Vol.29,

How to operate ⁸²Sr/⁸²Rb and ⁶⁸Ge/⁶⁸Ga generators used in the positron emission tomography scan process is explained, and the importance of ⁸²Sr and ⁶⁸Ge radionuclides for these generators is revealed. To produce medical ⁸²Sr and ⁶⁸Ge by means of a proton accelerator in an irradiation time of 24 h, a proton beam current of 250 µA, and an energy range E_proton=100→5 MeV, the cross sections and the neutron emission spectrum curves of (p,xn) reaction processes on Rb-85, Ga-69 and Ga-71 targets were calculated, and the activities and yields of the product were simulated for the reaction processes. Additionally, the integral yields of the reaction processes were determined via the calculated cross-section curves and the mass stopping power obtained from the X-PMSP program. Furthermore, based on the obtained results, the appropriate reaction processes for the production of ⁸²Sr and ⁶⁸Ge isotopes on Rb-85, Ga-69, and Ga-71 targets are discussed.

370

A Compton camera prototype has been developed using a pixelated CZT detector with 4 by 4 pixels. Signals of the detector are read out by a VASTAT ASIC that is controlled by a self-developed DAQ board. The DAQ software is developed using LabVIEW and the offline Compton imaging codes are written in C++. The prototype has been successfully calibrated and its capabilities for source detection, spectroscopy, and Compton imaging have been demonstrated using a Cs-137 source. The angular resolution of the 662 keV line is 36 degrees FWHM for the simple back projection method and 9.6 degrees FWHM for the MLEM reconstruction method. The system is ready to be extended to 11 by 11 pixels in the future and a better imaging quality can be expected due to the better relative position resolution.

454

Optically stimulated luminescence (OSL) reading systems are becoming smaller and capable of real-time detection. To improve real-time and multipurpose radiation dosimetry readings, we built a real-time continuous-wave (RCW) OSL reading system. This system is both small and lightweight, and it employs powerful laser excitation (478 mW/cm²) at the dosimetry probe location. We investigate the possibility of using the RCW mode to read the radiation luminescence (RL) or OSL by using a single-crystal Al₂O₃:C dosimeter in a low-dose-rate ¹³⁷Cs γg field. Our results indicate that the RL/OSL follows a stable and uniform distribution. The minimum detected doses associated with the RL, OSL, and RL + OSL signals are 2.1 × 10^-2, 3.17 × 10^-1, and 5.7 × 10^-2 μGy, respectively. This device provides a framework for the future development of applications for practical radiation dose measurements.

508

In biological systems, conformational transformations of nucleic acids play critical roles in genetic regulation. However, it remains a tricky task to design and optimize specific labeling strategies to track these changes. In this study, we exploited an intercalating fluorescent dye, GelRed, to characterize different DNA structures. We studied the correlation between fluorescence intensity and DNA structural properties. We showed that single-stranded DNAs with predicted self-folded secondary structures show much stronger fluorescence than those without such structures. For double-stranded DNAs, we observed that fluorescence intensity is positively correlated to their GC content. We also demonstrated that GelRed can be used to monitor DNA conformational changes upon temperature variations in real time. Based on these findings, we concluded that the fluorescence intensity of a GelRed-stained DNA structure has a good correlation with its thermostability in the form of a change in Gibbs free energy.

517

Photofission fragments mass yield for ²³²Th, ^234,238U, ²³⁷Np, and ^239,240,242Pu isotopes are investigated. The calculations are done using a developed approach based on Gorodisskiy’s phenomenological formalism. The Gorodisskiy’s method is developed to be applied for neutron induced fission. Here we revised it for application to photofission. The effect of emitted neutron prior to fission on fission fragment mass yields has also been studied. The peak to valley ratio is extracted for the ²⁴⁰Pu isotope as a function of energy. Obtained results of present formalism are compared with the available experimental data. Satisfactory agreement is achieved between results of present approach and experimental data.

502

The cross sections for the ⁶³Cu(n,α)^60(m+g)Co,⁶⁵Cu(n,2n)⁶⁴Cu, and ⁶⁵Cu(n,p)⁶⁵Ni reactions have been studied in the neutron energy range of 13.5–14.8 MeV using the activation technique. The neutron beams were produced via the ³H(d,n)⁴He reaction. The neutron energies of different directions in the measurements were determined beforehand by the method of cross section ratios for the ⁹⁰Zr(n,2n)^89m+gZr and ⁹³Nb(n,2n)^92mNb reactions. The results in the present work were discussed and compared with measurement results found in the literatures.

405

421

The dosage of environmental radon progeny is typically estimated according to the environmental radon exposure and the recommended radon-progeny equilibrium factor, F. To investigate the relationship between PM2.5 and the radon-progeny equilibrium factor, cigarettes are used to simulate the haze-fog in a multi-functional radon chamber to achieve a stable-radon concentration environment. A radon detector and a Portable Laser Aerosol Spectrometer are used to obtain the values for C_mean PM2.5, C_Rn, and C_p. The results show that the mean values of F conform with the typical value recommended by the United Nations Scientific Committee on the Effects of Atomic Radiation and are within the reasonable range of 0.1–0.9. In this study, a positive correlation is observed between the F values and PM2.5 concentrations.

478

An accelerator-driven subcritical system (ADS) is driven by an external spallation neutron source, which is generated from a heavy metal spallation target to maintain stable operation of the subcritical core, where the energy of the spallation neutrons can reach several hundred mega-electron volts. However, the upper neutron energy limit of nuclear cross section databases, which are widely used in critical reactor physics calculations, is generally 20 MeV. This is not suitable for simulating the transport of high-energy spallation neutrons in the ADS. We combine the Japanese JENDL-4.0/HE high-energy evaluation database and the ADS-HE and ADS 2.0 libraries from the International Atomic Energy Agency and process all the data files for nuclides with energies greater than 20 MeV. We use the continuous pointwise cross section program NJOY2016 to generate the ACE-formatted cross section data library IMPC-ADS at multiple temperature points. Using the IMPC-ADS library, we calculate 10 critical benchmarks of the International Criticality Safety Benchmark Evaluation Project manual, the 14 MeV fixed source problem of the Godiva sphere, and the neutron flux of the ADS subcritical core by MCNPX. To verify the correctness of the IMPC-ADS, the results were compared with those calculated using the ENDF/B-VII.0 library. The results showed that the IMPC-ADS is reliable in effective multiplication factor and neutron flux calculations, and it can be applied to physical analysis of the ADS subcritical reactor core.

444

A reactor core in a thorium molten salt reactor uses graphite as a moderator and reflector. The graphite core is a multi-layered arrangement of graphite bricks that are loosely connected to each other using a system of keys and dowels. Consequently, the graphite core is a type of discrete stack structure with highly nonlinear dynamic behavior. Hence, it is important to investigate the dynamic characteristics of the graphite core. In this study, a three-dimensional single-layer graphite core model, which is a part of the thorium molten salt reactor side reflector structure, was analyzed using the explicit method in ABAQUS 2016 to study the core dynamic behavior when subjected to different excitations. The design parameters, such as the diameter of the dowel, the gap between key and keyway and the bypass flow gap between two adjacent bricks, were also considered in this model. To reduce excessive demands on available computational resources considering the effect of molten salt, the spring-dashpot model was applied to model the interaction forces between the molten salt and graphite bricks. Numerical simulation results show that the effect of molten salt is a reduction in the peak maximal principal stress, and a larger gap between two bricks is beneficial to maintain the integrity of the graphite core under earthquake loading. The results obtained by the simulation can be used as a reference for future designs of a molten salt graphite core.

421

The mass attenuation coefficients (µ/ρ) for different parts (root, flower, stem, and leaf) of three medicinal aromatic plants (Teucrium chamaedrys L. subsp. sinuatum, Rheum ribes, and Chrysophthalmum montanum) were measured using an ²⁴¹Am photon source in a stable geometry and calculated using the Monte Carlo N-Particle Transport Code System-extended (MCNPX) code and the WinXCOM program. The experimental and theoretical MCNPX and WinXCOM values exhibited good agreement. The measured mass attenuation coefficient values were then used to compute the effective atomic number (Z_eff) and electron density (N_E)of the samples. The results reveal that S1-S (stem of Teucrium chamaedrys L. subsp. sinuatum) has the highest values of µ/ρand Z_eff.

447

A 325-MHz continuous-wave (CW) four-vane radiofrequency quadrupole (RFQ) is employed in Injector-I of the China Accelerator-Driven Subcritical System (China-ADS). The radiofrequency tuning and beam commissioning were performed from January 2014 to January 2017. In a cold test, a stability study showed that the design of the segmented resonantly coupling and dipole stabilizer rods can shift the harmful quadrupole and dipole mode from the fundamental mode to above 2.6 MHz. We also found a simplified tuning method for the field unflatness, involving changing the inserted length of a few plug tuners. For achieving CW beam commissioning, two full-size RFQs were constructed successively. The commissioning results indicate that the beam transmission rate decreased by approximately 3% as the normalized field unflatness decreased by 1%. A 10-MeV CW proton beam with an average beam current of 2.1 mA was achieved at the target of Injector-I, and the output beam energy of the RFQ was 3.18 MeV.

465

In this work, the radiation environment in the target area of a fragment separator is evaluated using FLUKA code. The energy deposition in quadrupole coils is presented to provide guidance for a radiation resistant magnets’ design. Results show that neutrons dominate in the prompt radiation field. A compact shielding design is recommended for high radiation areas along with the minimization of air activation in the tunnel in order to minimize the radiation effect on nearby beam lines. The displacements per atom (DPA) results for the graphite target and copper coils indicate that the effect is insignificant. In addition, the activation level of the target is estimated for workers under possible hands-on maintenance condition.

460

To study ultrafast processes at the sub-picosecond level, novel methods based on coherent harmonic generation technologies have been proposed to generate ultrashort radiation pulses in existing ring-based light sources. Using the High Energy Photon Source as an example, we numerically test the feasibility of implementing one coherent harmonic generation technology, i.e., the echo-enabled harmonic generation (EEHG) scheme, in a diffraction-limited storage ring (DLSR). Two different EEHG element layouts are considered and the effect of the EEHG process on the electron beam quality is also analyzed. Studies suggest that soft X-ray pulses, with pulse lengths of a few femtoseconds and peak powers of up to 1 MW, can be generated by using the EEHG scheme, while causing little perturbation to the regular operation of a DLSR.

371

High Energy Photon Source (HEPS) is a 6 GeV ultralow-emittance storage ring light source to be built in Beijing, China. Both the horizontal and vertical beam sizes of the HEPS storage ring are below 10 µm. It is a challenge to measure such a small beam size in both directions. To this end, measurement by a Kirkpatrick–Baez (KB) mirror imaging system was evaluated. A test KB system for the Shanghai Synchrotron Radiation Facility storage ring was designed and tested. Two crossed cylindrical mirrors were used to image the dipole source point. Both mirrors can be moved in and out so that the monitor is interchangeable with the original X-ray pinhole monitor. The aberration and point spread function, which would cause image blur, were evaluated. A beam-based calibration scheme was used by varying the beam size with different quadrupole settings and fitting them with the corresponding theoretical values. We updated the original X-ray camera with a new camera having a 5-μm-thick LuAG:Ce scintillator, and the imaging result shows greatly decreased image blur.

372