• Nuclear Engineering and Technology
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• 제56권1호
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• pp.56-63
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• 2024

In high radiation fields, gamma cameras suffer from pulse pile-up, resulting in poor energy resolution, count losses, and image distortion. To overcome this problem, various methods have been introduced to reduce the size of the aperture or pixel, reject the pile-up events, and correct the pile-up events, but these technologies have limitations in terms of mechanical design and real-time processing. The purpose of this study is to develop a real-time gamma camera to evaluate the radioactive contamination in high radiation fields. The gamma camera is composed of a pinhole collimator, NaI(Tl) scintillator, position sensitive photomultiplier (PSPMT), signal processing board, and data acquisition (DAQ). The pulse pile-up is corrected in real-time with a field programmable gate array (FPGA) using the start time correction (STC) method. The STC method corrects the amplitude of the pile-up event by correcting the time at the start point of the pile-up event. The performance of the gamma camera was evaluated using a high dose rate ¹³⁷Cs source. For pulse pile-up ratios (PPRs) of 0.45 and 0.30, the energy resolution improved by 61.5 and 20.3%, respectively. In addition, the image artifacts in the ¹³⁷Cs radioisotope image due to pile-up were reduced.

• 전자공학회논문지
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• 제50권8호
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• pp.162-167
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• 2013

X-선과, ${\gamma}$-선을 이용한 형광분석장치는 현재 널리 쓰이는 물질의 고유특성을 분석하는 장치이다. 하지만 여러 가지 원인으로 인해 장치사용 시 측정 신호에서 중첩 현상이 발생한다. 검출 신호의 높이는 측정 물질의 특성을 반영하며 측정 물질을 정확히 분석하기 위해서는 중첩된 신호를 제거하거나 복원을 해야 한다. 현재 trapezoidal 필터는 형광분석장치에 널리 사용되고 있으며 중첩펄스 검출에서도 좋은 결과를 보이고 있다. 본 논문에서는 측정 신호의 사다리꼴 변형에 기반 한 중첩펄스 처리방법을 제안한다. 제안방법은 사다리꼴 필터를 이용한 최대값 검출 알고리즘에 두 개의 카운터와 몇 개의 레지스터만을 추가하여 추가적인 중첩펄스 처리 알고리즘을 구현하기 때문에 기존 방법에 비해 하드웨어 복잡도가 훨씬 적으면서도 정확히 중첩펄스를 처리 할 수 있다.

• Nuclear Engineering and Technology
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• 제55권12호
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• pp.4350-4356
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• 2023

Radiation detection systems working at high count rates suffer from the overlapping of their output electric pulses, known as pulse pile-up phenomenon, resulting in spectrum distortion and degradation of the energy resolution. Pulse tail extrapolation is a pile-up correction method which tries to restore the shifted baseline of a piled-up pulse by extrapolating the overlapped part of its preceding pulse. This needs a mathematical model which is almost always nonlinear, fitted usually by a nonlinear least squares (NLS) technique. NLS is an iterative, potentially time-consuming method. The main idea of the present study is to replace the NLS technique by an integration-based non-iterative method (NIM) for pulse tail extrapolation by an exponential model. The idea of linear extrapolation, as another non-iterative method, is also investigated. Analysis of experimental data of a NaI(Tl) radiation detector shows that the proposed non-iterative method is able to provide a corrected spectrum quite similar with the NLS method, with a dramatically reduced computation time and complexity of the algorithm. The linear extrapolation approach suffers from a poor energy resolution and throughput rate in comparison with NIM and NLS techniques, but provides the shortest computation time.

• Nuclear Engineering and Technology
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• 제52권2호
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• pp.360-365
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• 2020

A technique for the reduction of pulse pile-up effect in digital pulse-shape discrimination (PSD) of neutrons and gamma-rays with organic scintillation detectors is presented. The technique is based on an electronic reduction of the effective decay-time constant of scintillation pulses while retaining the PSD information of the pulses. The experimental results obtained with a NE213 liquid scintillation detector in a mixed radiation field of neutrons and gamma-rays are presented, demonstrating a figure of merit (FOM) of 1.20 ± 0.05 with an energy threshold of 350 keVee (electron equivalent energy) when the effective length of the pulses is reduced to 50 ns.

• Journal of Radiation Protection and Research
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• 제31권4호
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• pp.173-179
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• 2006

개선된 몬테칼로 코드 CEARPPU는 고계수율 상황에서의 펄스 중첩 보정 스펙트럼을 제공한다. 중성자 방사화 분석을 위하여 CEARPPU를 이용하여 보정된 스펙트럼으로 라이브러리 최소자승 동위원소 방사능 분석을 수행하여 보정하지 않은 스펙트럼을 이용하는 방법보다 우수한 결과를 얻었다.

• Nuclear Engineering and Technology
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• 제50권7호
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• pp.1006-1016
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• 2018

Since the early forties, researchers from around the world have been studying the phenomenon of deadtime in radiation detectors. Many have attempted to develop models to represent this phenomenon. Two highly idealized models; paralyzable and non-paralyzable are commonly used by most individuals involved in radiation measurements. Most put little thought about the operating conditions and applicability of these ideal models for their experimental conditions. So far, there is no general agreement on the applicability of any given model for a specific detector under specific operating conditions, let alone a universal model for all detectors and all operating conditions. Further the related problem of pile-up is often confused with the deadtime phenomenon. Much work, is needed to devise a generalized and practical solution to these related problems. Many methods have been developed to measure and compensate for the detector deadtime count loss, and many researchers have addressed deadtime and pulse pile-up. The goal of this article is to summarize the state of science of deadtime; measurement and compensation techniques as proposed by some of the most significant work on these topics and to review the deadtime correction models applicable to present day radiation detection systems.

• Nuclear Engineering and Technology
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• 제54권3호
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• pp.781-789
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• 2022

KHNP had licensed Dynamic Control rod Reactivity Measurement (DCRM) method using detector current signals of PWRs in 2006. The method has been applied to all PWRs in Korea for about 15 years successfully. However, the original method was inapplicable to PWRs using low-sensitivity integral fission chamber as ex-core detectors because of their pulse pile-up and the nonlinearity of the mean-square voltage at low power region. Therefore, to overcome this disadvantage, a modified method, DCRM-EK, was developed using kinetics behavior after equilibrium condition where the pulse counts maintain the maximum value before pulse pile-up. Overall measurement, analysis procedure, and related computer codes were changed slightly to reflect the site test condition. The new method was applied to a total of 15 control rods of 1000 MWe and 1400 MWe PWRs in Korea with worths in the range of 200 pcm -1200 pcm. The results show the average difference of -0.4% and the maximum difference of 7.1% compared to the design values. Therefore, the new DCRM-EK will be applied to PWRs using low sensitivity integral fission chambers, and also can replace the original DCRM when the evaluation fails by big noises present in current or voltage signals of uncompensated/compensated ion chambers.

• 산업기술연구
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• 제19권
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• pp.1-7
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• 1999

This is the pre-study to pile up the basic technique for the electro-discharge machining in the field of micro-drilling. The machined chips are flowed out from the machining area by the flow arisen from the high speed rotation of the electrode. The cylindrical shape electrode, whose diameter is 0.5mm, is clamped by the three point clamping type clamper and the clamper is attached at the front shaft of the high speed rotating DC motor. The current for machining is controlled by pulse width modulation technique and the machining conditions such as frequency and duty ratio are changed to find out the effect of the variables for machined results.

• Nuclear Engineering and Technology
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• 제56권2호
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• pp.745-752
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• 2024

A method for gamma/neutron event classification based on frequency-domain analysis for mixed radiation environments is proposed. In contrast to the traditional charge comparison method for pulse-shape discrimination, which requires baseline removal and pulse alignment, our method does not need any preprocessing of the digitized data, apart from removing saturated traces in sporadic pile-up scenarios. It also features the identification of neutron events in the detector's full energy range with a single device, from thermal neutrons to fast neutrons, including low-energy pulses, and still provides a superior figure-of-merit for classification. The proposed frequency-domain analysis consists of computing the fast Fourier transform of a triggered trace and integrating it through a simplified version of the transform magnitude components that distinguish the neutron features from those of the gamma photons. Owing to this simplification, the proposed method may be easily ported to a real-time embedded deployment based on Field-Programmable Gate Arrays or Digital Signal Processors. We target an off-the-shelf detector based on a small CLYC (Cs2LiYCl6:Ce) crystal coupled to a silicon photomultiplier with an integrated bias and preamplifier, aiming at lightweight embedded mixed radiation monitors and dosimeter applications.

• Nuclear Engineering and Technology
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• 제55권11호
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• pp.4057-4065
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• 2023

Organic scintillators are widely used for neutron/gamma detection. Pulse shape discrimination algorithms have been commonly used to discriminate the detected radiations. These algorithms have several limits, in particular with plastic scintillator which has lower discrimination ability, compared to liquid scintillator. Recently, machine learning (ML) models have been explored to enhance discrimination performance. Nevertheless, obtaining an accurate ML model or evaluating any discrimination approach requires a reference neutron dataset. The preparation of this is challenging because neutron sources are also gamma-ray emitters. Therefore, this paper proposes a pipeline to prepare clean labeled neutron/gamma datasets acquired by an organic scintillator. The method is mainly based on a Time of Flight setup and Tail-to-Total integral ratio (TTT_ratio) discrimination algorithm. In the presented case, EJ276 plastic scintillator and ²⁵²Cf source were used to implement the acquisition chain. The results showed that this process can identify and remove mislabeled samples in the entire ToF spectrum, including those that contribute to peak values. Furthermore, the process cleans ToF dataset from pile-up events, which can significantly impact experimental results and the conclusions extracted from them.