MRI: Development of a High-Resolution Gamma Ray Spectrometer for Time Resolved Temperature Measurements of Confined Positronium.

意义广泛。正电子是一种奇异的物质--反物质原子，由一个电子与其反粒子--正电子结合而成。加州大学河滨分校的科学家们将开发一种新型仪器，用于测量正电子发射的光(光子)粒子。该仪器(光谱仪)将具有商业上可用的能力之外的能力，并将允许科学家测量正电子原子大爆发的温度作为时间的函数。这台新的光谱仪将成为生产和观测“玻色-爱因斯坦凝聚态”中致密的冷态正电子气体的技术。这种不同寻常的物质状态将是一种集中的能量来源，可能会导致各种应用，包括一种新型的激光。该光谱仪将与来自世界各地的科学家合作，用于各种应用中，这些科学家需要在短时间尺度上测量辐射损伤，获得有关材料结构的信息，并测量等离子体的密度和温度。技术说明。该仪器是一台高角度分辨率、多探测器双伽马湮没角相关能谱仪，将测量正电子原子在单重态湮灭时的速度分布。单个探测器的时间和双脉冲分辨率将远远小于正电子的~100 ns湮灭寿命，从而能够有效地测量正电子原子在微腔和多孔材料中形成后作为时间函数的大爆发的温度和热化率。该仪器的主要功能将是测量稠密正电子气体在经历向玻色-爱因斯坦凝聚态(BEC)的相变时的低动量分量的幅度。使用穿透湮没伽马辐射作为诊断，允许外部访问这些实验所需设备内部深处的湮没电子-正电子对的动量分布。测量将不受正电子形成靶的局部条件的影响，例如壁面或粒子间相互作用，而光学光谱学则不是这样。拟议的能谱仪的综合能力将有利于使用与BEC无关的致密冷正电子的其他正电子应用。特别是，测量正电子的热化率将有助于分子筛和低k电介质等多孔材料的正电子表征，而且在短时间尺度上测量低动量湮灭的能力可能有助于评估聚变反应堆所用材料的损害。

Broad significance. Positronium is an exotic matter-antimatter atom composed of an electron bound to its antiparticle, the positron. Scientists at the University of California Riverside will develop a new type of instrument that will measure the particles of light (photons) that are emitted by the positronium. The instrument (spectrometer) will have capabilities beyond those commercially available and will allow scientists to measure the temperature of large bursts of positronium atoms as a function of time. The new spectrometer will be the enabling technology leading to the production and observation of a dense gas of cold positronium in the "Bose-Einstein condensed state". This unusual state of matter will be a concentrated energy source which may lead to a variety of applications, including a new type of laser. The spectrometer will be used in a variety of applications in collaboration with scientists from around the world who need to measure radiation damage on short times scales, obtain information about the structure of materials, and measure the densities and temperatures of plasmas. Technical description. The proposed instrument is a high angular resolution, multi-detector two-gamma annihilation angular correlation spectrometer that will measure the velocity distribution of positronium atoms annihilating in the singlet state. The individual detectors will have time and double-pulse resolutions much less than the ~100 ns annihilation lifetime of positronium, enabling the efficient measurement of the temperature and thermalization rates of large bursts of positronium atoms as a function of time after their formation in micro-cavities and porous materials. The primary function of the proposed instrument will be to measure the amplitude of the low momentum component of a dense positronium gas as it undergoes a phase transition into the Bose-Einstein condensed (BEC) state. The use of the penetrating annihilation gamma radiation as a diagnostic allows external access to the momentum profiles of annihilating electron-positron pairs deep within the apparatus required for these experiments. The measurements will be unaffected by local conditions in the positronium-forming target, such as wall or inter-particle interactions, which would not be the case for optical spectroscopy. The combined capabilities of the proposed spectrometer will benefit other positronium applications using dense cold positronium not related to the BEC. In particular, measuring the thermalization rates of positronium would aid in the positronium characterization of porous materials such as zeolites and low-k dielectrics, and the ability to measure low momentum annihilations at short time scales may be useful for evaluating damage to materials used in fusion reactors.