A digital coincidence acquisition system applied to a portable liquid scintillation counting device is developed. The system which simplifies the device design consists of a digitizer card of Agilent U1066A DC438, a d...A digital coincidence acquisition system applied to a portable liquid scintillation counting device is developed. The system which simplifies the device design consists of a digitizer card of Agilent U1066A DC438, a discriminator and a host computer. The anode analog pulses from two photomultiplier tubes are captured by the system, which adopts the sequence acquisition storage mode. By choosing proper threshold for each channel, coincidence time window of ±30 ns, and comparing the pulse amplitudes from two channels, the portable scintillation counting device can be used to detect β particles. For the unquenched standard 3 H sample, the results show that the detection efficiency is (58.5±0.1)% and the background is (86.7±0.7) cpm. Meanwhile, 3 H β spectrum is obtained.展开更多
An accurate energy calibration of a BC501A liquid scintillator by means of Compton scattering of γ-rays is described.The energy resolution and the position of the Compton edge have been precisely determined using a ...An accurate energy calibration of a BC501A liquid scintillator by means of Compton scattering of γ-rays is described.The energy resolution and the position of the Compton edge have been precisely determined using a γ-γ coincidence technique and fitting the coincidence spectrum with a Gaussian function superimposed on a quadratic polynomial for the background.The position of the Compton edge relative to the position of the maximum and the half height of the distribution in dependence on the relevant energy resolution is discussed in detail.The results indicate that the maximum energy of the recoil Compton electron does not occur at the half height distribution but at 0.90±0.05 of the maximum height in the energy range considered.The energy resolution varies from 15.6% to 8.02% for electrons in the energy region from 0.5 MeV to 3 MeV.展开更多
A digital pulse shape discrimination system based on a programmable module NI-5772 has been established and tested with an EJ-301 liquid scintillation detector. The module was operated by running programs developed in...A digital pulse shape discrimination system based on a programmable module NI-5772 has been established and tested with an EJ-301 liquid scintillation detector. The module was operated by running programs developed in Lab VIEW, with a sampling frequency up to 1.6 GS/s. Standard gamma sources ^22 Na,^137Cs and ^60 Co were used to calibrate the EJ-301 liquid scintillation detector, and the gamma response function was obtained. Digital algorithms for the charge comparison method and zero-crossing method have been developed. The experimental results show that both digital signal processing（DSP） algorithms can discriminate neutrons from γ-rays. Moreover,the zero-crossing method shows better n-γ discrimination at 80 ke Vee and lower, whereas the charge comparison method gives better results at higher thresholds. In addition, the figure-of-merit（FOM） for detectors of two different dimensions were extracted at 9 energy thresholds, and it was found that the smaller detector presented better n-γseparation for fission neutrons.展开更多
A dedicated 4πβ（LS）-γ（HPGe） digital coincidence system with five acquisition channels has been developed. Three ADC acquisition channels with an acquisition resolution of 8 bits and acquisition rate of 1 GSPS a...A dedicated 4πβ（LS）-γ（HPGe） digital coincidence system with five acquisition channels has been developed. Three ADC acquisition channels with an acquisition resolution of 8 bits and acquisition rate of 1 GSPS are utilized to collect the signals from three PMTs which are used to detect β decay, and two acquisition channels with an acquisition resolution of 16 bits and acquisition rate of 50 MSPS are utilized to collect the signals from high-purity germanium（HPGe）, which is used to detect γ decay. In order to increase the accuracy of the coincidence system, all five acquisition channels are synchronous within 500 ps. The data collected by the five acquisition channels will be transmitted to the host PC through a PCI bus and saved as a file. Off-line software is utilized for the 4πβ（LS）-γ（HPGe） coincidence and data analysis as needed in practical applications. Tests of the system show that system can record pulse signals from 4πβ（LS）-γ（HPGe） synchronously for further coincidence calculation and the highest coincidence rate of the system is 20 K/s, which is sufficient for most applications. Compared with traditional coincidence modules like MAC3, the digital coincidence system has a higher flexibility of coincidence algorithm. In addition, due to the use of ADC, the structure of the coincidence system is simplified. This paper introduces the design of the hardware, the synchronization method and the test results of this system.展开更多
此仪器有两种扫描信号,一是数码管显示用快振荡扫描信号,频率为2.4 k Hz;二是打字用慢振荡扫描信号,频率为12.5Hz。慢振荡扫描信号经过H<sub>i</sub>计数器8分频为1.56Hz作为H<sub>0</sub>,H<sub>1</s...此仪器有两种扫描信号,一是数码管显示用快振荡扫描信号,频率为2.4 k Hz;二是打字用慢振荡扫描信号,频率为12.5Hz。慢振荡扫描信号经过H<sub>i</sub>计数器8分频为1.56Hz作为H<sub>0</sub>,H<sub>1</sub>…………H<sub>7</sub>重复频率,即H<sub>0</sub>—H<sub>7</sub>重复一次需要0.7s。1.56Hz又经打字V<sub>i</sub>展开更多
Frequency gradient analysis （FGA） effectively discriminates neutrons and γ rays by examining the frequency-domain features of the photomultiplier tube anode signal. This approach is insensitive to noise but is inev...Frequency gradient analysis （FGA） effectively discriminates neutrons and γ rays by examining the frequency-domain features of the photomultiplier tube anode signal. This approach is insensitive to noise but is inevitably affected by the baseline drift similar to other pulse shape discrimination methods. The baseline drift effect is attributed to factors such as power line fluctuation, dark current, noise disturbances, hum, and pulse tail in front-end electronics. This effect needs to be elucidated and quantified before the baseline shift can be estimated and removed from the captured signal. Therefore, the effect of baseline shift on the discrimination performance of neutrons and ~ rays with organic scintillation detectors using FGA is investigated in this paper. The relationship between the baseline shift and discrimination parameters of FGA is derived and verified by an experimental system consisting of an americium-beryllium source, a BC501A liquid scintillator detector, and a 5 GSample/s 8-bit oscilloscope. The theoretical and experimental results both show that the estimation of the baseline shift is necessary, and the removal of baseline drift from the pulse shapes can improve the discrimination performance of FGA.展开更多
基金Supported by National Natural Science Foundation of China(Nos.11135002 and 91026021)
文摘A digital coincidence acquisition system applied to a portable liquid scintillation counting device is developed. The system which simplifies the device design consists of a digitizer card of Agilent U1066A DC438, a discriminator and a host computer. The anode analog pulses from two photomultiplier tubes are captured by the system, which adopts the sequence acquisition storage mode. By choosing proper threshold for each channel, coincidence time window of ±30 ns, and comparing the pulse amplitudes from two channels, the portable scintillation counting device can be used to detect β particles. For the unquenched standard 3 H sample, the results show that the detection efficiency is (58.5±0.1)% and the background is (86.7±0.7) cpm. Meanwhile, 3 H β spectrum is obtained.
文摘An accurate energy calibration of a BC501A liquid scintillator by means of Compton scattering of γ-rays is described.The energy resolution and the position of the Compton edge have been precisely determined using a γ-γ coincidence technique and fitting the coincidence spectrum with a Gaussian function superimposed on a quadratic polynomial for the background.The position of the Compton edge relative to the position of the maximum and the half height of the distribution in dependence on the relevant energy resolution is discussed in detail.The results indicate that the maximum energy of the recoil Compton electron does not occur at the half height distribution but at 0.90±0.05 of the maximum height in the energy range considered.The energy resolution varies from 15.6% to 8.02% for electrons in the energy region from 0.5 MeV to 3 MeV.
基金Supported by National Natural Science Foundation of China(91226107,11305229)the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA03030300)
文摘A digital pulse shape discrimination system based on a programmable module NI-5772 has been established and tested with an EJ-301 liquid scintillation detector. The module was operated by running programs developed in Lab VIEW, with a sampling frequency up to 1.6 GS/s. Standard gamma sources ^22 Na,^137Cs and ^60 Co were used to calibrate the EJ-301 liquid scintillation detector, and the gamma response function was obtained. Digital algorithms for the charge comparison method and zero-crossing method have been developed. The experimental results show that both digital signal processing（DSP） algorithms can discriminate neutrons from γ-rays. Moreover,the zero-crossing method shows better n-γ discrimination at 80 ke Vee and lower, whereas the charge comparison method gives better results at higher thresholds. In addition, the figure-of-merit（FOM） for detectors of two different dimensions were extracted at 9 energy thresholds, and it was found that the smaller detector presented better n-γseparation for fission neutrons.
基金Supported by National Metrology Institute of China
文摘A dedicated 4πβ（LS）-γ（HPGe） digital coincidence system with five acquisition channels has been developed. Three ADC acquisition channels with an acquisition resolution of 8 bits and acquisition rate of 1 GSPS are utilized to collect the signals from three PMTs which are used to detect β decay, and two acquisition channels with an acquisition resolution of 16 bits and acquisition rate of 50 MSPS are utilized to collect the signals from high-purity germanium（HPGe）, which is used to detect γ decay. In order to increase the accuracy of the coincidence system, all five acquisition channels are synchronous within 500 ps. The data collected by the five acquisition channels will be transmitted to the host PC through a PCI bus and saved as a file. Off-line software is utilized for the 4πβ（LS）-γ（HPGe） coincidence and data analysis as needed in practical applications. Tests of the system show that system can record pulse signals from 4πβ（LS）-γ（HPGe） synchronously for further coincidence calculation and the highest coincidence rate of the system is 20 K/s, which is sufficient for most applications. Compared with traditional coincidence modules like MAC3, the digital coincidence system has a higher flexibility of coincidence algorithm. In addition, due to the use of ADC, the structure of the coincidence system is simplified. This paper introduces the design of the hardware, the synchronization method and the test results of this system.
文摘此仪器有两种扫描信号,一是数码管显示用快振荡扫描信号,频率为2.4 k Hz;二是打字用慢振荡扫描信号,频率为12.5Hz。慢振荡扫描信号经过H<sub>i</sub>计数器8分频为1.56Hz作为H<sub>0</sub>,H<sub>1</sub>…………H<sub>7</sub>重复频率,即H<sub>0</sub>—H<sub>7</sub>重复一次需要0.7s。1.56Hz又经打字V<sub>i</sub>
基金Supported by National Natural Science Foundation of China(11175254)the support of the Institute of Nuclear Physics and Chemistry, the Chinese Academy of Engineering Physics, Mianyang, China
文摘Frequency gradient analysis （FGA） effectively discriminates neutrons and γ rays by examining the frequency-domain features of the photomultiplier tube anode signal. This approach is insensitive to noise but is inevitably affected by the baseline drift similar to other pulse shape discrimination methods. The baseline drift effect is attributed to factors such as power line fluctuation, dark current, noise disturbances, hum, and pulse tail in front-end electronics. This effect needs to be elucidated and quantified before the baseline shift can be estimated and removed from the captured signal. Therefore, the effect of baseline shift on the discrimination performance of neutrons and ~ rays with organic scintillation detectors using FGA is investigated in this paper. The relationship between the baseline shift and discrimination parameters of FGA is derived and verified by an experimental system consisting of an americium-beryllium source, a BC501A liquid scintillator detector, and a 5 GSample/s 8-bit oscilloscope. The theoretical and experimental results both show that the estimation of the baseline shift is necessary, and the removal of baseline drift from the pulse shapes can improve the discrimination performance of FGA.
