Hillslope asymmetry update (4)

The last couple of weeks of research was pretty busy. My advisor and I spent some time moving the gamma detection lab from Millington to ISC 3. We have started to set up the detectors that we will use to count the Cesium-137 in the samples in order to help get the erosion rates if you recall. We have 2 detectors currently working, and one waiting to be fixed. These are gamma ray detectors. In order to be able to effectively count, these detectors need to be shielded from natural radiation. That is, there are many common radioactive elements that are decaying in the earth. Unless these are shielded from the detector, the detector would include these rays coming from the ground and the walls in the count, which we don’t want. In order to avoid this we used lead bricks and copper to build an effective shield. We surrounded the detector with a layer of copper first before extending the shield at least 4 inches in every direction with the lead bricks (We did more than 4 inches though for certainty). These lead bricks were generally about 8 by 2 inches and were very heavy. They proved annoying to work with, especially when I had to carry a few across campus to the metal shop (to get cut) in 95-degree weather and 90% humidity. Needless to say I may have temporarily developed back problems. In the end we built a pretty good shield (see picture below). Thankfully for the other detector there was a premade shield and a majority of what we had to do was put the detector in the premade shield. Once in the shield some smaller lead bricks were used to make a shield within the shield. Some copper was also placed over the lead, blocking the lead from the detector directly. It seemed as though the detectors were ready to go and start counting the samples. For these detectors to work they have to be chilled. They are connected to liquid nitrogen tanks that are refilled every couple days. In order to find out if the shields we made were effective, we started out by running a blank for a background count. We put in an empty petri dish, taped and wax sealed, just like the samples. After running background counts on the detectors it seemed as though the shield we built worked pretty well. In the last week I began counting the first of my samples. Unfortunately to get a good count it needs to run for about 24hours. Throughout the Fall semester the samples will be counted and hopefully give us the Cesium data needed to calculate erosion rates on the hill slopes being studied.

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hillslope asymmetry update (3)

As I previously wrote, my samples have to be sealed and sit for at least three weeks. While waiting for this time period to pass, much of what I’ve been doing has been reviewing my proposal and beginning to write the ‘Introduction’ and ‘Method’ sections for my thesis. For this reason this blog will be relatively short. In starting to write my Introduction and Method sections, much of it has consisted of a literature review. I’ve been reading different scientific articles regarding previous research on hillslope asymmetry and valley asymmetry. These articles have been good as they give a background on the subject and serve somewhat as a guide for the structure of my thesis. I’ve found some of the studies to be somewhat inconsistent, with varying causes of hillslope asymmetry found with different groups and study areas. Mechanisms of asymmetric hillslope formation proposed in the literature can generally be grouped into two categories: (1) asymmetry caused by differences in the lithology and bedrock structure and (2) microclimate induced asymmetry- asymmetry caused by differences in microclimate on opposing hillslope sides. I’ve so far gotten a very good start to these sections. I will continue to read these articles in order to gather enough information to give a solid synopsis of past research on the topic for my introduction, and to continue to structure my thesis.

Hillslope Asymmetry update (2)

Reading from my last post you know that we collected 117 samples for the purpose of detecting Cesium-137 concentrations. After collection of the samples they were oven dried at 105° C for at least 48 hours. I then spent a couple days weighing all the samples to obtain the oven dried mass. At this point the samples were all in chunky, hard blocks. The soil samples had to be ground down to a very fine clay like size in order for the gamma spectrometry to work. This was done pretty much manually, grinding them down with my hands or with the help of a shovel or hammer. The organic layer samples (consisting of leaves, twigs, roots etc.) were ground down carefully using a Wiley mill.

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Hillslope Asymmetry work update (1)

In continuing my work with hillslope asymmetry, one of the most helpful things will be getting the erosion rates on the slopes. In order to determine the erosion rates for the slopes I’ll be employing the use of Cs-137 concentrations as described in my first post. At the study area in the college woods, we decided to pick ten sample locations along a straight hillslope transect.

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Abstract: Analyzing Hillslope asymmetry using erosion rates calculated with radioactive Cesium-137


My name is Korede Olagbegi and I am rising senior here at William & Mary. I am a geology major at the college and I play soccer here as well. I will work on research this summer along side professors James Kaste and Gregory Hancock of the Geology department.

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