Nuclear Isomerism in Element 43

A case of nuclear isomerism in element 43 has been thoroughly studied and is described. An activity of 6.6 hours half-life, which grows from a 67-hour molybdenum activity and has been chemically identified as element 43, decays with the emission of a line spectrum of electrons and no observable nuclear beta-particles. Absorption measurements in aluminum and measurements with a magnetic spectrograph give an energy for the electrons of 116 kev. This line spectrum must be due to the conversion electrons of a highly converted gamma-ray of energy 136 kev and arises as the result of a transition from an excited state of this isotope of element 43. The ground state is either stable or very long-lived. X-rays are also observed, and critical absorption measurements, as well as observations with a bent crystal spectrograph, show that they are to be ascribed to the $K\alpha$ line of element 43, as is to be expected from this interpretation. The 6.6-hour activity also emits gamma-rays of about 180 kev energy; the measurements show that these are to be interpreted as following the transition which gives rise to the conversion electrons. A description of the chemical identification of the 6.6-hour activity is given. Other activities of element 43 are mentioned.