Every professional has a workhorse: something that makes life easier and better and they couldn’t live without. For Jamie Oliver-it’s a flagon of olive oil. For Jesus: sandals. For england’s cricket team: it’s the feeling you get when you lose. For the experimental petrologist among us, that thing is the laser ablation inductively coupled plasma mass spectrometer, or for short, the catchy acronym LAICPMS.
When people want to see what I do for a job, I normally show them the laser. Then I realize that its either off-its then just an inanimate object; or it’s on-and obnoxiously noisy and awful. However, the details are cool. Let me take you on a journey through light and space…
It all starts in a big orange box. I am not sure why it is so big, nor why it is orange. However the important thing is that in this box, a laser is generated. LAICPMS is sort of like inception, because the L stands for laser, which in itself stands for something. Nobody knows what it stands for, but it probably has something to do with invading people’s dreams.
The laser is then bounced around a series of mirrors and lenses… the lenses turn it from a mild sunburn-inducing laser to a highly focused, 1/100th of a mm wide beam, capable of CUTTING THROUGH SOLID ROCK. Now, this is nowhere near as exciting as a laser beam such as that possessed by the death star-it is unable to destroy planets (I haven’t tried but my supervisor wouldn’t be too happy) nor is it able to cut through James Bond type characters from the groin up. However, this ability to very accurately and precisely cut through rock is our friend-we take the little fragments burned out by the laser, send them down a tube, and into the PLASMA…
The rock thought it had been to hell and back after the lasering. Turns out, it wasn’t even started. The ICP of LAICPMS refers to an inductively coupled plasma – a plasma is sort of like a gas – except in this case, its really really hot. I mean, really hot. The plasma in our lab is burning at around 8000 degrees, not too dissimilar to the surface of the sun. The rock pieces that have been torn away from their brothers by the laser are then cast into the plasma. They never stood a chance. The poor bastards get ionised (or ionized if you are American and can’t spell) – they are stripped of electrons and turned into ions – the inferior, highly charged little brothers of atoms.
Following this, the little ions are thrown into a mass spectrometer, the atomic version of being inside a jetstar plane trying to land. By that I mean, they get thrown all over the place. Little ions, those of light elements (the top of the periodic table) get swung in a tight arc around a magnet, and get captured at the end of their ride by a detector – a little cup that counts every time it gets hit by an ion of the mass it expects. The heavy ions take a different path- – they swing on a different trajectory and are caught by the detectors in a different place.
The most amazing part of this is… the whole process from laser generation to counting ions can take as little as 0.5 seconds. Hardly enough time to get a cup of tea.
And after all this – what do we get? The mass spectrometer tells us how many of all the ions we are interested hit the detector in a certain time, and from this, we can work out (with the assistance of a computer or a local mathemagician) how much of each element is there. And from this, we can learn anything we like – the temperature the rock has been to, the pressure, how much oxygen was around, how long it stayed there or when it all happened. The possibilities are endless.
So next time you see a planet being exploded by lasers, or a man being cut in half, think about all the more useful things they could be doing. Like telling a few geologists some minor details they probably didn’t want to know anyway.