Neutrino [Book Review]

As an applied physicist (engineer), I do like to play the game where I read about the far-from-applicable forms of physics while dreaming up about its possible applications and uses >100 years from now. Hence, this book review details a little about the flow, the story of this field in physics, what we know, and what can we do with Neutrinos.

The book of interest, Neutrino by Frank Close, describes the story of how some radiation methods did not follow the laws of “conservation of mass/energy.” For example, a free neutron decays (relatively fast if not in an atom, surprisingly) into a proton and an electrons. Makes sense; charge is conserved. The Neutron is heavier than the proton and electron combined. Where did the difference go? Whatever energy release from E = mc^2 did not bridge the gap. So, scientists initially just make up a new particle, calling it a “tiny neutron” (in italian translate to Neutrino. The name stuck after that).

Initially scientists through the Neutron and Neutrino, both have no charge, were the same thing, with just different amounts of mass. Well, that was wrong.

Neutrinos. Are weird. Period. They are smaller (or exhibit less mass) than atoms, quarks, electrons, you name it. We don’t even know if they have mass (only the theory says it does), let alone how much. They have no charge. And the probability of a neutrino interacting with anything is like 1/(10^50) or something exuberant. The probability of it hitting an atom in a lead brick 1 light-year (a form of distance) long is less than 10%. However, there are substantially more neutrinos than atoms in the universe. And if that isn’t confusing, their energy differs based off the nuclear process that it came from, and there are also three “flavors” of neutrinos that all act differently [electron, muon, tau].

This means that neutrinos are like the next step up from x-ray technology. Neutrinos can pass through extremely large, opaque structures for imaging. We have “imaged” the inside of the sun in that aspect, because light particles have a hard, tortuous time leaving the core of the sun where it’s formed from Hydrogen->Helium fusion. [There was this prevailing theory that the sun stopped working a long time ago, and the sun was just releasing old energy, gradually dimming in the process].

Unfortunately, the other side of the double-edged sword is in the form of detection. While we have black plates for x-rays, there is no such thing as a sensitive neutrino detector. The first successful neutrino detector was a large tank consisting of 400,000 LITRES of Chlorine Gas ~1500 meters underground. Neutrinos pass through the Earth, everything else doesn’t. Just a massive liquid chamber. A neutrino “may” hit a Chlorine atom and turn it to Argon. This happened……like once every three days. Also, the new Argon has a half life of ~30 days, so they don’t really accumulate that much. This isn’t imaging, it just is a thumbs-up or thumbs-down machine.

We only started neutrino imaging in the last 20-30 years, by digging a massive pit, filling it with pure water, and lining the tank with high-sensitivity light detectors. When a neutrino hits an atom in the water, the molecule ejects a larger particle (proton, electron, something NOT a neutrino) and this new particle emits light as it zips through the water. I always chuckle to myself in amazement when I see this image from the following website :

www-sk.icrr.u-tokyo.ac.jp/sk/gallery/wme/sk_01h-wm.jpg

By looking at how much light is given off, the direction of the particle, and lots of signal processing, we can do some crude imaging, called Neutrinography. The first image of the sun was an amazing 400 pixels! (Not mega, just 400 squares).

From my standpoint, the only way we can increase neutrino sensitivity is by creating unique forms of matter that are more susceptible to neutrinos. However, I truly believe that these forms will collapse/decay way sooner than the odds of neutrino detection will ever occur.

But back to the book, it’s always a treat when the story gives much of the thinking behind the scientists back then (based off of what they knew at the time), and even the insights to the various theories they concluded with (including the completely wrong ones). The author also throws in enough particle physics to entertain the science-background audience with a few charts, Feynman diagrams, and descriptions on forms of nuclear decay (the majority of those found in the Sun). The book does demonstrate that such a small “particle” requires a lot of collaboration between minds, foundations, and grants. It’s also another great example of “what did we acquire”, “how much did we really uncover,” and “with every question answered, 10 more pop up.” Relatively fresh, there is still a lot of academic ground to cement, let alone cover and expand.

On the other hand, the obscurity behind Neutrinos could easily pull an academic coup, where they may be something so different that we may have to break our foundations of science to truly understand. It wasn’t long ago that we thought to have measured neutrinos traveling faster than the speed of light! Only the future may tell.

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