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Structural and optical investigation of nonpolar a-plane GaN grown by metal-organic chemical vapour deposition on r-plane sapphire by neutron irradiation

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Chinese Physics B 2012年第2期21卷 531-535页

作者：许晟瑞张金风谷文萍郝跃张进成周小伟林志宇毛维 National Key Laboratory of Fundamental Science for Wide Band-Gap Semiconductor Technology School of MicroelectronicsXidian UniversityXi'an 710071China

Nonpolar （1150） a-plane GaN films are grown by metal-organic chemical vapour deposition （MOCVD） on r-plane （1102） sapphire. The samples are irradiated with neutrons under a dose of 1× 1015 cm-2. The surface morphology, the crystal defects and the optical properties of the samples before and after irradiation are analysed using atomic force microscopy （AFM）, high resolution X-ray diffraction （HRXRD） and photoluminescence （PL）. The AFM result shows deteriorated sample surface after the irradiation. Careful fitting of the XRD rocking curve is carried out to obtain the Lorentzian weight fraction. Broadening due to Lorentzian type is more obvious in the as-grown sample compared with that of the irradiated sample, indicating that more point defects appear in the irradiated sample. The variations of line width and intensity of the PL band edge emission peak are consistent with the XRD results. The activation energy decreases from 82.5 meV to 29.9 meV after irradiation by neutron.

关键词： GaN neutron nonpolar photoluminescence

Calculation of photon shielding properties for some neutron shielding materials

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Nuclear Science and Techniques 2017年第5期28卷 74-80页

作者： A. M. El-Khayatt Physics Department College of Science Al Imam Mohammad Ibn Saud Islamic University (IMSIU) RiyadhSaudi Arabia Reactor Physics Department NRC Atomic Energy Authority 13759 Cairo Egypt

The objective of the present study is to calculate photon shielding parameters for seven polyethylene-based neutron shielding materials. The parameters include the effective atomic number(Z_(eff)), the effective electron density(N_(eff)) for photon interaction and photon energy absorption,and gamma-ray kerma coefficient(kc). The calculations of Z_(eff)are presented as a single-valued and are energy dependent. While Z_(eff)values were calculated via simplistic powerlaw method, the energy-dependent Z_(eff)for photon interaction(Z_(PI-eff)) and photon energy absorption(Z_(PEA-eff)) are obtained via the direct method for energy ranges of 1 keV–100 GeV and 1 keV–20 Me V, respectively. The kccoefficients are calculated by summing the contributions of the major partial photon interactions for energy range of 1 keV–100 MeV. In most cases, data are presented relative to pure polyethylene to allow direct comparison over a range of energy. The results show that combination of polyethylene with other elements such as lithium and aluminum leads to neutron shielding material with more ability to absorb neutron and crays. Also, the kerma coefficient first increases with Z of the additive element at low photon energies and then converges with pure polyethylene at energies greater than 100 keV.

关键词： neutron shielding materials Effective atomic number Kerma coefficient c-rays

Influence of Fast neutron Irradiation on Critical Current Densities of Bi-2223/Ag Tape

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Journal of Rare Earths 2004年第Z2期22卷 118-122页

作者： Duan Zhenzhong Research Contor of Superconducting Materials General Research Institute for Non-Ferrous MatelsBeijing 100088China

Experimental results on the magnetic field behavior of the critical current in silver sheathed Bi-2223 tapes are presented. The experiments consist of transport and magnetic measurements in a wide temperature range and in external magnetic field up to 6 T. Significant enhancement of the intragrain critical current densities Jc are observed after irradiation with fast neutron. This is attributed to an improvement of flux pinning capability by the neutron induced defects, but the weak link structure is somewhat damaged as evidenced by the small degradation of transport critical current at low field. According to the measurement of remanent magnetic moment before and after irradiation with fast neutron, the connectivity in Bi-2223 tapes is reduced by 50% after irradiated to a fluence of 2 × 1021 m-2, which resulted in the critical currents degradated by a factor of 10%.

关键词： neutron irradiation critical current flux pinning weak link

Radiation Damage and Recovery in neutron-Irradiated MgO Crystal

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Journal of Rare Earths 2006年第Z1期24卷 56-58页

作者： Ruan Yongfeng Ma Pengfei Liu Jian Li Wenrun Liu Changlong School of Science Tianjin University Tianjin 300072 China School of Science Tianjin University Tianjin 300072 China School of Science Tianjin University Tianjin 300072 China School of Science Tianjin University Tianjin 300072 China School of Science Tianjin University Tianjin 300072 China

MgO single crystal was irradiated by neutron up to a dose of 5.74×1018 cm-2. The radiation damage and its recovery were studied by means of UV-VIS and EM spectroscopy. The results indicate that the irradiation generates large amount of optically detectable defects such as single anion vacancies (F+ center), anion divacancies (F2) and some higher order defects. Through isochronal annealing, these defects started a series of processes of diminishing and transforming, and finally all disappeared while annealing at 900 ℃. It seems that the absorption bands of 573 nm are resulted from a higher order and more complex aggregated center than that of 424, 451 nm bands.

关键词： MgO neutron irradiation defects absorption spectra

Defects in Fast-neutron Irradiated Nitrogen-Doped Czochralski Silicon after Annealing at High Temperature

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Journal of Rare Earths 2006年第Z1期24卷 91-93页

作者： Liu Lili Li Yangxian Ma Qiaoyun Chen Guifeng Sun Yong Yang Shuai School of Material Science and Engineering Hebei University of Technology Tianjin 300130 China School of Material Science and Engineering Hebei University of Technology Tianjin 300130 China School of Material Science and Engineering Hebei University of Technology Tianjin 300130 China School of Material Science and Engineering Hebei University of Technology Tianjin 300130 China School of Material Science and Engineering Hebei University of Technology Tianjin 300130 China School of Material Science and Engineering Hebei University of Technology Tianjin 300130 China

Fast-neutron irradiated nitrogen-doped Czochralski silicon (NCZ-Si) was annealed at 1100 ℃ for different time, then FTIR and optical microscope were used to study the behavior of oxygen. It is found that [Oi] increase at the early stage then decrease along with the increasing of anneal time. High density induced-defects can be found in the cleavage plane. By comparing NCZ-Si with Czochralski silicon (CZ-Si), [Oi] in NCZ-Si decrease more after anneal 24 h.

关键词： nitrogen-doped Czochralski silicon (NCZ-Si) neutron irradiation oxygen precipitation FTIR

Consideration about the Single-neutron Microbeam Facility

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Plasma Science and Technology 2004年第3期6卷 2350-2352页

作者：吴瑜王绍虎余增亮 Institute of Plasma Physics the Chinese Academy of Sciences Hefei 230031 China

A conception of the single-neutron microbeam facility was put forward in this paper. The specific particle (e.g. H+, 2d+ or a ) bombarding a specific target can generate neutron, when the particle energy is more than a threshold (e.g., H+ energy is more than 2 MeV). And if the specific beam spot on the target is very small, the neutron beam along the direction of the specific beam spot will be very small too. If the neutron beam is weak and a neutron detector is mounted after the specific neutron collimator, the single- neutron will be obtained. Therefore, if the specific target and the neutron detector are installed after the proton accelerator and the microbeam system, the single-neutron microbeam will probably be obtained.

关键词： single-neutron microbeam neutron

Persistent photoconductivity in neutron irradiated GaN

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Journal of Semiconductors 2013年第9期34卷 32-34页

作者：张明兰杨瑞霞刘乃鑫王晓亮 College of Information Engineering Hebei University of Technology Key Laboratory of Semiconductor Materials Science Institute of SemiconductorsChinese Academy of Sciences Semiconductor Lighting R & D Center Institute of SemiconductorsChinese Academy of Sciences

Unintentionally doped GaN films grown by MOCVD were irradiated with neutrons at room temperature. In order to investigate the influence of neutron irradiation on the optical properties of GaN films, persistent pho toconductivity （PPC） and low temperature photoluminescence （PL） measurements were carried out. Pronounced PPC was observed in the samples before and after neutron irradiation without the appearance of a yellow lumi- nescence （YL） band in the PL spectrum, suggesting that the origin of PPC and YL are not related. Moreover, PPC phenomenon was enhanced by neutron irradiation and quenched by the followed annealing process at 900 ℃. The possible origin of PPC is discussed.

关键词： GaN irradiation neutron persistent photoconductivity

neutron Diffraction Studies of the Magnetic Structure of Ho_2Fe_9Ga_(8～x)Alx

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Chinese journal of nuclear physics 1997年第1期19卷 44-47页

作者： Chen Dongfeng Gou Cheng Sun Kai China Institute of Atomic Energy,P.O.Box 275-30,Beijing 102413Yan Qiwei Zhang Panlin Shen Baogen Cheng Zhaohua State Key Laboratory of Magnetism,Intstitute of Physics,the Chinese Academy of Sciences,P.O.Box 603,Beijing 100080 中国原子能科学院北京中科院物理所磁学国家重点实验室北京

The crystallographic and magnetic structures of Ho2Fe9Ga8～xAlx（x=2,4 and 6）arestudied by powder neutron diffraction at room temperature.The atom fractional occupancies ofGa and AI and the atom magnetic moments of Ho and Fe are obtained by Rietveld analysisprogram.The magnetic structure of the phase with x=2 shows an easy-axis anisotropy and themagnetic moments of all atoms are parallel to c axis.The saturation magnetization and Curietemperatures of samples with x in the range 0～8 are investigated.

关键词： neutron diffraction Magnetic structure

Measurement of k_(eff) by delayed neutron multiplication in subcritical systems

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Nuclear Science and Techniques 2018年第2期29卷 118-124页

作者： Bin Ye Chao-Wen Yang Chun Zheng College of Physical Science and Technology Sichuan University Institute of Nuclear Physics and Chemistry China Academy of Engineering Physics

In this paper, we build on the concept of equivalent fundamental-mode source to propose using delayed neutrons as a neutron source in multiplication experiments to acquire the effective multiplication factor keffof subcritical systems, which is difficult to acquire directly from conventional neutron source multiplication method. We analyzed the difference between a fundamental-mode fission source and delayed neutron source,then adopted a factor to convert delayed neutron distribution to an equivalent fundamental-mode source distribution, and employed Monte Carlo code to acquire this factor.The delayed neutron multiplication measurement method was established for the first time, and corresponding experiments were conducted in subcritical systems. The multiplication of delayed neutrons was measured based on Chinese Fast Burst Reactor-Ⅱ(CFBR-Ⅱ) at subcritical states, and keffwas acquired from delayed neutron multiplication successfully(0.9921 and 0.9969, respectively).The relative difference between k_(eff)obtained by the new method and previous values acquired by the positive period method is less than 1% for these two studied cases.

关键词： keff Delayed neutrons neutron source multiplication Subcritical system