Thursday, May 23, 2013

Beta Decay and Neutrinos over Cocktails

This was going to be so much longer and more detailed, but as you may or may not be aware, seven month olds occasionally decide of their own volition to pull all nighters, (much like grad students).  So, I leave you with a few somewhat less than scattered thoughts, and an incredible video on the topic of neutrinos.

After yesterday's post on the possibility of the variation of radioactive decay rates with neutrino activity from the sun, I spent my free time today reading about beta decay and neutrinos.  The references I mention below are very complete, but this post won't be.  I present to you a series of notes and factoids about beta decay and the history of the neutrino, kind of a backgrounder for cocktail party level discussions of the topic if you will.

Beta Decay
I wanted to look into beta decay first because it's the type of radioactive decay, (as opposed to alpha or gamma), that involves neutrinos.  It seemed like the natural place to start.  Since we're talking about the possibility of neutrinos effecting a decay process, why not look at the decay process that emits neutrinos?  The standard type of beta decay that most people are familiar with is electron emission beta decay (picture 1).  In this type of decay, a neutron in the radioactive atom decays into a proton and emits an electron and an electron anti-neutrino in the process.  There's an awesome television show produced by the BBC detailing the experimental discovery of both the neutrino and neutrino oscillations, (more on these below).  +Oliver Thewalt pointed the show out to me on youtube[5].

There are two other types of beta decay, one that is more or less a mirror image of the one described above in which a positron and an electron neutrino are emitted, and the weird K capture one.  In K capture, the nucleus grabs an electron out of the innermost electron shell, turning into an atom with an atomic charge of one less, (the negative electron charge cancels one of the proton charges), and emits an electron neutrino.  This is also the electron capture process often mentioned in LENR[7] research that seems to have so peeved the author of this Physics Central article[6] on the subject.

Neutrino Oscillations or "No Virginia, Light Doesn't Perceive Time"
As a last note today, the video mentioned above pointed out that there are three types of neutrinos named after the three types of electron-like particles known as leptons.  There's the electron neutrino I mentioned above as well as a muon neutrino and a tau neutrino.  First, the littlest bit of background.  The familiar electron is related to two heavier particles  the muon, and the tau.  The electron, muon, and tau all behvae in the same manner, but each one is significantly more massive than the one before it.  Each of these partcles is associated with the neutrinos already mentioned.

The fascinating thing is that a neutrino that starts out as one flavor, (electron, muon, or tau), will oscillate into the other two flavors and back over time.  This was a huge surprise to the physics community because it was originally thought that neutrinos were massless.  As a massless particle, the neutrino, like a photon, (the massless particle that transmits light), should move at the speed of light.  The physicists in the BBC video point out that if the neutrino actually moved at the speed of light then it would not be able to perceive time, (according to special relativity), and therefore not be able to change its flavor over time.  From this it was deduced that the neutrino must in fact have mass and travel slightly slower than the speed of light.  This is all very cool, and yet another example of light speed particles not perceiving time, something I wrote about in a cautionary tale on another site[8].

1.  First detection of free neutrinos
Cowan C.L., Reines F., Harrison F.B., Kruse H.W. & McGuire A.D. (1956). Detection of the Free Neutrino: a Confirmation, Science, 124 (3212) 103-104. DOI:

3.  Much more useful, (and open access), annotated version of the same picture on Wikipedia

4.  Article on the early history of neutrino experiments
Reines F. (1979). The Early Days of Experimental Neutrino Physics, Science, 203 (4375) 11-16. DOI:

5.  BBC show on the discovery of the neutrino and neutrino oscillations

6.  Physics Central on LENR

7.  Widom and Larsen on low energy nuclear reactions.  This appears to be open access.

8.  On not being overly mean in science

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