Magnetic and quadrupole interactions in Hg 197m. Angular correlations

Abstract

A series of electron-gamma angular correlation studies of the 165 keV–134 keV cascade in Hg 197m and the 130 keV–279 keV cascade in the decay-product Au 197m are reported. The experiments have been undertaken primarily to settle the much discussed problem of the possible existence of a time dependent coupling between the nucleus and the electron core excited by virtue of a preceding conversion or electron-capture process. For the Au 197m cascade no observable attenuations of the angular correlation pattern were found due to the short lifetime (2.3 × 10 −11s) of the intermediate level. In Hg 197m, where the corresponding lifetime is 1 × 10 −3s, the correlation was found to be attenuated by a static quadrupole interaction for carrier-free sources deposited onto different metal and insulator backings. No measurable attenuation due to an interaction with the electron core was seen for metallic source backings. However, an additional attenuation attributed to the after-effects of the conversion-process was found for sources embedded in insulating environments. The interplay between the two different types of interaction gives a complicated attenuation mechanism, which, however, can be disentangled by means of time-differential angular correlations. A direct proof of the existence of an attenuation-effect due to the excitation of the electron core is furnished by a magnetic decoupling experiment, confirming the results obtained in the correlation experiments.