A precision measurement of the gravitational constant G has been made using a beam balance. Special attention has been given to determining the calibration, the effect of a possible nonlinearity of the balance and the zero-point variation of the balance. The equipment, the measurements and the analysis are described in detail. The value obtained for G is 6.674252(109)(54) ×10 −11 m 3 kg −1 s −2 . The relative statistical and systematic uncertainties of this result are 16.3×10 −6 and 8.1 ×10 −6 , respectively.
Experiments to measure the mass of the electron antineutrino from tritium &decay are reviewed. The spectrum shape and various distribc*:ons, needed for the analysis of a measured pspectrum, are discussed. Their relative importance is pointed out and possible systematic errors u e discussed. Recently published measurements gave no indication for a non-zero mass and upper limits in the range 9.3 to 15.4 eV were claimed. These experiments are critically reviewed. It is concluded that the only previous experiment suggesting a mass of about 30 eY must be wrong. Possible reasons for this are discussed. A brief survey of the masses of the other neutrino types and of neutrino mixing is given and some recent results are summarized. Also the experimental situation of Simpson's 17 keV neumno is discussed.This review was receix7ed in October 1991. W34-4885/92/071035+57$18 M) @ 1'192 IOP Publlshlng Ild 1035 than the 3TCI detector and are expected to shed more light on this problem (KirSten 1991, Abazov et ol 1991).References A b a m A I e1 d 1991 NucL
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