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

广泛的意义。正电子素是一种奇异的物质-反物质原子，由一个电子和它的反粒子正电子结合而成。加州滨江大学的科学家们将开发一种新型仪器，用于测量电子偶素发射的光粒子（光子）。 该仪器（光谱仪）的能力将超过商业上可获得的能力，并将使科学家能够测量正电子素原子大爆发的温度随时间的变化。新的光谱仪将是一种使能技术，导致在“玻色-爱因斯坦凝聚态”中产生和观察冷正电子素的稠密气体。这种不寻常的物质状态将是一种集中的能量源，可能会导致各种应用，包括新型激光器。光谱仪将与来自世界各地的科学家合作用于各种应用，他们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。建议的仪器是一个高角分辨率，多探测器的两个伽马湮没角相关谱仪，将测量的速度分布的正电子素原子湮灭在单重态。单个探测器的时间和双脉冲分辨率将远小于正电子素的~100 ns湮灭寿命，从而能够有效测量正电子素原子在微腔和多孔材料中形成后随时间变化的温度和热化率。该仪器的主要功能是测量致密正电子素气体的低动量分量的振幅，因为它经历了到玻色-爱因斯坦凝聚态（BEC）的相变。 使用穿透湮灭伽马辐射作为诊断允许外部访问的湮灭电子-正电子对的动量分布在这些实验所需的设备深处。测量将不受正电子素形成目标中的局部条件的影响，例如壁或粒子间的相互作用，这对于光学光谱学来说是不可能的。所提出的光谱仪的综合能力将有利于其他正电子偶素的应用，使用密集的冷正电子偶素不相关的BEC。特别是，测量的热化率的正电子素将有助于多孔材料，如沸石和低k的正电子素的特性，并在短的时间尺度测量低动量湮灭的能力可能是有用的，用于评估在聚变反应堆中使用的材料的损坏。

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.