The spectral energy distribution of radiation from water bombarded by radium gamma-rays or P<sup>32</sup> beta-rays is that expected for Cerenkov radiation. A solution of p<sup>32</sup> in water furnishes a source of Cerenkov radiation which is convenient for the determination of the spectral sensitivity of photographic emulsions.
M. A. GREENFIELD, A. NORMAN, A. H. DOWDY, and P. M. KRATZ, "Beta- and Gamma-Induced Čerenkov Radiation in Water," J. Opt. Soc. Am. 43, 42-43 (1953)