REFRACTIVE INDEX OF He 4 : LIQUID
1958; NRC Research Press; Volume: 36; Issue: 7 Linguagem: Inglês
10.1139/p58-095
ISSN1208-6045
Autores Tópico(s)Quantum, superfluid, helium dynamics
ResumoChanges in the phase refractive index n with temperature have been measured between 1.6 and 4.2° K at λ = 5462.27 Å, for liquid He 4 at its saturated vapor pressure, using a metal optical cryostat and a Jamin interferometer. A novel adaptation of the Jamin interferometer has been made so that, in addition, an absolute determination of the group refractive index, n G , could be made using white light of "effective wavelength" 5595 ± 40 Å. When the dispersion correction is made, the phase index for the Hg green line at T 55E = 3.700° K is n = 1.026124 ± 0.000035. The relative measurements have been adjusted to this value. The more than 200 experimental points show a random scatter of less than 5 × 10 −6 in index. Using Kerr's density data the polarizability is thus (N 0α ) = (0.12454 ± 0.00021) cm 3 mole −1 at λ = 5462.27 Å, for liquid He 4 at 3.7 °K. Within experimental error (N 0α ) is found to be independent of temperature. Thus the refractive index data may be considered as a measurement of the liquid density and coefficient of expansion.The region near the λ-point is of special interest. The expansion coefficient determined from the refractive index, β n , may be represented within experimental error by 10 3 β nI = +41.5 + 14.5 log|T−T λ | for T > T λ , from about 0.1° above T λ to within 0.01° of T λ ; and by 10 3 β nII = −1.5 + 14.5 log |T−T λ | for T < T λ , from about 0.1° below T λ to within 0.002° of T λ . This implies that the density–temperature curve has both a vertical tangent and a point of inflection at the λ-point; and that the maximum in density occurs about 0.001° above the λ-point.
Referência(s)