Harold V. Parks

Simple Pendulum Determination of the Gravitational Constant

We determined the Newtonian constant of gravitation G by interferometrically measuring the change in spacing between two free-hanging pendulum masses caused by the gravitational field from large tungsten source masses. We find a value for G of (6.672 34±0.000 14)×10(-11)  m3  kg(-1)  s(-2). This value is in good agreement with the 1986 Committee on Data for Science and Technology (CODATA) value of (6.672 59±0.000 85)×10(-11)   m3  kg(-1)  s(-2) [Rev. Mod. Phys. 59, 1121 (1987)] but differs from some more recent determinations as well as the latest CODATA recommendation of (6.674 28±0.000 67)×10(-11)   m3  kg(-1)  s(-2) [Rev. Mod. Phys. 80, 633 (2008)].

The Seventh Intercomparison of Josephson Voltage Standards in North America

The seventh interlaboratory comparison of Josephson voltage standards (JVS) at 10 V, sponsored by the National Conference of Standard Laboratories International, took place from April to October 2005 with 15 participating laboratories. A traveling JVS system of the National Institute of Standards and Technology was used to make five comparisons with the subpivot laboratories. This paper describes the protocol used for the JVS intercomparison and the improvements achieved by the use of the transportable JVS

A suspended laser interferometer for determining the Newtonian constant of gravitation

Progress is reported on an experiment to measure the Newtonian constant of gravitation, G, with a suspended Fabry-Perot laser interferometer. With this technique, we measure the deflection of simple pendulums due to the gravitational attraction of tungsten masses. A result for G is expected with an accuracy of roughly 30 ppm.

A simple pendulum laser interferometer for determining the gravitational constant.

We present a detailed account of our 2004 experiment to measure the Newtonian constant of gravitation with a suspended laser interferometer. The apparatus consists of two simple pendulums hanging from a common support. Each pendulum has a length of 72 cm and their separation is 34 cm. A mirror is embedded in each pendulum bob, which then in combination form a Fabry–Perot cavity. A laser locked to the cavity measures the change in pendulum separation as the gravitational field is modulated due to the displacement of four 120 kg tungsten masses.

The 2008 NCSLi Josephson Voltage Standards Interlaboratory Comparison

Abstract: Josephson voltage standards (JVS) provide a highly accurate representation of the volt. Although the Josephson Effect provides an intrinsic standard of voltage, intercomparisons between different systems are important to insure that potential sources of systematic error are under control and to provide an explicit link to the volt as maintained by a national metrology institute. The results from the 8th Josephson voltage standards interlaboratory comparison (ILC) sponsored by the National Conference of Standards Laboratories International (NCSLI) are presented and compared with the results of the previous three ILCs which used the same Zener standards and protocols. The 8th interlaboratory comparison was conducted between March and July, 2008 with 14 participating laboratories in North America. It began with direct array-to-array comparison between the National Institute of Standards and Technology (NIST) compact Josephson voltage standard (CJVS) system and the pivot laboratory system at Lockheed Martin Mission Services in Denver. The two systems agreed to well within the k = 2 uncertainty of the comparison of 6.6 nV at 10 V. Once the NIST-pivot laboratory comparison was complete, four traveling Zeners were sent from the pivot laboratory to the participant laboratories in a series of four loops with a pivot laboratory measurement between the loops. The standard deviation of the 10 V bank average as measured by the participants with respect to the drift line established by the pivot laboratory was 68 nV. There were some indications of non-normal behavior in the residuals and an expanded uncertainty for the comparison of 190 nV at a 95 % level of confidence was adopted.

A suspended Fabry-Perot interferometer for determining the Newtonian constant of gravitation

Of all the fundamental constants of nature, the Newtonian constant of gravitation, G, has been one of the most difficult to measure. The current CODATA value of G has an uncertainty of 1.5 parts in 1000. Although recent experiments have produced values with uncertainties smaller than this, the adopted CODATA uncertainty reflects the fact that there is still substantial disagreement between the values from these experiments. The majority of previous measurements have used torsion pendulums or balances to convert the small gravitational attraction of a laboratory source mass into a relatively large mechanical displacement. However, our approach is to use simple pendulums, which results in a small displacement that we measure very accurately. This means that the attraction of the source masses is measured against a restoring force provided by earths gravity rather than the less well-understood torsion of a wire. Also, the shorter period of our pendulums allows us to make measurements much more rapidly than in most other experiments. In our apparatus, two mirrors, each suspended as a simple pendulum, form a Fabry-Perot cavity. A He-Ne laser locked to this cavity monitors the relative displacement of these two pendulums (through changes in its frequency) as laboratory source masses are moved, altering the gravitational pull on the mirrors.

A Suspended Laser Interferometer Determination of the Newtonian Constant of Gravitation

We are completing an experiment to measure the Newtonian constant of gravitation, G, with a suspended Fabry-Perot laser interferometer. The apparatus is operational and systematic errors have been found and eliminated. A result for G is hoped for in summer 2004 with an accuracy of roughly 30 ppm

The Mark II Version of the BIPM Torsion-Strip Balance for the Measurement of G

The BIPM torsion-strip balance used to produce a value for G published in 2001 has been modified with a view to reducing the uncertainty from the 2001 value of about 40 ppm down to about 10 ppm. The poster will not contain a new value for G