Beta-Rays of Radium-D

WE take this opportunity of replying to the criticisms expressed in Prof. Stahel's letter printed above. Prof. Stahel has investigated 1 the β-particle emission of radium-D, using a point counter as was first accomplished by Riehl. 2 Through a collodion window of 0.8 mm. air equivalent thickness 0.83 particles per disintegration were registered. Stahel maintains that all these particles were photoelectrons produced by the known γ-ray of 47.2 ekv. energy. He bases this contention ( a ) on Petrová's 3 interpretation of a range distribution constructed from Wilson chamber observations, and ( b ) upon certain control experiments made upon the absorption in the counter window in his own researches. 1