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

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的值的认识存在严重的不一致。以前对G的所有测量都使用了由高密度金属制成的大质量，这在人们如何很好地发现其中的微小空洞方面存在一些固有的限制。这些空洞如果存在，会导致质量密度的微小变化，并在G的测量中引入误差。该项目中的工作旨在通过开发高密度透明材料来帮助缓解这个问题，例如钨酸铅，用于测量G的实验中使用。这些材料的密度变化比金属小得多，而且由于是透明的，人们可以绘制微小的空洞，而不需要切开它们。这些微小的空洞将通过两种不同的技术进行成像，可以相互比较。一种方法将使用激光束对材料进行光学检查，第二种方法将使用一束中子来扫描材料。除了测量G的实验外，这项研究还将惠及其他科技领域。例如，由于钨酸铅用于建造核物理和高能物理探测器，该项目可能会改善钨酸铅的均匀性，并有助于改进这些大型探测器系统。此外，内部密度变化的定量测量方法可以帮助建立适用于非常广泛的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。该项目为各自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教育提供一个极好的氛围。G是唯一一个基本常数，其不确定度随着时间的推移而增加，因为进行的测量越来越多。该项目有可能帮助解决这一相当令人困惑的情况，通过帮助消除所有先前测量的已知限制之一，即测试和源质量的计量。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，用于在下一代实验中用作测试和源质量。这种新材料的选择是因为玻璃和单晶中的密度变化明显小于金属中的密度变化，并且可以进行非破坏性测量。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构成的源和测试质量中的内部密度梯度，并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，使其好于百万分之10，从而将它们对G测量的系统不确定度的贡献降低到百万分之0.5以下。

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.