Tag Archives: nuclei

An Interesting Data Point on Climate

Particles are just so cool, and so very useful.  Scientists can learn about the past — for example, past climate — using “carbon dating”, a combination of biology and nuclear physics.

In this article in Geophysics Letters, covered in this Colorado University press release (with a somewhat inaccurate title), the abstract contains the statements…

…the extent to which recent Arctic warming has been anomalous with respect to long-term natural climate variability remains uncertain. Here we use 145 radiocarbon dates on rooted tundra plants revealed by receding cold-based ice caps in the Eastern Canadian Arctic to show that 5000 years of regional summertime cooling has been reversed, with average summer temperatures of the last ~100 years now higher than during any century in more than 44,000 years,…

Now how does this work? Continue reading

Why Do Protons and Neutrons Form Nuclei, and Why Are The Nuclei So Small?

The Structure of Matter series continues: last week’s article on the basics of atomic nuclei is now supplemented with an article discussing the “residual” strong nuclear force which binds protons and neutrons inside of nuclei.  It further explains why nuclei are so small compared to atoms.  Or rather, it explains it in part, because I have to also explain why protons and neutrons themselves are so small — which I will do soon enough.

As always, readers are encouraged to comment on things that don’t seem clear or correct.  And any nuclear physics experts who want to weigh in on my presentation — suggesting how it might be improved or extended, or identifying misconceptions on my part — are encouraged to speak up (publicly or privately as you prefer).

Meanwhile, we’re entering the March conference season, when many new results from the Large Hadron Collider [LHC] (based on analysis of last year’s data) and from other important experiments will start appearing.  Since the LHC’s proton-proton collisions went til December in 2012 (in 2011 they stopped in October) the time for LHC data analysis has been rather short.  I therefore think it likely that any really surprising results from the LHC will be delayed for extra scrutiny — and may not appear until late spring or summer, when there are other conferences.  But I could be wrong!  And one thing we’re all waiting for is the measurement by CMS (one of the two general purpose LHC experiments) of the rate for the recently discovered Higgs particle to decay to two photons.   However, we won’t see that result until CMS is absolutely confident in it.

Additional Atomic Articles

I’ve been adding to my series of layperson’s articles on The Structure of Matter, which eventually will serve as an introduction to particle physics for those coming to this site for the first time. You might recall that in early December I supplemented my older article on molecules with an article on atoms. I got some terrific reader feedback, in the form of incisive constructive criticism, which allowed me to greatly improve the latter article. Well, readers, you’ve got another chance to help me out if you would like to — or you can just enjoy the read. I have three new articles (two of them short) which were put up over the last few weeks. These are:

Incidentally, the next stage in this series will be to describe electrons, and then I will turn to atomic nuclei, to the neutrons and protons that they contain, and eventually to the quarks and gluons that make up the neutrons and protons.

The Stability and Instability of the Neutron

One of the strange but crucial features of our world is that every type of atom except hydrogen contains neutrons in its nucleus, even though neutrons, on their own, decay (to a proton, electron and anti-neutrino) within about 15 minutes on average.  At first glance this seems puzzling.  At second glance too.  How can stable matter be made from unstable ingredients?

The reason this is possible has everything to do with Einstein’s special relativity, and the way mass and energy are intertwined there.  A crucial role is played by the energy that is most important for binding things together, which I’ve called “interaction energy”.

I’ve now written an article explaining why neutrons inside of nuclei can be stable, giving the example of the deuteron (one proton bound to one neutron) which is the nucleus of “heavy hydrogen”, or “deuterium”.  If you understand this example, you’ll basically understand the point for other nuclei as well.

[For those of you in the New York City area: I’ll be joined by the wonderfully talented singer-songwriter-pianist Andrea Wittgens in giving a physics/music joint performance/presentation at the storied Cornelia Street Cafe, Sunday May 13th at 6 p.m., as part of their Entertaining Science series.  It’s entitled Rhapsody for Piano and Universe, and intended for the general public.  The place is pretty small, so get reservations in advance.]