Collaborative Research: New Source and Test Masses and their Metrology for Big-G Experiments

合作研究：大 G 实验的新源和测试质量及其计量学

• 批准号: 1708120
• 负责人: William Snow
• 金额: $ 14.18万
• 依托单位: Indiana University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-06-01 至 2021-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1708120&HistoricalAwards=false
• 关键词: Collaborative; Research; New; Source; Test

The research supported by this award focuses on conducting high precision measurements of G, Newton's gravitational constant. Despite a long history of experiments, there are serious inconsistencies in our current knowledge of the value of G. All previous measurements of G have used large masses made from high density metals, which have some inherent limitations on how well one can find tiny cavities inside them. These cavities, if present, cause small variations in the density of the masses and introduce errors in the measurement of G. The work in this project seeks to help mitigate this problem by developing high density transparent materials, such as lead tungstate, for use in experiments that measure G. These materials have much smaller variation in their density compared to metals and, being transparent, one can map the tiny cavities without cutting them open. These tiny cavities will be imaged by two different techniques that can be compared against each other. One method will use a laser beam to optically inspect the material and the second method will use a beam of neutrons to scan the material. In addition to experiments measuring G, this research will also benefit other scientific and technical areas. For example, since lead tungstate is used to build detectors for nuclear and high energy physics, this project could lead to improvements in the uniformity of lead tungstate and help improve these large detector systems. Additionally, the methods for the quantitative measurement of internal density variations could help establish absolute standards applicable to the very wide variety of materials. One of the most important impacts of this research will be education of young scientific researchers. The project offers an intellectually stimulating environment for the scientific and educational activities of undergraduates and graduate students in the respective universities. This challenging project will provide an excellent atmosphere for first-rate education in experimental physics.G is the only fundamental constant for which the uncertainty has risen over time as more and more measurements are made. This project has the potential to help resolve this rather puzzling situation by helping eliminate one of the known limitations of all previous measurements, the metrology of test and source masses. The group proposes to address these limitations by developing high density transparent materials, such as lead tungstate, for use as test and source masses in the next generation of experiments. This choice of new materials is motivated by the fact that the density variations in glass and single crystals are significantly smaller than in metals and they can be measured non destructively. Consequently, the group proposes to develop a laser interferometer for the non destructive measurement of the internal density gradients in source and test masses constructed from high density transparent materials, and to validate such measurements with neutron interferometry. The team will measure the density gradients in the test and source masses to better than 10 parts per million, thereby, reducing their contribution to the systematic uncertainty in the measurement of G to less than 0.5 parts per million.

该奖项支持的研究重点是对牛顿引力常数G进行高精度测量。尽管有很长的实验历史，但我们目前对G值的认识存在严重的不一致。所有以前的G测量都使用了由高密度金属制成的大质量，这对于人们在其中找到微小空腔的程度有一些固有的限制。这些空腔，如果存在的话，会引起质量密度的微小变化，并在G的测量中引入误差。该项目的工作旨在通过开发高密度透明材料（如钨酸铅）来帮助缓解这一问题，用于测量G的实验。与金属相比，这些材料的密度变化要小得多，并且是透明的，人们可以在不切开它们的情况下绘制微小的空腔。这些微小的空洞将通过两种不同的技术成像，可以相互比较。一种方法将使用激光束来光学检查材料，第二种方法将使用中子束来扫描材料。除了测量G的实验之外，这项研究还将有益于其他科学和技术领域。例如，由于钨酸铅用于建造核和高能物理探测器，该项目可能会导致钨酸铅均匀性的改善，并有助于改善这些大型探测器系统。此外，定量测量内部密度变化的方法可以帮助建立适用于各种材料的绝对标准。这项研究最重要的影响之一将是对年轻科学研究人员的教育。该项目为各大学的本科生和研究生的科学和教育活动提供了一个激发智力的环境。这个具有挑战性的项目将为一流的实验物理学教育提供良好的氛围。G是唯一的基本常数，随着越来越多的测量，其不确定性随着时间的推移而上升。这个项目有可能帮助解决这个相当令人困惑的情况，帮助消除所有以前的测量，测试和源质量的计量学的已知限制之一。该小组建议通过开发高密度透明材料来解决这些限制，例如钨酸铅，用于下一代实验中的测试和源质量。选择这种新材料的动机是玻璃和单晶的密度变化明显小于金属，并且可以非破坏性地测量。因此，该小组建议开发一种激光干涉仪，用于无损测量由高密度透明材料制成的源和测试质量中的内部密度梯度，并使用中子干涉法验证这种测量。该团队将测量测试和源质量中的密度梯度，使其优于百万分之10，从而将它们对G测量的系统不确定性的贡献降低到百万分之0.5以下。