Friday, September 26, 2014

Nick Emits Antimatter

Nick emits: 1 positron every 12 seconds
Fausto Marcon recently drew my attention to a blog post  by "tertiary source" entitled What's the Antimatter Content of a Banana? .

I guessed "Zero" but I was wrong.

I know that bananas are radioactive because they contain a lot of Potassium. And some of that Potassium exists as Potassium-40 (K-40), a long-lived radio-isotope left over from the creation of the Earth. But I had imagined, that K-40, like most naturally occurring radio-active substances, emitted beta and gamma rays which are just high-speed electrons and high-frequency light. In other words, ordinary matter -- just a bit more highly excited than the matter in your lipstick and in your coffee cup.

And that's for the most part correct.

But if you look up Potassium-40 in Wikipedia (which can be trusted on subjects as uncontroversial as the properties of atoms), you will find that this isotope possesses three separate decay modes. And that one of these decay modes involves the emission of a positron (or anti-electron) which is a fundamental particle with the same mass as the electron but with opposite charge. The positron is the simplest example of "antimatter" with the property that when an electron (matter) meets up with a positron (antimatter) both particles disappear in a flash of light (gamma rays) -- a process aptly named matter-antimatter annihilation. The positron was the first anti-particle discovered (by Carl Andersen in 1932) but every known particle has an antimatter partner, all of whom (I believe) have now been detected.

So along with a bunch of ordinary radioactivity, a banana emits antimatter as well, at a rate "tertiary source" estimates to be about 1 positron every 75 minutes -- or about 20 positrons per day.

But my body is filled with Potassium too. And I weigh a lot more than a banana. How much antimatter does Nick emit per day?

Let's face it. Everybody emits radiation whether they are aware of it or not. The main bodily radioisotopes are Potassium-40 and Carbon-14. If you are of average height and build, your radioactive Potassium will produce about 5000 decays per second while your radioactive Carbon produces 3000 decays per second. Much of this radioactivity is absorbed by the body but some escapes and can be detected by a sensitive radiation detector.

Though no fault of your own your body is radioactive.

During the past 60 seconds, the Potassium and Carbon inside your body have produced nearly 1/2 a million radioactive decays. But only a small fraction of these half-million decays are made of antimatter. The body's positron emission rate is about 5 per minute.

A banana takes about 75 minutes to create a single positron, but Nick emits antimatter every 12 seconds.

Nick emits antimatter every 12 seconds.

And so do you.


Iona said...

Gives new meaning to 'Going Bananas'.

Jungle Girl said...

Can I fart myself into nonexistence?

AlLundell said...

So, if 12 of us get together, that's one positron a second on average. Any chance we could listen to our emissions, like some kind of anti-matter geiger counter?

nick herbert said...

Physicists currently believe that the Universe is constructed out of only two kinds of particles-- BOSONS, with integral spins, such as photons and gluons (spin-1) and Higgsons (spin-0); and FERMIONS, with 1/2 integral spins, such as quarks and leptons (both possessing spin-1/2). Prof John Cramer reminds me that ONLY FERMIONS ARE MATCHED WITH ANTIPARTICLES. So I was mistaken when I said that every particle has a corresponding anti-particle. Only Fermions possess anti-Fermions.