp;\u0026acute;\u0026nbsp;3 mm\u0026nbsp;\u0026acute;\u0026nbsp;5 mm. The GAGG scintillator has a high density of 6.3 g/cm\u003csup\u003e3\u003c/sup\u003e, which is effective for detecting high-energy radiation, and has an excellent light yield (50,000 photons/MeV), which offers outstanding energy resolution [16]. In addition, as it does not generate background radiation, it does not affect the energy of the radiation to be measured, thus enables only the signal of the corresponding radiation to be measured. The GAGG scintillator and light sensor were combined to configure a detector, and the signal was measured using the Na-22 radiation source. The detection system is connected to a cable that supplies 20 V direct current (DC) power, and an Ethernet cable for transmitting both input data for controlling the data acquisition system and output data consisting of the detected gamma-ray waveform to a computer.\u003c/p\u003e\n\u003cp\u003e3.\u0026nbsp; \u0026nbsp;\u0026nbsp;Data acquisition\u003c/p\u003e\n\u003cp\u003eThe signals generated by the Na-22 radiation source were acquired using the configured detector with the gamma camera. The signal waveform for each gamma-ray event was acquired using the MAETEL ver. 1.42 software. The data for the 4 channels can be acquired from one signal. The data of these 4 channels is a signal in which the signal of each 64 MPPC pixel channel of X+, X-, Y+, Y- is reduced to 4 channels, and the addition of the signals of each of the 4 channels can be expressed as one detected gamma-ray energy.\u003c/p\u003e\n\u003cp\u003eAnalysis of the characteristics of the signal of each channel reveals that the rising time and peak value of the signals are all the same. This means that changes in the measured energy would change the rising slope, which means that the signals can be converted into energy by measuring the rising slope. Based thereupon, the energy spectrum was constructed by measuring the rising slope of the signal generated by measuring the Na-22 radiation source. This energy spectrum was then compared and evaluated with the energy spectrum constructed by measuring all values of the signal. The method that entails measuring the slope through the signal waveform is illustrated in Fig. 5. A signal of which the magnitude exceeds the threshold is set to be collected. Using three clocks, the first signal value is collected at the time on the first clock, and the second signal value is collected at the time on the second clock. After that, by connecting to the ground at the third clock and initializing the generated signal value, this signal sampling process allows radiation measurement with only 3 clocks. Even if a low-speed ADC is used, sufficiently fast radiation measurement is possible. In addition, this method can prevent coefficient loss due to signal pile-up.\u003c/p\u003e"},{"header":"Ⅲ. Results and Discussion","content":"\u003cp\u003eCounting the photons of X-rays and measuring the energy of radiation in very strong radiation fields requires a very fast measurement system. For this purpose, existing systems are designed to perform fast measurement by using a dedicated ASIC, which is designed to fit the system to be used. However, even in these systems, signal pile-up occurs when a very large amount of radiation is incident. This inspired us to develop a signal measurement method to address the problem of signal pile-up for use in existing general-purpose systems. When a radiation signal is generated, the slope of the waveform produced by the signal quickly rises before levelling off at the peak, where after the slope of the waveform decreases more gradually. Considering that the rising time in the same measurement system is the same for all the signals regardless of the energy of the radiation being measured, we devised a method for measuring the energy of radiation by assuming that the rising slope depends on the energy of the radiation and this was confirmed through experiments. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the waveform of the signal of the Na-22 radiation source measured for each channel using the data acquisition system of ARALE Laboratory Co., Ltd. Because the measured energy for each channel is different, the height of the waveform is different for each channel. However, the time points where the peak values ​​appear are all the same. Here, the rising slope can be measured for conversion into radiation energy. The slope was calculated from the 49th to the 50th sampling values ​​from the point where the signal waveform was stored. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e shows the energy spectrum of the Na-22 radiation source. More specifically, Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a) shows the entire energy spectrum of all the signal waveforms that were measured, and Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b) shows the part of the energy spectrum that was constructed by measuring the slope. The photopeak area of ​​the energy spectrum in (b), which was not produced by measuring the signal waveform, is clearly shifted to the left. This means that the total amount of energy that was measured was smaller. The energy spectrum has photopeaks of 511 keV and 1275 keV. The energy resolution is 7.9% in (a) and 17.7% in (b), which indicates that it is preferable to measure all the signal waveforms. It takes about 200 ns to measure all the signal shapes, whereas only 30 ns is needed to measure the slope. In other words, the signal can be measured very quickly. Our experiments confirmed that signals can be measured within several tens of nanoseconds even if the system is not equipped with a dedicated ASIC. The proposed method of determining the radiation energy by measuring the slope can largely prevent signal pile-up by employing fast signal measurement, although signal pile-up would still be possible when a very large amount of radiation is incident for a very short time. However, by measuring the slope, measurement is possible as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, which enables the pile-up signal to be separated and the radiation energy to be measured. That is, the second signal in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e is in a form that can appear due to the incident radiation during the process of decreasing the first signal, and by designing the slope measurement such that it is collected when the signal rises, it is considered possible to separate the pile-up signal for measurement.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Ⅳ. Conclusion","content":"\u003cp\u003eARALE Laboratory Co., Ltd. developed a method to resolve the phenomenon of signal pile-up that can occur when a very large amount of radiation is incident on a gamma camera in a very short period of time. A very fast measurement system is therefore required to count the photons of X-rays. Towards this goal, fast signal measurement systems equipped with dedicated ASIC systems have been developed. Because these systems are developed exclusively, they can only be used in the system in question, and their development and production is expensive. This led us to develop a method that can be used in general-purpose systems and that require minimal changes to existing systems and the operating method. When a radiation signal is generated, the slope of the generated waveform increases sharply before levelling off until the peak value is reached, after which the slope of the waveform declines more slowly. Even if the energy of the radiation differs, the point at which the peak value appears is the same. In other words, after confirming that the energy of the radiation can be measured by measuring the rising slope of the signal, the possibility was confirmed through experiments. After measuring the signal size at the two points in the rising part of the waveform of the generated signal, the difference was accumulated to form a radiation energy spectrum. In other words, the experiments confirmed that conversion into radiation energy was possible by measuring the slope of the signal. Compared to the measurement of the signals of all waveforms, the energy resolution is lower, but the measurement time is greatly shortened. In fact, the measurement time is shortened from 200 ns to 30 ns, thus a very fast measurement time can be achieved. This time was measured with an ADC with a speed of 100 MSPS, and is expected to be shortened even further by using a faster ADC. This shortened measurement time can prevent signal pile-up, and even if signal pile-up was to occur, the piled up signal could be separated and measured by measuring the point at which the signal waveform starts rising. This method is sufficiently applicable to existing systems, and a very fast measurement time is expected to be achievable even with a relatively low-speed ADC. In addition, since a sufficiently fast measurement time can be secured even without developing a dedicated system, the development of a highly efficient system that could achieve a very fast measurement time at a very low cost is foreseen to be possible.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eS.-J.L. designed and performed the experiments, collected and analyzed the data, and prepared the initial draft of the manuscript. C.-H.B. conceived the study, supervised the research, and contributed to interpretation of the results. S.-J.L. and C.-H.B. wrote the main manuscript text together. All authors reviewed and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eACKNOWLEDGMENTS\u003c/h2\u003e\u003cp\u003eThis work was conducted during the sabbatical year of Dongseo University in 2025.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eK. Shimazoe, D. Kim, M. Hamdan, Y. Kobayashi, K. Kamada, M. Yoshino, Y. Shoji, K. Sakamoto, F. Acerbi, and A. Gola, Comms. Eng., \u003cstrong\u003e3\u003c/strong\u003e, 167 (2024).\u003c/li\u003e\n\u003cli\u003eP. Otfinowski, G. W. Deptuch, and P. Maj, J. Instrum., \u003cstrong\u003e15\u003c/strong\u003e, C01016 (2020).\u003c/li\u003e\n\u003cli\u003eR. Ballabriga, J. Alozy, G. Blaj, M. Campbell, M. Fiederle, E. Frojdh, E. H. M. Heijne, X. Llopart, M. Pichotka, S. Procz, L. Tlustos and W. Wong, J. Instrum., \u003cstrong\u003e8\u003c/strong\u003e, C02016 (2013).\u003c/li\u003e\n\u003cli\u003eT. Poikela, J. Plosila, T. Westerlund, M. Campbell, M. De Gaspari, X. Llopart, V. Gromov, R. Kluit, M. van Beuzekom. F. Zappon, V. Zivkovic, C. Brezina, K. Desch, Y. Fu and A. Kruth, J. Instrum., \u003cstrong\u003e9\u003c/strong\u003e, C05013 (2014).\u003c/li\u003e\n\u003cli\u003eR. Bellazzini, G. Spandre, A. Brez, M. Minuti, M. Pinchera and P. Mozzo, J. 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Technol., \u003cstrong\u003e52\u003c/strong\u003e, 1029 (2020).\u003c/li\u003e\n\u003cli\u003eK. Treb, J. Radtke, W. S. Culberson, K. Li, Phys. Med. Biol., \u003cstrong\u003e68\u003c/strong\u003e, 155003 (2023).\u003c/li\u003e\n\u003cli\u003eS. G\u0026oacute;mez, D. S\u0026aacute;nchez, J. Mauricio, E. Picatoste, A. Sanuy, A. Sanmukh, M. Rib\u0026oacute; and D. Gasc\u0026oacute;n, Electronics, \u003cstrong\u003e10\u003c/strong\u003e, 961 (2021).\u003c/li\u003e\n\u003cli\u003eCompact Gamma Camera data acquisition system, ALARE Laboratory Web. https://www.aralelab.com/index.html#section-02\u003c/li\u003e\n\u003cli\u003eMPPC array, Hamamatsu Web. https://www.hamamatsu.com/content/dam/hamamatsu-photonics/sites/documents/99_SALES_LIBRARY/ssd/s13361-3050_series_kapd1054e.pdf\u003c/li\u003e\n\u003cli\u003eADS5296A, Texas Instruments Web. https://www.ti.com/lit/ds/symlink/ads5296a.pdf\u003c/li\u003e\n\u003cli\u003eGAGG scintillator, Epic-Crystal Web. https://www.epic-crystal.com/data/upload/20240409/6614a154ea168.pdf\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"photon counting, pile up, signal waveform, slope, detector","lastPublishedDoi":"10.21203/rs.3.rs-7448685/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7448685/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eDetection systems based on photon counting utilize a system that makes use of a dedicated application specific integrated circuit (ASIC) for very fast radiation measurement. However, even with a high-speed system, the signal pile-up phenomenon still occurs. In this study, a general-purpose method that can measure radiation very fast, and can measure radiation lost due to pile-up was developed. This method determines the energy by analyzing the signal waveform, and by converting the rising slope of the signal into energy. Analysis of the slope, instead of measuring the entire waveform, enables the measurement time to be greatly reduced, and by measuring the rising slope, each individual radiation signal can be separated and measured even in signals where pile-up occurred. This method, which eliminates the need for a dedicated ASIC, can be applied to existing systems. In addition, this method is expected to enable a very efficient detection system to be developed because the loss of photon counting can be minimized in high radiation fields.\u003c/p\u003e","manuscriptTitle":"Development of a method for fast radiation measurement as a solution to signal pile-up by measuring the rising slope of the signal waveform","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-16 10:07:36","doi":"10.21203/rs.3.rs-7448685/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"bceb21dd-7439-4916-b56e-b94861666a74","owner":[],"postedDate":"September 16th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-03-31T14:12:25+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-16 10:07:36","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7448685","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7448685","identity":"rs-7448685","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}