Vol.31,

To improve the anti-corrosion properties of 316L stainless steel, titanium (Ti) metal films were electroplated on it using LiCl-KCl molten salts as the electrolyte, and low valence Ti^x+ (2<x<3) as the solute. The solute was produced by the reaction of Ti⁴⁺ and Ti⁰ via mixing K₂TiF₆, and Ti metal (sponge Ti) in the melts. Anti-corrosion test has shown significant enhancement in the stability of the Ti-coated 316L due to the presence of Ti film. However, the anti-corrosion properties did not enhance with an increase in the thickness of the Ti layers owing to a possible defect in the thicker Ti layers.

468

This study aims to produce ²²⁹Th using an innovative nuclear reactor concept, i.e., accelerator-driven system (ADS) reactor. Herein, we investigated the feasibility of producing ²²⁹Th from neutron transmutation of ²²⁶Ra to expand the availability of ²²⁵Ac and ²¹³Bi in a simple model of ADS reactor. ADS reactor comprises two zones, i.e., an inner zone with a fast neutron spectrum and outer zone with thermal neutron spectrum, which is a subcritical core coupled with an external neutron source. Transmutation behavior, activity, and mass ratio of the obtained isotopes were investigated using the Monte-Carlo tool. In addition with offering the capability, flexibility, and safety of radioactive waste transmutation, the proposed ADS model provides high ²²⁹Th yield and requires less time than a critical reactor with the same neutron flux and irradiated quantity of ²²⁶Ra.

388

A longitudinal accumulation scheme based on a triple-frequency RF system, in which the static radio frequency (RF) bucket is lengthened to be compatible with the realizable raise time of a fast pulse kicker, is proposed in this paper. With this technique, the bunch from a booster can be captured by the longitudinal acceptance without any disturbance to the stored bunch, which remains at the center. This composite RF system consists of three different frequencies, which can be regarded as the conventional bunch lengthening RF system (usually containing fundamental and third harmonic cavities) extended by an additional second harmonic RF cavity. In this paper, we discuss the RF jitter and the transverse mode-coupling instability (TMCI) when using this special RF system. Considering several different bunch profiles, we discuss the beam stability with regard to the RF jitter. However, for the TMCI we assume an ideal bunch profile, where the bunch is exactly lengthened to the maximum extent. While macro-particle simulation is the main method used to study the impact of the RF jitter, numerical analysis and simulations for the TMCI while using a triple-frequency RF system are also presented in this paper. An approximation formula, based on the existing model, is also derived to estimate the impact of the TMCI on the single bunch current threshold when using harmonic cavities.

322

Extracting the amplitude and time information from the shaped pulse is an important step in nuclear physics experiments. For this purpose, a neural network can be an alternative in offline data processing. For processing the data in real time and reducing the offline data storage required in a trigger event, we designed a customized neural network accelerator on a field programmable gate array platform to implement specific layers in a convolutional neural network. The latter is then used in the front-end electronics of the detector. With fully reconfigurable hardware, a tested neural network structure was used for accurate timing of shaped pulses common in front-end electronics. This design can handle up to four channels of pulse signals at once. The peak performance of each channel is 1.665 Giga Operations Per Second (GOPS) at a working frequency of 25 MHz.

463

In this study, a compact 16-channel integrated charge-sensitive preamplifier named the smart preamplifier (SPA) was developed to support the large-scale detector array used in modern nuclear physics experiments. Two types of SPA, namely SPA02 and SPA03 (with external field effect transistor), have been manufactured to match silicon detectors with small and large capacitances, respectively. The characteristics of the SPA include fast response of typically less than 6 ns for pulse rising time and low equivalent noise of 1.5 keV at zero input capacitance. The energy sensitivity and pulse decay time can be easily adjusted by changing the feedback capacitance C_f and resistance R_f in various applications. A good energy resolution of 24.4 keV for 5.803-MeV alpha particles from ²⁴⁴Cm was achieved using a small-sized Si-PIN detector; for the silicon strip detectors in the test with the alpha source, a typical energy resolution of 0.6–0.8% was achieved. The integrated SPA has been employed in several experiments of silicon strip detectors with hundreds of channels, and a good performance has been realized.

463

The shape transition between the vibrational U(5) and deformed γ-unstable O(6) dynamical symmetries of sd interacting boson model has been investigated by considering a modified O(6) Hamiltonian providing that the coefficients of the Casimir operator of O(5) are N-dependent, where N is the total number of bosons. The modified O(6) Hamiltonian does not contain the number operator of the d boson, which is responsible for the vibrational motions. In addition, the deformation features can be achieved without using the SU(3) limit by adding to the O(6) dynamical symmetry the three-body interaction [QQQ]⁽⁰⁾, where Q is the O(6) symmetric quadrupole operator. Moreover, triaxiality can be generated through the inclusion of the cubic d-boson interaction [d†d†d†](3)⋅[d˜d˜d˜](3). The classical limit of the potential energy surface (PES), which represents the expected value of the total Hamiltonian in a coherent state is studied and examined. The modified O(6) model is applied to the even-even ^124-132Xe isotopes. The parameters for the Hamiltonian and the PESs are calculated using a simulated search program to obtain the minimum root mean square deviation between the calculated and experimental excitation energies and B(E2) values for a number of low-lying levels. A good agreement between the calculations and experiment results is found.

438

A ⁶Li + ⁸⁹Y experiment was conducted at the Laboratori Nazinali di Legnaro, INFN, Italy. The 550 μg/cm²-thick ⁸⁹Y target was backed on a 340 μg/cm ² thick ¹²C foil. The several γ rays in the experiment with energies higher than 3000 keV can most likely be ascribed to the transitions in the ¹³C nuclei, which can be formed through various interactions between the ⁶Li beam and the ¹²C foil. The high-energy properties of γ rays in¹³C are employed for energy calibrating HPGe detectors, especially for the >3000 keV region, which is impossible to reach by common standard sources (¹⁵²Eu, ¹³³Ba etc.). Furthermore, γ-γ and particle-γ coincidence measurements were performed to investigate the formation of ¹³C.

452

Intrinsic radiation of materials is one of the major backgrounds for many rare-event search experiments. Thus, the production of pure materials in an underground laboratory is a promising approach for eliminating cosmogenic radionuclides. In this paper, we demonstrate a procedure to evaluate the yields of cosmogenic radionuclides in copper and germanium in the second phase of the China Jinping Underground Laboratory. Our results show that for copper and germanium materials, the largest cosmogenic background comes from ³H and ^57,58,60Co, and ³H and ⁶⁸Ge, respectively, which all have yields on the order of 10^-7 kg^-1 day^-1. The corresponding radioactivities after 90 days pf exposure underground are estimated to be lower than 10^-6 μBq kg^-1.

333

The effect of source size and emission time on the proton-proton (p-p) momentum correlation function (C_pp(q)) has been studied systematically. Assuming a spherical Gaussian source with space and time profile according to the function S(r,t)∼exp(−r2/2r02−t/τ) in the correlation function calculation code (CRAB), the results indicate that one C_pp(q) distribution corresponds to a unique combination of source size r₀ and emission time τ. Considering the possible nuclear deformation from a spherical nucleus, an ellipsoidal Gaussian source characterized by the deformation parameter ϵ=ΔR/R has been simulated. There is almost no difference of C_pp(q) between the results of spherically and ellipsoidally shaped sources with small deformation. These results indicate that a unique source size r₀ and emission time could be extracted from the p-p momentum correlation function, which is especially important for identifying the mechanism of two-proton emission from proton-rich nuclei. Furthermore, considering the possible existence of cluster structures within a nucleus, the double Gaussian source is assumed. The results show that the p-p momentum correlation function for a source with or without cluster structures has large systematical differences with the variance of r₀ and τ. This may provide a possible method for experimentally observing the cluster structures in proton-rich nuclei.

543

As essential elements of the graphite reflector in thorium-based molten salt reactor (TMSR), dowel-brick structures are used to withstand complex working loads in the reactor core and their failure may lead to serious damage of the graphite reactor core. It is crucial to investigate the stress behavior of dowel-brick structures for safe operation of the graphite reactor. In this study, three groups of finite element analyses (FEA) and a strain test were carried out to investigate how the geometric parameters of the dowels affect the stress behavior of the dowel-brick structure. The numerical results indicate that the stress behavior of a dowel-brick structure is significantly affected by the diameter, length, and aspect ratio of the dowels. The maximum stress in the lower and upper bricks decreases with increase of the dowel length. The location of maximum stress on both lower and upper bricks shifts from the root of the socket to the edge of that socket beside the contact region, as the length of the dowel increases. The shift of the maximum stress location occurs earlier for the upper bricks than for the lower bricks. The results of strain tests show good agreement with those of numerical analyses.

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