The Precision Measurement Of Newtonian Gravitational Constant G By Using Double Spherical Source Masses With The Time-of-swing Method

Since 1798 Cavendish had obtained the first G value in history,people has made great effort in this field to improve its precision.However,due to the difficulties in technology, the precision of G still remains in the level of 100ppm while that of other fundamental physical constants reached 1ppm or even lower.Besides that,the values of G obtained by different groups were in poor agreement with each other,which indicated that there are possible unknown systematical errors in these G measurements.We have determined G using torsion pendulum with the time-of-swing method and obtained a result with precision of 105ppm,which was adopted by CODATA 98 and named as HUST-99.Following research showed that there exists two systematical errors in the measurement.One is the inhomogeneous density of the cylinder source masses and the other is the effect of the air buoyancy.In order to obtain a more precise and reliable value of G,we designed a new scheme in which the precision of geometric measurements have improved greatly due to several improvements,such as the precision of determination of the turntable center reached 2μm by using a photoelectric sensor;the precision of the surface separation and the diameters of the source masses reached 0.06μm and 0.3μm respectively by using the improved gauge-rotate-method;the precision of determination of the pendulum position reached 13μm by using the the photoelectric sensor and telescopes.Finally the uncertainty contributed to G due to the geometric measurement was lowered from 73ppm to 11ppm.On the other hand,although the period shift in the new scheme is about 300 times smaller than that in HUST-99,the uncertainty contributed by period shift was lowered form 75ppm to 14ppm by applying some improvements such as the using of the phase method, the magnetic damper,the correction of the abient temperature and the compensation of the contact potential on the pendulum body as well as the A-B-A method.In order to minimize the influence of the subjectivity,the whole measurement was repeated by different subgroup independently and the two results yielded were in good consistent. The final G value was G=(6.67349±0.00018)×10^-11m³kg^-1s^-2 with a relative uncertainty of 26ppm.This work is partly supported by the National Natural Science Foundation of China(10121503,10805021) and the National Basic Research Program of China (2003CB716300).