• Title/Summary/Keyword: Scintillation

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A technique for the reduction of pulse pile-up effect in pulse-shape discrimination of organic scintillation detectors

  • Nakhostin, M.
    • Nuclear Engineering and Technology
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    • v.52 no.2
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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.

Error Probabilities for Digital Transmission in Correlated Gaussian Fading Channels (상관가우스 페이딩 채널에서 디지틀전송에 대한 오율)

  • 한영렬
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.9 no.1
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    • pp.18-24
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    • 1984
  • Calculation of error probabilities for a coherent phase-shilft keyed communication system operating in a transionospheric scintillation channel is accomplished by means of the Gauss-quadrature integration formula. The channel model used, patterned after Rino's work, is slowly flat fading wherein the envelope of the received signal is modeled as the envelope of correlated Gaussian quadrature random processes. The error probability for the scintillation channel is calculated using actual ionospheric scintillation data for transmission in the UHF region(30-300MHz).

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Comparison of Image Uniformity with Photon Counting and Conventional Scintillation Single-Photon Emission Computed Tomography System: A Monte Carlo Simulation Study

  • Kim, Ho Chul;Kim, Hee-Joung;Kim, Kyuseok;Lee, Min-Hee;Lee, Youngjin
    • Nuclear Engineering and Technology
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    • v.49 no.4
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    • pp.776-780
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    • 2017
  • To avoid imaging artifacts and interpretation mistakes, an improvement of the uniformity in gamma camera systems is a very important point. We can expect excellent uniformity using cadmium zinc telluride (CZT) photon counting detector (PCD) because of the direct conversion of the gamma rays energy into electrons. In addition, the uniformity performance such as integral uniformity (IU), differential uniformity (DU), scatter fraction (SF), and contrast-to-noise ratio (CNR) varies according to the energy window setting. In this study, we compared a PCD and conventional scintillation detector with respect to the energy windows (5%, 10%, 15%, and 20%) using a $^{99m}Tc$ gamma source with a Geant4 Application for Tomography Emission simulation tool. The gamma camera systems used in this work are a CZT PCD and NaI(Tl) conventional scintillation detector with a 1-mm thickness. According to the results, although the IU and DU results were improved with the energy window, the SF and CNR results deteriorated with the energy window. In particular, the uniformity for the PCD was higher than that of the conventional scintillation detector in all cases. In conclusion, our results demonstrated that the uniformity of the CZT PCD was higher than that of the conventional scintillation detector.

Digital Position Measurement with MLPE of PET detector using a Small Number of Photosensors (적은 수의 광센서를 사용한 PET 검출기의 최대우도함수를 적용한 디지털 위치 측정)

  • Kang, Seunghun;Lee, Seung-Jae
    • Journal of the Korean Society of Radiology
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    • v.16 no.2
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    • pp.151-156
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    • 2022
  • A detector using a small number of photosensors was designed, and the position of a scintillation pixel that interacted with gamma rays through a maximum likelihood position estimation(MLPE) was measured as a digital position. For this purpose, simulation was performed using DETECT2000, which can simulate the movement of light within the scintillator, and the accuracy of position measurement was evaluated. A detector was configured using a 6 × 6 scintillation pixel array and 4 photosensors, and a gamma ray event was generated at the center of each scintillation pixel to create a look-up table through the ratio of acquired light. The gamma-ray event generated at the new position was applied as the input value of the MLPE, and the positiion of the scintillation pixel was converted into a digital positiion after comparison with the look-up table. All scintillation pixels were evaluated, and as a result, a high accuracy of 99.1% was obtained. When this method is applied to the currently usesd system, it is concidered that the process of determining the position of the scintillation pixel will be simplified.

Digital Position Acquisition Method of PET Detector Module using Maximum Likelihood Position Estimation (최대우도함수를 이용한 양전자방출단층촬영기기의 검출기 모듈의 디지털 위치 획득 방법)

  • Lee, Seung-Jae;Baek, Cheol-Ha
    • Journal of the Korean Society of Radiology
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    • v.15 no.1
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    • pp.1-7
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    • 2021
  • In order to acquire an image in a positron emission tomography, it is necessary to draw the position coordinates of the scintillation pixels of the detector module measured at the same time. To this end, in a detector module using a plurality of scintillation pixels and a small number of photosensors, it is necessary to obtain a flood image and divide a region of each scintillation pixel to obtain a position of a scintillation pixel interacting with a gamma ray. Alternatively, when the number of scintillation pixels and the number of photosensors to be used are the same, the position coordinates for the position of the scintillation pixels can be directly acquired as digital signal coordinates. A method of using a plurality of scintillation pixels and a small number of photosensors requires a process of obtaining digital signal coordinates requires a plurality of photosensors and a signal processing system. This complicates the signal processing process and raises the cost. To solve this problem, in this study, we developed a method of obtaining digital signal coordinates without performing the process of separating the planar image and region using a plurality of flash pixels and a small number of optical sensors. This is a method of obtaining the position coordinate values of the flash pixels interacting with the gamma ray as a digital signal through a look-up table created through the signals acquired from each flash pixel using the maximum likelihood function. Simulation was performed using DETECT2000, and verification was performed on the proposed method. As a result, accurate digital signal coordinates could be obtained from all the flash pixels, and if this is applied to the existing system, it is considered that faster image acquisition is possible by simplifying the signal processing process.

DOI Detector Design using Different Sized Scintillators in Each Layer (각 층의 서로 다른 크기의 섬광체를 사용한 반응 깊이 측정 검출기 설계)

  • Seung-Jae, Lee
    • Journal of the Korean Society of Radiology
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    • v.17 no.1
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    • pp.11-16
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    • 2023
  • In preclinical positron emisson tomography(PET), spatial resolution degradation occurs outside the field of view(FOV). To solve this problem, a depth of interaction(DOI) detector was developed that measures the position where gamma rays and the scintillator interact. There are a method in which a scintillation pixel array is composed of multiple layers, a method in which photosensors are arranged at both ends of a single layer, a method in which a scintillation pixel array is constituted in several layers and a photosensor is arranged in each layer. In this study, a new type of DOI detector was designed by analyzing the characteristics of the previously developed detectors. In the two-layer detector, different sizes of scintillation pixels were used for each layer, and the array size was configured differently. When configured in this form, the positions of the scintillation pixels for each layer are arranged to be shifted from each other, so that they are imaged at different positions in a flood image. DETECT2000 simulation was performed to confirm the possibility of measuring the depth of interaction of the designed detector. A flood image was reconstructed from a light signal acquired by a gamma-ray event generated at the center of each scintillation pixel. As a result, it was confirmed that all scintillation pixels for each layer were separated from the reconstructed flood image and imaged to measure the interaction depth. When this detector is applied to preclinical PET, it is considered that excellent images can be obtained by improving spatial resolution.

Study on the Radiocarbon Dating with Liquid Scintillation Counting (액체섬광계수법을 이용한 방사성탄소 연대측정법 연구)

  • Kim, Nak Bae;Woo, Hyung Joo;Hong, Wan;Cho, Soo Young
    • Analytical Science and Technology
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    • v.5 no.4
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    • pp.381-387
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    • 1992
  • Optimum counting condition of a low level liquid scintillation counter for radiocarbon dating has been determined to minimize the contribution of tritium activity and get the highest FOM by the variation of scintillation solutions, scintillation solution to benzene ratio, and ${\beta}$-ray spectrum counting ranges. Under the condition, background count rate has been reduced to $2.26{\pm}0.03cpm$, and the maximum measurable age reached to about 40,000 years. And the practicality of counting system has been verified by the analysis of shell and peat samples.

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A Rapid Method for the Measurement of the Absolute Activity of Carbon-14 in Pea Plant Tissue

  • Kendall, F.H.;Park, Chang-Kyu;Mer, C.L.
    • Applied Biological Chemistry
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    • v.18 no.2
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    • pp.56-60
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    • 1975
  • A rapid method for the measurement of the absolute activity of carbon-14 in cotyledons and root of etiolated pea seedlings has been developed. Fresh tissue was frozen in liquid air, ground and suspended in gel phosphor and subjected to measurement for its radioactivity by liquid scintillation counter. Apparent activity of the suspended tissue sample calculated by counting efficiency value obtained by internal standardisation, was found to be related to absolute activity of the tissue, determined by flask combustion technique, by a constant factor. Once this factor is determined experimentally, analysis of C-14 lebelled tissue involves only fairly simple suspension counting by liquid scintillation counter. Present method appears to be applicable to other tissues tagged with C-14.

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