![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
Entry tags:
A very analytical week
This has been a week of new data acquisition for my thesis project. On Monday I spent eight hours using the Laser ICPMS. This involves using a laser to zap away layers of a mineral and then Inductively coupled plasma mass spectrometry (ICPMS) to analyse the gasses released to determine what isotopes of specific elements are present. You tell it which elements/isotopes to look for, and it tells you how much, if any, is released when the laser vaporizes a layer of the mineral. Needless to say, you set it up with a specific list of things to look for based upon what mineral you are using, and what information you are looking for. On Monday I actually wound up analysing three different minerals, zircon, rutile, and monazite. The zircons we were calculating the amount of time which has elapsed since they crystallized, the rutile we were checking to see at what temperature they formed, and the monazite was just two grains to see if the amount of time since crystallization matches the "young" generation of 500 million year old grains, or the "old" generation around 1200 million years old that I've seen in other samples from the region. (these were old).
Using the Laser ICPMS is an interesting process. First you find a grain to analyse, then you turn the laser down to 1 Hz and zap the grain for six seconds, to remove the outermost layer (which may well contain contamination from the polishing compound or other sources). This is done using the left hand computer & mouse. Then, using the computer & mouse on the right, you tell the screen which is analysing the vapour released by the laser to "re-start run" (thereby discarding the contaminated measurements). Then, returning to the left-hand computer/mouse you close the gate over the laser so that it can't reach the sample, and push the laser fire button (which triggers the measuring to begin on the right-hand computer) and change the laser strength up to your actual working level (I used 5 Hz) and wait until the right hand computer has collected 30 seconds of "background" data, then you open the gate so that the laser, which has been on for the full 30 seconds, starts zapping the sample again. After another 30 seconds of collecting real data, the data collection window closes, and it is time to stop the laser (left hand mouse) and record the amount of energy it reports having use in the spreadsheet (right hand computer/mouse) before moving to a new grain and staring the process over. In addition to switching between these two computers, I also had my computer present, with a photograph of the entire sample open in CorelDraw so that during the 30 second intervals in which I was waiting I could label the photograph marking which grains I zapped with the number recorded in the analysis results spreadsheet. Needless to say, after analysing some standards, followed by a dozen grains of my sample, followed by more standards, followed by another dozen of my grains, followed by more standards, etc. the repetitive nature of the project means that you start to make silly mistakes, like grabbing the wrong mouse and having nothing happen when you try to start or stop the laser. The good news is that because you are sitting right there as it does the analysis, you can be certain that the grain you are analysing is actually the mineral you expect. The zircons have a pattern wherein the yellow and the green lines are very much higher than any of the other lines. Therefore if you start zapping a grain and those two don't rise you can hit the "restart run" button and move on to a new grain.
On Tuesday morning I received an e-mail telling me that the microprobe has been repaired, and that if I am keen I could use it that evening starting at 16:00. I had already arranged to be at uni at 15:00 because one of the two sample mounts we'd prepared for the laser the week before turned out to not have enough zircon in it, but the guy helping me thought that if we returned to the remaining lose grains we hadn't mounted that he would be able to separate out the monazites, which are very common in that sample, using a thinner piece of paper over the magnet. So I said "yes" to the probe time and took an early nap so as to be alert in the early evening. It was actually a joy to be back on the microprobe, I very much like that machine. It has both an optical camera and it provides one with back scatter electron images (amongst other options). It is quite easy to distinguish minerals in the BSE images based on their brightness. Quartz, being comprised of "light" elements (Si and O) is very dark and garnet, having heavier elements (including Fe, Mg) is brighter, and monazite is brighter yet (because of things like U, Th, Pb). Since my goal with the microprobe is to calculate the temperature and pressure of formation of minerals, I need to analyse all of the major minerals present, and keep a record of which grains are which. Once upon a time people kept a record by making a drawing of the grains they were analysing. These days I take a photo, print it out, and write on the photo. *Much* easier! Then, when I get my results, I plot the x-y coordinates in ArcMap and import the photo and align them with the analysis spots, so that I can easily tell which grains were analysed, and which spots on the grains.
On Wednesday evening I returned to the Laser to analyse the zircons in the new sample mount we'd made on Tuesday. Someone else was scheduled to use the laser during business hours, so I came in at five to get started. They got me set up, showed me how to turn everything off at the end of the evening, and left me to work. Around 8:30 I finished up, shut things down and went home. It is actually really delightful to be trusted with both the Microprobe and the Laser to work on my own, and in the case of the 'probe, set it up and tell it to "run" and go home, and in the case of the Laser be trusted with the keys to go shut down the plasma, the argon, and the helium (all located outside the building in little sheds).
It has been fun to return to data collection, and I hope that the new information will give good results. But in the mean time, I've made no new further progress on my thesis writing. At least I got that job application sent off.
Using the Laser ICPMS is an interesting process. First you find a grain to analyse, then you turn the laser down to 1 Hz and zap the grain for six seconds, to remove the outermost layer (which may well contain contamination from the polishing compound or other sources). This is done using the left hand computer & mouse. Then, using the computer & mouse on the right, you tell the screen which is analysing the vapour released by the laser to "re-start run" (thereby discarding the contaminated measurements). Then, returning to the left-hand computer/mouse you close the gate over the laser so that it can't reach the sample, and push the laser fire button (which triggers the measuring to begin on the right-hand computer) and change the laser strength up to your actual working level (I used 5 Hz) and wait until the right hand computer has collected 30 seconds of "background" data, then you open the gate so that the laser, which has been on for the full 30 seconds, starts zapping the sample again. After another 30 seconds of collecting real data, the data collection window closes, and it is time to stop the laser (left hand mouse) and record the amount of energy it reports having use in the spreadsheet (right hand computer/mouse) before moving to a new grain and staring the process over. In addition to switching between these two computers, I also had my computer present, with a photograph of the entire sample open in CorelDraw so that during the 30 second intervals in which I was waiting I could label the photograph marking which grains I zapped with the number recorded in the analysis results spreadsheet. Needless to say, after analysing some standards, followed by a dozen grains of my sample, followed by more standards, followed by another dozen of my grains, followed by more standards, etc. the repetitive nature of the project means that you start to make silly mistakes, like grabbing the wrong mouse and having nothing happen when you try to start or stop the laser. The good news is that because you are sitting right there as it does the analysis, you can be certain that the grain you are analysing is actually the mineral you expect. The zircons have a pattern wherein the yellow and the green lines are very much higher than any of the other lines. Therefore if you start zapping a grain and those two don't rise you can hit the "restart run" button and move on to a new grain.
On Tuesday morning I received an e-mail telling me that the microprobe has been repaired, and that if I am keen I could use it that evening starting at 16:00. I had already arranged to be at uni at 15:00 because one of the two sample mounts we'd prepared for the laser the week before turned out to not have enough zircon in it, but the guy helping me thought that if we returned to the remaining lose grains we hadn't mounted that he would be able to separate out the monazites, which are very common in that sample, using a thinner piece of paper over the magnet. So I said "yes" to the probe time and took an early nap so as to be alert in the early evening. It was actually a joy to be back on the microprobe, I very much like that machine. It has both an optical camera and it provides one with back scatter electron images (amongst other options). It is quite easy to distinguish minerals in the BSE images based on their brightness. Quartz, being comprised of "light" elements (Si and O) is very dark and garnet, having heavier elements (including Fe, Mg) is brighter, and monazite is brighter yet (because of things like U, Th, Pb). Since my goal with the microprobe is to calculate the temperature and pressure of formation of minerals, I need to analyse all of the major minerals present, and keep a record of which grains are which. Once upon a time people kept a record by making a drawing of the grains they were analysing. These days I take a photo, print it out, and write on the photo. *Much* easier! Then, when I get my results, I plot the x-y coordinates in ArcMap and import the photo and align them with the analysis spots, so that I can easily tell which grains were analysed, and which spots on the grains.
On Wednesday evening I returned to the Laser to analyse the zircons in the new sample mount we'd made on Tuesday. Someone else was scheduled to use the laser during business hours, so I came in at five to get started. They got me set up, showed me how to turn everything off at the end of the evening, and left me to work. Around 8:30 I finished up, shut things down and went home. It is actually really delightful to be trusted with both the Microprobe and the Laser to work on my own, and in the case of the 'probe, set it up and tell it to "run" and go home, and in the case of the Laser be trusted with the keys to go shut down the plasma, the argon, and the helium (all located outside the building in little sheds).
It has been fun to return to data collection, and I hope that the new information will give good results. But in the mean time, I've made no new further progress on my thesis writing. At least I got that job application sent off.