Search

Elemental imaging plays an important role in characterizing the chemical and physical properties of large samples. In this work, a position-sensitive technique using prompt gamma ray neutron activation analysis (PGNAA) was applied to image the internal composition of large samples with 10–20 cm thicknesses. An inelastic neutron scattering system consisting of a D-T neutron generator and a high-purity germanium (HPGe) detector was built and used for elemental distribution analysis of a large metal sample containing iron, titanium, and copper. The 2D elemental imaging of the three elements was performed using the designed system. The effect of inhomogeneous neutron field was also corrected using Monte Carlo simulations. The results indicate that ~4 cm spatial resolution can be achieved. The position-sensitive elemental analysis based on inelastic neutron scattering reaction is efficient for bulk metal sample analysis.

As a part of R&D work for the high intensity proton linac of China Accelerator Driven Sub-critical System project, a superconducting half-wave cavity with a frequency of 162.5 MHz and an optimal beta of 0.15 (HWR015) has been developed at Institute of Modern Physics (IMP), Chinese Academy of Sciences. In this paper, the design and test results will be described in detail. We introduced a new stiffening strategy for the HWR cavity, the simulation results show that the cavity has much lower frequency sensitivity coefficient (df/dp), Lorentz force detuning coefficient (KL), and can achieve more stable mechanical properties. The performance of the HWR cavity operated in cryostat will be also reported.

252Cf neutron source has been widely used in biological effects of neutron radiation, neutron activation analysis and nuclear data acquisition. A seed irradiation device based on 252Cf fission neutron source was designed in this paper to study mutation breeding induced by neutron irradiation and biological effects of radiation. Based on the Monte Carlo method, neutron absorbed dose of pea seed samples in the designed irradiation region was simulated and calculated by MCNP. Results demonstrated that the relative standard deviation of the absorbed dose of pea seed samples in the three-layer partition is controlled lower than 10%, indicating the high dose uniformity in designed irradiation region. The experiment verified that the design of shield in this device meet the irradiation protection requirements.

The design of a compact D–D neutron generator with a neutron yield greater than 1 × 1 0 8 n/s is presented in this paper. A duoplasmatron ion source is used to supply the deuteron beam. Deuterium ions are extracted and accelerated by a single-gap accelerating column and then bombard onto a drive-in molybdenum target where neutrons are produced through D–D fusion reactions. The target is cooled by the circulating deionized water. The extraction-accelerating electrode and the target system are enclosed inside a stainless steel vacuum vessel. The ion source is at ground potential, and the target is biased to a negative potential. The electric field distribution inside the vacuum vessel, the ion beam optic, the thermal analysis of the target and the effect of secondary electron suppression are calculated. And these calculation results are used to optimize and evaluate the designed scheme. Calculation results show that the design of the neutron generator satisfies necessary engineering requirements.

The EJ309 liquid scintillator detector and the developed gamma spectrum unfolding procedure are used to study the complex gamma spectra. The EJ309 liquid scintillator detector is calibrated by using measured response functions of the standard gamma sources 133Ba, 137Cs, and 60Co, which are verified by Monte Carlo simulations for detector calibration accuracy. A gamma spectra unfolding procedure is developed based on the One-fold Gold algorithm, which is used for unfolding simulated complex gamma spectra, experimentally measured response function of 133Ba and 137Cs, and composed complex gamma spectra using measured response function of 133Ba and 137Cs with different relative intensities (RI). The data of unfolded gamma-ray spectra are compared with the standard data. The results show that the EJ309 liquid scintillator detector and the developed gamma spectra unfolding procedure can quantitative and qualitative analysis of complex gamma spectra with reasonable accuracy.

A Secondary Electrons Profile Monitor (SEPM) is developed as part of the beam dose delivery system in a clinical gantry of the Heavy Ion Medical Machine (HIMM). With the purpose of less disturbance to the beam, a thin foil with a thickness of 0 . 7 μ m and an accelerating grid with a diameter of 15 μ m are employed to produce and accelerate the secondary electrons, and two microchannel plates (MCPs) are used to multiply the electrons. Providing the real-time information of beam size, position, flatness, and symmetry in front of the scanning magnet, the beam monitor features an active area of 989 mm 2 , beam intensities between 1.0 × 1 0 3 to 1.0 × 1 0 8 particles per pulse (ppp) and a wide range of beam energies. A prototype is tested at the horizontal treatment room of the HIMM. Using different beam positions, sizes, and energies of 12C 6 + beams, test experiments show that the beam monitor maintains good consistency with a Multi-Strip Ionization Chamber (MSIC). Compared to the MSIC, the SEPM shows a better signal-to-noise ratio (SNR) and higher sensitivity to the variation of the beam.

An intense D-T/D-D neutron generator is currently being developed at the Lanzhou University. The Cockcroft–Walton accelerator, as a part of the neutron generator, will be used to accelerate and transport the high-current low-energy beam from the duoplasmatron ion source to the rotating target. The design of a high-current low-energy beam transport (LEBT) line and the dynamics simulations of the mixed beam were carried out using the TRACK code. The results illustrate that the designed beam line facilitates smooth transportation of a deuteron beam of 40 mA, and the number of undesired ions can be reduced effectively using two apertures.

Si@SiO2@C core double-shell nanocomposites are successfully synthesized by a facile method. The inside shell of SiO2 with a stable mechanical structure can completely limit the volume expansion of Si during charge/discharge cycles and beneficial for a dense carbon shell formation on the surface of SiO2. The outside carbon shell serves as an effective electron conductor to enhance the electronic conductivity of the nanocomposite. This mechanical constraining double-shell protection is good for the electrode to form a stable solid electrolyte film during cycling. The Si@SiO2@C nanocomposites achieve outstanding long-term cycling stability and high rate performance. High capacity of 775 mAh g−1 is obtained after 1000 cycles at 1.0 A g−1 and 617 mAh g−1 after 400 cycles at 2.0 A g−1. The full-cell coupled with LiNi0.8Mn0.1Co0.1O2 cathode exhibits good cycling ability. This excellent electrochemical performance is much improved when compared with other Si/SiOx based anode materials. These structural features make the Si@SiO2@C as promising anode materials for high energy storage lithium-ion batteries.

The micro-channel plate based particle tracking detector described here is part of the detector system used in a series of measurements of astrophysical ( α , p) reactions, which will be studied at the Radioactive Ion Beam Line in Lanzhou, China. This detector will provide on a particle-by-particle basis tracking information and arrival time of radioactive beams with intensities up to 1 0 5 particles per second. The key requirements of the experiments to the detector are that the spatial resolution is below 1 mm, the time resolution is better than 1 ns and the energy loss is less than for a parallel plate avalanche counter. The current prototype is composed of two micro-channel plate detectors with a compact electrostatic field construction and a delay-line readout. Based on the results of α -particle tests, one micro-channel detector can achieve a position resolution of 552 μ m full width at half maximum on the x axis and 735 μ m on the y axis. The tracking system can achieve 705 ps time resolution and can cope with a beam intensity of up to 5 × 1 0 6 particles per second.

A measuring method with associated particles has been developed and tested to monitor the D–D neutron yield at a ZF-300 intense neutron generator in Lanzhou University. The experiment has been carried out in an environment of 236 keV and 0.5 mA of deuteron beam with a thick titanium-filmed target of molybdenum substrate at 135° for proton emission. All correction factors, including anisotropy factors and the yield ratio of neutron and proton, have been calculated, and the uncertainty of calculation result has been discussed.

The tobacco leaves were treated with low-temperature plasma in Ar, N2, O2, and air atmospheres at different powers (60—130 W). The surface-elemental components, their relative contents, and the functional groups of the surface components of the tobacco leaves were determined using XPS (X-ray photoelectron spectroscopy). The experimental results showed that the percentage of the elements C, N, and O had changed considerably and a large number of polar functional groups containing oxygen atoms were incorporated into the components on the tobacco surfaces. The measurements of the surface contact angle showed that the surface contact angle of the modified tobacco leaves was 0 degree, whereas it was 110 degrees before the plasma treatment. These results indicate that the wettability of the modified tobacco leaves improved dramatically. This work may be significant for future researches on the surface modification of the tobacco leaves.

Design and development of an intense 14 MeV neutron source for cancer therapy is in progress at the Institute of Nuclear Research of Lanzhou University. The neutrons from the T(d,n)4He reaction are produced by bombarding a rotating titanium tritide target with a 40 mA deuteron beam at 600 keV. The designed neutron yield is 8×1012 n/s and the maximum dose rate at a 100 cm source-to-skin distance is 25 cGy/min. The HV terminal, accelerating column and HV power supply are enclosed inside a stainless steel pressure vessel containing 6 atm SF6 gas to provide the electrical insulation.