Search

In nuclear astrophysics, the nuclides 151 Eu and 153 Eu are both in the path of the s-process, and their (n, γ ) cross sections are important input parameters for the calculation of the nuclear astrophysics network. According to the EXFOR database, the neutron capture cross section of natural europium in the resonance region has not been fully measured. The (n, γ ) cross section of nat Eu was measured using the time-of-flight (TOF) technique at the Back-n white neutron source facility of the China Spallation Neutron Source (CSNS) in the 1 eV–to 500 keV range. Four C 6 D 6 liquid scintillator detectors and pulse height weighting techniques were used to measure prompt γ rays and analyze the data. The results of the analysis were compared with the evaluated data of ENDF/B-VIII.0 and JENDL-5.0. It shows that there are some differences between the measurement results and different evaluated data libraries. The resonance parameters of 151 Eu and 153 Eu were extracted in the 1 eV–150 eV region using the R-Matrix code SAMMY. The accurate Maxwellian-averaged capture cross section (MACS) is derived over the temperature range of the s-process nucleosynthesis model. The result shows that at kT=30 keV, the MACS value of 151 Eu is 3417 ± 297 mb and the value of 153 Eu is 2718 ± 237 mb. [ABSTRACT FROM AUTHOR]

Precise measurement under high counting rates has been a major challenge for γ -ray spectroscopy, where signals generally pile up with each other and their characteristic values are deeply coupled. An off-line pile-up pulse recovery algorithm based on template matching is developed for LaBr 3 scintillation detectors and has been applied to data from China Spallation Neutron Source (CSNS) Back-n white neutron beamline. As an improvement to the traditional Template Matching methods, the predetermined template shape is associated with pulse amplitudes, which is found crucial to achieve the best fitting results. Moreover, a universal strategy of setting the initial values of fitting allows to resolve signals that are separated in time by less than the characteristic rise time. Processing of simulated pulses demonstrates that the lower limit of interval to distinguish successive events is 10 ns, which is a significant improvement to the previous works. The algorithm performs well under a counting rate of 6 × 1 0 7 s−1, and is still effective up to 1 0 8 s−1. Analysis of experimental data indicates that this algorithm recovers over 98% count yield under a counting rates of no more than 4 × 1 0 6 s−1 in this work, providing a more reliable approach to deduce neutron-induced reaction cross sections. [ABSTRACT FROM AUTHOR]

Due to the shortage of the 3He gas and its rapidly increasing price, scintillator detectors, the advantages of which are high spatial resolution and capability of detection in real time, become widely used in many neutron instruments. In this work, a position-sensitive neutron detector consisting of a 6LiF/ZnS scintillation screen and a silicon photomultiplier array linked to a capacitive network to detect the positions of incident neutrons, is constructed and tested. To evaluate the detector performance, a series of neutron beam experiments with the detector prototype were performed in the BL20 at the China Spallation Neutron Source. The spatial resolution was measured, and the energy-selective neutron imaging and Bragg edge measurements of a 316L stainless steel sample were performed. A sub-millimeter spatial resolution could be obtained for the detector prototype under study. The detector with such a high spatial resolution is promising for applications in neutron scattering experimental installations, especially for neutron single-crystal diffractometers. [ABSTRACT FROM AUTHOR]

A 128-channel positron detection system will be constructed at Experimental Muon Source (EMuS) of China Spallation Neutron Source (CSNS) to conduct muon spin rotation/relaxation/resonance ($\mu $ SR) measurements. Each detector channel consists of a scintillator, a light guide, and a photomultiplier tube (PMT). The long light guide is bent to an “L” shape to propagate optical photons from the scintillator to the PMT. A series of Geant4 simulations and experiments has been performed to optimize the light collection performance of the L-bent detector. Geometry deformation induced by the bending process has been well modeled. Simulation results agree with the experimental tests. Accordingly, a novel hybrid wrapping method (scintillator with polytetrafluoroethylene (PTFE) and light guide with aluminum tape) has been developed to improve the amplitude of detector signals greatly. Compared to wrapping the detector with merely PTFE tapes or aluminum tapes, this method leads to an enhancement in light collection efficiency of 73% or 14%, respectively. Two optimally manufactured prototype detectors using the novel wrapping method have been tested at the ISIS Muon Facility. The beam tests demonstrated that the L-bent detectors can precisely measure the behavior of muon spins inside samples. Therefore, the L-bent detector design is competent for $\mu $ SR applications at CSNS/EMuS. [ABSTRACT FROM AUTHOR]

Two inorganic scintillator detectors consisting of Yb:YAG scintillators and photomultiplier tubes, and an oscilloscope were used to studied the neutron sensitivities of Yb:YAG scintillators at the China Spallation Neutron Source (CSNS) Back-n white neutron source. The relative neutron sensitivity curves of two Yb:YAG scintillators in the energy region between 0.5 and 20 MeV were obtained for the first time. As the measured relative neutron sensitivity curves of Yb:YAG scintillators cannot be verified by the Monte Carlo method and there was no referable data, the neutron sensitivity curve of a ST401 scintillator was also studied in the same method and a Geant4 simulation of ST401 scintillator was conducted to verify the experiment method in this paper. The result showed that the experimental and simulation results were approximately consistent between 17–20 MeV, and agreed well between 1–17 MeV. A comparison between the experimental result and references of ST401 scintillator was also applied and the result showed that the curve tendency of the experimental result and references was matched. The above results imply that the measured relative neutron sensitivity curves and the experimental method used herein were reliable. It also demonstrated the feasibility of studying the neutron sensitivity of inorganic scintillator based on the white neutron source. [ABSTRACT FROM AUTHOR]

Terbium doped gadolinium oxysulfide (GOS:Tb) ceramics were successfully fabricated by pre-sintering in vacuum and HIP post-treatment in Ar atmosphere. Ceramic densification in vacuum and HIP was discussed in the detail mainly by relative density and FESEM characterizations. The fabricated GOS:Tb ceramics were translucent with 0.5 mm thickness after HIP post-treatment. Optical and scintillation properties of GOS:Tb ceramics were also investigated. Temperature-dependent X-ray excited spectra were recorded using a homemade XEL spectrometer. Neutron scintillation light output was also measured in China Spallation Neutron Source (CSNS). The light output was measured to be about 284 photons per neutron with different thicknesses of GOS:Tb ceramics. • Highly dense GOS:Tb ceramics were prepared by vacuum sintering combined with HIP post-treatment. • The light output of GOS:Tb ceramic scintillator screen is increased by 23% compared with powder form. • The fabricated GOS:Tb ceramic is very promising for using as scintillator in neutron imaging technology. [ABSTRACT FROM AUTHOR]

Combined photon and neutron radiography can integrate merits of X/gamma-ray radiography and energy-selective neutron radiography and has the potential of simultaneously visualizing objects composed of high-Z materials, low-Z materials and particular isotopes that resonantly absorb neutrons at certain energies. Intense pulsed gamma bursts and wide energy spectrum neutrons at spallation sources provide a unique opportunity to perform such combined radiography research. We present the results of the combined radiography experiments performed at the back-streaming white neutron (back-n) beamline at China Spallation Neutron Source (CSNS). Gamma-ray and energy-selective neutron radiographic images of multi-element samples were taken by an ICCD camera coupled with scintillators using the time of flight (TOF) technique. High-Z (Pb, Au, W, Ta, et al.) components were visualized with the intense gamma-ray bursts. The low-Z (10B) component was confirmed with varied image contrast when neutrons with varied energies were selected. The specific elements ( nat In, 197Au and nat W) were identified with neutrons at corresponding resonant energies. The experimental results prove the potential for simultaneously visualizing and identifying high-Z materials, low-Z materials and particular nuclides via combined X-ray radiography and energy-selective neutron radiography. [ABSTRACT FROM AUTHOR]