Daily Archives: June 9, 2010

That River in Egypt

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You Are Not So Smart

You Are Not So Smart is a blog devoted to self delusion and irrational thinking.

There’s a lot of research out there suggesting you have no idea why you act or think the way you do.

It feels awful to accept such things, so you create narratives to explain your own feelings and behavior.

On the Dunning-Kruger Effect

Have you ever wondered why people with advanced degrees in climate science or biology don’t get online and debate global warming or evolution? Yet, people without a degree in psychology will write 1,200 words about a psychological bias.

The less you know about a subject, the less you believe there is to know in total. Only once you have some experience do you start to recognize the breadth and depth you have yet to plunder.

Cap and Trade

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The Virtuosi: My Pepsi* Challenge

The basement of the Physics building has a Pepsi machine. Over the course of two semesters Alemi and I have deposited roughly the equivalent of the GDP of, say, Monaco to this very same Pepsi machine (see left, with most of Landau and Lifshitz to scale). It just so happens that Pepsi is now having a contest, called “Caps for Caps,” in which it is possible to win a baseball hat. There are several nice things about this contest. Firstly, I drink a lot of soda. Secondly, I like baseball hats. So far so good. Lastly (and most important for this post), is that it is fairly straightforward to calculate the statistics of winning (or at least simulate them).

On the surface this is a lesson in basic statistics and simulations. But the other lesson here is that physics graduate students have been conditioned to not value their time paricularly highly.

Magic Magic

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I’m confounded by magic.

Radioactive isotope of tin confirmed to have doubly magic nucleus

Magic proton or neutron numbers give the nucleus greater stability and stronger binding, and are therefore usually more common than nuclei with unfilled orbital shells. In doubly magic nuclei both proton and neutron shells are filled, leading to even stronger binding and stability. The outer shells of doubly magic nuclei are rigidly spherical.

OK, here’s an instance where someone is using inconsistent and/or confusing terminology. If magic numbers refer to filled shells, then Sn-132, having 50 protons and 82 neutrons, is doubly-magic by definition. The only thing you have to confirm is that it’s Sn-132. The Tin isotope whips out its ID card, and you’re done.

But no, apparently that’s not enough.

Other confirmed doubly magic nuclei include helium-4, oxygen-16, lead-208, calcium-49, and nickel-48, which are abundant and stable, and nickel-56, which was discovered in 1998 and is less stable than the others, having a half-life of just 5.9 days. Tin-132 is even more unstable with a half-life of only four seconds, which has made confirmation of its doubly magic nature difficult. It has 50 protons and 82 neutrons, and is the first confirmed doubly magic isotope that is both neutron-rich and radioactive.

The scientists investigating this seem to already know it has magic numbers of both, but that doesn’t confirm the doubly-magic nature of the isotope. They had to verify that it is spherical as well, by looking at Sn-133 and saw that it behaved as expected of having a single excess neutron (I assume in terms of a quadrupole moment). But if it hadn’t, would the nucleus still be doubly-magic? Or would it be that the model of doubly-magic nuclei was wrong? I think it’s the latter; magic numbers refer to the numbers (hence the name), and models of nuclear shape are something separate.

On a related note, I wonder if anyone is looking at Sn-100, which is also doubly-magic (using my definition). It’s listed on the table of nuclides as having a half-life of 0.94 seconds, which implies it’s been made in the lab and studied to some extent. Then again, the table of nuclides lists Sn-132 has having a half-life of 39.7 seconds, which is an order of magnitude longer than what’s given in the article. So I’m thoroughly confused. But as a Gemini, I never know what to expect.