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Enhancement of M1 Transition Rates at High Spin in 90Mo
WU Xiao-Guang, LI Guang-Sheng, PENG Zhao-Hua, WEN Shu-Xian, HAN Guang-Bing, LI Cheng-Po, LU Shao-Jun, WU Shao-Yong, YUAN Guan-Jun, YANG Chun-Xiang
Chin. Phys. Lett. 2001, 18 (4):
505-507
.
High spin states in 90Mo have been populated through the 59Co (35Cl,2p2n) 90Mo reaction at beam energy of 116 MeV. Level lifetimes of the positive-parity decay sequence are measured by using the Doppler shift attenuation method. It is observed that the M1 transition strengths show a substantial enhancement at high spin. This behaviour may be related to occupation of high Ω orbitals by a pair of g9/2 protons. A deformed shape with oblate is suggested above the 13+ state.
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Scintillation Characteristics of Doped PbWO4 Crystals
SHAO Ming, CHEN Hong-Fang, LI Cheng, XU Tong, SHI Chao-Shu, WU Jian, CHEN Hui, XU Zi-Zong, WANG Zhao-Min, WANG Xiao-Lian, DENG Qun, YIN Zhi-Wen
Chin. Phys. Lett. 2001, 18 (4):
513-515
.
Emission spectra, longitudinal transmission and light output for the Sb-doped and Y-doped PbWO4 crystals are presented. Scintillation decay kinetics has been measured by using gate integration and single photon counting method with blue and green filters. Radiation hardness has also been measured by using 60Co γ-ray irradiation under different dose rates and different dose rate profiles. The light yield and radiation hardness of the Sb-doped and Y-doped PbWO4 crystals are improved as compared to the undoped crystals and are suitable for the requirements of compact muon solenoid.
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Energy Transfer Pathways in Reaction Center upon Femtosecond
Excitation of Accessory Bacteriochlorophylls
GUO Li-Jun, MA Guo-Hong, ZOU Yong-Long, XU Chun-He, LIU Ye, MI Jun, QIAN Shi-Xiong, LIU Jian-Hua
Chin. Phys. Lett. 2001, 18 (4):
522-524
.
The energy transfer pathways from the excited accessory
bacteriochlorophylls (B*) within native and modified (pheophytin-exchanged) reaction center isolated from Rhodobacter
sphaeroides (RS601) have been investigated by using the femtosecond pump-probe technique. For native RS601, B* decays with time constant of 240 fs, followed by a partial recovery of the ground state bleaching with time scale of about 2 ps. In modified RS601(Phe), however, B* decays with time constant of 800 fs for magic angle (54.7°) polarization configuration. In addition to the general assumption of energy transfer pathway from B* to the special pair P, an alternative pathway for energy transfer probably operates as well.
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Zeeman-Birefringence He-Ne Dual Frequency Lasers
JIN Yu-Ye, ZHANG Shu-Lian**, LI Yan, GUO Ji-Hua, LI Jia Qiang
Chin. Phys. Lett. 2001, 18 (4):
533-536
.
We demonstrate an approach to obtain the frequency differences from 1 MHz to hundreds of MHz including 3-40 MHz, which was a blank range of the frequency difference in the traditional dual frequency lasers. We employ an intra-cavity stress-birefringence element in an He-Ne laser, and at the same time apply a transverse magnetic field to the laser. The intra-cavity stress birefringence element, which is the window plate or the mirror substrate applied by a force, is used to split a frequency into two; i.e. to make a single-frequency laser outputting two frequencies. Moreover, the transverse magnetic field is used to decrease greatly the mode competition between the two frequencies so that they are able to oscillate simultaneously. The minimum value of magnetic field for efficiently eliminating the mode competition to ensure the two frequencies working together is studied experimentally. The power tuning performance of the two frequencies (o-light and e-light) is investigated.
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All-Solid-State Multi-Wavelength Laser System from 208 to 830 nm
ZHAO Shang-Hong, CHEN Guo-Fu, ZHAO Wei, WANG Yi-Shan, YU Lian-Jun
Chin. Phys. Lett. 2001, 18 (4):
537-538
.
Four-wavelength lasers from near-infrared to deep-ultraviolet range, 532, 830, 415 and 208 nm, have been developed in one all-solid-state laser system. The laser system is pumped by a diode-Q-YLF laser at 532 nm, a Ti:sapphire laser and the nonlinear second-harmonic-generation crystals LBO and BBO are used to generate different wavelengths. Maximum average powers (repetition rate 1 kHz) of 1.1 W at 830 nm, 380 mW at 415 nm, and 39 mW at 208 nm are obtained when the pumping power is 3.6 W. The main characteristics of this system are presented.
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Red and Blue Light Generation in an LiTaO3 Crystal
with a Double Grating Domain Structure
LIU Zhao-Wei, ZHU Shi-Ning, ZHU Yong-Yuan, WANG Hui-Tian, LUO Guo-Zhen, LIU Hui, MIN Nai-Ben, LIANG Xiao-Yan, XU Zu-Yan
Chin. Phys. Lett. 2001, 18 (4):
539-540
.
Simultaneous red and blue light generation in an LiTaO3 crystal with a double grating structure is first reported. The double grating consists of two separate domain reversal sequences (superlattices) in series and is fabricated by field poling technique at room temperature. Using a picosecond 532 nm laser as a pump source, the red light at 631 nm and blue light at 460 nm are generated at the same time. A possible application of the superlattice crystal is presented.
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Absorption Measurement of Radiatively-Heated Low-z Mixture
YANG Jia-Min, DING Yao-Nan, ZHANG Bao-Han, YANG Guo-Hong, ZHENG Zhi-Jian, ZHANG Wen-Hai, WANG Yao-Mei, YAN Jun, LI Jia-Ming
Chin. Phys. Lett. 2001, 18 (4):
550-552
.
High-resolution transmission spectra of radiatively-heated low-z C10H16O6 plasma have been measured on‘Xingguang II’ laser facility by using flat field grating spectrometer. Absorption lines of oxygen and carbon ions in the region of 1.6 to 5.0 nm have been observed clearly and identified. Using the unresolved transition array model, we also calculated the transmission spectra of C10H16O6 plasma. The measured transmission spectrum has been compared with the calculated ones.
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Identification of Defects in Undoped Semi-insulating InP
by Positron Lifetime
MAO Wei-Dong, WANG Shao-Jie, WANG Zhu, SUN Nie-Feng, SUN Tong-Nian, ZHAO You-Wen
Chin. Phys. Lett. 2001, 18 (4):
574-576
.
Positron lifetime measurements, carried out over the temperature range of 10-300 K, have been used to investigate defects in two undoped semi-insulating InP samples. The positron lifetime spectra were analysed by both PATFIT and MELT techniques. The results at room temperature reveal a positron lifetime around 273 ps, which is associated with indium vacancies VIn or VIn-hydrogen complexes. The positron average lifetime is temperature dependent and decreases with increasing temperature at the beginning (≤ 80 K and ≤ 120 K), and then keeps unchanged, which is attributed to the influence of negative vacancies and detrapping of the positron from those negative ions of Mg, Zn, Ag, and Ca with ionization level (1-).
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X-Ray Diffraction Study of Carbon Nanotubes Under High Pressure
CHEN Liang-Chen, WANG Li-Jun, TANG Dong-Sheng, XIE Si-Shen, JIN Chang-Qing
Chin. Phys. Lett. 2001, 18 (4):
577-578
.
The structure and physical properties of carbon nanotubes have been investigated by using in situ high pressure energy dispersive x-ray diffraction with synchrotron radiation at pressures up to 50.7 GPa. At atmospheric pressure, the structure of carbon nanotubes is similar to the hexagonal close-packed lattice of graphite with the interplanar spacing of the diffraction line (002) d002 = 0.3404 nm and that of the line (100) d100 = 0.2116 nm. According to the high pressure x-ray diffraction results, the diffraction line (002) is broadened and weakened above 8 GPa, and carbon nanotubes become partly amorphous. When the pressures of 10 and 20 GPa are decreased down to zero, the diffraction line (002) is partly recovered. While at the maximum pressure of 50.7 GPa, they entirely become amorphous and this amorphous transition is irreversible. We used the equation of state of Birch-Murnaghan to fit the P-V data of carbon nanotubes and obtained the bulk modulus K0 = 54.3±3.2 GPa (at K'0 = 4.0).
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Effects of GaAs on Photoluminescence Properties of Self-Assembled InAs Quantum Dots
WANG Xin-Qiang, ZHANG Ye-Jin, DU Guo-Tong, LI Xian-Jie, YIN Jing-Zhi, CHEN Wei-You, YANG Shu-Ren
Chin. Phys. Lett. 2001, 18 (4):
579-581
.
Room temperature photoluminescence(PL) spectra of InAs self-assembled quantum dots (QDs) deposited on a GaAs/InP and InP substrate are investigated. From the PL spectra, we find that the peak position of InAs QDs appears red-shift from 0.795 to 0.785 eV after we insert a thin tensile GaAs layer between InAs QD layer and InP buffer layer. In order to explain this phenomenon in theory, we examine the strain tensor in InAs quantum dots by using a valence force field model and use a five-band k . p formalism to obtain the electronic structure. The calculated results show that the ground transition energy decreases from 0.789 to 0.780 eV when the thin GaAs layer is inserted. Therefore, the PL peak position should appear red-shift as shown in the experiment.
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Preparation and Characterization of the New Superconductor
MgB2
SUN Yu-Ping, SONG Wen-Hai, DAI Jian-Ming, WU Xing-Cai, WANG Kai-You, ZHAO Bing, XIAO Hong, DU Jia-Ju, WEN Hai-Hu, ZHAO Zhong-Xian
Chin. Phys. Lett. 2001, 18 (4):
587-588
.
Polycrystalline samples of the new superconductor MgB2 are prepared by solid state reaction using Mg and B powders. The resistance measurement shows that the onset transition temperature and zero resistance transition temperature are Tonsetc = 43.8 K and Tc0 = 37 K, respectively. The Tc0 depends on measuring current strongly. The diamagnetic transition temperature of ~38 K is obtained by the ac susceptibility measurement. X-ray powder diffraction spectra of MgB2 can be indexed using hexagonal structure with space group P6/mmm and lattice parameters a=0.30864 and c=0.35212 nm. A second phase, probably MgO, is also found.
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Statistic Ensemble Theory of Small Superconducting Grains
CHEN Zhi-Qian, ZHENG Ren-Rong,
Chin. Phys. Lett. 2001, 18 (4):
592-594
.
We apply random matrix theory to small metallic grains in different spin-states of S=0, 1/2, 1, 3/2, 2, 5/2, ..., and find that there exist theoretical critical level spacings dc at which the superconductivity would break down. We also find that the higher the spin-state, the smaller the critical level spacing, and for the state of S = 0 there actually exists the superconducting enhancement.
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Robustness of the Sunyaev-Zel’dovich Effect as a Measure of the Hubble Constant
CAO Li, ZHANG Yuan-Zhong, ZHU Zong-Hong,
Chin. Phys. Lett. 2001, 18 (4):
622-624
.
After inversing the x-ray surface brightness of the cooling flow cluster Abell 1689 through the isothermal β model, the isothermal double β model and the x-ray surface brightness distribution model derived from the universal dark matter density profile, we calculate the electron distribution and the Sunyaev-Zel'dovich (SZ) effect of the cluster. The resulting temperature decrements, which are inversely proportional to the square root of H0, are very different for the three models, with uncertainty of 15%. Thus, the SZ/x-ray route can not be taken as a precise measurement of H0 until further observations (e.g. from the satellite AXAF) constrain well the amount and distribution of cluster gas.
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53 articles
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