Emission Times and Yields ofKX Rays Coincident withCf252Spontaneous Fission

Internal conversion is primarily responsible for most of the electron vacancies that give rise to x rays emitted by fission fragments of ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$. The electronic transitions that fill these vacancies take place very quickly (≈ ${10}^{-16\mathrm{}}$ sec), while the x rays are emitted much later (≈ ${10}^{-9\mathrm{}}$ sec). Thus, the time of emission of fission x rays is determined by the nuclear transitions being converted. Both the number of x ray per fragment and the times at which they are emitted are important for understanding these transitions. In this work, measurements were made of the yield per fragment and time of emission of $K$ x rays coincident with ${}_{}{}^{252}{}_{}{}^{}\mathrm{Cf}$ fission, both as a function of fragment mass. The mean lives for emission of $K$ x rays were measured using a time-of-flight technique. The measured x-ray yields are in substantial agreement with those obtained by other workers, and the spectrum of time versus mass is in excellent agreement with results obtained by Kapoor, Bowman, and Thompson using a very different technique. Our results indicate that both the yields per fragment and mean lives are reflection-symmetric about a mass near the doubly magic nucleus of 50 protons and 82 neutrons.