Data-driven simultaneous vertex and energy reconstruction for large liquid scintillator detectors

High-precision vertex and energy reconstruction are crucial for large liquid scintillator detectors such as that at the Jiangmen Underground Neutrino Observatory(JUNO),especially for the determination of neutrino mass ordering by analyzing the energy spectrum of reactor neutrinos.This paper presents a data-driven method to obtain a more realistic and accurate expected PMT response of positron events in JUNO and develops a simultaneous vertex and energy reconstruction method that combines the charge and time information of PMTs.For the JUNO detector,the impact of the vertex inaccuracy on the energy resolution is approximately 0.6%.

Event vertex and time reconstruction in large-volume liquid scintillator detectors

Large-volume liquid scintillator detectors with ultra-low background levels have been widely used to study neutrino physics and search for dark matter.Event vertex and event time are not only useful for event selection but also essential for the reconstruction of event energy.In this study,four event vertex and event time reconstruction algorithms using charge and time information collected by photomultiplier tubes were analyzed comprehensively.The effects of photomultiplier tube properties were also investigated.The results indicate that the transit time spread is the main effect degrading the vertex reconstruction,while the effect of dark noise is limited.In addition,when the event is close to the detector boundary,the charge information provides better performance for vertex reconstruction than the time information.

Improvement of machine learning-based vertex reconstruction for large liquid scintillator detectors with multiple types of PMTs

The precise vertex reconstruction for large liquid scintillator detectors is essential.A novel machine learning-based method was successfully developed to reconstruct an event vertex in JUNO.In this study,the performance of machine learning-based vertex reconstruction was further improved by optimizing the input images of neural networks.By separating the information of different types of PMTs and adding the information of the second hit of PMTs,the vertex resolution was improved by approximately 9.4% at 1 MeV and 9.8% at 11 MeV.

Unambiguously Resolving the Potential Neutrino Magnetic Moment Signal at Large Liquid Scintillator Detectors

Non-vanishing electromagnetic properties of neutrinos have been predicted by many theories beyond the Standard Model, and an enhanced neutrino magnetic moment can have profound implications for fundamental physics. The XENON1T experiment recently detected an excess of electron recoil events in the 1–7 keV energy range, which can be compatible with solar neutrino magnetic moment interaction at a most probable value of μ_(v) = 2.1 × 10^(-11)μ_(B).However, tritium backgrounds or solar axion interaction in this energy window are equally plausible causes.Upcoming multi-tonne noble liquid detectors will test these scenarios more in depth, but will continue to face similar ambiguity. We report a unique capability of future large liquid scintillator detectors to help resolve the potential neutrino magnetic moment scenario. With O(100) kton·year exposure of liquid scintillator to solar neutrinos, a sensitivity of μ_(v) < 10^(-11)μ_(B) can be reached at an energy threshold greater than 40 keV, where no tritium or solar axion events but only neutrino magnetic moment signal is still present.

Plastic scintillator detector for qualitative and quantitative measurements of gamma radiation

Background Plastic scintillator detectors are rugged and easily manufactured in desired shape,sizes and response time to gamma radiation is prompt as compared with any other scintillator detectors.Being popular these detectors are used in radiation monitors one of the application to restrict radioactive material movement.These are used in gross counting mode to know the presence of radioactivity.Therefore secondary survey is required to know the nature of the radionuclides.Purpose The feasibility study of Cylindrical Plastic Scintillator Detector(CPSD)was carried out for the qualitative and quantitative assessment of gamma emitting radionuclides.Methods In this work limited gamma spectrometry was carried out using NE110 equivalent cylindrical plastic scintillating material of 5.1 cm diameter and 100 cm long.CPSD is optically coupled to photomultiplier tube(PMT).The detector signal is processed using preamplifier,shaping amplifier and further analysed by a multi channel analyser(MCA).CPSD gamma spectrum consists of Compton continuum and Gaussian shaped Compton edge energy(λ_(e))appearing as Compton maxima energy(λ_(max)).Photon transport simulation is used to characterizeλ_(max) as a signature for radionuclides emitting gamma energy/energies.In case of unresolved gamma energies,it appears as weighted effective Compton maxima energy.The prominent gamma energies observed across nuclear industries are in the energy range 0.03–3 MeV.It is grouped as low energy,intermediate energy,high energy and ultra-high energy window.The simulated spectrum is obtained suing Gaussian broadening parameters deduced from experimentally measured spectrum.The efficiency response function is developed from simulated response of detector to standard gamma sources under known source detector configurations.Results The mono energetic gamma emitting radioisotopes are identified againstλ_(max) from data library.Qualitative analysis of spectrum is used to discriminate artificial radioactive material from naturally occurring radioactive material using gamma photon,corresponding Compton edge and expected Compton maxima in each energy window.The provisional quantitative assessment is carried out using efficiency deduced from response function.The detection efficiency varies within 1%–0.2%for 0.03 to 3 MeV gamma energies.In this study efficiency for ^(137)Cs source is 0.26%with FWHM 0.092 MeV and the results re within 15%for the measured activity.Estimated sensitivity and spectral dose rate coefficient for CPSD are 77 cps/µR/h and 44.29 nGy/kcps respectively.The MDA or MDL of the most prominent radioisotopes used in nuclear industry are estimated.CPSD showed an ability to detect 149 kBq,^(137)Cs radioisotope at 1 m distance.Conclusion CPSD can be utilised for gamma isotope identification with limited gamma spectroscopy tool in contamination and dose rate measurements monitors.

Performance optimization of scintillator neutron detectors for EMD in CSNS

Chinese Spallation Neutron Source(CSNS) has successfully produced its first neutron beam in 28th August 2017. It has been running steadily from March, 2018. According to the construction plan, the engineering materials diffractometer(EMD) will be installed between 2019–2023. This instrument requires the neutron detectors with the cover area near3 m2in two 90° neutron diffraction angle positions, the neutron detecting efficiency is better than 40%@1A, and the spatial resolution is better than 4 mm×200 mm in horizontal and vertical directions respectively. We have developed a onedimensional position-sensitive neutron detector based on the oblique6Li F/Zn S(Ag) scintillators, wavelength shifting fibers,and Si PMs(silicon photomultipliers) readout. The inhomogeneity of the neutron detection efficiency between each pixel and each detector module, which caused by the inconsistency of the wave-length shifting fibers in collecting scintillation photons, needs to be mitigated before the installation. A performance optimization experiment of the detector modules was carried out on the BL20(beam line 20) of CSNS. Using water sample, the neutron beam with Φ5 mm exit hole was dispersed related evenly into the forward space. According to the neutron counts of each pixel of the detector module, the readout electronics threshold of each pixel is adjusted. Compared with the unadjusted detector module, the inhomogeneity of the detection efficiency for the adjusted one has been improved from 69% to 90%. The test result of the diffraction peak of the standard sample Si showed that the adjusted detector module works well.

A preliminary simulation study of influence of backsplash on the plastic scintillator detector design in HERD experiment

Background The plastic scintillator detector(PSD)is one of the detectors in the high energy cosmic radiation detection(HERD)facility,which is designed for gamma-ray detection and a redundant charge measurement.Backsplash will lead to a decrease in PSD’s performance of gamma-ray detection and charge measurement,which should be carefully considered.Purpose Two preliminary segmentation schemes of the PSD and two veto strategies have been proposed to suppress the backsplash effect.In this paper,we focus on the influence of the backsplash caused by gamma rays.The gamma-ray trigger efficiency and identification efficiency were studied in the case of different cell sizes and veto strategies,which can provide guidance on the PSD design.Methods A Monte Carlo simulation based on Geant4 has been performed.To simplify the simulation,the PSD is segmented into 1 cm3 cubes which can be easily aggregated into cells with different sizes during analysis.Results and conclusion Side_Veto can be used as a baseline design of veto strategy,whereas Smart_Veto can be selected as an upgraded design.Both the PSD bar cell with a width of less than 11 cm and the PSD tile cell with a width of less than 20 cm can achieve a sufficiently high gamma-ray trigger efficiency(>80%),which realizes the primary goal of the PSD.Meanwhile,both the PSD bar cell with a width of less than 3 cm and the PSD tile cell with a width of less than 20 cm can ensure a sufficiently high gamma-ray identification efficiency(>80%)for photons up to 800 GeV.

Discrimination of pp solar neutrinos and^(14)C double pile-up events in a large-scale LS detector

As a unique probe,the precision measurement of pp solar neutrinos is important for studying the sun’s energy mechanism as it enables monitoring the thermodynamic equilibrium and studying neutrino oscillations in the vacuum-dominated region.For a large-scale liquid scintillator detector,a bottleneck for pp solar neutrino detection is the pile-up events of intrinsic14C decay.This paper presents a few approaches to discriminating between pp solar neutrinos and ^(14)C pile-up events by considering the differences in their time and spatial distributions.In this study,a Geant4-based Monte Carlo simulation is conducted.Multivariate analysis and deep learning technology are adopted to investigate the capability of ^(14)C pile-up reduction.The BDTG (boosted decision trees with gradient boosting) model and VGG network demonstrate good performance in discriminating pp solar neutrinos and ^(14)C double pile-up events.Under the ^(14)C concentration assumption of 5×10-18g/g,the signal significance can achieve 10.3 and 15.6 using the statistics of only one day.In this case,the signal efficiency for discrimination using the BDTG model while rejecting 99.18% ^(14)C double pile-up events is 51.1%,and that for the case where the VGG network is used while rejecting 99.81%of the ^(14)C double pile-up events is 42.7%.

Calibration and Unfolding of the Pulse Height Spectra of Liquid Scintillator-Based Neutron Detectors Using Photon Sources

An accurate energy calibration of a 5＂× 2＂ BC501A liquid scintillator-based neutron detector by means of photon sources and the unfolding of pulse height spectra are described. The photon responses were measured with 22Na, 137Cs and 54Mn photon sources and simulated using the GRESP code, which was developed at the Physiknlisch Technische Bundesanstalt in Germany. Pulse height spectra produced by three different photon sources were employed to investigate the effects of the unfolding techniques. It was found that the four unfolding codes of the HEPRO and UMG3.3 packages, including GRAVEL, UNFANA, MIEKE and MAXED, performed well with the test spectra and produced generally consistent results. They could therefore be used to obtain neutron energy spectra in toknmak experiments.

Simulation study on performance optimization of a prototype scintillation detector for the GRANDProto35 experiment

As a proposed detector,the giant radio array for neutrino detection(GRAND)is primarily designed to discover and study the origin of ultra-high-energy cosmic rays,with ultra-high-energy neutrinos presenting the main method for detecting ultra-high-energy cosmic rays and their sources.The main principle is to detect radio emissions generated by ultra-high-energy neutrinos interacting with the atmosphere as they travel.GRAND is the largest neutrino detection array to be built in China.GRANDProto35,as the first stage of the GRAND experiment,is a coincidence array composed of radio antennas and a scintillation detector,the latter of which,as a traditional detector,is used to perform cross-validation with radio detection,thus verifying the radio detection efficiency and enabling study of the background exclusion method.This study focused on the implementation of the optimization simulation and experimental testing of the performance of the prototype scintillation detector used in GRANDProto35.A package based on GEANT4 was used to simulate the details of the scintillation detector,including the optical properties of its materials,the height of the light guide box,and position inhomogeneity.The surface of the scintillator and the reflective materials used in the detector was optimized,and the influence of light guide heights and position inhomogeneity on the energy and time resolutions of the detector was studied.According to the simulation study,the number of scintillator photoelectrons increased when changing from the polished surface to the ground surface,with the appropriate design height for the light guide box being 50 cm and the appropriate design area for the scintillator being 0.5 m^(2).The performance of the detector was tested in detail through a coincidence experiment,and the test results showed that the number of photoelectrons collected in the detector was$84 with a time resolution of~1 ns,indicating good performance.The simulation results were consistent with those obtained from the tests,which also verified the reliability of the simulation software.These studies provided a full understanding of the performance of the scintillation detector and guidance for the subsequent operation and analysis of the GRANDProto35 experimental array.

Compact CubeSat Gamma-ray detector for GRID mission

Gamma-Ray Integrated Detectors(GRID)mis-sion is a student project designed to use multiple gamma-ray detectors carried by nanosatellites(CubeSats),forming a full-time all-sky gamma-ray detection network that monitors the transient gamma-ray sky in the multi-mes-senger astronomy era.A compact CubeSat gamma-ray detector,including its hardware and firmware,was designed and implemented for the mission.The detector employs four Gd 2 Al 2 Ga 3 O 12:Ce(GAGG:Ce)scintillators coupled with four silicon photomultiplier(SiPM)arrays to achieve a high gamma-ray detection efficiency between 10 keV and 2 MeV with low power and small dimensions.The first detector designed by the undergraduate student team onboard a commercial CubeSat was launched into a Sun-synchronous orbit on October 29,2018.The detector was in a normal observation state and accumulated data for approximately one month after on-orbit functional and performance tests,which were conducted in 2019.

Design and development of a plastic scintillator based whole body β/γ contamination monitoring system

Plastic scintillation detectors based whole body β/γ contamination monitors are developed for use in radiation facilities.This microcontroller-based multi-detector system uses 13 plastic scintillator detectors,with minimized dead detection zones,monitoring the whole body,and conforming to the contamination limit prescribed by the regulatory authority.This system has the features for monitoring hands,feet,head,and faceβ/γusing contamination monitors and portal exit monitors.It can detect gamma sources at a dose rate of 10 n Gyh^(-1).The system is calibrated using b sources^(90)Sr/^(90)Y,^(204)Tl,and^(36)Cl,and the efficiency is found to be 29%,22%,and 18%,respectively.Theminimumdetectableβ/γcontaminationis0.15 Bqcm^(-2),which is significantly less than the minimum detection objectives on head,face,hands,and feet.

A LN2-based cooling system for a next-generation liquid xenon dark matter detector

In recent years, cooling technology for liquid xenon(LXe) detectors has advanced driven by the development of dark matter(DM) detectors with target mass in the 100–1000 kg range. The next generation of DM detectors based on LXe will be in the 50,000 kg(50 t)range requiring more than 1 k W of cooling power. Most of the prior cooling methods become impractical at this level.For cooling a 50 t scale LXe detector, a method is proposed in which liquid nitrogen(LN2) in a small local reservoir cools the xenon gas via a cold finger. The cold finger incorporates a heating unit to provide temperature regulation. The proposed cooling method is simple, reliable, and suitable for the required long-term operation for a rare event search. The device can be easily integrated into present cooling systems, for example the ‘‘Cooling Bus’ ’employed for the Panda X I and II experiments. It is still possible to cool indirectly with no part of the cooling or temperature control system getting in direct contact with the clean xenon in the detector. Also, the cooling device can be mounted at a large distance, i.e., the detector is cooled remotely from a distance of 5–10 m. The method was tested in a laboratory setup at Columbia University to carry out different measurements with a small LXe detector and behaved exactly as predicted.

HPGe and Scintillation Detectors Comparisons on Waste Drums Radioactivity Measurement

Two measurement systems, one being comprised of three HPGe detectors and the other being a 4π measurement system of the assembly of 10 sets of scintillation detectors, were compared for their measurement performance in operations of radioactive waste drum radioactivity measurement and clearance and release operation of decommissioning. The system features of the former were high costs, capable of identifying radionuclides, a measurement time of about 1000 sec. The system features of the latter were high sensibility, capable of identifying hotspots, a measurement time of about 100 sec. Various comparisons were made for the differences of the two systems on reference drums, whole-drum homogeneous and non-homogeneous metal drums and non-metal drums, whole-drums of different filling rates. The aim was to compare the differences of the two measurement systems in measuring radioactivity of critical radionuclides of 137Cs, 54Mn and 60Co.

Direct Analytical Method to Calculate Photopeak Efficiency and Photopeak Attenuation Coefficient of NaI(Tl) Well-Type Detector

In this paper full-energy peak (photopeak) efficiency and photopeak attenuation coefficient of 3'' × 3'' NaI(Tl) well-type scintillation detector were calculated using gamma-rayisotropic radiating point sources (with photon energy: 0.245, 0.344, 0.662, 0.779, 0.964, 1.1732, 1.333 and 1.408 MeV) placed outside the detector well. These energies were obtained from 152Eu, 137Cs and 60Co. The relations between the full energy peak efficiency and photopeak attenuation coefficients, were plotted vs. photon energy at different sources to detector distance, and it found that the full energy peak efficiency decreased by increasing the distance between the source and the detector.

Advances in nuclear detection and readout techniques

“A Craftsman Must Sharpen His Tools to Do His Job,”said Confucius.Nuclear detection and readout techniques are the foundation of particle physics,nuclear physics,and particle astrophysics to reveal the nature of the universe.Also,they are being increasingly used in other disciplines like nuclear power generation,life sciences,environmental sciences,medical sciences,etc.The article reviews the short history,recent development,and trend of nuclear detection and readout techniques,covering Semiconductor Detector,Gaseous Detector,Scintillation Detector,Cherenkov Detector,Transition Radiation Detector,and Readout Techniques.By explaining the principle and using examples,we hope to help the interested reader underst and this research field and bring exciting information to the community.

FPGA implementation of 500-MHz high-count-rate high-time-resolution real-time digital neutron-gamma discrimination for fast liquid detectors

Fast neutron flux measurements with high count rates and high time resolution have important applications in equipment such as tokamaks.In this study,real-time neutron and gamma discrimination was implemented on a self-developed 500-Msps,12-bit digitizer,and the neutron and gamma spectra were calculated directly on an FPGA.A fast neutron flux measurement system with BC-501A and EJ-309 liquid scintillator detectors was developed and a fast neutron measurement experiment was successfully performed on the HL-2 M tokamak at the Southwestern Institute of Physics,China.The experimental results demonstrated that the system obtained the neutron and gamma spectra with a time accuracy of 1 ms.At count rates of up to 1 Mcps,the figure of merit was greater than 1.05 for energies between 50 keV and 2.8 MeV.

Simulation study on cosmic ray background at large zenith angle based on GRANDProto35 coincidence array experiment

Neutrino detection in the 100 PeV energy region is the ultimate means of studying the origin of ultra-highenergy cosmic rays,in which the large radio detection array giant radio array for neutrino detection(GRAND)project aims to use to decipher this century-old problem.The GRANDProto35 compact array is a microform of 35 radio prototype detectors for the GRAND experiment,which verifies the reliability of GRAND performance through operation,and data analysis of the prototype detectors.As radio detectors are a novel development in recent years,and their indexes need to be verified by traditional detectors,the GRAND Cooperation Group designed and constructed the GRANDProto35 coincidence array composed of radio detectors and scintillation detectors.This study simulated the changes in detection efficiency,effective area,and event rate of cosmic rays with zenith angle based on this coincidence array.The study found that the 1017 eV energy region is sensitive to GRANDProto35 detection.When the energy exceeded 1017 eV,the array detection efficiency could reach more than 95%and the effective area was up to*29106 m2.A simulation study on cosmic ray events with large zenith angles showed that the event rate detected by the array decreased significantly with increasing zenith angle,and the event rate of cosmic rays was approximately 0.1 per day for a zenith angle of 75.This serves as the background pollution rate for neutrino observation caused by largeangle cosmic-ray events,providing an important reference for further experiments.The study results will be verified after the joint operation of the coincidence array.

Study of a position-sensitive scintillator neutron detector

The investigation of a novel thermal neutron detector is developed to fulfill the requirements of the high intensity power diffractometer （HIPD） at the Chinese Spallation Neutron Source （CSNS）. It consists of two layers of 6LiF/ZnS（Ag） scintillators, two layers of crossed WLSF arrays, several multi-anode photo multiplier tubes （MA-PMT）, and the matching readout electronics. The neutron detection efficiency of the scintilltors, the light transportation ability of the WLSF, and the spatial linearity of the readout electronics are measured and discussed in this paper. It shows that the sandwich structure and the compact readout electronics could fulfill the needs of the HIPD. A prototype with a 10 cm×10 cm sensitive area has been constructed to further study the characteristics of the neutron scintillator detector.

In-situ evaluation for activated concrete in accelerator facility with scintillation-type gamma-ray spectrometer

The assessment of activated concrete is particularly difficult during the decommissioning of an accelerator facility.Destructive analysis by core boring is the only method of investigating the activity of concrete material.To address this problem,an in-situ and nondestructive analysis method was developed to determineγ-ray-emitting nuclides and their specific activities in the concrete walls and floor by using a portable germanium semiconductor detector.In this work,we examined a substitute for Ge detector to establish a simpler and more convenient method.As candidates,we focused on some scintillation type spectrometers,and the possibility of a substitute for a Ge detector was examined by both simulation and experiment.The detection limits were roughly estimated through Monte Carlo simulation for various scintillation crystals,and it was found that 1.5-inch LaBr3,CeBr3,and SrI2 could distinguish the clearance level.It was confirmed that the 1.5-inch LaBr3 could reproduce the calibration curve of the Ge detector in the experiment.The required thickness and length of the radiation shield for suppressing the background radiation during the measurement was also determined for the convenience of an actual decommissioning work.