This week, scientists have reported that they have made incredible observation of physics using liquid xenon. Officially, the rarest nuclear decay – and indeed, the rarest events of any kind – are sometimes directly measured.
How rare? As I wrote in my previous article on the result, "The average time in which half of the xenon atoms in the sample will be subjected to this reaction is 1.8 × 1022 years … It's roughly a trillion times from the time of the Universe. "My ears symbolically began to leak with a brain juice, trying to understand this, so I thought I would try to crash as scientists are able to measure such a rare event.
To be reciprocated: On Wednesday, researchers working on the XENON1T experiment reported that they made pioneering observation of a kind of nuclear decay called double-neutrino double electronic recording. In essence, a pair of protons in the core of the atom spontaneously absorb one of the electrons of the atom at the same time. This results in the release of a pair of neutrinos and x-rays.
Physicists have theorized the existence of this nuclear decay since 1955, and are most interested in this because it is a stepping stone to the more interesting physical results. Another kind of event, electronic capture without neutrinos (when the neutrons of the atom spontaneously emit electrons and neutrinos, but neutrinos disappear, destroying each other in gamma rays) can reveal deep truths about the nature of the mysterious neutrino, the second most common particle in the universe.
But let's go back to a little about 1.8 × 1022 years. How is it possible to directly measure an event that you seem to have to wait long after all the stars burn to experience it? Well, fortunately, it's not really like half a job. The concept of half-life essentially says that if you have a series of atoms, half-life is how long it takes half of the atoms to undergo the nuclear decay that you study. The more atoms you have, the more likely you'll see the nuclear decay you are looking for.
The XENON1T experiment includes 3,500 pounds of liquid xenon buried deep underground in a mountain in Italy. Its primary goal is to measure particles of dark matter interacting with atoms (something that has not yet been done). But from 3,500 kilograms, approximately 2 kilograms of flavor is a xenon flavor that can pass on this two-neutrino double electron capture event, an isotope called xenon-124 (since the number of protons and neutrons at its core is 124), the author of the study Christian A student at the University of Münster in Germany, Witweg, told Gizmodo.
A quick assessment using high school chemistry would say that it is equal to about 1025 xenon-124 atoms. If it takes 1.8 × 1022 for half of these xenon atoms decay, and then for a year, a few hundred or so will decompose (thanks to Wolfram Alpha).
Indeed, scientists have reported that they have seen 126 of two-neutrino double-sided electronic swings in the wind of liquid xenon.
This is the earliest disintegration ever measured directly, although scientists have detected indirect evidence of other nuclear decays with longer half-life. But you can imagine where a physicist might like to go from here. The neutrons double beta decay and the neutron dual electron phase would have longer lives, and seeing a reasonable number of such events – what physicists want to do to prove that they exist in the real world, and not just in theory – will require in a reasonable time period even larger cubes of atoms. Indeed, physicists are already working on such experiments and hope to continue to strengthen existing detectors to hunt for these rare disintegrations.
Thus, the measurement that the XENON1T experiment made was one of the rarest nuclear decays that had ever been observed. But when you see a sufficiently large bundle of atoms, you have a shot at seeing a one-in-one sextile event.