Tag Archives: Nuclear Physics

Five Years Since the 2011 Earthquake in Japan

It’s now been five years since the huge earthquake off the coast of Japan in 2011 and the subsequent tsunami and reactor meltdowns at the Fukushima Daiichi plant in Fukushima prefecture. Japan is just starting to try to turn some reactors back on and the Fukushima site still isn’t completely secured. The Fukushima Daiichi disaster is the second largest nuclear accident ever recorded (Chernobyl remains the worst). It’ll still be a long time before things are really cleaned up.

At the same time, there’s still plenty of fear-mongering about nuclear power. I’ve had people try to tell me that much of that region of Japan is now basically a radioactive wasteland (something that happens in a town like Boulder), which is very far from the truth. There is a closed zone around the plant (I’ve never been particularly close though) but even a few towns away things are safe.


Moniz Speaks on the Iran Deal

Last week, Boulder got a visit by the Secretary of Energy, Ernie Moniz, who gave a talk at the CU Law School on the Iran deal. While the DoE is one of the primary funding agencies for nuclear and particle physics, the general public doesn’t seem to realize what the DoE does. One of the main purposes of the DoE has always been nuclear research and security. Thus, the DoE is one of the main agencies that can evaluate the efficacy of nuclear nonproliferation agreements.

Moniz mostly gave a summary of the deal, which reportedly is much stronger than any previous such nuclear deal with any other country. I was hoping for some more technical discussion, but since this was a law school talk, it mostly dealt with the general terms and not too many technical details. Moniz did highlight the importance of the DoE and its staff in helping the US negotiation team.

Again, as this was a law school talk, time had to be spent on political reactions to the deal. Moniz obviously is pushing the position of the Obama administration, and I find his main argument to be pretty persuasive. The Iran deal as it stands now has been agreed to by all the countries involved (the so-called P5+1). Failing to pass the deal in the US does not bring the international sanctions back and the US has already had sanctions on Iran for so long that our sanctions alone can’t do much of anything. No one has offered a credible alternative (even military action isn’t particularly credible and would undermine US interests on all sorts of issues). My understanding is that building a basic nuclear weapon (similar to the ones the US built in 1945) is not actually that difficult once scientists work out how to enrich fuel, so the only long term solution to stopping someone from building a bomb is to convince them that they don’t need one. Basically, if the US hopes to achieve its foreign policy goals (and not just on this issue), approving the deal is the only realistic option. Anything else would make the US government seem like an unreliable partner in major international problems.

Borexino Measures Solar pp Neutrinos

Borexino has a new preprint where they try to measure neutrinos from proton-proton fusion in the sun. For a star the size of the sun, this is the main fusion reaction creating neutrinos and also releasing the energy that heats the sun. For a heavier star with a hotter core, the CNO cycle becomes the dominant fusion source. Proton-proton fusion generates most of the solar neutrino flux but is difficult to measure because the neutrinos don’t have much energy (less than an MeV). This energy range means that not only are other neutrino-generating processes important, but radioactive contamination in the detector, which has an active volume made of liquid scintillator, are important as well. Because there are significant backgrounds, the analysis needs to find the signal within a complicated spectrum of irreducible but well understood backgrounds.

The final result is consistent with theoretical predictions, so nothing surprising seems to be in the data. Borexino says that a measurement of pp neutrinos can help constrain the possibility of alternative models of solar power production.

New Geoneutrino Paper

The Borexino collaboration put out a new paper on geoneutrinos last week. Geoneutrinos are just the neutrinos left over from beta decays occurring within the Earth. They look for inverse beta decay events, which can be identified by looking for the signal of neutron absorption by hydrogen in the scintillator, which typically happens a few hundred microseconds after the primary event. The paper reports a spectrum of the initial scintillation signal (from an electron [neutrino] or positron [antineutrino]) for geoneutrinos and reactor neutrinos and then report an estimate of the total power output of uranium and thorium in the Earth. Interestingly, the value is actually quite close to the total power output from man-made sources.

National Labs and Nuclear Negotiations

The New York Times has a recent article about the role of the Department of Energy laboratory system in the nuclear negotiations with Iran. Many of the labs, such as Los Alamos, Oak Ridge, Livermore, and Sandia were founded largely to produce nuclear weapons. While weapons research is still something that the labs do, they have turned a lot of their efforts toward civilian science and energy projects. Helping with nuclear negotiations is something that the labs are highly qualified to do and is also a way to use nuclear weapons infrastructure for the purpose of nonproliferation.

New CUORE Double Beta Decay Result

CUORE has a new paper on searching for neutrinoless double beta decay in decays of tellurium-130. CUORE is a dedicated double beta decay experiment based in the LNGS (Gran Sasso) facility in Italy. The detector consists of bolometers made of tellurium dioxide crystals. The natural tellurium includes Te-130, which can undergo double beta decay. They find no evidence for neutrinoless double beta decay and thus set a limit on the half-life for that kind of decay of 2.7×1024 years, far longer than the age of the universe. They are also able to use different models to get sub-eV limits on the Majorana mass.