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LiF-BeF2-ZrF4-UF4 and LiF-BeF2 have been employed as fuel salt and coolant in liquid fueled molten salt reactor, respectively. A heat exchanger containing both fuel salt and cooling salt is placed inside the reactor vessel to dissipate the heat produced by the reactor. A molten salttoair heat exchanger outside the reactor vessel is used to cool the molten salt, and a molten salt pump is used to drive the circulation of the entire circuit of coolant system. As of the molten salt, LiF-BeF2 coolant, flows through the molten salt heat exchanger located inside the reactor vessel, nuclides in the coolant are activated by 19F(n, α)16N, 19F(n, γ)20F, and 19F(n, p)19O reactions with neutrons in the reactor core, and thus radionuclides such as 16N, 20F and 19O are produced. These radionuclides have radiation impact on the surrounding environment and equipment if they enter the rooms where equipment for molten salt coolant circuit locate. According to the flow process and distribution law of the cooling salt, theoretical calculation formulas to calculate the amount of radionuclide were given. Using theoretical formulas, calculated radioactivities of the three most important radionuclides 16N, 20F and 19O per unit volume of cooling salt are 9.05×106, 8.33×106 and 2.69×105 Bq/cm3 at the outlet of the molten salt heat exchanger, while the radioactivities of the three radionuclides at the same location calculated by ORIGENS program are 8.98×106, 8.58×106 and 2.76×105 Bq/cm3, respectively. The results calculated by the formulas are in good agreement with the data of the ORIGENS program, and the maximum relative deviation between the results of the two methods is 292%, indicating that applying the derived formulas to carry out cooling salt activation analysis is reasonable and feasible. These radionuclides, 16N, 20F and 19O, produced in the cooling salt of molten salt reactor release highenergy gamma rays as they decay. The total gamma emissivities of the cooling salt in equipment and pipelines located in the cooling salt storage tank room, in the molten salt-to-air heat exchanger room and in the cooling salt pump room are 8.71×1011, 9.51×1011 and 1.93×1012 s-1, respectively, and the most radioactive area is in the cooling salt pump room. The maximum absorbed dose rate at the location of the cooling salt auxiliary equipment is 45.7 mGy/h without shielding, which cannot meet the requirement of the radiation dose, and which should be less than 50 Gy for the entire life of the equipment (300 full power days). By setting a 30 cm thick concrete shielding wall between the cooling salt auxiliary equipment and the cooling salt pump, the absorbed dose rate at the location of the auxiliary equipment can be reduced to less than 7 mGy/h, thereby the radiation protection requirements for the cooling salt auxiliary equipment can be met.

BackgroundIn rare decay experiments, for instance dark matter and neutrino experiments, rays produced by the radioavtive decay in detector material induce extra experiment background, the energy deposition would contaminate the concerned region. Accurately measuring radioactivity of detector materials, better understanding background source, and controlling experimental background are extremely important to improve sensitivity for those detections. With high energy resolution, flexibility for sample geometry and non-destructive processing for samples, high-purity germanium (HPGe) γ spectroscopy is a widely used ultra-low radioactive technology. The PandaX collaboration set up two high-purity germanium γ spectroscopies, so-call JP1 and JP2, in Jinping underground laboratory.PurposeThis study aims to improve the sensitivity of γ spectroscopies, precisely measure materials with lower radioactivity and screen lower radioactive material for dark matter and neutrino experiments by designing a gamma spectroscopy system with dual high-purity germanium detectors based on the existing JP1.MethodsTwo approaches, i.e., enhancing efficiency and suppressing background were adopted to improve the sensitivity of both HPGe detectors, and the Monto Carlo method was employed to analyze the efficiency and background source of JP1, hence the improved result of dual high-purity germanium detectors was estimated.ResultsFor different nuclides concerned in dark matter and neutrino experiments, the minimum detectable activity of dual high-purity germanium γ spectroscopy system is expected to improve by factor of 2~4. This new system can also measure the radioactivity with γ-γ coincidence method to improve the sensitivity for small size samples.ConclusionsDual high-purity germanium γ spectroscopy can improve sensitivity of factor 2~4 and apply to developing a new γ-γ coincidence method.

BackgroundCopper is one of materials often used in rare decay experiments due to its low intrinsic radioactivity. During the installation and assembly of detectors, copper parts may be exposed to air-born radon, therefore the decay daughters of radon (210Pb, 210Bi and 210Po) will be deposited on copper surfaces, and their α, β and γ decays will result in the increase of the experimental radioactive background.PurposeThis study aims to suppress this background by carefully cleaning the radioisotopes on copper surface.MethodsFirst of all, eight pickling recipes were used to test the efficacy of 210Po removal from copper surfaces. Copper test samples were prepared by exposing to high concentration radon gas environment. Then, counting rates of deposited 210Po on copper surfaces were measured by an alpha detector before and after cleaning for the calculation of 210Po removal efficiency. The relationship between removal efficiencies and concentration of pickling cocktails were investigated and pickling recipe with the highest removal efficiency was obtained. Finally, with the highest removal efficiency pickling cocktail, the radioactivity of 232Th/238U on copper surface was measured by an inductively coupled plasma mass spectrometry (ICP-MS) to estimate the radioactive contamination level in passivation layer.ResultsMixing 5% C6H8O7 and 8% H2O2 as pickling solution can remove 99% of 210Po, and 232Th/238U concentration in passivation layer is less than ng·g-1 level.ConclusionsThis best pickling recipe found by this study can be used in rare decay experiments to remove radon daughters (210Po) from copper surfaces to suppress the background induced by radon daughters.

Objective: Observing and evaluating the clinical effects of panretinal photocoagulation with Argon laser for diabetic retinopathy., Methods: According to the results of fundus fluorescence angiography (FFA), panretinal photocoagulation with Argon laser were performed on 143 eyes (87 cases) of diabetic retinopathy, including 79 eyes with preproliferative diabetic retinopathy eyes with proliferative diabetic retinopathy (PPDR), 64 (PDR). Examination about FFA, visual acuity and fundus condition were carried out before laser treatment and 3 months after photocoagulation. The regular following up lasted for 6 months to 2 years., Results: Laser photocoagulation proved effective in 122 eyes (85.31%) with diabetic retinopathy, including 73 eyes (92.41%) with PPDR, 49 eyes (76.56%) with PDR. The visual acuity were improved in 32 eyes (23.38%), no changes in 87 eyes (60. 84%), decrease in 24 eyes (16.78%). No complication was found in all patients., Conclusions: Panretinal photocoagulation with Argon laser is a safe and effective method to control the condition of diabetic retinopathy.