Nuclear weapons without 90%-enriched uranium

A correction. Some days ago I said that one needs to enrich uranium to at least 90% to build a bomb. However, the nuclear engeneer Sérgio Guerreiro Ribeiro remembered in "O Globo" (in Portuguese) that it is not necessarily so. It is also possible to make it with plutonium-239 (Pu-239), that is produced as “waste” in common nuclear power plants. And a bomb needs about 8 kg of Pu-239, against 25 kg of uranium-235. Plutonium produced normally in power plants have 60% of Pu-239 and a weapon needs 93%, but there are techniques to reach this proportion. Useful numbers to assess scenarios...

Science in Africa

Wading through the web, I found an interesting set of texts about African science, collected by Scidev. According to one of them (in PDF), by three Thomson Reuters experts, the countries with the largest numbers of scientific papers in that continent are South Africa, Egypt, Algeria, Kenya and Nigeria. Now prepare yourself for some surprises. Namibia ranks third in... space science researches. Just as Uganda in immunology and Ethiopia in... economics & business. The last two are normally associated only with poverty, famine and war. I’m glad to say, reality is just more complex than that.

Nanomemory

Writing about nanowires that exhibit memory effects. When light containing information hits it, this nanowire can, in some cases, absorb the light and keep part of the information in the energetic levels (excitations) of its atoms for some time – and then reemit the light back. In other cases, it has no memory effects. Having or not having memory can be controlled with the incident light – and this is the major achievement of a research made in Brazilian and Cuban universities and published last year. Slowly we see the pieces of nanoscale artifacts being thought, built and put together!

An old samba

Ludic interlude. Here is a song that cites who is considered the greatest Brazilian physicist, Cesar Lattes (1924-2005): “Ciência e Arte” (“Science and Art”), by Cartola and Carlos Cachaça, released in 1979. It mentions also the great architet Pedro Américo – one scientist and one artist. One can listen Gilberto Gil’s version in his CD “Quanta”, that has some other songs about “science and art”, in a very poetic way – and also a letter from Lattes himself (in Portuguese) that finishes quoting another architet, João Batista Artigas: “When Science clams up, Art talks”. Good listening!