The purpose of this proposed study is to determine the maximum radiation dose of detrital epidote-group minerals collected from large river delta sediments. Because these minerals are sufficiently resistant to chemical weathering and survive into delta sediments, the maximum radiation dose measured will reflect a threshold of solubility. Based on previous studies completed on zircon and epidote-group minerals, the hypothesis of this study is that detrital epidote-group mineral grains that have experienced radiation doses less than ~3.5 * 1015 α-decay mg-1 will be resistant to chemical weathering.
Epidote-group mineral grains will be extracted from Nile and Yangtze River delta sediments as both sites contain significant quantities of epidote and allanite. The Nile and Yangtze Rivers possess two of the world?s largest watersheds. Because the delta sediments originated from large watersheds underlain by crystalline silicate bedrock of varying age and lithology, the suite of epidote-group minerals derived from these sediments should span the range of compositions and radiation damage commonly observed in nature for grains resistant to dissolution.
The grains extracted from the delta sediments will be verified as being epidote-group by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). For each epidote-group mineral grain utilized in this proposed study, major and trace element analyses will be completed. Major element analyses will be determined by electron microprobe (EMPA), and trace elements (e.g., U, Th, REE) determined by laser-ablation microprobe-inductively coupled-mass spectrometry (LAM-ICP-MS). The α-decay damage in the individual epidote-group mineral grains will be calculated using their age and radionuclide concentration.
The broader impacts of this proposed study will be addressed in three different ways. First, Millersville University is an undergraduate institution and as a result undergraduates will be actively involved in the project. Second, this project will permit establishment of a relationship between undergraduate Millersville University and the Ph.D.-granting Memorial University of Newfoundland, Canada. Third, there will be development of an exhibit at the Lancaster Science Factory, located approximately 6 km from Millersville University near downtown Lancaster, Pennsylvania. The Lancaster Science Factory provides numerous hands-on, interactive technology and science exhibits relating to the physical sciences, engineering, technology, and mathematics. The hands-on exhibit will be entitled ?Radiation in the Environment,? and will provide a digital Geiger counter with a wand that interfaces to a computer allowing for the detection of radioactivity among different materials. The materials will include rocks and minerals, including samples of epidote-group minerals, as well as more common household items such as pieces of granite countertop and ceramic bowls.
Bedrock forms at high temperatures well below the Earth’s surface. When erosion exposes bedrock at the Earth’s surface and the bedrock encounters atmospheric precipitation, some of the individual minerals that constitute the bedrock will dissolve. The mineral dissolution process involves consumption of carbon dioxide from the atmosphere. The minerals and carbon dioxide become dissolved in stream water that ultimately reaches the ocean. Once in the ocean, the dissolved minerals and carbon dioxide chemically react to form bedrock. As a result of this entire process, carbon dioxide is transferred from a gas in the atmosphere to solid bedrock in the ocean, thereby reducing the concentration of carbon dioxide in the atmosphere. Because elevated concentrations of carbon dioxide in the atmosphere may be capable of changing the global climate, identifying natural processes that remove carbon dioxide from the atmosphere is very important. Allanite is a mineral that occurs in very low abundances in bedrock, but its dissolution in precipitation at the Earth’s surface is capable of consuming disproportionately large quantities of atmospheric carbon dioxide. The reason for allanite being easily dissolved in atmospheric precipitation is that it contains radioactive elements that destroy the crystal structure of the mineral over time. From previous research it appears that allanite resists being dissolved until it reaches a specific level of radiation damage. That level of radiation damage is determined by the age of the allanite grain and the concentration of radioactive elements it contains. The purpose of this study has been to calculate the level of radiation at which allanite becomes easily dissolved at the Earth’s surface. It has been determined that the level of radiation at which allanite becomes easily dissolved is approximately twice as high as hypothesized. In other words, allanite is much more resistant to radiation damage than determined for other minerals. Knowing this allows future researchers to predict whether or not allanite at a given location will succumb to, or resist, being dissolved. If easily dissolved, then the quantity of atmospheric carbon dioxide consumed by its dissolving can be calculated. This discovery also has implications for the storage of nuclear waste, and contradicts earlier research. Because allanite is a very complex mineral, the results of this study may imply that any long-term nuclear waste repository should be constructed of materials with complex crystal structures and chemistries. To facilitate understanding of radiation and its use in our society, an exhibit at the Lancaster Science Factory, Lancaster, Pennsylvania, has been established. This exhibit includes a looping video that shows how radioactive elements undergo radioactive decay. In addition, numerous items are available, both natural and manufactured, against which a Geiger counter may be placed to detect any radiation being emitted. The manufactured items include fluorescent wrist-watch paint and fiestaware. Posters within the exhibit include all of the beneficial uses of radiation, including food sanitation, medicine, and energy.
