A METHOD FOR DETERMINING THE DENSITY OF SMALL SI-28 SAMPLES

In view of a possible uncertainty reduction of the Avogadro constant v ia using a small mono-nuclidic silicon single crystal a method was dev eloped for measuring the density of small Si-28 samples with highest a ccuracy. For this purpose a hollow silicon cylinder was prepared until its density deviated by only a few parts per million from the density of a temporarily available Si-28 sample. Thus the density of the smal l volumed Si-28 sample (V almost-equal-to 77 cm3) could be related to the density of the larger hollow cylinder (V almost-equal-to 343 cm3) in a flotation experiment with a very low relative uncertainty (3. 10( -7)). After the density determination of the hollow cylinder, the Si-2 8 small sample's density was evaluated with a relative uncertainty of 9 . 10(-7) - mainly originating from the uncertainty of the density st andards.