固体气泡损伤探测器探测高能重离子的研究

用高能重离子Ar和C进行的实验表明：（1）高能重离子可以在固体气泡损伤探测器中产生径迹，重离子径迹呈直线形，由一连串微小气泡组成；（2）固体气泡损伤探测器探测重离子具有阈特性，阈的实质近似为临界能量损失率（dE／dX）C，这一阈特性与蚀刻径迹探测器类似。固体气泡损伤探测器的阈值为（dE／dX）c=2220MeV／g·cm2，可用于重离子物理、宇宙射线和宇宙暗物质探测以及癌症治疗模拟等领域。

POC fluxes from euphotic zone estimated from ^(234)Th deficiency in winter in the northwestern North Pacific Ocean

Dissolved and particulate 234 Th, particulate organic carbon(PON), nitrogen, and chlorophyll-a concentrations in the upper 200 m of water columns from seven stations in the northwestern North Pacific Ocean were determined in the winter of 1997.The dissolved, particulate, and total 234 Th activities (dissolved plus particulate)show a pronounced deficiency with respect to its parent 238 U in the euphotic zone whereas the total 234 Th shows a near-equilibrium at the depth greater than 100 m.The 234 Th data are used to derive the mean residence time, export fluxes of 234 Th, and fluxes of particulate organic carbon and nitrogen out of the euphotic zone. In the Subarctic Current area, the residence time of dissolved 234 Th with respect to its removal onto particles is 40 ~50 d while the residence time of dissolved 234Th in the subtropical area is about 20 d due to the Kuroshio's influence.The particulate organic carbon(POC)and particulate organic nitroge(PON)fluxes in winter range over 3.8～8.2 and 0.50～0.98 mmol/(m2 ·d), respectively, and are higher in the west region than in the east, and higher in the south than in the north. The co-influence of Kuroshio-Oyashio Currents with supply of nutrient substances from the coastal area and the light condition are two factors determining the horizontal distribution of POC fluxes in winter.The depth distribution of the chlorophyll-a as well as the consistence of the ratio of POC to PON with the Redfield ratio suggest that phytoplankton is the main contributor to the export of POC in this area in winter.The POC fluxes in the northwestern North Pacific Ocean in winter are comparable to some areas in the world oceans in spring and summer seasons.

Production of radioactive ~9C ion beam and its optimization

To explore the medical use of a radioactive 9C-ion beam in tumor treatment, which is a double radiation source coming from the external beam itself and the delayed particles emitted internally, some physical experiments are performed at the Secondary Beam Line (SBL) of Heavy Ion Medical Accelerator, Chiba (HIMAC) in Japan be- fore radiobiological research for exhibiting therapeutic value of the 9C beam. Intention of the experiments is for pro- ducing a radioactive 9C-ion beam with higher production rate and purity by means of optimizing the beam line pa- rameters. Finally, a produced 9C beam with the production rate of 9.07×10-6 and purity of 82.88% at full momentum acceptance has been obtained under the optimal conditions of 40 mm-thick beryllium target and 10 mm-thick alumi- num degrader. Both momentum distribution and contaminations for the produced 9C beam under the optimal condi- tions are measured. In order to execute further biological experiments of the 9C beam project, a uniform irradiation field is made with the wobbling magnets and its homogeneity is up to 93.8% inside central area of 20mm in diameter.

Expression of JunB Induced by X-rays in Mice

Objective To explore JunB gene expression in spleen cells of mice after the whole body irradiation as well as in normal hematopoietic and leukemia cells in the primary culture after different dosages of X-ray irradiation. Methods Spleen cells were isolated from the mice irradiated with 3 Gy X-rays. Primary cultured cells from mice were incubated in different intervals after X-irradiation at different dosages. Total RNA was extracted from the cells and the fluctuation of JunB mRNA level was assessed by the RNA ratio of JunB/b-actin measured by quantitative Northern blot hybridization. Results After the mice were exposed to 3 Gy X-rays irradiation, JunB expression in spleen cells was remarkably and rapidly increased, and reached its peak 0.5 h later in C3H/He mice and 1 h later in Balb/c mice. In the primary culture of normal spleen and leukemia cells, JunB mRNA levels increased 30 min after irradiation. The enhanced levels of JunB mRNA were returned to a normal level within 240 min after irradiation. Conclusions JunB gene is responsive to ionizing irradiation and is induced at immediate-early phase after the stimulation. This suggests that the JunB gene plays an important role in the early process of the cells against radiation.

Calibration Experiments for Identification of Space Heavy Ions by CR-39

A subject "Study of mechanism and application of space radiation induced mutation breeding on rice" has been established in NSFC, China. In order to verify space heavy particles being main cause (in addition, microgravity, vacuum, magnetic field etc.) of induced biological effects in space and in order to study correlation of various mutation and its serious degree with different particle parameters, measurement and identification of the particles are necessary. CR-39 sheets are a part of a sandwich detecting system. The system consists of rice seeds and CR-39 solid state nuclear track detectors. The seeds hit by space particles could be determined withetched tracks in CR-39. Furthermore, the space heavy particles could be identified with measured parameters of the tracks such as residual range and etch rate.

Biological effects of radioactive ~9C-ion beams on cells

The distinguishing feature and current technique progress of tumor treatment with heavy-ion beams is introduced in the paper. Additional superiority to tumor treatment from a radioactive ion beam (RIB) is emphatically discussed. The experimental research of the radioactive 9C-ion beams aimed at tumor treatment at Heavy Ion Medical Accelerator in Chiba (HIMAC), National Institute of Radiological Sciences (NIRS), Japan is described in detail, La-eluding production of the beams, optimization of parameters, distribution of depth dose, survival effect of cell and comparison of RBE between 9C- and 12C-beams. Results show that under 40 mm thick Beryllium target and 10 mm thick aluminum degrader at full (5%) momentum acceptance, the production rate and purity of the produced 9C-beams are 9.07×10-6 and 82.88% respectively with the primary 12C-beams of 430 MeV/u and 1.8×109 pps. A uniform irradiation field with homogeneity up to 89.6% inside central area 10 mm in diameter is obtained by using spot scanning. In this case, the dose rate at the entrance is 0.5 Gy/h. In survival experiment of cells, the average relative biological effectiveness (RBE) of 9C-beams is 5.28 and 2.93 for 12C-beams in the region around Bragg peak. The RBE of 9C-beams is 1.8 times higher than that of 12C-beams. It indicates that cell-killing efficiency of 9C-beams is stronger than that of 12C-beams. 9C-beams are more efficacious for tumor treatment than 12C-beams.