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[HQR06-P01] Dependencies of ESR intensities for trapped charges in quartz on depth from outcrop surface
Keywords:electron spin resonance, sediment, depth, quartz, trapped charge
Electron spin resonance (ESR) dating of a quaternary sediment is a technology with the poten-tial to directly determine the age of the last sedimentation[1, 2]. This method assumes that charges trapped in defects (trapped charges) in quartz in a sediment have been released by sunlight expo-sure (optically bleaching) during processes of erosion, transportation, and/or sedimentation, then trapped charges are accumulated by natural radiation during a process of burial. The number of the trapped charge depends on the radiation dose. Hence, dividing the total dose obtained from the number of the accumulated trapped charges up to the present by an annual dose, a depositional age can be estimated. A sediment which has exposed to sunlight during a burial process must avoid being used for ESR dating, because its depositional age is underestimated. Thus, the sample is col-lected with a dark curtain, a plastic tube, or metal tube and its section of ~5 cm depth from an out-crop surface in strike direction is conventionally removed[3]. However, the correct depth to be re-move is not clearly demonstrated and unchecked each time. Previous studies have reported that the closer to the surface, the lower the number of trapped charges detected by optically-stimulated lu-minescence measurements and the longer sunlight exposure bleaches the trapped charges deeper into the rock[4]. Therefore, it is crucial to reveal the effect of sunlight exposure on trapped charges detected by ESR measurements in a surface layer of an outcrop. This study aims to quantitatively investigate relationships between three different trapped charges and depth in the strike direction.
Two samples were collected with poly vinyl chloride pipes with a diameter of 4 cm and a length of 35 cm from a terrace deposit located at the altitude of 30–33 m in Nanao-shi, Ishikawa prefecture. One sample is silty aeolian loam and the other is silt to fine marine sand. Sample prepa-ration was performed in a red-light room. The loam and marine sand samples were cut into three and seven pieces, respectively. Quartz grains with a diameter of 73–250 µm were isolated by siev-ing, HCl, H2O2, magnetic separation using a neodymium magnet, heavy liquid separation using sodium polydentate, and hydrofluoric acid. ESR measurements to detect the E1’ center[5], the Al center[6] and the Ti center[7] were conducted for the quartz grains with weights of 84–200 mg. The peak-to-peak heights at g value ≈ 2.001, g = 2.018–1.993, g = 1.913 of the E1’ center, the Al center, and the Ti center, respectively, calibrated by that of the standard material were calculated as their ESR intensities.
For the loam sample, ESR intensity for the E1’ center remained constant regardless of depth in the strike direction. Whereas ESR intensities for the Al and Ti center at depths of 20 and 30 cm were greater than that at a depth of 10 cm, respectively. For the marine sand sample, ESR intensi-ties for all the trapped charges at depths of 3–14, and 33 cm were approximately equal, whereas the intensities were greater than those at depth of 20–30 cm.
Funding: This study was funded by the Ministry of Economy, Trade and Industry (METI), Japan as part of its R&D supporting program titled “Establishment of Advanced Technology for Evaluating the Long-term Geosphere Stability on Geological Disposal Project of Radioactive Waste (Grant Number: JPJ007597, Fiscal Year 2022)”.
References:
[1] Yokoyama et al., 1985. Nucl. Tracks Radiat. Meas., 10, 921–928. [2] Quaegebeur and Yokoyama, 1981. Ab-solute dating and Isotope Analysis in Prehistory-Methods and limits (Edited by Lumley H. de and Labeyrie J.), 557–564. [3] Moreno et al., 2017. Quaternaire, 28, 161–166. [4] Ageby et al., 2023. Radiat. Meas., 166, 106962. [5] Rudra and Fowler, 1987. Phys. Rev. B 35, 8223–8230. [6] Nuttall and Weil, 1981. Can. J. Phys., 59, 1696-1708. [7] Isoya et al., 1983. Chem. Phys., 78, 1735–1746.
Two samples were collected with poly vinyl chloride pipes with a diameter of 4 cm and a length of 35 cm from a terrace deposit located at the altitude of 30–33 m in Nanao-shi, Ishikawa prefecture. One sample is silty aeolian loam and the other is silt to fine marine sand. Sample prepa-ration was performed in a red-light room. The loam and marine sand samples were cut into three and seven pieces, respectively. Quartz grains with a diameter of 73–250 µm were isolated by siev-ing, HCl, H2O2, magnetic separation using a neodymium magnet, heavy liquid separation using sodium polydentate, and hydrofluoric acid. ESR measurements to detect the E1’ center[5], the Al center[6] and the Ti center[7] were conducted for the quartz grains with weights of 84–200 mg. The peak-to-peak heights at g value ≈ 2.001, g = 2.018–1.993, g = 1.913 of the E1’ center, the Al center, and the Ti center, respectively, calibrated by that of the standard material were calculated as their ESR intensities.
For the loam sample, ESR intensity for the E1’ center remained constant regardless of depth in the strike direction. Whereas ESR intensities for the Al and Ti center at depths of 20 and 30 cm were greater than that at a depth of 10 cm, respectively. For the marine sand sample, ESR intensi-ties for all the trapped charges at depths of 3–14, and 33 cm were approximately equal, whereas the intensities were greater than those at depth of 20–30 cm.
Funding: This study was funded by the Ministry of Economy, Trade and Industry (METI), Japan as part of its R&D supporting program titled “Establishment of Advanced Technology for Evaluating the Long-term Geosphere Stability on Geological Disposal Project of Radioactive Waste (Grant Number: JPJ007597, Fiscal Year 2022)”.
References:
[1] Yokoyama et al., 1985. Nucl. Tracks Radiat. Meas., 10, 921–928. [2] Quaegebeur and Yokoyama, 1981. Ab-solute dating and Isotope Analysis in Prehistory-Methods and limits (Edited by Lumley H. de and Labeyrie J.), 557–564. [3] Moreno et al., 2017. Quaternaire, 28, 161–166. [4] Ageby et al., 2023. Radiat. Meas., 166, 106962. [5] Rudra and Fowler, 1987. Phys. Rev. B 35, 8223–8230. [6] Nuttall and Weil, 1981. Can. J. Phys., 59, 1696-1708. [7] Isoya et al., 1983. Chem. Phys., 78, 1735–1746.