Transition in 26-minU235mof Less Than 23 Electron Volts

Abstract

The conversion electron spectrum from the decay of 26-min ${\mathrm{U}}^{235m}$ has been examined by both magnetic spectrometry employing preacceleration and by electrostatic spectrometry. The energy distribution is peaked at 0.5 electron volts, with evidence of structure at 5 ev and at 19 ev, leading to an estimated upper limit of 23 ev for the transition energy. Tests of the performance of the apparatus were made with the conversion spectrum of the low-energy transition in 6-hr ${\mathrm{Tc}}^{99m}$, redetermined as 2.15 kev; with the "zero energy" peak of ${\mathrm{Am}}^{241}$ and with the spectrum of photoelectrons excited from silver with ultraviolet light.