• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.7 no.2
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• pp.78-86
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• 2002

Abundance, carbon biomass and chlorophyll a concentration of each size-fractionated plankton on the basis of trophical level were investigated in terms of spacial and temporal distribution, and interactions between each biological parameter and environmental factors in Jungmun coastal waters of Jeju Island from July 1999 to June 2000. Heterotrophic picoplankton (HPP) abundance averaged 1.4${\times}$$10^{6}$ cells ${\cdot}$ $ml^{-1}$ at of offshore and 8.3${\times}$$10^{5}$ cells ${\cdot}$ $ml^{-1}$ at inshore, while autotrophic picoplankton (APP) abundance 9.9${\times}$$10^{4}$ cells ${\cdot}$ $ml^{-1}$ at of offshore and 7.1${\times}$$10^{4}$ cells ${\cdot}$ $ml^{-1}$ at inshore. They were more abundant at of offshore than at inshore, and also more abundant than the other areas of Korean waters. On the other hand, heterotrophic and autotrophic nanoplankton (HNP, ANP) were more abundant at inshore than at of offshore. Microplankton (AMP) abundance was affected by diatom (r=0.962, P${\le}$0.001) at inshore and by dinoflagellate (r=0.868, P${\le}$0.001) at of offshore. However correlations between each plankton group in terms of size and trophic level were not significant. Carbon biomass showed as same as the distribution pattern of abundance, but composition percentage of each biomass of plankton group were quite different from that of abundance, representing the highest percentage in ANP. Seasonal fluctuation of chlorophyll a were different according to size class, showing the highest with 0.42 ${\mu}g$CHl-${\alpha}$${\cdot}$$1^{-1}$(57.9%) of APP in March 2000, 1.42 ${\mu}g$CHl-${\alpha}$${\cdot}$$1^{-1}$(74.7%) of ANP in May 2000, and 1.51 ${\mu}g$CHl-${\alpha}$${\cdot}$$1^{-1}$(81.8%) of AMP in July 1999. Correlation between biological parameters and environmental factors by principle component analysis revealed that the first factor as main explanation is the increasing of phosphorus and silica and the increasing of the at both of offshore and inshore. The N:P ratio were 36.4 at inshore and 32.6 at of offshore, showing the lack of phosphorus. Thus we suggest that phosphorus might be a main limiting factor to affect phytoplankton community in the study area.

• The Journal of Korean Society for Radiation Therapy
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• v.17 no.2
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• pp.141-145
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• 2005

Purpose : It is known that the neutron is generally generated from the photon, its energy is larger than 10 MV. The neutron is leaked in the container inspection system installed at the customs though its energy is below 9 MV. It is needed that the spacial effect of the neutrons released from radiation treatment machine, linac, installed in the medical canter. Materials and Methods : The medical linear accelerator(Clinac 1800, varian, USA) was used in the experiment. Measuring neutron was used bubble detector(Bubble detector, BDPND type, BTI, Canada) which was created bubble by neutron. The bubble detector is located on the medical linear accelerator outskirt in three different distance, 30, 50, 120 cm and upper, lower four point from the iso-center. In addition, for effect on protect material we have measured eight points which are 50 cm distance from iso-center. The SAD(source-axis-distance), distance from photon source to iso-center, is adjusted to 100 cm and the field size is adjusted to $15{\times}15cm^2$. Irradiate 20 MU and calculate the dose rate in mrem/MU by measuring the number of bubble. Results : The neutron is more detected at 5 position in 30, 50 cm, 7 position in 120 cm and with wedge, and 2 position without mount. Conclusion : Though detection position is laid in the same distance in neutron measurement, the different value is shown in measuring results. Also, neutron dose is affected by the additional structure, the different value is obtained in each measurement positions. So, it is needed to measure and evaluate the neutron dose in the whole space considering the effect of the distance, angular distribution and additional structure.