The weakness of interaction lends its name to the weak force, wimpy among the four basic forces – the others being the strong force (the residue of which holds nuclei together), electromagnetism, and gravity. Their existence was first proposed by Enrico Fermi in order to claim that energy and momentum (quantity of movement) were conserved in some nuclear reactions such as the one we’re talking about. Now they are “routinely” detected with very sensitive instruments – think of giant tanks of pure chemicals or elements, in which the massive flux of neutrinos from the Sun create a few new nuclei per week! We on Earth are personally exposed to about 100 billion neutrinos per second per square centimeter of our surface. There’s almost zero chance of creating a new atomic nucleus in us. If 100 billion sounds large, you might compare that to the number of particles of visible light, the photons, that hit the same square centimeter of us. On a nice, clear Las Cruces day, facing the Sun we intercept about 0.1 watt per square centimeter. That’s not much energy by our commonplace standards (until you get a sunburn) but it represents 280 quadrillion photons! Each little photon carries on average only about 3.5×10-19 joules of energy.
A few more notes about neutrinos: first, they are truly lightweight particles. Their masses are so small that they haven’t been measured yet; we only know upper bounds – for example, the lightest one of three types is lighter than 0.086 electron-volts or less than 1/6th of a millionth the mass of the electron. However, they must have mass, since they can change into one another, and appear to do so on their way to us from the Sun. The in-flight change explained the dearth of solar neutrinos detected in the Homestake Mine experiment by Raymond Davis, Jr. and John N. Bahcall. They placed 100,000 gallons (380 cubic meters) of ultrapure perchlorethylene cleaning fluid in a tank. The tank was located nearly 1500 meters below ground to avoid interfering processes. With extreme rarity a solar neutrino would hit a chlorine nucleus to turn it into argon. The argon was swept out (sparged) every few weeks by bubbling helium gas through the tank. That’s looking for a needle in a haystack! You may readily find other sources of information on the concept of neutrino oscillation or the solar neutrino problem.
Recently, neutrinos have been invoked in a hypothesis to explain why ordinary matter exists. The Big Bang began as pure energy, creating equal amounts of matter and antimatter, it would seem as happens in positron-electron pair creation by energetic gamma rays. The matter and antimatter should have then annihilated each other, leaving again only energy as photons. That clearly didn’t happen. One theoretical way out of this is if the three types of neutrinos, muon, electron, and tau neutrinos, don’t have exact antiparticles, leaving some regular matter, and, thus, us at this point in time. Measurements at the gigantic SuperKamiokande detector in Japan have evidence that is tantalizing. Muon neutrinos turn into electron neutrinos at a higher rate than muon antineutrinos turn into electron antineutrinos, as the research team reported on 15 April 2020. Stay tuned to find out why we are here.
Researchers service the massive SuperKamiokande detector from inflatable boats.
That’s 13,000 photomultiplier tubes that surround 50,000 tons of ultrapure water.
KAMIOKA OBSERVATORY/ICRR (INSTITUTE FOR COSMIC RAY RESEARCH)/UNIVERSITY OF TOKYO