• The Journal of the Petrological Society of Korea
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• v.23 no.3
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• pp.239-247
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• 2014

The (U-Th)/He dating utilizes the production of alpha particles ($^4He$ atoms) during natural radioactive decays of $^{238}U$, $^{235}U$ and $^{232}Th$. (U-Th)/He age can be determined from the abundances of the parent nuclides $^{238}U$, $^{235}U$ and $^{232}Th$ and the radiogenic $^4He$. Because helium is one of the noble gases (non-reactive) with a relatively small radius, it diffuses rapidly in many geological materials, even at low temperatures. Therefore, ingrowth of $^4He$ during radioactive decay competes with diffusive loss at elevated temperatures during the geologic time scale, determining the amount of $^4He$ existing today in natural samples. For example, He diffusion in apatite is known to be very rapid compared to that in most other minerals, causing a significant diffusive loss at ${\sim}80^{\circ}C$ or higher. At ${\sim}40^{\circ}C$, He diffusion in apatite becomes slow enough to preserve most $^4He$ in the sample. Thus, an apatite's (U-Th)/He age represents the timing when the sample passed through the temperature range of $80-40^{\circ}C$. The crustal depth corresponding to this temperature range is called a "partial retention zone." Normal closure temperatures for a typical grain size and cooling rate are ${\sim}60-70^{\circ}C$ for apatite and ${\sim}200^{\circ}C$ for zircon and titanite. Because the apatite He closure temperature is lower than that of most other thermochronometers, it can provide critical constraints on relatively recent or shallow-crustal exhumation histories.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.11 no.2
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• pp.75-86
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• 2008

The wetlands have functions those were retention of diverse biota, purification of water quality, control of climate and flood, eco-tourism and supply of agricultural water, and that was the ecosystem of high biodiversity as the zone of transition between inland and water. Therefore, this study showed the conservation and management plan by analyzing in the abiotic and biotic environment of forest swamp, Gyeongsangbuk-do. The results were as follows. Examining the management plan of the abiotic environment, there will need to establish the hydrological plan in continuous expediting the supply of water to maintain a humid soil of swamp, and to try to find the organic farming, use of low toxic agrichemicals and so on to prevent occurring a non-point source pollutants. To prevent changing the flowing of ground water and inflow of earth and sand in modifying the land character, there will be needed to restrict the construction of farmland and slope around swamp. To manage the biotic environment, there needed to offer the habitat by removing the regular interval and individual of a dead tree, and to improve the growth environment of vegetation. Because the naturalized plants disturb the natural vegetation, they will be removed. The afforested trees like Robinia pseudoacacia and Amorpha truticosa will be renewed to prevent the heterogeneity of landscape ecology, and the active conservation plan on wetland species will be established. As this study was carried out to study on the partial swamp, Gyeongsanbuk-do, the ecological environments distributing a swamp in Korea show a some problem. In the future, the study will accomplish to study the accurately and objectively ecological environment and management of a swamp by analyzing the extensive sites.