Observation of high-energy neutrinos using Cerenkov detectors embedded deep in Antarctic ice

Neutrinos are elementary particles that carry no electric charge and have little mass. As they interact only weakly with other particles, they can penetrate enormous amounts of matter, and therefore have the potential to directly convey astrophysical information from the edge of the Universe and from deep inside the most cataclysmic high-energy regions. The neutrino's great penetrating power, however, also makes this particle difficult to detect. Underground detectors have observed low-energy neutrinos from the Sun and a nearby supernova, as well as neutrinos generated in the Earth's atmosphere. But the very low fluxes of high-energy neutrinos from cosmic sources can be observed only by much larger, expandable detectors in, for example, deep water or ice. Here we report the detection of upwardly propagating atmospheric neutrinos by the ice-based Antarctic muon and neutrino detector array (AMANDA). These results establish a technology with which to build a kilometre-scale neutrino observatory necessary for astrophysical observations.     

An absence of neutrinos associated with cosmic-ray acceleration in γ-ray bursts

Very energetic astrophysical events are required to accelerate cosmic rays to above 10(18)?electronvolts. GRBs (γ-ray bursts) have been proposed as possible candidate sources. In the GRB 'fireball' model, cosmic-ray acceleration should be accompanied by neutrinos produced in the decay of charged pions created in interactions between the high-energy cosmic-ray protons and γ-rays. Previous searches for such neutrinos found none, but the constraints were weak because the sensitivity was at best approximately equal to the predicted flux. Here we report an upper limit on the flux of energetic neutrinos associated with GRBs that is at least a factor of 3.7 below the predictions. This implies either that GRBs are not the only sources of cosmic rays with energies exceeding 10(18)?electronvolts or that the efficiency of neutrino production is much lower than has been predicted.     

天文用阻挡杂质带红外探测器

低温目标红外辐射的灵敏探测和成像在航天和深空探测中具有重要的应用价值.300 K以下低温目标的辐射强度很弱,辐射特征波长位于中远红外区.阻挡杂质带红外探测器是中远红外探测器中重要的一员,具有覆盖波段宽、灵敏度高、暗电流低、抗辐射性能高等优点,能够胜任空间技术和天文探测在中远红外波段探测的苛刻要求.本文以红外天文探测对红外探测器的应用需求作为出发点,主要就国内外红外天文学、红外天文探测器发展概况,阻挡杂质带红外探测器发展历史及其材料、器件结构等方面做了简要综述,并简明扼要地介绍了阻挡杂质带探测器的器件物理模型.     

寻找宇宙中的暗物质

宇宙中存在暗物质已经得到大量天文观测的证实,但关于暗物质粒子的本质我们仍旧一无所知。为了理解暗物质的性质,许多暗物质探测实验正在展开。直接探测实验探测的是暗物质粒子与探测器物质碰撞所留下的信号,而间接探测实验则寻找暗物质湮灭的产物,如高能伽马射线、高能中微子、正电子和反质子等。理解暗物质所产生的这些信号需要我们了解暗物质的微观粒子的性质,同时也需要了解暗物质在星系或星系团中的分布形式等宏观性质。随着更大规模、更高灵敏度的实验不断投入运行,暗物质之谜有可能在不久的将来得以破解。     

追踪宇宙“信使”冲击世纪谜题——高海拔宇宙线观测站简介

 宇宙线的研究具有悠久的历史,取得了许多划时代的发现性成果。但是人类对宇宙线的起源、加速和传播等问题仍存在诸多疑惑。大型高海拔空气簇射观测站（LHAASO）独具高海拔和大规模优势,计划利用多种探测手段开展联合观测,大幅提升对伽马和宇宙线粒子的鉴别能力。LHAASO有望获得史上最高的伽玛探测灵敏度,并在很宽的能量范围内精确测量宇宙线能谱,为宇宙线物理、高能天体物理、宇宙学和新物理学规律研究做出贡献。介绍了LHAASO的探测器结构、性能优势和科学目标。     

硅基阻挡杂质带红外探测材料与器件研究进展

红外探测在天文物理研究领域具有极其重要的应用前景,由于天文深空探测对象的特殊性,对红外探测器的性能要求十分苛刻.阻挡杂质带(BIB)红外探测器,因其具有响应波段宽、噪声低、灵敏度高以及抗辐射性能好等优点,在过去30年中发展成为国际上天文领域首选的红外探测器.BIB红外探测器的探测波长覆盖中红外到远红外波段,它的推广应用促进人类在天文深空探测领域取得了一系列重大的科学成果.我国在BIB红外探测器的研究起步较晚,近年来也取得了较大进展,但是与国际领先水平相比尚有较大差距.本文主要回顾、评述了过去5年多我国在BIB红外探测器领域的研究进展,对BIB红外探测材料及其相应BIB器件的制备工艺、物性表征和光电响应特性,以及表面等离激元对器件光电响应的调控等做了详尽介绍,为我国BIB红外探测器的发展提供参考和实验依据.     

大科学装置与高能宇宙线起源的探索

大科学装置已经成为全球创新系统中具有支撑作用的框架结构,对中国作为一个国家和宇宙线物理作为一个研究领域来说也是一样的.在其一百年发展史中,传统的宇宙线研究并非完全以大科学装置为依托.20世纪80年代以后,为了探索宇宙中微子和极高能宇宙线粒子,那必不可少的巨大中微子灵敏体积和至少上千平方公里的极高能宇宙线探测面积才给这个古老的学科设定了新的标准,而随之提出的几个大科学装置相继建成并在近几十年的宇宙线研究的辉煌成就中占据了核心地位,尤其在甚高能伽马射线天文学.在过去的20年内,中国为发展巡天普查伽马射线源的广延空气簇射技术做出了巨大的努力,成功地运行了ASγ和ARGO-YBJ两个高海拔国际宇宙线实验.现在,我们提出独具特色的高海拔空气簇射测量装置LHAASO的建设计划,建设面积达一平方公里的复合探测器阵列,以多种探测手段的有机组合寻求发现高能宇宙线起源,挑战新世纪里未解之科学难题.凭借其30 TeV以上最高的探测灵敏度,LHAASO将成为整个宇宙线研究领域的支柱项目之一.     

A characteristic size of approximately 10 Mpc for the ionized bubbles at the end of cosmic reionization

The first galaxies to appear in the Universe at redshifts z > 20 created ionized bubbles in the intergalactic medium of neutral hydrogen left over from the Big Bang. The ionized bubbles grew with time, surrounding clusters of dwarf galaxies and eventually overlapped quickly throughout the Universe over a narrow redshift interval near z approximately 6. This event signalled the end of the reionization epoch when the Universe was a billion years old. Measuring the size distribution of the bubbles at their final overlap phase is a focus of forthcoming programmes to observe highly redshifted radio emission from atomic hydrogen. Here we show that the combined constraints of cosmic variance and light travel time imply an observed bubble size at the end of the overlap epoch of approximately 10 physical Mpc, and a scatter in the observed redshift of overlap along different lines-of-sight of approximately 0.15. This scatter is consistent with observational constraints from recent spectroscopic data on the farthest known quasars. This implies that future radio experiments should be tuned to a characteristic angular scale of 0.5 degrees and have a minimum frequency bandwidth of approximately 8 MHz for an optimal detection of 21-cm flux fluctuations near the end of reionization.     

A broadband superconducting detector suitable for use in large arrays

Cryogenic detectors are extremely sensitive and have a wide variety of applications (particularly in astronomy), but are difficult to integrate into large arrays like a modern CCD (charge-coupled device) camera. As current detectors of the cosmic microwave background (CMB) already have sensitivities comparable to the noise arising from the random arrival of CMB photons, the further gains in sensitivity needed to probe the very early Universe will have to arise from large arrays. A similar situation is encountered at other wavelengths. Single-pixel X-ray detectors now have a resolving power of DeltaE < 5 eV for single 6-keV photons, and future X-ray astronomy missions anticipate the need for 1,000-pixel arrays. Here we report the demonstration of a superconducting detector that is easily fabricated and can readily be incorporated into such an array. Its sensitivity is already within an order of magnitude of that needed for CMB observations, and its energy resolution is similarly close to the targets required for future X-ray astronomy missions.     

A velocity dipole in the distribution of radio galaxies

The motion of our Galaxy through the Universe is reflected in a systematic shift in the temperature of the cosmic microwave background-because of the Doppler effect, the temperature of the background is about 0.1 per cent higher in the direction of motion, with a correspondingly lower temperature in the opposite direction. This effect is known as dipole anisotropy. If our standard cosmological model is correct, a related dipole effect should also be present as an enhancement in the surface density of distant galaxies in the direction of motion. The main obstacle to finding this signal is the uneven distribution of galaxies in the local supercluster, which drowns out the small cosmological signal. Here we report a detection of the expected cosmological dipole anisotropy in the distribution of galaxies. We use a survey of radio galaxies that are mainly located at cosmological distances, so the contamination from nearby clusters is small. When local radio galaxies are removed from the sample, the resulting dipole is in the same direction as the temperature anisotropy of the microwave background, and close to the expected amplitude. The result therefore confirms the standard cosmological interpretation of the microwave background.     

GaN金属-半导体-金属紫外光电探测器的研制

用金属有机物化学汽相沉积(MOCVD)方法在蓝宝石衬底上制备了GaN单晶薄膜,并对样品进行X射线衍射和光致发光谱测量.利用GaN样品成功地制备了金属-半导体-金属(MSM)结构GaN紫外光电探测器,并对其I-V特性、光谱响应及击穿电压等性能进行测试和分析.结果表明,探测器在-5 V偏压下的光电流与暗电流之比大于400倍;探测器光响应在352 nm附近达到响应峰值,并在364 nm附近出现截止,即具备可见盲特性;器件的光响应度最好达0.21A/W.     

Detection of low enersy solar neutrinos by a two-phase cryosenic e-bubble detector

A new two-phase cryogenic neutrino detector using electron bubble （e-bubble） specifically in liquid helium is proposed and being developed for real time, high rate measurements of low-energy p-p reac- tion neutrinos from the sun. The e-bubble detector is a time projection chamber-like （TPC） tracking detector. The task of such a neutrino detector is to detect the ionization of the elastically scattered target electrons by incident neutrinos, and then to characterize their energy and direction and to dis- tinguish them from radioactive backgrounds. The ionization signals are expected to be small and hence undergo avalanche amplification in the saturated vapor above the liquid phase by gas electron multi- pliers （GEMs） at high gain. Higher granularity and intrinsically suppressed ion feedback give a good spatial resolution and are the major advantages of this technology. It should be possible to construct such a detector to track charged particles down to 100--200 keV in a massive liquid helium target with fractional millimeter spatial resolution in three-dimensional space, using the GEM-based TPC with a high-resolution CCD camera, for both the electronic and light readout.     

The obscuration by dust of most of the growth of supermassive black holes

Supermassive black holes underwent periods of exponential growth during which we see them as quasars in the distant Universe. The summed emission from these quasars generates the cosmic X-ray background, the spectrum of which has been used to argue that most black-hole growth is obscured. There are clear examples of obscured black-hole growth in the form of 'type-2' quasars, but their numbers are fewer than expected from modelling of the X-ray background. Here we report the direct detection of a population of distant type-2 quasars, which is at least comparable in size to the well-known unobscured type-1 population. We selected objects that have mid-infrared and radio emissions characteristic of quasars, but which are faint at near-infrared and optical wavelengths. We conclude that this population is responsible for most of the black-hole growth in the young Universe and that, throughout cosmic history, black-hole growth occurs in the dusty, gas-rich centres of active galaxies.     

弯曲磁场中相对论性电子辐射的自吸收性质及等离子体影响

根据同步曲率辐射理论，论文推导了真空中和等离子体中弯曲磁场下相对论性电子辐射的自吸收系数，发现真空中同步曲率辐射与同步辐射一样没有负吸收放大作用，而等离子体对辐射谱和自吸收性质有重大影响，存在脉泽放大效应。这些结果有可能对宇宙中多种射电源的射电高亮温度等问题提供可能的解释。     

Study of the Characteristic of Nuclear Interactions Span Knee Region

大气契伦柯夫脉冲波形和光强探测器用于研究跨越宇宙线能谱膝区的核作用特征．结果表明,当跨越膝区时延伸率及相应的核作用参数发生变化．     

一种基于独特型网络的入侵检测方法

为解决神经网络检测方法中检测器需要定期更新、未知攻击检测性能低等问题,利用人工独特型网络的记忆、学习和动态调整能力实现入侵检测.提出一种可用作检测器的多变异模式人工独特型网络,并根据免疫响应原理设计检测算法,使检测器能实时学习新行为特征.仿真结果表明,多变异模式独特型网络检测方法与多层感知器检测方法相比,平均误报率下降了17.43%,未知攻击的平均检测准确率提高了24.17%.     

A median redshift of 2.4 for galaxies bright at submillimetre wavelengths

A significant fraction of the energy emitted in the early Universe came from very luminous galaxies that are largely hidden at optical wavelengths (because of interstellar dust grains); this energy now forms part of the cosmic background radiation at wavelengths near 1 mm (ref. 1). Some submillimetre (submm) galaxies have been resolved from the background radiation, but they have been difficult to study because of instrumental limitations. This has impeded the determination of their redshifts (z), which is a crucial element in understanding their nature and evolution. Here we report spectroscopic redshifts for ten submm galaxies that were identified using high-resolution radio observations. The median redshift for our sample is 2.4, with a quartile range of 1.9-2.8. This population therefore coexists with the peak activity of quasars, suggesting a close relationship between the growth of massive black holes and luminous dusty galaxies. The space density of submm galaxies at redshifts over 2 is about 1,000 times greater than that of similarly luminous galaxies in the present-day Universe, so they represent an important component of star formation at high redshifts.     

基于Pt电极的TiO2紫外探测器研究

针对宽禁带半导体紫外探测器响应不够灵敏和响应度偏低等问题,将具有高功函数的Pt电极引入TiO₂紫外探测器,采用溶胶凝胶法制备了纳米TiO₂薄膜。以金属Pt为电极,采用磁控溅射的方法,将Pt电极溅射在TiO₂纳米薄膜上,制作了MSM (Metal Semiconductor Metal)型紫外探测器件。在5 V偏压下,探测器的暗电流为4.5 nA,260 nm波长光照下的光电流为5.7 μA。在260 nm的紫外光照射下,探测器的响应度达到最大值,约为447A/W,与其他紫外探测器（200 A/W左右）的响应度均值相比有了很大的提升。最后,设计外围电路,制作出功能完整的紫外强度测试仪。实验表明,该探测器成功地解决了传统宽禁带半导体紫外探测器灵敏度及响应度偏低等问题。     

Inscribed matter as an energy-efficient means of communication with an extraterrestrial civilization

It is well known that electromagnetic radiation-radio waves-can in principle be used to communicate over interstellar distances. By contrast, sending physical artefacts has seemed extravagantly wasteful of energy, and imagining human travel between the stars even more so. The key consideration in earlier work, however, was the perceived need for haste. If extraterrestrial civilizations existed within a few tens of light years, radio could be used for two-way communication on timescales comparable to human lifetimes (or at least the longevities of human institutions). Here we show that if haste is unimportant, sending messages inscribed on some material can be strikingly more energy efficient than communicating by electromagnetic waves. Because messages require protection from cosmic radiation and small messages could be difficult to find among the material clutter near a recipient, 'inscribed matter' is most effective for long archival messages (as opposed to potentially short "we exist" announcements). The results suggest that our initial contact with extraterrestrial civilizations may be more likely to occur through physical artefacts-essentially messages in a bottle-than via electromagnetic communication.     

焦平面探测器基型化的优化方法

针对焦平面(FPA)探测器品种规格大量发展的问题,提出焦平面探测器品种优化的技术途径,选取了对焦平面探测器性能及应用敏感的材料、辐射灵敏度、工作温度、可获得性、成本等因素作为品种优化的因素,提出了指导探测器优化的材料选择域、性能定位、规格选择等知识模型,建立了支持探测器定量优选的矩阵数学模型,构建了定性与定量相结合的探测器优选方法,从130多种规格的探测器中优化选取了4个焦平面探测器作为标准基型探测器,4个标准基型探测器可覆盖大部分军事应用.该方法对其它产品的品种优化也有借鉴作用.