Spatial distribution and modelling of 239+240Pu in the sediments and seawater columns of the South China Sea and Indian Ocean.

In order to investigate the 239+240Pu potential influence in the ocean, and develop a new method for rapidly monitoring radioactive pollution, the 239+240Pu spatial distribution in the South China Sea (SCS) and the Indian Ocean (IND) sediments is analyzed by SF-ICP-MS (ELEMENT 2). The inventory-weighted mean activities of 239+240Pu were 0.413 ± 0.333 mBq/g, 0.128 ± 0.044 mBq/g, and 0.483 ± 0.606 mBq/g in the sediments of the SCS, eastern IND, and Arabian Sea, respectively. The 239+240Pu activity spatial distribution in the SCS sediments was influenced by the current, the vertical distribution of Pu in seawater, and the transport of particulate matter. The 239+240Pu activity spatial distribution in the IND sediments could be impacted by Antarctic Intermediate Water. The average of 240Pu/239Pu atomic ratios were 0.258 ± 0.034, 0.219 ± 0.031, and 0.212 ± 0.028 in the sediments of the SCS, eastern IND, and Arabian Sea, respectively. The 240Pu/239Pu atomic ratios in the SCS and IND indicate that Pu from the Pacific Proving Ground (PPG) is transported to the IND via the SCS internal current and transverse ocean currents within Indonesia. In addition, a seawater advection-dispersion equation (S-ADE) model is established based on the actual physical processes of radionuclides in the seawater column and well fitting results were obtained (R2 = 0.49 to 0.99). The 239+240Pu data and the geographic information from the sample site were used to correct the Pu distribution in the seawater. The calculated 239+240Pu mean concentrations in the surface seawater were 2.465 mBq/m3 and 2.205 mBq/m3 for the SCS and the eastern IND seawater, respectively, and the result is consistent with the previous measurements. Then, the 239+240Pu stored in the study area of SCS and eastern IND was estimated to be approximately 1.0-1.4% of the global ocean based on the model. This study provides a useful model for guiding and designing future monitoring of pollution by anthropogenic Pu and other isotopes.

Assessment of the depositional characteristics of the Yellow River estuary from 1960s by 239+240Pu and 137Cs.

The spatial and vertical distribution of 239+240Pu and 137Cs in the sediments of the Yellow River Delta was studied to evaluate the deposition dynamics in the Yellow River estuary from 1960s. The activity of 239+240Pu and 137Cs in sediment core ranged from 0.001 to 0.212 Bq/kg and 0.52-2.53 Bq/kg, respectively. A maximum accumulation peak and two secondary accumulation peaks appeared in the sediment core YR2. The average deposition rate of 8.3 cm/y for the Yellow River estuary from 1964 to 1976 was obtained. The proportion of Pu from the Yellow River net input and direct deposition to the total inventory of Pu in the estuary was assessed, with a total inventory of Pu in the abandoned estuary of 7.4 × 1010 Bq and a net input of 2.2 × 1010 Bq from the Yellow River. Pu deposited in the estuary only accounts for 18 % of the total Pu transported by the Yellow River, and most of the Pu is injected into the Bohai Sea with the Yellow River.

Spatial distribution, source identification, and transportation paths of plutonium in the Beibu Gulf, South China Sea.

To investigate the spatial distribution and source of plutonium isotopes in the Beibu Gulf, surface sediments were collected and analyzed using sector field inductively coupled plasma mass spectrometry (SF-ICP-MS). The activities of 239+240Pu in surface sediments ranged from 0.012 to 0.451 mBq/g (mean: 0.171 ± 0.138 mBq/g, n = 36), indicating a decreasing trend in a counterclockwise direction from the southern bay mouth. The counterclockwise decreasing trend in the south of the bay mouth is similar to the current in the Beibu Gulf. The 240Pu/239Pu atom ratios in surface sediments ranged from 0.156 to 0.283 (mean: 0.236 ± 0.031, n = 36), slightly higher than that of the global fallout value of 0.18. This suggests that the Pu in the Beibu Gulf was a combination of global fallout and Pacific Proving Ground (PPG). The average contribution of the plutonium (Pu) derived from the PPG in the sediment was estimated to be 52 % ± 24 %.

Radioactivity research in mosses from typical Karst Regions in Leye Tiankeng, Southern China.

Radionuclides in environmental ecosystems have ecotoxicity and health impact on human and environment, so radioactive contamination has always been one of the global concerns. This study mainly focused on the radioactivity of mosses collected from the Leye Tiankeng Group in Guangxi. The activities of 239+240Pu measured by SF-ICP-MS and 137Cs measured by HPGe in moss and soil samples are as follows: 0-2.29 Bq/kg in mosses and 1.5-11.9 Bq/kg in soils for 137Cs, and 0.025-0.25Bq/kg in mosses and 0.07-0.51Bq/kg in soils for 239+240Pu. The range of 240Pu/239Pu atom ratios (0.201 in mosses and 0.184 in soils) and 239+240Pu/137Cs activity ratios (0.128 in mosses and 0.044 in soils) indicated that the 137Cs and 239+240Pu in study area were mainly contributed by global fallout. 137Cs and 239+240Pu showed similar distribution in soils. However, their behaviors in mosses were quite different due to the differences in the growth environment of mosses. The transfer factors of 137Cs and 239+240Pu from soil to moss varied in different growth stages and specific environments. A weak positive correlation among 137Cs, 239+240Pu in mosses and soil-derived radionuclides suggested that resettlement was predominant here. The negative correlation between 7Be, 210Pb and soil-derived radionuclides indicated that 7Be and 210Pb came from atmospheric components, while the weak correlation between them suggested that their specific sources were different. The Cu and Ni were moderately enriched in mosses here due to the use of agricultural fertilizers, At the same time, Zn was at a high level in the Lilang area, where transportation was more developed.

Beam alignment based on two-dimensional power spectral density of a near-field image.

Beam alignment is crucial to high-power laser facilities and is used to adjust the laser beams quickly and accurately to meet stringent requirements of pointing and centering. In this paper, a novel alignment method is presented, which employs data processing of the two-dimensional power spectral density (2D-PSD) for a near-field image and resolves the beam pointing error relative to the spatial filter pinhole directly. Combining this with a near-field fiducial mark, the operation of beam alignment is achieved. It is experimentally demonstrated that this scheme realizes a far-field alignment precision of approximately 3% of the pinhole size. This scheme adopts only one near-field camera to construct the alignment system, which provides a simple, efficient, and low-cost way to align lasers.