New Limits on the Diameters of Radio Sources

The interplanetary scintillations of seventy radio sources have been studied in detail The width of the spectrum of scintillation fluctuations gives a measure of source diameter Upper limits from 0'.'5 to 0'104 are obtained It is shown that most sources are not disks but probably consist of small-scale and large-scale components. The strength of scintillations is a measure of the strength of the small-scale component. A table is also given of sizty-eight sources which do not show scintillation. There is excellent agreement between diameters (or limits thereto) deduced from scintillation observations and those obtained from interferometer observations Scintillating and non-scintillating galaxies have similar distributions of radio-frequency spectral index, but scintillating and non-scintillating quasars have different distributions. The former contain a predominance of curved and flat spectra; the latter are clustered between a = 0.8 and 11.