The picture
shows the inside of the water shield surrounding the
XENON1T
dark-matter detector at the INFN Gran Sasso National
Laboratory near L’Aquila in Italy. In this week’s issue of
the Nature science journal, the XENON
Collaboration reveals that the set-up has recorded a type of
nuclear decay that is particularly hard to detect. The team
has directly observed two-neutrino double electron capture
in xenon-124, the half-life of which is roughly a trillion
times the age of the Universe. The XENON1T detector contains
3.2 tonnes of ultra-pure xenon, and allowed the researchers
to detect the X-rays emitted when xenon-124 decays into
tellurium-124. They measured the half-life of this decay to
be 1.8 × 10^22 years, which is in line with predictions. The
team says that this detection is a useful step on the road
to detecting neutrinoless double electron capture, which
could provide a deeper understanding of the neutrino.