External Bremsstrahlung spectra produced by the complete absorption of beta particles from 90 Sr to 90 Y, 147 Pm and 204 Tl in nuclear radiation detection compounds like Cesium iodide (CsI) and Sodium Iodide (NaI) has been measured using 0.038m×0.038m NaI(Tl) crystal and is compared with Tseng–Pratt theory. The Bremsstrahlung yields are calculated using the unfolded spectra. This paper also describes a new procedure for the calculation of effective absorption coefficient of Bremsstrahlung from the Bremsstrahlung spectra. The measured spectra show fairly good agreement at low energy end of spectrum and some deviation at higher energy end of spectrum with the theory. The measured Bremsstrahlung yields may be useful to apply corrections, whenever beta particle passes through CsI and NaI detectors.