Ce Scintillation Detectors Research Articles

Demonstration of narrowband X-ray beam by inverse Compton scattering with stored spontaneous emission

We achieved the generation of narrowband X-ray beams by inverse Compton scattering using stored spontaneous emission and electron bunches in the infrared free-electron laser system of the storage ring NIJI-IV. Using stored spontaneous emission with a resonant wavelength of 1530 nm and an electron beam with an energy of 310 MeV, an X-ray beam with the energy spread of approximately 10% and the Compton edge of 1.2 MeV was observed using a LaBr3(Ce) scintillation detector in the 3-bunch operation. X-ray beams were generated by inverse Compton scattering using stored spontaneous emission in the full-bunch (16-bunch) operation, and an increase in the bunch number is shown to be effective for increasing the Compton X-ray yield. The total yield of the Compton X-ray beam reached 3.1 × 104 photons/s at the electron-beam current of 43.5 mA in the full-bunch operation. These experimental results are likely to be useful for the development of narrowband X-ray beams with energies above 1 MeV, for use in energy recovery linacs and third-generation storage rings.

Fast timing measurement using an labr3(Ce) scintillator detector array coupled with gammasphere

Fast timing measurement using an labr3(Ce) scintillator detector array coupled with gammasphere

Calculation of the ambient dose equivalent H*(10) from gamma-ray spectra obtained with scintillation detectors

The measurement of the ambient dose equivalent H*(10) with automatic real-time radioactivity monitors using gamma-ray spectrometry provides valuable information at short integration times and serves as an alternative to conventional peak analysis of spectra. In this paper, a full methodology for the calculation of this quantity using Monte Carlo (MC) simulations is described and applied to real spectrometric measurements with LaBr3(Ce) scintillation detectors. The methodology involves the calculation of the fluence-to-H*(10) conversion factors and a method for obtaining the fluence from gamma-ray spectra. The combination of these two elements makes it possible to calculate the H*(10). The obtained results are compared with the H*(10) measurements of a Geiger-Müller (GM) detector. Finally, the necessary activity concentration to produce a certain increment on the H*(10) is discussed for some isotopes. This is used to discuss the analysis capabilities of the spectrometric detectors when compared to GM ones.

The ROSPHERE γ-ray spectroscopy array

The ROmanian array for SPectroscopy in HEavy ion REactions (ROSPHERE) has been designed as a multi-detector setup dedicated to γ-ray spectroscopy studies at the Bucharest 9MV Tandem accelerator. Consisting of up to 25 detectors (either Compton suppressed HPGe detectors or fast LaBr3(Ce) scintillator detectors) together with a state of the art plunger device, ROSPHERE is a powerful tool for lifetime measurements using the Recoil Distance Doppler Shift (RDDS) and the in-beam Fast Electronic Scintillation Timing (FEST) methods. The array's geometry, detectors, electronics and data acquisition system are described. Selected results from the first experimental campaigns are also presented.

Development of Compton imaging system for nuclear material monitoring at pyroprocessing test-bed facility

ABSTRACTThe Korea Atomic Energy Research Institute (KAERI) has constructed a test-bed facility, named PRIDE (PyRoprocess Integrated inactive DEmonstration), for demonstration of pyroprocessing technology. Even though the PRIDE facility utilizes depleted uranium, instead of actual spent fuel, as process material, it will play an important role not only from the process perspective, but also from the safeguards standpoint. In the present study, a Compton imaging system based on pixelated GAGG:Ce scintillation detectors was constructed and tested to determine its utility for accurate imaging of nuclear material locations and, thus, its applicability as a safeguards monitoring system at the PRIDE facility. In a lab-scale performance evaluation, when the dose rate induced by a 137Cs point-like source was ∼0.1 μSv/h, the source location was imaged within 5 min. The image resolutions were 22° and 7.6° for real-time monitoring using a back-projection algorithm and for near-real-time monitoring using a statistical iterative algorithm, respectively. The developed Compton imaging system was finally applied to low-enriched uranium and also to depleted uranium, which latter is the process material of the PRIDE facility, and it was indicated that the Compton imaging system can localize nuclear materials within a few minutes under conditions similar to those prevailing at the PRIDE facility. The results of this study show that the Compton imaging system, and Compton imaging technology in general, has a great potential for utilization as a nuclear material monitoring tool at the PRIDE facility.

Reprint of experiments and theory of 138La radioactive decay

We measured with unprecedented accuracy key features of the 138La radioactive decays as β particle energy distribution from 0.5keV to the end-point and ratios of electron capture probabilities PL/PK, PM/PK and PM/PL. This was achieved by making use of LaBr3:Ce and CeBr3 scintillator detectors. The advantage of the presented technique relies on the double role of LaBr3:Ce as source of 138La and detector medium resulting in a relatively efficient counting statistics and unaltered β energy detection. The experimental results are compared to advanced computational techniques and significant deviation is found below 20keV with the computational spectrum showing a 5% excess of β particle relative to the experimental spectrum at 10keV.

On the time response of background obtained in [formula omitted]-ray spectroscopy experiments using LaBr3(Ce) detectors with different shielding

Employing the γ-γ fast-timing technique with LaBr3(Ce) scintillator detectors allows the direct determination of lifetimes of nuclear excited states with a lower limit of about 5ps. This limit is increased as soon as background is present in the coincidence spectra underneath the full-energy peaks of the γ-γ cascade. Our aim was to identify the components of the γ-ray background by systematic γ-γ fast-timing measurements using different types of γ shielding within a large γ-ray spectrometer. The energy dependent physical zero-time response was measured using background-free full-energy peak events from the 152Eu γ-ray source. This is compared with the time response of the (Compton-) background distribution as obtained using the prompt 60Co γ-ray source. The time response of the typical Compton background is about 15ps faster than the time response of background-free full-energy peak events. Below about 500keV, a second type of background contributes by the detection of Compton-scattered γ rays generated in the materials of the spectrometer around the detector. Due to the additional time-of-flight of the Compton-scattered γ rays, this low-energy background is largely delayed. Compared with a bare cylindrical 1.5in.×1.5in. LaBr3(Ce) detector, the BGO-shielded detector in the Compton-suppression mode improves the peak-to-total ratio by a factor of 1.66(5), while the Pb-shielded detector only slightly reduces the low-energy background.

Experiments and theory of 138La radioactive decay

We measured with unprecedented accuracy key features of the 138La radioactive decays as β particle energy distribution from 0.5keV to the end-point and ratios of electron capture probabilities PL/PK, PM/PK and PM/PL. This was achieved by making use of LaBr3:Ce and CeBr3 scintillator detectors. The advantage of the presented technique relies on the double role of LaBr3:Ce as source of 138La and detector medium resulting in a relatively efficient counting statistics and unaltered β energy detection. The experimental results are compared to advanced computational techniques and significant deviation is found below 20keV with the computational spectrum showing a 5% excess of β particle relative to the experimental spectrum at 10keV.

Distribution of the 134Cs/137Cs ratio around the Fukushima Daiichi nuclear power plant using an unmanned helicopter radiation monitoring system

Large amounts of radioactive substances were released into the environment by the Fukushima Daiichi nuclear power plant (FDNPP) accident. Several research institutes have mapped the distribution of nuclides with long half-lives, such as 134Cs and 137Cs. Although the ratio of 134Cs and 137Cs has been believed to be equal without depending on the location of the contaminated area, several researchers report that it is different depending on places quite a little. We measured the energy spectrum of gamma rays in high resolution within an approximately 3-km radius of the FDNPP by using an unmanned helicopter equipped with a LaBr3(Ce) scintillation detector. Then, we analyzed the 134Cs/137Cs ratio in the area from these measured data in detail. The results show that the 134Cs/137Cs ratio is different between the plume trace extending north and the other plume traces. We have obtained valuable data for identification of which radioactive substances were released by individual reactor units.

Verification of the method of average angular response for dose measurement on different detectors

At present most radiation dose meters have serious problems on aspects of energy response and angular response. In order to improve the accuracy of dose measurements, a method of average angular response has been proposed. The method can not only correct the energy response, but also the angular response. This method has been verified on NaI(Tl)(50 mm× 50 mm) scintillation detectors, but has not been proved on other types and sizes of detectors, In this paper the method is also verified for LaBr3(Ce) scintillation detectors and HPGe detector To apply the method, first of all, five detectors are simulated by Geant4 and average angular response values are calculated. Then experiments are performed to get the count rates of full energy peak by standard point source of 137Cs, 60Co and 152Eu. After that the dose values of five detectors are calculated with the method of average angular response. Finally experimental results are got. These results are divided into two groups to analyze the impact of detectors of various types and sizes. The result of the first group shows that the method is appropriate for different types of detector to measure dose, with deviations of less than 5% compared with theoretical values. Moreover, when the detector's energy resolution is better and the count rate of the full energy peak is calculated more precisely, the measured dose can be obtained more precisely. At the same time, the result of the second group illustrates that the method is also suited for different sizes of detectors, with deviations of less than 8% compared with theoretical values.

On-line experiments on rapid detection of radionuclides based on sequential Bayesian analysis

A rapid detection method based on sequential Bayesian analysis provides a new perspective on national security in preventing the smuggling and illegal transportation of nuclear materials. In this paper, a sequential Bayesian analysis system, which mainly consists of a LaBr3(Ce) scintillator detector, a pulse analyzer based on a field-programmable gate array technique, and a sequential Bayesian analysis processor, is developed to directly validate the feasibility of sequential Bayesian analysis. The detection ability of 60Co, 137Cs, 133Ba, and 152Eu for a specific radioactivity is studied and quantified using the maximum detection distance and the equivalent minimum detection activity.

The Generalized Centroid Difference method for lifetime measurements viaγ-γcoincidences using large fast-timing arrays

A novel method for direct electronic “fast-timing” lifetime measurements of nuclear excited states via γ-γ coincidences using an array equipped with N very fast high-resolution LaBr3(Ce) scintillator detectors is presented. The generalized centroid difference method provides two independent “start” and “stop” time spectra obtained without any correction by a superposition of the N(N – 1)/2 calibrated γ-γ time difference spectra of the N detector fast-timing system. The two fast-timing array time spectra correspond to a forward and reverse gating of a specific γ-γ cascade and the centroid difference as the time shift between the centroids of the two time spectra provides a picosecond-sensitive mirror-symmetric observable of the set-up. The energydependent mean prompt response difference between the start and stop events is calibrated and used as a single correction for lifetime determination. These combined fast-timing array mean γ-γ zero-time responses can be determined for 40 keV < Eγ < 1.4 MeV with a precision better than 10 ps using a 152Eu γ-ray source. The new method is described with examples of (n,γ) and (n,f,γ) experiments performed at the intense cold-neutron beam facility PF1B of the Institut Laue-Langevin in Grenoble, France, using 16 LaBr3(Ce) detectors within the EXILL&FATIMA campaign in 2013. The results are discussed with respect to possible systematic errors induced by background contributions.

Digital processing of signals from LaBr3:Ce scintillation detectors

In this paper, we report on the results of digital signal processing of LaBr3(Ce) detectors. The photomultiplier (PMT) output signals from two cylindrical LaBr3(Ce) detectors (1.5′′ diameter and 2′′ tall) were directly digitized with an ultrafast digitizer (sampling rate up to 4 GSample/s and 10-bits resolution) and the energy and timing information were extracted through offline analysis of the pulses. It is shown that at high sampling rates (4 GS/s) a simple integration of pulses is sufficient to reproduce the analogue energy resolution of the detectors (3.5% at 662 keV energy) and by employing a digital version of constant-fraction discrimination (CFD) timing a time resolution of 240 ps (FWHM) is achieved at the energy lines of 60Co. The effects of pulse sampling rate were studied, indicating a degradation of the performance of the detectors with reducing the pulse sampling rate. In particular, it was found that at sampling rates below 1 GS/s, the digital timing can be limited by the aliasing error. By using an anti-aliasing filter, a time resolution of 375 ps (FWHM) and an energy resolution of 3.5% at 662 keV were achieved with a sampling rate of 500 MS/s.

The sensitivity of LaBr3:Ce scintillation detectors to low energy neutrons: Measurement and Monte Carlo simulation

The neutron sensitivity of a cylindrical ⊘1.5in.×1.5in. LaBr3:Ce scintillation detector was measured using quasi-monoenergetic neutron beams in the energy range from 40keV to 2.5MeV. In this energy range the detector is sensitive to γ-rays generated in neutron inelastic and capture processes. The experimental energy response was compared with Monte Carlo simulations performed with the Geant4 simulation toolkit using the so-called High Precision Neutron Models. These models rely on relevant information stored in evaluated nuclear data libraries. The performance of the Geant4 Neutron Data Library as well as several standard nuclear data libraries was investigated. In the latter case this was made possible by the use of a conversion tool that allowed the direct use of the data from other libraries in Geant4. Overall it was found that there was good agreement with experiment for some of the neutron data bases like ENDF/B-VII.0 or JENDL-3.3 but not with the others such as ENDF/B-VI.8 or JEFF-3.1.

A transportable source of gamma rays with discrete energies and wide range for calibration and on-site testing of gamma-ray detectors

We describe a compact and transportable wide energy range, gamma-ray station for the calibration of gamma-ray sensitive devices. The station was specifically designed for the on-site testing and calibration of gamma-ray sensitive spacecraft payloads, intended for space flight on the BepiColombo and SoIar Orbiter missions of the European Space Agency. The source is intended to serve as a calibrated reference for post test center qualification of integrated payload instruments and for preflight evaluation of scientific radiation sensors. Discrete gamma rays in the energy range 100keV–9MeV are produced in the station with reasonable intensity using a radionuclide neutron source and 100l of distilled water with 22kg salt dissolved. The gamma-rays generated contain many discrete lines conveniently evenly distributed over the entire energy range. The neutron and gamma-ray fields have been simulated by Monte Carlo calculations. Results of the numerical calculations are given in the form of neutron and gamma-ray spectra as well as dose equivalent rate. The dose rate was also determined directly by dedicated dosemetric measurements. The gamma-ray field produced in the station was characterized using a conventional HPGe detector. The application of the station is demonstrated by measurements taken with a flight-qualified LaBr3:Ce scintillation detector. Gamma-ray spectra acquired by both detectors are presented. The minimum measuring times for calibration of the flight-version detector, was between 2 and 10min (up to 6.2MeV) and 20–30min (up to 8MeV), when the detector was placed at a distance 2–5m from the station.

Timing and Energy Resolution of new near-UV SiPMs coupled to LaBr3:Ce for TOF-PET.

The high light output and fast decay time of LaBr3:Ce scintillation detectors leads to excellent timing performance. To realize the potential of timing resolution with LaBr3:Ce we have investigated the performance with SiPMs, which enable 1-to-1 coupling to individual crystals, and which have been optimized for the near-ultraviolet (NUV) scintillation light emission of LaBr3:Ce. Coincidence timing resolution (CTR) of 100 ps was measured for a 4×4×5 mm3 LaBr3:30%Ce crystal directly coupled to a large-area 4×4 mm2 NUV-SiPM. Results show very little dependence on temperature, in the range of -20° to 20°C, and bias voltage, from 2 V to 5 V over breakdown. Optimal performance was achieved at an over-voltage (OV) range of 3 V - 5 V, at which high gain and high photon detection efficiency are achieved. Though saturation was evident at 511 keV, an energy resolution of 6.8% was measured after correcting for non-linearity. We also measured a CTR of 110 ps for a 4×4×5mm3 LaBr3:5%Ce crystal and 245 ps for a 4×4×30 mm3 LaBr3:5%Ce crystal using the NUV-SIPM. The poorer timing measurement for the 30-mm long crystal is due mainly to a systematic shift in the time pick-off as a function of the depth-of-interaction. The excellent temperature stability, fast rise time, high gain, and low noise of the NUV-SiPM make it a practical and highly appealing photodetector for the readout of a LaBr3:Ce TOF-PET detector.

On-line 60Co monitor for reactor recirculation system piping in primary containment vessel during reactor operation

Water chemistry control during reactor operation and installation of temporary radiation shielding prior to scheduled outages are carried out in order to reduce workers’ dose exposure caused by 60Co which is the main radiation source during scheduled outages of boiling water reactor (BWR) power plants. It is necessary to monitor the deposited 60Co on inner surfaces of reactor recirculation system (RRS) piping to evaluate effects of water chemistry control. We have developed an on-line 60Co monitor (OLCM) for this purpose. The OLCM applies a pulse integral method as a new method to measure gamma-ray counts of more than 1.0×106 counts per second (cps) and a coincidence counting method to reduce an effect of background gamma rays caused by 16N in the measurement of 60Co cascade gamma rays. Energy resolution at 1.4×106cps is 33keV using the pulse integral method and single LaBr3:Ce scintillation detector. The energy resolutions of this detector using the fast response photo multiplier tube (PMT) are 50keV at 1.5×106cps and 59keV at 2.1×106cps. Furthermore, we measured the energy spectra using the pulse integral method, the coincidence counting method and two LaBr3:Ce scintillation detectors and examined the transition of coincidence counting for 60Co detection under high dose rate during reactor operation at the Kyoto University Research Reactor (KUR). The coincidence counting of 60Co cascade gamma rays could be detected, and the result was average values of 47.9 counts per 40min and standard deviations of 34%, 58.3 counts per 60min and 31%, and 77.3 counts per 80min and 19%. From the results and the environmental conditions in the PCV, it was confirmed that the lower detection limit of 60Co activity per unit area was 2.3×104Bq/cm2 when the measurement frequency was once a month. The OLCM performance can be adjusted based on the measurement frequency and the environmental conditions of the nuclear power plant in which it will be used.

Measurement of radionuclide activities induced in target components of an IBA CYCLONE 18/9 by gamma-ray spectrometry with HPGe and LaBr3: Ce detectors.

Cyclotrons are used worldwide to produce radiopharmaceuticals by proton irradiation of a suitable target. The intense secondary neutron beam generated by proton interactions with the target induce high radionuclide activities in the target assembly parts that may result in an exposure to high dose levels of the operators during maintenance. The main goal of this work is to evaluate gamma-emitting radionuclide activities induced in Havar foils and titanium windows of a target assembly and carousel stripper forks of an IBA CYCLONE 18/9 cyclotron. The knowledge of radionuclide inventory for each component is required by many companies to assess risk for operators before waste handling and disposal. Gamma-ray spectrometric analyses were carried out with High Purity Germanium (HPGe) and Lanthanum bromide (LaBr3:Ce) scintillation detectors. HPGe is the most used detector for its high energy resolution although it is more suitable for use in a laboratory. The use of LaBr3:Ce can be considered a viable option, particularly in realizing a portable spectrometric system to perform "on-site" measurements and a fast dose rate evaluation before the disposal of activated parts. Due to a high activity of target assembly components replaced after a typical irradiation cycle (about 5000 μAh integrated beam current), gamma-ray spectrometric measurements were performed at a large distance from the detector, even more than 100 cm, or by using a purposely realized Lead-walled collimator. The identification of some key-radionuclides allows to evaluate through simple formulations the dose rate behavior for each component as function of decay time from the last irradiation. The knowledge of the dose rate behavior is a significant piece of information to health physicists for waste handling with safety at work. For an Havar™ foil, the dose rate will be reduced to about 1/1,000 of the starting value after a decay period of approximately 4 y (about 1,500 d), with a relatively safety at product disposal work. For a longer time, only long-lived radionuclides (57)Co, (60)Co, and (54)Mn contribute to dose rate.

Development and Calibration of a Real-Time Airborne Radioactivity Monitor Using Gamma-Ray Spectrometry on a Particulate Filter

In this work, we present the development and calibration of a Real-time Airborne Radioactivity Monitor using gamma-ray spectrometry on a particulate Filter (RARM-F) to be used in an automatic environmental radiation surveillance network. The RARM-F collects a constant flow of air that passes across a particulate filter, where airborne aerosols are collected. Then, the filter is faced toward a NaI(Tl) or LaBr3(Ce) scintillation detector that is used for gamma-ray spectrometry. This permits the identification and quantification of airborne radioactive isotopes in real time. The RARM-F was fully calibrated with a combination of experimental data and Monte Carlo simulations. For the simulations, a user code, including a model of the system geometry, was prepared for the EGS5 code system and validated with experimental measurements. The calibration methodology is independent of the scintillation crystal used; however, the measurement capabilities and the performance of the RARM-F are not. Thus, we also discuss some characteristics of the RARM-F when using different crystals.

Stress Analysis and Optimization Design of Pressure Vessel of Underwater Gamma Spectrometer

Pressure vessel makes the underwater gamma spectrometer can operation in underwater environment. In this paper, a kind of cylindrical pressure vessel has been simulated and analyzed using CAD software named Solidworks. Analysis results show the end covers are much thicker than the side wall to satisfy the same design safety factor and the centers of the end covers are the stress concentration areas. Further more, a 2× 2 LaBr3: Ce scintillation detector and a series of pressure vessels with various design safety factors and same inner space have been simulated by Monte Carlo code MCNP. Calculation indicates that the thicker the shell, the lower the detection efficiency. Further more, calculation shows the impact of the pressure vessel on detection efficiency of underwater gamma spectrometer varies with the photon energy. The law is that the higher the photon energy, the lower the influence on the detection efficiency.