Application of an acrylic vessel supported by a stainless-steel truss for the JUNO central detector

After the success of the Daya Bay experiment, the Jiangmen Underground Neutrino Observatory （JUNO） was launched to measure neutrino-mass hierarchy and oscillation parameters and to study other neutrino physics. Its central detector is set for antineutrinos from reactors, the Earth, the atmosphere, and the Sun. The main requirements of the central detector are con- tainment of 20 kt of liquid scintillator, as the target mass, and 3% energy resolution. It is about a ball-shape detector of 38.5 m with -75% coverage of PMT on its inner surface. The design of such a huge detector is a big challenge because it must meet the requirements for several different types of physics measurement and possess the feasibility and reliability in its structure and engineering, all at reasonable time and cost. One option for the JUNO central detector is a hyper-scale acrylic ball sub- merged in the water to shield the background. This paper proposes a structural scheme for such an acrylic ball that is supported by a stainless-steel truss, inspired by point-supported glass-curtain walls in civil engineering. The preliminary design of the scheme is completed and verified by finite element （FE） method using ABAQUS. FE analysis shows that the scheme can con- trol the stress level of the acrylic ball within the limit of 5 to 10 MPa, in accordance with the demand of the design objective of the central detector. The scheme is of outstanding global stability and allows various chocces on local connections. We prove that the scheme is of good feasibility and should be a reasonable option for the central detector.

Muon tracking with the fastest light in the JUNO central detector

Background:The Jiangmen Underground Neutrino Observatory(JUNO)is a multi-purpose neutrino experiment designed to measure the neutrino mass hierarchy using a central detector(CD),which contains 20 kton liquid scintillator(LS)surrounded by about 18,000 photomultiplier tubes(PMTs),located 700 m underground.Purpose:The rate of cosmic muons reaching the JUNO detector is about 3 Hz,and the muon-induced neutrons and isotopes are major backgrounds for the neutrino detection.Reconstruction of the muon trajectory in the detector is crucial for the study and rejection of those backgrounds.Methods:This paper will introduce the muon-tracking algorithm in the JUNO CD,with a least-squares method of PMTs’first-hit time(FHT).Correction of the FHT for each PMT was found to be important to reduce the reconstruction bias.Results:The spatial resolution and angular resolution are better than 3 cm and 0.4 degree,respectively,and the tracking efficiency is greater than 90%up to 16 m far from the detector center.

The measurement system of acrylic transmittance for the JUNO central detector

Background The Jiangmen Underground Neutrino Observatory(JUNO)has 20 kilo-ton liquid scintillator as target mass contained by a huge acrylic sphere to carry out the research on neutrino physics.Acrylic transmittance is considered as an important optical performance of the JUNO Central Detector as it has a direct relationship to the number of photons detected by the JUNO Central Detector and further affects the energy resolution of JUNO.Motivation The transmittance requirement of acrylic spherical panel for the JUNO Central Detector is exceeding 96%at the wavelength of 420 nm in ultrapure water and a specific measurement system was built and studied in Institute of High Energy Physics for this purpose,as the existing equipment cannot perform the sample test in the liquid and support the long sample length of 120 mm.Methods After improving the technology of thermoforming,the transmittances of the acrylic spherical panels meet the requirement of JUNO,which guarantees the batch production of acrylic panels on time.The design of the measurement system,the constitution of hardware,the development of control and data acquisition software are introduced,and the measurement uncertainty of the system and the transmittance results of the acrylic samples from the spherical panel are discussed in this article.

Thermal reliability analysis of the central detector of JUNO

Introduction The Jiangmen Underground Neutrino Observatory(JUNO)is a multipurpose neutrino experiment designed to determine neutrino mass hierarchy,precisely measure oscillation parameters and study solar neutrinos,supernova neutrinos and geo-neutrinos,etc.The central detector(CD)of JUNO has 20,000 tons liquid scintillator as target mass,which contains inside a huge acrylic sphere with inner diameter of 35.4 m,supported by a stainless steel structure.The whole structure of CD will be installed inside a cylindrical water pool,and the acrylic sphere will be submerged in the center of water pool.The operating temperature of CD is designed to be 21℃ as long as over 20 years,which is determined by the mechanical requirement of the structure and physics consideration.Methods For this operating temperature,a special cooling system will be used to maintain the temperature inside the water pool.The main structure of CD is composed of acrylic and stainless steel,and they have much different thermal expansion coefficients,strengths and life times.Change in temperature may affect the safety of CD.As part of reliability analysis,the effect of cooling system failure on the CD is considered,and finite element method is used in our thermal calculation.In this article,the temperature fields before and after cooling system failure are calculated and analyzed,and the temperatures of different locations of water pool after cooling system failure are compared and discussed in detail.

Fast muon simulation in the JUNO central detector

The Jiangmen Underground Neutrino Observatory （JUNO） is a multi-purpose neutrino experiment designed to measure the neutrino mass hierarchy using a central detector （CD）, which contains 20 kton liquid scintillator （LS） surrounded by about 17000 photomultiplier tubes （PMTs）. Due to the large fiducial volume and huge number of PMTs, the simulation of a muon particle passing through the CD with the Geant4 toolkit becomes an extremely computation-intensive task. This paper presents a fast simulation implementation using a so-called voxel method： for scintillation photons generated in a certain LS voxel, the PMT＇s response is produced beforehand with Geant4 and then introduced into the simulation at runtime. This parameterisation method successfully speeds up the most CPU consuming process, the optical photon＇s propagation in the LS, by a factor of 50. In the paper, the comparison of physics performance between fast and full simulation is also given.

Research on the measurement of connecting bars'axial force of JUNO central detector

Background The Jiangmen Underground Neutrino Observatory(JUNO)is a multipurpose neutrino experiment designed to determine neutrino mass hierarchy and precisely measure oscillation parameters and study the solar neutrino,supernova neutrino,geo-neutrino,etc.JUNO's central detector(CD)has 20 kilo-ton liquid scintillator as target mass,which is contained by a huge acrylic sphere with the inner diameter of 35.4 m,and the acrylic sphere is supported by a stainless steel structure through 590 connecting bars.Motivation Part of the connecting bars bear pull force and the other bars bear push force.There is a direct relationship between the stress of connecting bars and that of acrylic sphere.For the installation process of the CD,the pretightening force and axial force of the connecting bars should be monitored with accuracy,and for the filling process and running condition,the precise measurement of axial force can indicate the safety of structure of the CD.Methods Statistical method was used to evaluate the performance of measurement schemes,and 4-fiber Bragg grating measurement scheme was determined to be the final scheme,which can get the measurement uncertainty better than 0.7 kN.Performance of different measurement schemes are discussed in detail,and some related finite element analysis and evalu-ation method are also introduced in this paper.

Study on acrylic transmittance for JUNO Central Detector

Background The Central Detector(CD)of the Jiangmen Underground Neutrino Observatory(JUNO)uses 20,000 tons of liquid scintillator as target mass,and the design value of energy resolution of neutrino is 3%at 1 meV.Acrylic transmittance is an important parameter for CD in order to maximize the detection of scintillating photons.Motivation The composition and processing techniques of acrylic can surely affect its transmittance.How the composition,thermoforming temperature,heat preservation time and surface treatment process of acrylic affect its transmittance was measured and analyzed.Methods According to these studies,JUNO determined its special acrylic composition and processing techniques:no components of plasticizer or anti-UV in the composition,decreasing the time span and temperature during the demolding of flat panel,and adopting suitable thermoforming temperature of spherical panel.Results Finally,the preproduction of spherical acrylic panels meets the JUNO requirement confirming a transmittance in ultrapure water greater than 96%at the wavelength of 420 nm.

Structure design and load test of the small prototype for the JUNO Central Detector

Introduction The structure of the Jiangmen Underground Neutrino Observatory(JUNO)CentralDetector(CD)was designed using finite element methods(FEM).The structure of the small JUNOCDprototypewas also designed using the same structural scheme and method as those of the CD,and the load test was carried out after the accomplishment of structure design and manufacturing.Methods The load test can help verify the performance and reliability of the mechanical monitoring system and liquid filling system of the CD,verify the consistency of FEM calculations and axial force measurement results of the sensors,and accumulate experience for the installation of the connecting bars.Conclusion The measurement scheme was considered and determined,and the connecting bars’axial forces under different liquid filling conditions were measured and compared with the FEM results,the consistencies of which were good.The mechanical monitoring system and liquid filling system of theCDwere verified during the load test,which met the requirements of design and experiment.

The design of the small prototype for the central detector of JUNO

Background The Jiangmen Underground Neutrino Observatory(JUNO)is a multipurpose neutrino experiment designed to determine neutrino mass hierarchy,precisely measure oscillation parameters and study solar neutrinos,supernova neutrinos and geo-neutrinos.The JUNO Central Detector 20 kton liquid scintillator target mass is contained by a huge acrylic sphere with a 35.4 m inner diameter,supported by a stainless steel structure,and the sphere is eventually submerged in pure water.Motivation Before the JUNO Central Detector is built,a small prototype has been designed and static loading experiments will be carried out to verify the consistency of the finite-element calculations and static loading experiments and test the subsystems performances,such as the monitoring system and liquid scintillator filling system.Methods The small prototype is composed of an acrylic sphere with a 3 m inner diameter and an aluminum alloy support structure.In this article,the structure of the small prototype is briefly described.A detailed simulation study using finite element analysis is conducted to account for liquid-filled condition,temperature variation and existence of high load(due to vacuum pumping)and demonstrate a satisfying mechanical performance of the small prototype.The experimental plan about the prototype on the basis of the simulation will also be mentioned.

近30年来滇中城市群生态用地变化轨迹时空演变特征及其驱动机制

[目的]生态用地在维持生态平衡和支撑经济发展方面发挥着重要作用。研究滇中城市群生态用地的时空演变特征和驱动机制对优化生态安全格局、推进云南生态文明建设、筑牢国家西南生态安全屏障具有重要现实意义。[方法]利用Google Earth Engine(GEE)云平台对滇中城市群1990—2020年生态用地进行识别的基础上,采用变化轨迹分析、热点分析和地理探测器对滇中城市群生态用地时空变化轨迹和驱动机制进行了探索。[结果](1)滇中城市群生态用地变化以非生态用地与林地互换为主,并集中发生在林地和非生态用地的过渡地带,而生态用地内部之间(林地和草地)的转换主要发生在研究区北部和南部的山地区域。(2)生态用地变化以低频次变化为主,高频次较少,频次变化在元江干热河谷、金沙江干热河谷区域、滇东滇东南喀斯特地带表现出明显的聚集效应。(3)耕地面积变化是影响滇中城市群生态用地变化的主要驱动力,社会经济因素对生态用地的影响力显著高于自然因素,在自然环境、耕地扩张、生态修复政策等多重驱动下,多因子交互作用对生态用地变化更具解释力。[结论]滇中城市群生态用地破碎,自然环境的改变和人类活动的日益增强极易导致生态用地发生变化,亟需分区域合理制定生态保护措施,筑牢国家西南生态安全屏障。

基于Geodetector的滇中岩溶区石漠化空间分布特征及影响因子分析

为探究滇中岩溶区石漠化在不同影响因子上的空间分布特征以及对影响因子定量归因,基于Landsat、DEM等遥感数据和社会经济数据,结合RS-GIS技术和地理探测器模型(Geodetector)获取石漠化信息和各影响因子的贡献率。结果表明:(1)滇中岩溶区石漠化总面积为3015.04 km^(2),占研究区总土地面积的5%,占岩溶面积的13.36%。(2)在不同岩性中,石漠化主要分布在碳酸盐岩与碎屑岩中,占总石漠化面积的62%;在不同土地利用方式中,石漠化主要分布在草地,占总石漠化面积的48.62%;在不同坡度下,石漠化主要分布在8°-15°范围内,占总石漠化面积的32.01%;从人口密度和第一生产总值看,石漠化主要分布在100-200人/km^(2)和>40×10^(8)元范围内,占总石漠化面积的比例分别为54.77%和44.33%。(3)地理探测器揭示了滇中岩溶区石漠化驱动因子的权重大小为:土地利用(q=0.42)>坡度(q=0.29)>岩性(q=0.17)>第一生产总值(q=0.14)>人口密度(q=0.14);交互探测器揭示了2个因子共同作用时,对石漠化形成的贡献率最大的是土地利用和坡度(q=0.58),其次是土地利用和岩性(q=0.50)。研究区石漠化在不同影响因子上的分布具有显著差异,人为和自然因素中最显著的影响因子分别是土地利用类型和坡度。

A practical image reconstruction and processing method for symmetrically off-center detector CBCT system

CBCT scanners have been widely used in angiography,radiotherapy guidance,mammography and oral maxillofacial imaging.To cut detector size,reduce manufacturing costs and radiation dose while keeping a reasonable FOV,the flat panel detector can be placed off-center horizontally.This scanning configuration extends the FOV effectively.However,each projection is transversely truncated,bringing errors and artifacts in reconstruction.In this paper,a simple but practical method is proposed for this scanning geometry based on truncation compensation and the modified FDK algorithm.Numerical simulations with jaw phantom were conducted to evaluate the accuracy and practicability of the proposed method.A novel CBCT system for maxillofacial imaging is used for clinical test,which is equipped with an off-center small size flat panel detector.Results show that reconstruction accuracy is acceptable for clinical use,and the image quality appears sufficient for specific diagnostic requirements.It provides a novel solution for clinical CBCT system,in order to reduce radiation dose and manufacturing cost.

基于面向对象分割的耕地集中连片经营分布提取及其影响因素研究——以大同市云州区四乡镇为例

为探讨如何促进耕地集中连片与规模经营,本研究基于第三次土地调查耕地图斑、Google Earth高分辨率遥感影像和实地调研的问卷数据,以大同市云州区四乡镇为研究对象,采用面向对象的分割方法对耕地斑块进行分割,得到耕地经营斑块,运用景观格局软件Fragstats 4.2、统计软件SPSS及地理探测器模型,分析了云州区四乡镇的耕地集中连片经营空间分布现状以及主要影响因素。结果表明:云州区四乡镇位于大同盆地腹地,地势平坦,聚合度指数均大于80,整体耕地斑块分布较为集中,耕地集中连片聚类分析结果表明第Ⅲ、Ⅳ类的耕地面积占比较大,共占58.63%。影响因子对耕地集中连片经营的影响力度从大到小依次为耕地流转率、黄花菜面积占比、人均收入、高等学历人数占比、纯农型农户占比、合作社数量、收入来源,其分异决定力指标(q值)均在0.1以上,交互作用探测结果呈现非线性增强为主、双因子增强为辅,黄花菜种植面积占比与合作社数量的交互作用影响最为显著,凸显了黄花菜种植面积的驱动作用。研究表明,耕地的有效流转、黄花菜的种植和合作社的建立促进了耕地集中连片经营。

基于POI数据的城市用地功能时空格局演变与驱动力研究——以长株潭中心城区为例

城市用地功能时空格局演变研究对优化调整城市土地利用结构具有重要意义。本文基于长株潭中心城区2014年、2018年及2022年兴趣点(POI)数据,运用词频-逆文本频率指数模型算法、标准差椭圆分析法、核密度分析法,利用地理信息系统(GIS)软件对城市功能用地空间格局进行识别与特征分析,进而运用地理探测器对长株潭中心城区功能空间驱动力进行探测。结果表明:长株潭中心城区单一功能用地和混合功能用地数量都在逐年增多,且单一功能用地数量始终多于混合功能用地数量;长株潭中心城区城市功能用地大致呈现“多核心—外围”分布格局,研究区南部和北部存在明显差异;长株潭中心城区城市用地功能空间分布是多种驱动力综合作用的结果,行政中心坐标因子的影响力最大,而双因子交互呈现不同程度的双因子增强和非线性增强,自然环境和区位条件平均交互作用的解释力较强。

基于多源数据的商业空间格局及影响因素分析——以珠海市中心城区为例

为了了解珠海市商业空间分布现状,基于多源数据,运用核密度和热点分析等方法,识别珠海市中心城区的商业空间格局形态,并利用地理探测器对其影响因素进行分析.结果表明:(1)珠海市中心城区的商业空间格局呈现“多中心、多层次”的形态,环绕板障山形成八大商圈;(2)商业设施热点区总体呈“双核心,多层级”分布,不同类型设施表现为“单核心”和“双核心”2种分布特征,其中购物、餐饮和生活服务等热点区呈现“双核心”式分布,住宿、商务及金融保险服务等热点区呈现“单核心”式分布;(3)路网密度是影响研究区商业格局的主要因素,不同类型商业设施空间格局的影响因素存在差异.

云台扫描式激光可燃气体探测器在天然气站场的应用与实践

随着油气管道运营单位集中监视运行模式的推广,单位对于露天工艺区气体发生泄漏的实时检测要求大大提升。在站场的非巡检时段,若天然气泄漏不能及时报警,将引发十分严重的后果。因此,亟须一种安全、经济、可靠、准确的泄漏检测手段提供检测报警,并将报警信息通过区域化在各站控系统及集团公司主生产调度室显示,供生产、调度人员决策。

线阵InGaAs扫描FBG反射谱的传感解调方法

研究并实现了一种基于256像元线阵In Ga As扫描的光纤布拉格光栅传感解调系统。针对线阵In Ga As探测器,分析了光纤光栅反射谱中心波长定位原理,可实现多个FBG光谱的同时解调,单通道解调传感器数量取决于FBG的带宽和中心波长漂移范围。对256个像素点的光谱数据,通过设置的阈值判断反射谱的个数,分别对每一个谱峰进行拟合,基于高斯指数曲线模型实现了寻峰算法,获得了中心波长。搭建FBG解调系统采集光谱数据,寻峰算法的稳定性达到±0.5 pm。该解调方法无机械移动部件,实现了多光纤光栅波长寻峰的并行快速响应,波长解调范围为1 525~1 570 nm,为多光纤光栅传感提供了高速解调方案。

CT静脉血管成像在中心静脉导管功能障碍中的应用

目的探讨多层CT静脉血管成像(multi-detector computed tomography venography,MDCTV)在中心静脉导管功能障碍评估中的应用价值。方法中心静脉导管动能障碍但胸片及颈内静脉超声无异常发现的患者31例,行MDCTV观察导管走形、中心静脉狭窄、血栓形成、纤维蛋白鞘形成等。结果 MDCTV示导管位置异常10例,中心静脉狭窄5例,中心静脉血栓形成4例(2例伴有颈内静脉血栓形成),管周纤维鞘形成7例,无明显异常者5例。结论 MDCTV可有效评估中心静脉导管功能障碍,有临床推广价值。

县域中心城区的扩张及其驱动力——以山西省灵丘县为例

以速度、强度、分形维数和空间重心等指数分析了1980—2018年灵丘县中心城区的时空演变特征,并运用地理探测器识别城镇扩张的驱动因素.结果表明,1980—2018年间灵丘县城镇建设用地呈快速扩张趋势,由1980年的173.69 hm^(2)增长到2018年的1180.57 hm^(2),扩张规模近7倍,分时段研究显示,城镇扩张的速度和强度均在2000—2010年达到最大值;在空间上呈现出向东、西、北3个方向的扩张,形态规则度在2000—2010年间有较大波动,中心城区重心向北部移动明显;对中心城区扩张影响最大的因子为到城镇中心的距离,其次为综合医院和路网密度,自然环境对城镇扩张的影响力较弱;不同因子之间产生交互作用,表现为双因子增强和非线性增强,其中,距城镇中心距离和距耕地距离与其他因子交互后影响力增强显著.

探测器性能研究

大亚湾中微子实验是一个异地建设的实验,中心探测器和反符合探测器的运行和维护要采取现场值班监控、远程网络检查相结合的办法,oncall人员要及时跟踪关键监测数据,准备各种配件、部件、仪器和设备,以备有问题时及时更换。大亚湾实验探测器由两部分构成：一是探测反应堆反电子中微子的中微子探测器,即“中心探测器”;二是探测宇宙线本底的μ子探测器,即“反符合系统”。反符合系统包括两个独立的探测器：阻性板探测器（RPC）和水切伦科夫探测器,可以相互检验并联合确定μ子探测效率。水切伦科夫探测器选择纯净水作为介质,在探测宇宙线μ子的同时作为屏蔽介质,中心探测器置于其中。对于远点有四个中心探测器模块,对于两个近点有两个中心探测器模块。阻性板探测器（RPC）放置于水切仑科夫探测器上方,由多个模块交叠铺放以放置探测死区,每个模块内有4层阻性板探测器。探测器的优异性能是高水平物理研究的基础。为保证高质量的数据,需要长期运行和维护探测器,理解探测器响应,通过数据分析研究并提升探测器性能。关于探测器性能的研究,我们将采取实验获取数据、刻度数据和计算机模拟相结合进行分析的方法。大亚湾的探测器从时间上要运行5~10年,从空间上包括3个厅的多个探测器,所以,我们也将从时间和空间上进行比对研究。关于液闪的研究,我们将把研究对象分为两类进行不同研究：一是已经安装入探测器的液闪,这个我们要跟踪分析其性能的变化;二是安装探测器后剩余的液闪和小模型试验的液闪,我们可以进行独立的物理化学性能研究。