INTERNAL BREMSSTRAHLUNG SPECTRA OF TM-170 AND SR-89

The internal bremsstrahlung spectra accompanying the non-unique first forbidden beta decay of(170)Tm and unique first forbidden beta decay o f Sr-89 have been measured using an extrapolation procedure with the b eta stopper method. In order to avoid errors in the source strength me asurement and uncertainty of the normalization procedure, the experime ntal and the theoretical results are compared in terms of the number o f photons of energy k per unit energy interval per unit photon yield. The results for Tm-170 show better agreement with the Lewis and Ford t heory, particularly in the lower and mid-energy regions, than the Knip p, Uhlenbeck and Bloch (KUB) and Nilsson theories. However the experim ental results are higher than those of these theories at the high-ener gy end. For Sr-89, the experimental results are in agreement with the Lewis and Ford theory in the whole energy region covered by the presen t measurements and do not favour the KUB and Nilsson theories beyond a photon energy of400keV.