It is that time of the year again, summer is here and classes are done! Working in the lab this semester has been exciting as I’ve transitioned back into a more analytical position compared to first semester. Where as in the beginning of the year we were still trying to iron out all the kinks associated with the leaching process, I spent this semester trying to see the results of that labor. So far its been….mostly cooperative. I realized as I started writing this that I don’t think I’ve laid out the project as a whole so far, so here it is! The whole aim of leaching the samples is to more accurately understand the activity of certain fallout radionuclides (FRNs), which can then lead a more thorough understanding of erosive patterns and where sediment is being sourced. The radionuclides we are looking at in particular are Beryllium-7 (7-Be), Lead-210 (210-Pb), and Cesium-137 (137-Cs).
Sediments build up these isotopes in two manners; as indicated by the F—for fallout—soil exposed to precipitation, as well as through the natural decay of other elements that already exist within the grains. The FRNs that are obtained through precipitation are considered meteoric, or unsupported, while the ones that are the result of radioactive decay are called in-situ, or supported. Understanding the relationship between unsupported and supported lead, cesium and beryllium allows for a greater insight into erosional patterns. Traditional techniques to obtain unsupported values allow a lot of uncertainty to exist; measurements are gathered by subtracting the total lead activity from the supported lead activity—two large numbers—thus getting a very small number. The leaching procedure that was developed by a former student in the lab, Adrian Singleton, seeks to remove this issue by being able to separate the grain coatings, where the unsupported isotopes should live, from the residue, where the supported isotopes should live.
There are three main samples that have been the primary points of interest in understanding this methodology: CH-122, CH-127 and V101. The two CH samples are from a previous field expedition to China and the V101 is from the Vermilion river right here in Ohio (pictures and a quick recap about that experience here). These samples are of particular interest because we sieved them to five specific grain sizes before conducting analysis. We followed the already established practice of sieving to <63 microns, 63-125 microns, 125-250 microns, 250-500 microns, and 500-850 microns. To make referencing each sample easier, we refer to the smallest one as A and progress through the alphabet until we get to the largest one. With each of these samples now being broken up into five, smaller and more defined samples, we then started leaching. This process involves adding four times the mass of the sample of 6M HCl to it, putting the sample in a sonic bath for 24hrs, and then centrifuging the resulting sludge-like content until you have a residue beaker and a leachate beaker, which then both need to be dried down completely. It’s a lovely process which started to have some interesting interactions with our fume hoods. We now neutralize the leachate containers before drying them down.
Just a side-note, CH-122, CH-127 and V101 were not neutralized before being dried down. Once the samples are dry we run them through a germanium detector to do gamma spectroscopy. This machine, (we call ours Harbin, Monica and Simon’s winter term post has a selfie with him in it) provides us the raw information about the activities of various FRNs. Anyways, most of that information probably could be found in older posts, but I just wanted to have one place that gives an overview of what this part of the lab does to prepare samples. What I did this semester was (try to in some cases) find and process (and run if need be) all of the relevant information about these samples. Processing the information involved incorporating various data associated with each sample, such as mass, sample height, and composition. With all of these values on hand, we’re able to put in a program that was made for us which does the calculations. Unfortunately, as with everything in the world, there are some hiccups and glitches that keep plaguing the program; as such some of the data we definitely do have is missing from the results. Here is what I was able to get though!
In order to be able to create a comparison between each of the samples, I looked at the subtracted area results produced from Harbin. This is the total counts reported subtracted by the background noise associated with the atmosphere of each FRN. The only sample actually missing data within this set is CH-127, the AL, BL, and CL samples for some reason wont return results. CH-122 AL, AR, and BR appear to be missing results but actually just have reported significantly higher than the rest of the data set, with values of 1162, 1005 and 927 respectively.
There is a clear trend displayed with CH-122 and V101 where the counts of lead decrease from A-CL and then start to rise again from there on out. The residue from CH-122 500-850, ER, does show negative count values for lead, which is surprising as the other two samples both indicate the residue having a greater value with the residue than what is seen in the leachate. CH-127 is kind of all over the place and hard to make out as it is missing so much information. The beryllium and cesium information is harder to make out since, for the most part, it is negative. Within the two CH samples it appears to be positive after C, which would indicate that it is only the larger grains which are holding those FRNs in particular. This trend is not clearly expressed within V101 though, as it produces an almost sin-like curve.
Overall, this semester—and year too—have been a blast. Getting to see information that is a result of our leaching work is really exciting. I’m looking forward to these errors and glitches being fixed so that the rest of the relevant information about these samples can be analyzed too. As for my future work in this lab, I’ll be switching gears and focusing on a different location entirely. This summer I’ll be working in the Dominica, doing similar research on that region as a part of this years frontier KECK project. Amanda and I will be there for the second half of June actually collecting the sediment and then flying to Union College in New York to begin analysis for another two weeks. After that is over I’ll be back in the lab, continuing to work on that project!
Until next time,