Sensitivity vs. Stability

As a result of some really sloppy behavior on the part of our instrument yesterday, we tore the whole front end apart, put it back together, and then tuned it back up from first principles. It was a kick-ass learning experience, even if it did take all morning, because when we tuned it back up, we tuned for stability instead of sensitivity. I haven’t actually done that before.

Sensitivity is all the rage these days. You’d think that the geological community’s ICP-MS scientists were a bunch of SNAGS at a speed dating festival, the way they constantly go on and on about their sensitivity, counts per ppm and limits of detection. But stability is also important. Especially in certain contexts.

Yesterday, for example, we were measuring lithophiles in basalt. This sort of measurement doesn’t require sensitivity- any triple-thumbed numbnuts could detect them. In fact, the dilution factor is generally increased to prevent excess detector wear. The errors on the elemental ratios are not count-rate limited; they are limited by the drift in relative sensitivity for the various elements. So we managed to address that really well, and everybody went home happy on Friday afternoon.

Say "hello" to my little friends

Who would have thought that a few simple filaments of hydrated mantle could add so much complication to a home renovation? First person to correctly identify these minerals wins a rodent-sized isolation suit. I'll post more details once I get some sleep.
-LL

Tear down the walls.

My wife and I tore out our kitchen today, Good Friday. If we are lucky, a new kitchen will rise from the grave on Sunday. However, the timescale of this sort of miracle is sufficiently long that I suspect we will have to wait for the contractors. And pay them.

Clean insulators are a man’s best friend

Like all ICP mass spectrometers, our machine spews a lot of ionized gunk into the extraction lens and first lens stack, so after a couple of weeks of operation, these tend to get a little bit grimy. Usually this is no big deal. We swap in the clean sets, clean the dirty ones, and continue on our merry way. But halfway through last month, this technique stopped working.

The clean set of lenses was running at bizarre voltages, and the sensitivity was rather ordinary. So, we cleaned them again, but to no avail. In fact, we ended up purposely running the old, dirty set while we tried to figure out why the clean lenses were not working.

It turns out that taking the gunk off the lenses was necessary, but not sufficient, to restore the machine to its usual happy state. The insulators also had to be replaced, since they had gunked up as well.

So, dirty lens gunk seems to have the bizarre quality that it is insulative enough to build up a static charge sufficient to deflect the beam, but conductive enough to let voltage leak off the lenses. It just takes insulators a lot longer to gunk up to the point where they stop functioning properly, so we can get out of the habit of checking them. This just goes to prove that Murphy’s Law applies to dirt.

I have no idea what this gunk actually is. Most of the material that gets aspirated into the mass spectrometer is argon, which is well known for its reluctance to take solid forms. I suppose that if I really wanted to know what it was, I could just whack a spare dirty lens in the machine and blast away at the gunk deposits. But that would damage the lens more than the gunk does, since craters aren’t easily removed with a bit of polishing compound and some elbow grease.

Besides, it doesn’t really matter what it is, as long as we can prevent it from building up to the point where the machine stops working. It’s not like that knowledge would allow us to scrub less vigorously in order to remove it. So that question, for now, will continue to remain unknown.

Why I became a geologist

Occasionally, I have to do a little science to remind my boss why he pays me. The science I do is geology. It’s a good science- all about the science, not the egos or the cult of personality. Disciplines like physics or biology are filled with great men, and lofty ideas. Earth science is not lofty. Not even when dealing with atmospheres. We don’t go for lofty. We go for interesting, pretty, or cool.

Geology doesn’t have great men, either. There are historically important geologists. But they are men that only other geologists have heard of. And some of them, like Inge Lehmann and Mary Anning, are not actually men at all.

This is not to say that the great men of other disciplines haven’t had any impact on geology. Charles Darwin made important observations in the field of igneous petrology, and Ernest Rutherford was involved in some of the earliest geochronology attempts. But the practice of geology requires a certain amount of perspective; this tends to put the egotists and their self-importance in their properly insignificant place. Everyone in Earth science knows that, no matter how grand their theories or widely applicable their methods, Mother Earth is smarter than they are. Lest we forget, there is always the story of Lord Kelvin to remind us of the dangers of brash predictions.

Lord Kelvin is, of course, the big man of 19th century physics and thermodynamics. He was smart, he was proud, he was arrogant, and he decided that he would use his mighty intellect to determine the age of the earth. So, he measured and calculated, deduced and deducted, and came up with an age of 100 million years.

All the mud-digging, fossil picking geologists scratched their heads and said, “Look, buddy. No disrespect or nuthin’, but that number seems to be a bit on the small side. You know, `no vestige of a beginning, no prospect of an end’?” But Lord Kelvin would have none of it. He did the calculations, he did the maths, he solved the fundamental physics, and it was simply beyond rational comprehension that he could be wrong.

Only he was. Kelvin’s age was too young. 4,460 million years too young. Even the sedimentary rocks that underlie most of England are generally older than his estimate. Because, while he thought he had all the answers, the reality was that he didn’t know as much as he thought he did. And the unknown kicked his ass.

In geology, arrogance isn’t just an obnoxious personal trait. It is a professional hazard, and those who practice it invariably end up making themselves look monumentally stupid, on scales that boggle the mind. That is the main reason I like this profession.

The other, minor reasons are almost inconsequential. Obviously I don’t mind the fact that major meetings serve free beer at morning and afternoon tea. Sure, it’s great, but that is a minor perk, really. I could do better by tending bar for a living.

Geology also often involves a lot of travel. I don’t mind travelling. In fact, I rather enjoy it. But was this a major factor in my professional career? Absolutely not. In fact, I vehemently deny any suggestions that such a base motivation as tourism influenced my choice of an Australian PhD, with field work in Brazil. The meetings in Sydney, Cape Town, and Washington DC were a chore, not a perk. It was tough, serious science, and this is demonstrated by my forthcoming papers, “Porites point break: the impact of intensive surfing on the coral reef ecosystem”, and “The variable effect of sunscreen accumulation on cosmogenic nuclide production in beach sands: Gold Coast vs. Copa Cabana.”

Fire and Ice

Some say the world will end in fire;
Some say in ice.*

Tomorrow we have a total fire ban declared for 24 hours starting at midnight tonight. We also have snow flurries predicted for areas above 1400 meters. I’ve lived in Canberra for over nine years now, but at no time have we had fire and snow forecast for the same day. Gotta love the local climate…

*Some Yank poet