Spectral and Angular Distribution of Ultraviolet Radiation from the 300-Mev Cornell Synchrotron

Abstract

The spectral characteristics of the radiation emitted by high-energy centripetally accelerated electrons have been examined for various electron energies over a wide wavelength range extending down to 60 A. Following preliminary remarks concerning the source and spectral distribution laws deduced from theory, the paper describes an experimental investigation of the spectrum. The spectrum is examined in the quartz region but the major portion of the work deals with measurements in the soft x-ray region where a grazing incidence vacuum spectrograph is used to record the average power spectrum emitted over a partial or full synchrotron acceleration interval during which the electron energy reaches the values of 233 Mev or 321 Mev, respectively. In each case the radiation is detected photographically and photometric proceedures are followed in reducing the spectrograms. The method of reduction takes into account aspects of the actual source, and a variety of instrumental factors dealing with the dispersion, the transmission, the spectral response, and also the geometrical effects of the optical system involved. The calibration of the emulsion is carried out according to schemes appropriate to each wavelength region. While heterochromatic photometry can be employed in the quartz region, in the vacuum region the emulsion response is taken as constant for fixed energy independent of wavelength. The wavelength dependence of the grating reflecting power is determined by calculations based on measurements with nearly monochromatic sources. This information makes it possible to reduce the exposures obtained with the synchrotron continuum over the wavelength region extending from 60 A to about 200 A. At longer wavelengths the grating response is deduced by treating a portion of the 233-Mev spectrum as known; the grating efficiency obtained in this manner is then used to reduce the corresponding portion of the 321-Mev exposure.The results on the spectral distributions are in reasonably good agreement with the corresponding predictions from classical radiation theory of accelerated electrons. The observed distribution in the spatial spread of the radiation at various positions in the spectrum can also be accounted for if a plausible model is adopted for the diffuseness of the actual source in verifying the theoretical expressions for the angular distribution due to a single radiator. It is pointed out that such continuous radiation may serve as a suitable source for making absorption measurements in the far ultraviolet. The absorption spectra of metallic Be and Al are obtained by the use of the continuum. The Be-$K$ and Al-${L}_{2,3}$ discontinuities, occurring at 111 A and 170 A, respectively, are clearly visible in two orders. It is also suggested that the source may possibly be utilized as a standard for the purpose of calibrating detectors in the ultraviolet region.