Abstract
The 10.5-day isomer in {sup 193}Ir decays by a single 80.2-keV M4 transition directly to the ground state of that nucleus. We have measured the total intensity of K x rays relative to 80.2-keV {gamma} rays for this transition to be 98.7(6). With the K-shell fluorescent yield for iridium taken to be 0.958(4), this result yields {alpha}{sub K}=103.0(8) for the K-shell internal conversion coefficient (ICC). The calculated {alpha}{sub K} for this transition is particularly sensitive to the treatment of the hole that is created by conversion in the atomic K shell. Recent ICC tables, which ignore the hole, yield {alpha}{sub K}=92.0. We demonstrate that calculations incorporating the hole produce values between 99.6 and 103.3 depending on the approximation used. Our result strongly supports the need to include the hole.
Highlights
Internal conversion coefficients (ICCs) play an essential role in the analysis of nuclear decay schemes
In 1973 a precision measurement±0.5% ͒ on an M4 transition in 117Sn and an accompanying survey of 15 other experimental ICCs for well-characterized E3 and M4 transitions [5] did point to a systematic discrepancy
When the experimental results were compared with the preferred calculation of the day [1], it was found that the theoretical values were systematically higher than experiment by 2%– 3%
Summary
Internal conversion coefficients (ICCs) play an essential role in the analysis of nuclear decay schemes. The body of world ICC data includes very few measurements of high precision—say, ഛ1% It is only in the average over many different transitions that a discrepancy between experiment and theory at this level can be discerned at all, and it could be argued that the 1% difference in experimental agreement between the two calculations—one with the hole and the other without—is hardly a definitive test of one calculation’s validity. For an experiment to establish definitively which treatment of the atomic hole is best, what is required is an individual transition whose calculated ICC is sensitive to the presence of the hole and which can be measured with high precision In their 2002 survey, Raman et al identified such a transition: the 80.2-keV M4 isomeric decay of the second excited state in 193Ir. The transition energy is very close to the K-shell binding energy in iridium, which is at 76.112 keV [14], and the value of the calculated K-shell ICC, ␣K, differs by more than 10% depending on whether the hole is incorporated in the calculation or not. V we will discuss the impact of our result on the calculation and future use of ICCs
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