The study suggests that the germanium isotope actually has an 11-day half-life

The search for the elusive neutrino takes many forms. Several experiments use detectors consisting of many tons of gallium because neutrino interactions can occur on stable gallium-71 (⁷¹Ga) nucleus and turns it into a radioactive isotope of germanium (⁷¹Ge) with an 11-day half-life, which can then be observed with traditional radiation detectors.

However, the rate ⁷¹Ge production from these interactions was observed to fall short of expectations. This turned out to be what’s called a “gallium anomaly”—a significant discrepancy that occurs when electron neutrinos bombard gallium and create ⁷¹Ge.

This anomaly cannot be explained by current theories. Consequently, this has led to speculation that this could be a sign that the neutrino can transform into other exotic particles, such as sterile neutrinos, which interact with matter even less than the normal neutrino; if confirmed, it would be a huge discovery.

It has recently been suggested that this anomaly could instead be explained by something more mundane – a poorly measured half-life ⁷¹Ge core. This is because the predicted rate of neutrino interactions depends on this half-life.

To test this possible explanation for the gallium anomaly, a team of scientists from the Lawrence Berkeley and Lawrence Livermore National Laboratories determined ⁷¹The half-life of Ge with a set of carefully performed measurements including two performed side-by-side with other long-lived radioactive isotopes with well-known half-lives. The research appears in Physical overview C.

The team was able to capture ⁷¹The half-life is approximately four times better than any previous measurement. The work eliminates erroneous measurements ⁷¹Ge as an explanation of the anomaly, which must therefore have a different origin – perhaps in the existence of a fourth type of neutrino, called the sterile neutrino.

“The new half-life obtained by our team confirmed earlier results, but put it on a much firmer footing, definitively ruling out the possible explanation that the missing neutrino was instead caused by an incorrect ⁷¹Ge half-life,” said LLNL scientist and lead author Nick Scielzo. “That’s why the gallium anomaly remains a real mystery—one that potentially still requires some kind of unexpected new neutrino behavior to understand.”

Other LLNL study authors include Narek Gharibyan, Ken Gregorich, Brian Sammis, Jennifer Shusterman and Keenan Thomas.