One of the experimental facilities at the German laboratory GSI Helmholtz Centre for Heavy Ion Research in Darmstadt is an Experimental Storage Ring (ESR) with electron cooling in which large numbers of highly charged radioactive ions can be stored for extended periods of time.
Also, such a high degree of ionization is typical in stellar environments where such decays play an important role in nucleosynthesis.
[2] In 2007 an ESR experiment reported the observation of unexpected modulation in time of the rate of electron capture decays of highly ionized heavy atoms — 140Pr58+, which have a lifetime of 3.39 min.
The experimental group considered it very improbable that the appearance of the phenomenon is due to a technical artefact because they report that their detection technique provides—during the whole observation time—complete and uninterrupted information upon the status of each stored ion.
[4] In 2013, a similar experimental group at the ESR now called the Two-Body-Weak-Decays Collaboration reported further observations of the phenomenon with measurements on 142Pm60+ with much higher precision in period and amplitude.