Monday, May 30, 2011

Geochemical googling

Razib over at Gene Expression has recently pointed out a new Google tool, which allows one to look for correlated searches and the geographic breakdown of those searches. Surprisingly, he failed to apply it to geochemistry. So I shall.

Here is the distribution for “Geochronology”

The three top correlated words or phrases were:
0.9361 porphyry
0.9315 f 650 gs
0.9309 bmw f 650

Which suggests that the f-series beamer bikes have been around for a geologically significant time period. I suspect the correlation refers to percentage of total searches from each state. I am not particularly surprised that the rocky mountain west is more geochemical than the rest of the country.

Not surprisingly, Zircon has a fairly similar distribution.

The matched terms are also bizarre:
0.8794 high density foam
0.8757 garmin geko
0.8719 snowboard gear

Archean is interesting:

The main distribution maps fairly well with the Archean Wyoming craton, one of the two Archean cratons in the US. I don’t know why the residents of the Superior craton are so disinterested in their geology.

It matches up with:
0.8993 motocross tires
0.8921 were wolves
0.8907 proterozoic

And finally, for a bit of soft-rock affirmative action, I looked at the distribution for global warming.

This was much more widespread, and interestingly, was somewhat inversely correlated with the temperature anomaly for the last 90 days (from NOAA):

Friday, May 27, 2011

Draft Asbestos statement deadline

A brief reminder that the comment period for the mineralogical society's draft asbestos statement ends tomorrow. Details here.

Tuesday, May 24, 2011

Work-life balance

Here in the lemming household, last night went something like this:

Pick up the little lemmings from daycare shortly after five, and Mrs. Lemming after that. Grab takeaway food, and have a family dinner before Mrs. Lemming heads back out for the night shift. Bath and story and bed the kids, clean up their mess, and grab a catnap while Mrs. Lemming works. When she gets back around midnight, grab the car and work in lab until 3 in the morning.

I apologize if the blog has been a bit quiet of late.

Monday, May 23, 2011

Rare Earth Revelry #5: Fission and neutron capture products

ResearchBlogging.orgWith interest in the Fukishima reactor disaster decaying at an exponential rate, I thought it would be an opportune time to take the long view of this phenomenon, and consider what sort of isotopic anomalies are left behind billions of years after an uncontained uranium fission reactor. And the best place to find these, of course, is Gabon.

Gabon is not known for its nuclear ambitions or industrial fiascos. It is a sparsely populated sub-saharan country known mostly for tropical rainforest and oil reserves. But crucially, it is also the host of the Oklo natural reactors. These are uranium deposits which naturally achieved criticality about 2050 million years ago. At that time, natural uranium had a much higher proportion of the fissionable 235U than modern uranium does, because the 235U had not yet radioactively decayed. So at this time, all uranium had a similar isotopic ratio to the isotopically enriched uranium used to commercial reactors (~3%). In the Oklo reactors, this allowed parts of these uranium deposits to achieve criticality, and they bubbled away as natural boiling water reactors for tens to hundreds of thousands of years.

Because there was no containment system- it was just a rock- these fossilized reactors are great for tracking the movement of radioactive materials and their daughter products. These have been extensively studied, and the study we’ll focus on today is Hidaka and Kikuchi (2010).

There are two main types of tell-tale isotopes produced in nuclear reactions.

The first are the fission decay products. When a uranium atom splits, these are the fragments left over. Must fission decay products are neutron rich and highly radioactive, and they to quickly decay by beta decay to form stable isotopes of the same nominal mass. The mass of fission decay products can be quite variable, but the heavier ones, with a mass greater than 139 amu, end up decaying to form light rare earth elements such as cerium or neodymium. The ratio of isotopes produced by fission is different to the ratio of isotopes produced by stellar nucleosynthesis, so fissionogenic Nd or Ce be distinguished from naturally occurring Nd or Ce by its isotopic ratio.

Nuclear fission of uranium does not just produce fission products. It also produces free neutrons. The neutrons are what allow the process to continue. A 235U nucleus which absorbs a neutron will often fission, releasing additional neutrons, so when the 235U is concentrated enough for one neutron from each fission to cause another fission, the reaction is considered critical, and will be self-sustaining.

Of course, 235U is not the only nucleus which can absorb a neutron. A variety of nuclear reactions can absorb neutrons. One of the most common is neutron capture, where a neucleas simply captures the neutron, increasing its atomic mass by one and releasing the excess binding energy as a gamma ray. The ability of nuclei to capture neutrons is expressed as their neutron capture cross section, and the cross sections of various nucleii vary by many orders of magnitude.
Three of the nuclei with the largest cross sections are rare earth elements, 149Sm, 155Gd, and 157Gd. These react with neutrons to form 150Sm, 156Gd, and 158Gd, respectively, and these reaction products have much lower cross sections, so are unlikely to absorb further neutrons. As a result, the Sm and Gd isotopic ratio of pre-existing Gd and Sm in the reactor zone will change. Table two shows that in the reactor zone, the 149/147 ratio can be two orders of magnitude lower than the non-radiogenic value.

What the Hidaka and Kikuchi study does is to look at the isotopic ratios of Ce, Nd, and Sm (along with other non-REE isotopes) in individual mineral grains from various Oklo rocks using the SHRIMP. This allows them to determine where the isotopically distinct REE from the reactor zone have traveled, and which mineral phases and reactions have caused them to be immobilized.

What the study shows is that the isotopcially anomalous REE dispersed quite easily through the underlying sandstone, but were effectively adsorbed by the clay overlying the deposit, so that the black shales above the clay layer show lower degrees of REE migration from the reactor core. The study also shows that this migration most likely occurred 1200 million years after the reactor went critical, in response to heating from a nearby mafic dyke intrusion.

Hidaka, H., & Kikuchi, M. (2010). SHRIMP in situ isotopic analyses of REE, Pb and U in micro-minerals bearing fission products in the Oklo and Bangombé natural reactors: A review of a natural analogue study for the migration of fission products Precambrian Research, 183 (1), 158-165 DOI: 10.1016/j.precamres.2010.07.012

Monday, May 09, 2011

Australia and the carbon tax

Tomorrow is budget day, the day in which the federal treasurer announces all the revenue raising and spending plans for the next fiscal year. One of the expectations for this year is the introduction of a carbon tax, which is being touted as the next best thing after the government failed to get an emissions trading scheme running about two years ago.

Australia is in an interesting position, ith regards to carbon dioxide pollution and climate change. The 21 million residents of this country are sitting on about 76 billion tons of coal. If burned and kept in the atmosphere, that is enough carbon to increase the worldwide atmospheric carbon dioxide concentrations by about 10%, or 35 ppm.

Much of Australia’s food production areas are notoriously marginal, and both floods and drought can be devastating. So climate change could potentially do severe damage to both the agricultural sector, and many urban centers, in the form of bushfire, cyclones, flash floods, and other natural disasters.

On the other hand, at a ball-park price of $100 per ton, those 76 billion tons of coal are worth over 7 trillion dollars, assuming you can dig the lot up for free. But that isn’t a simple $300,000 per person. Both the coal reserves and the mining profits are distributed rather unequally at present.

About a quarter of this coal is used for producing electricity here in Australia, or for heavy industry like steelmaking. The rest is exported, mostly to Asian countries which are not bound by the Kyoto protocol. But even excluding the coal (and natural gas) exports, on domestic consumption alone Australians are among the most greenhouse intensive people on the planet.

However, despite the prevalence of coal, there are also amble supplies of sunshine, wind, uranium, geothermal, and natural gas here in Australia. So this is not a resource poor country.

As a result, there is huge scope for intelligent, detailed, and creative debate about how Australia should manage its climate exposure, greenhouse gas emissions, and other resources to maximize the benefit to our country. Simply finding the best way to do this is a broad enough topic to have many contrasting views and informed arguments. So it is really a shame that no such intelligent conversation has ever been had.

Instead, we have labor governments putting together packages in back-door deals and then trying to sell them with condescending slogans. And on the other side of politics, there is nothing but denial and obstructionism to even considering the questions. And the greens just want to freeze us all in the dark.

The result is that nobody has any idea what the released plan is, most people are sick of the wrangling and the issue, and despite endless posturing over the subject, Australians aren’t that much more knowledgeable about their energy situation. The only tyhing we can be sure of is that key industry groups and factions will have been taken care of, presumably at our expense.