Vol.29,

Efficiency is an important factor in quantitative and qualitative analysis of radionuclides, and the gamma point source efficiency is related to the radial angle, detection distance, and gamma-ray energy. In this work, on the basis of a back-propagation (BP) neural network model, a method to determine the gamma point source efficiency is developed and validated. The efficiency of the point sources ¹³⁷Cs and ⁶⁰Co at discrete radial angles, detection distances, and gamma-ray energies are measured, and the BP neural network prediction model is constructed using MATLAB. The gamma point source efficiencies at different radial angles, detection distances, and gamma-ray energies is predicted quickly and accurately using this nonlinear prediction model. The results show that the maximum error between the predicted and experimental values is 3.732% at 661.661 keV, 11π/24, and 35 cm, and those under other conditions are less than 3%. The gamma point source efficiencies obtained using the BP neural network model are in good agreement with experimental data.

932

A method of spectrometry analysis based on approximation coefficients and deep belief networks was developed. Detection rate and accurate radionuclide identification distance were used to evaluate the performance of the proposed method in identifying radionuclides. Experimental results show that identification performance was not affected by detection time, number of radionuclides, or detection distance when the minimum detectable activity of a single radionuclide was satisfied. Moreover, the proposed method could accurately predict isotopic compositions from the spectra of moving radionuclides. Thus, the designed method can be used for radiation monitoring instruments that identify radionuclides.

629

A double-sided silicon strip detector (DSSD) with active area of 48 mm×48 mm and thickness of 300 μM has been developed. Each side of DSSD consists of 48 strips, each with width of 0.9 mm and inter-strip separation of 0.1 mm. Electrical properties and detection performances including full depletion bias voltage, reverse leakage current, rise time, energy resolution and crosstalk have been studied. At a bias of 80 V, leakage current in each strip is less than 15 nA, and rise time for alpha particle at 5157 keV is approximately 15 ns on both sides. Good energy resolutions have been achieved with 0.65% - 0.80% for the junction strips and 0.85% - 1.00% for the ohmic strips. The crosstalk is found to be negligible on both sides. The overall good performance of DSSD indicates its readiness for various nuclear physics experiments.

614

Axial gas–liquid separators have been adopted in fission gas removal systems for the development of thorium molten salt reactors. In our previous study, we observed an unsteady flow phenomenon in which the flow pattern is directly dependent on the backpressure in a gas–liquid separator; however, the underlying flow mechanism is still unknown. In order to move a step further in clarifying how the flow pattern evolves with a variation in backpressure, a large eddy simulation (LES) was adopted to study the flow field evolution. In the simulation, an artificial boundary was applied at the separator outlet under the assumption that the backpressure increases linearly. The numerical results indicate that the unsteady flow feature is captured by the LES approach, and the flow transition is mainly due to the axial velocity profile redistribution induced by the backpressure variation. With the increase in backpressure, the axial velocity near the downstream orifice transits from negative to positive. This change in the axial velocity sign forces the unstable spiral vortex to become a stable rectilinear vortex.

655

Tritium concentrations in precipitation can be used as a criterion to evaluate the tritium baseline of the environment. The tritium concentration in precipitation in Shanghai during 2014–2015 was determined. Values ranged from 0.68 ± 0.04 to 4.11 ± 0.39 Bq/L, and it showed a decreasing trend compared with historical data; however, the values were slightly higher than the natural background tritium level. Additionally, the tritium concentration shows a seasonal variation: it was higher in autumn and winter and lower in summer and spring. A comparison of concentrations in precipitation in Shanghai and around the Qinshan Nuclear Power Plant reveals no correlation, implying that the nuclear power plant operations may not affect the environment of Shanghai. Thus, the raised tritium concentrations in Shanghai might be due to the effects of monsoons, spring leak, raindrop, or other activities that generate tritium there. Those activities may include chemistry research that uses tritium as a tracer.

532

Radioiodine-131 is one of the pernicious radionuclides released during nuclear accidents, as its radioactivity can potentially affect public health and safety. To prevent radioiodine-131 from being released into the environment, the use of adsorbents that are highly efficient at high temperatures is significantly important. The radioactive gas from the nuclear core in an accident, such as the Fukushima nuclear accident, is usually released occurs under high-temperature conditions. Therefore, in this study, a 10 wt.% silver phosphate-loaded alumina (Ag₃PO₄/Al₂O₃) adsorbent was prepared. Further, its performance toward radioiodine adsorption was tested at high temperatures up to 750 ℃, using Al₂O₃ and traditional 10 wt.% Ag/Al₂O₃ adsorbent as controls. The results of the iodine adsorption test indicated that the 10 wt.% Ag₃PO₄/Al₂O₃ adsorbent showed a higher decontamination factor than did the 10 wt.% Ag/Al₂O₃ adsorbent by two orders of magnitude at 650 and 750 ℃. Results of the iodine desorption test revealed that the new adsorbent could be effectively used at 750 ℃. The characteristic powder X-ray diffraction, nitrogen adsorption-desorption isotherm, X-ray photoelectron spectroscopy, and thermogravimetric analysis-differential scanning calorimetry data indicated that the enhanced adsorption ability at high temperatures was attributed to the formation of a solid solution between silver iodide and Ag₃PO₄.

600

In this study, solutions of hydrazine and its derivatives were irradiated using a pulsed electron beam to determine the half-reaction time of radiolysis. 3D structures of the hydrazine derivatives were optimized and their energies were calculated using density functional theory with the B3LYP method and 6-311+(3d, 3p) basis set. For the first time, the 3D quantitative structure-activity relationship (QSAR) equation describing the relationship between the hydrazine derivative structures and rate of radiolysis has been established using SPSS software. Pearson correlation analysis revealed a close correlation between the total energies of the molecules and half-reaction times. In the QSAR equation, Y = −7583.464 + 54.687X₁ + 94333.586X₂, Y, X₁, and X₂ are the half-reaction time, total energy of the molecule, and orbital transition energy, respectively. The significance levels of the regression coefficients were 0.006 and 0.031, i.e., both less than 0.05. Thus, this model fully explains the relationship between hydrazine derivatives and β radiolysis stability. The results show that the total energy of the molecule and orbital transition energy are the main factors that influence the β radiolysis stability of these hydrazine derivatives.

678

For precise and accurate patient dose delivery, the dosimetry system must be calibrated properly according to the recommendations of standard dosimetry protocols such as TG-51, TRS-398, etc. However, the dosimetry protocol followed by a calibration laboratory is usually different from the protocols that are followed by different clinics, which may result in variations in the patient dose. Our prime objective in this study was to investigate the effect of the two protocols on dosimetry measurements. Dose measurements were performed for a Co-60 teletherapy unit and a high-energy Varian linear accelerator with 6 and 15 MV photon and 6, 9, 12, and 15 MeV electron beams, following the recommendations and procedures of the AAPM TG- 51 and IAEA TRS-398 dosimetry protocols. The dosimetry systems used for this study were calibrated in a Co-60 radiation beam at the Secondary Standard Dosimetry Laboratory (SSDL) PINSTECH, Pakistan, following the IAEA TRS-398 protocol. The ratio of the measured absorbed doses to water in clinical setting, D_w (TG-51/TRS-398), were 0.999 and 0.997 for 6 and 15 MV photon beams, whereas these ratios were 1.013, 1.009, 1.003, and 1.000 for 6, 9, 12, and 15 MeV electron beams, respectively. This difference in the absorbed doses to water D_w ratio may be attributed mainly due to beam quality (K_Q) and ion recombination correction factor.

719

To establish and validate a method for cell irradiation in 96-well and 6-well plates using a linear accelerator, three irradiation methods (G0B0F40, G0B1.5F40, and G180B1.5F40) were designed to irradiate cell culture plasticware simulated with RW3 slab phantom and polystyrene. The difference between the actual physical measured dose and the preset dose was compared among the three methods under the preparatory conditions of 2, 4, 6, 8, and 10 Gy. MDA-MB-231 cells were analyzed by using a cell proliferation assay and a clonogenic assay to verify the difference between the three cell irradiation methods on cell radiosensitivity. For each preset dose, the difference between the actual measured dose and the preset dose was the lowest for Method G0B1.5F40, the second lowest for Method G180B1.5F40, and the maximum for Method G0B0F40. The ranges of the differences were −0.28% to 0.02%, −2.17% to −1.80%, and −4.92% to −4.55%, and 0.31% to −0.12%, −3.42% to −2.86%, and −7.31% to −6.92%, respectively, for 96-well and 6-well plates. The cell culture experiments proved that Method G0B1.5F40 was an accurate, effective, simple, and practical irradiation method. The most accurate and effective cell irradiation method should always be used, as it will reduce dose differences and instability factors, and provide improved accuracy and comparability for laboratories researching cellular radiosensitivity.

664

The effect of dissolved oxygen (DO) on the stress corrosion cracking (SCC) of 310S in supercritical water was investigated using slow strain-rate tensile tests. The tensile properties, fracture morphology, and distribution of the chemical composition of the oxide were analyzed to evaluate the SCC susceptibility of 310S. The results showed that the rupture elongation decreased significantly as the degree of DO increased. A brittle fracture mode was observed on the fracture surface, and only intergranular cracking was observed on the surface of the gauge section, regardless of the DO. Cracks were widely distributed on the gauge surface near the fracture surface. Oxides were observed in the cracks with two-layered structures, i.e., a Cr-rich inner oxide layer and an Fe-rich outer oxide layer.

535

Beamline BL17U1 at Shanghai Synchrotron Radiation Facility is an energy-tunable macromolecular crystallography beamline that has been in user operation since 2009. Growing demand from the user community for a small beam and related experimental methods have motivated upgrades of the devices in the endstation. Minibeam modes have already been developed for operation. A self-integrated diffractometer reduces the sphere of confusion of the rotatory axis to 1 µm. The new diffractometer is equipped with an upgraded on-axis viewing system that can improve the resolving power. Additionally, the area detector was also upgraded to the newest generation of detectors, the EIGER X 16M, which can collect data at 133 Hz. After these upgrades, the endstation became virtually new. This paper covers the upgrade of the endstation devices and gives the first data collection results.

613

Longitudinal electron bunch length plays a significant role in single-pass free-electron lasers (FEL), as the high-gain FEL process depends strongly on the high peak current of electron bunches. Longitudinal electron bunch length was measured by detecting the interferogram of coherent transition radiation generated by electron bunches using a THz interferometer and a Golay Cell (spectral range: 0.02–20 THz) at Shanghai X-ray free-electron laser. The detailed process of measurement and data analysis are discussed herein. Furthermore, the electron bunch length was estimated based on the dispersive strength R56 of the bunch compressor and the energy spread δ of electron bunches, which were obtained via experiments. The comparison showed that the measured bunch length was consistent with the estimated bunch length.

479

Identifying the unknown geometric and material information of a multi-shield object by analyzing the radiation signature measurements is always an important problem in national and global security. In order to identify the unknown shielding layer thicknesses of a source/shield system with gamma-ray spectra, we have developed a derivative-free inverse radiation transport model based on a differential evolution algorithm with global and local neighborhoods (IRT-DEGL). In the present paper, the IRT-DEGL model is further extended for estimating the unknown thicknesses with random initial guesses and material mass densities of multi-shielding layers as well as their combinations. Using the detected gamma-ray spectra, the illustration of inverse studies are implemented and the main influence factors for inverse results are also analyzed.

448

A bialkali photocathode with the quantum efficiency(QE) in the range of a few percent was fabricated for the 704 MHz SRF gun at Brookhaven National Laboratory. The photoemission properties of the bialkali photocathode in the superconducting radio frequency (SRF) gun were measured for the first time, and a good beam experiment result was obtained. The performance of the bialkali photocathode was investigated during the commissioning process of the 704 MHz SRF gun. The effect of electric field on the QE of the cryo-cooled cathode was characterized by an analytical model and a code for the first time.

867

Simulation experiments were performed to investigate the characteristics of information extraction in multiple-image radiography (MIR) based on geometrical optics approximation. Different Poisson noise levels were added to the simulation, and the results show that Poisson noise deteriorates the extraction results, with the degree of refraction > USAXS > absorption. The effects of Poisson noise are negligible when the detector’s photon counts are about 1000 ph/pixel. A wider sampling range allows more accurate extraction results, but a narrower sampling range has a better signal-to-noise ratio (SNR) for high Poisson noise levels, e.g., PN(10). The sampling interval can be suitably increased with a minor impact on the extraction results for low Poisson noise levels (PN(10000)). The extraction results are incomplete because a portion of the sample-rocking curve (RC) is beyond the sampling range. This induces artifacts in the images, especially for strong refraction and USAXS signals. The artifacts are not obvious when the refraction angle and standard deviation of the USAXS are smaller than the sampling range by an order of magnitude. In general, the absorption barely affects the extraction results. However, additional Poisson noise will be generated when the sample is made of high-Z elements or has a large size due to the strong absorption. Here, the extraction results will deteriorate, and additional exposure time is required. This simulation provides important details on practical applications of MIR, with improvements in information extraction.

648