首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
With the aid of rf, microwave and dc discharges, an optogalvanic (OG) signal, due to the photodetachment of negative oxygen ions, has been observed. The OG signal intensity in an rf discharge was successfully estimated from the discharge parameters. Thus, the OG technique may be potentially useful as a plasma diagnostic method. Furthermore, the OG signal from negative oxygen ions is found to be strong in the diffusion-controlled positive column, while the OG signal due to the excited levels of atomic oxygen is strong in the cathode fall region. Preliminary results for the observation of the OG signal in discharges of H2, CO, H2O2, and (COCH3)2 are also described.  相似文献   

2.
A new method for studying the processes of the establishment of the thermodynamic equilibrium in the adsorbed 3He layers in highly porous media has been proposed. Using this method, the thermalization of adsorbed 3He on silica aerogel at a temperature of 1.5 K has been studied. The process of the establishment of the thermodynamic equilibrium has been controlled by measuring the pressure in an experimental cell, the amplitude of the NMR signal, and the nuclear spin-spin and spin-lattice relaxation times of adsorbed 3He. It has been shown that the establishment of the thermodynamic equilibrium in the adsorbed 3He-aerogel system is characterized by a time of 26 min.  相似文献   

3.
We report the dynamical properties of the exciton orientation in GaAs thin films using the orientational grating (OG) technique. From the results of excitation-power dependence of OG signal, we confirmed that the OG signal comes from the optical nonlinearity of weakly confined excitons. In addition, the OG-decay time decreases with an increase of excitation power due to exciton–exciton interaction, and the shortest decay time is below 1 ps. Our results may imply the potential application of optical nonlinearity of weakly confined exciton to ultrafast switching devices operating at 1 Tbit/s.  相似文献   

4.
A computer program for the positive exponential sum method of inverting Laplace transform of photon autocorrelation curves has been written and applied to both simulated and experimental data. The method recovers the decay time spectra from autocorrelation curves by replacing the decay time distribution by a set of delta peaks whose envelope roughly follows this distribution. Spacing of this set becomes slightly denser with decreasing noise and is about two peaks per decade under usual conditions (noise level about 10–3). Occasional irregularities in peak spacing and an appearance of weak artifact peaks in regions where the decay time spectrum is of zero density may make the physical interpretation of results difficult.  相似文献   

5.
The properties of liquid 3He in a low-density aerogel preliminarily covered with a few monolayers of 4He were studied by pulsed and nonlinear CW NMR techniques. It was found that an NMR frequency shift from the Larmor value exhibits a sharp increase at a magnetization tilting angle exceeding 104°. Nonlinear CW NMR signals related to the formation of a macroscopic region featuring homogeneous precession of the magnetization (homogeneous precession domain) were observed. The experimental results confirm that the low-temperature superfluid 3He phase in the aerogel is analogous to the B-phase in bulk 3He and indicate that the spin supercurrents play an important role in the spin dynamics of superfluid 3He in aerogel.  相似文献   

6.
The optogalvanic (OG) spectrum — over the tuning range of R 6G dye (568 nm to 605 nm) — of a Pr/Ne discharge tube is studied. The positive OG signals are approximately two orders of magnitude larger than the negative OG signals. The magnitude of the signals depend mainly on the operating regime of the discharge. Specifically, operation of the discharge in the abnormal glow regime leads to an enhancement in the negative OG signals. The operating point on theV-I characteristic of the discharge should be stipulated. To study the variation of the OG signal with the intensity of the laser beam two OG signals, of different polarities, were examined. We observed that with respect to positive OG signals, there is a trend towards pumping saturation. A minimum threshold of 0.3 kW laser power is required to generate negative OG signals. For the same attenuation in the laser beam there is a ten times more efficient reduction in the negative OG signals than in the case of positive OG signals. This confirms the important role of metastable atoms in the conduction in gas discharges.The hypothesis that negative OG signals can be obtained only abnormal glow regime needs more experimental data. The required study of the temporal variation in the OG signal with increase in the discharge current is being carried out and the results are to be published.  相似文献   

7.
A study of optogalvanic (OG) signals in a uranium hollow cathode discharge using a tunable pulsed dye laser with intensities above saturation revealed certain systematic trends. The peaks of OG signals, for a given hollow cathode current, due to all transitions involving the ground state are within a certain range of values. The same is true of the OG signals due to transitions involving the 620 cm-1 and 3800 cm-1 lower metastable levels. For all transitions involving the same lower state, the peaks of OG signal vary linearly with the discharge current. The slopes of such straight lines are different for transitions involving different lower levels of uranium. Effects of radiation trapping are seen in the OG signals due to transitions involving the ground state of uranium at currents above 60 mA. Details of our observations are presented and discussed.  相似文献   

8.
The kinetics of luminescence of Eu3+ ions in Lu2O3:Eu nanospheres with diameters of 100–270 nm and a small standard deviation of the size distribution <15% has been studied. A sharp decrease in the decay time of luminescence of Eu3+ ions in the red range with an increase in the diameter of nanospheres has been attributed to the appearance of a photon mode accelerating spontaneous luminescence, which is confirmed by the calculation of ranges of existence of whispering-gallery modes in studied nanospheres.  相似文献   

9.
Some experimental results on the temporal decay of the fluorescence induced by a resonant laser pulse excitation focused onto a helium gas discharge are presented. In particular, excitation transfer between singlet-singlet and singlet- triplet sub-levels has been studied when 21 S → 31 P and 21 P → 41 D transitions of He I are optically pumped.  相似文献   

10.
The Relativistic Heavy Ions Collider (RHIC) has accelerated polarized proton beams for physics since 2001. As part of the future eRHIC program and in order to enhance access to the down quark, a program to accelerate polarized 3He in the AGS and RHIC is envisioned. To that end, a polarized 3He source is being built at MIT. This will be installed on the BNL EBIS source in preparation for injection into the booster and AGS. As an early exercise, in June 2012, unpolarized 3He beams have been accelerated in the AGS. This paper will peruse some potential ideas for 3He polarimetry and calibration that could be utilized at the AGS as well as RHIC. The current proton polarimetry program serves as a guide.  相似文献   

11.
Inclusivep, d and3He cross sections have been obtained using experimental data on p4He collisions over an incident proton energy range of 46-400 GeV. Considering the slopes of spectra, the effective nuclear temperature has been found to be T0=11 MeV, which is in good agreement with experimental results for lower energies and heavier targets. The shape of the3He inclusive spectrum suggests the existence of two different3He production mechanisms. The experimental3He cross section is compared with theoretical predictions assuming fragment formation as a result of the spectator and cluster knockout mechanisms. The4He→3He +n vertex constant has been found to be G2=10.9±0.2 fm.  相似文献   

12.
A new method for the detection of the optogalvanic (OG) effect in a flame has been developed. In the experimental scheme, the reflected microwave power is measured for the detection of the OG effect inside a microwave resonant cavity. In a preliminary experiment, the OG signal of sodium atom aspirated into a propane/O2 flame was observed at a concentration below 10 ng/ml.  相似文献   

13.
A. Deloff 《Nuclear Physics A》1974,236(2):469-490
Angular distributions and energy spectra for the decay modes Λ4He→π?p3He, Λ4H → π?p3H, Λ4H → π?n3He are calculated and compared with experiment. Final state nuclear interactions have been adjusted to fit the corresponding scattering data. With S-, P- and D-wave interactions we were able to obtain reasonably good agreement with the experimental decay spectra. It is suggested that the Λ4H → π?n3He decay spectra may be decisive in selecting the right set of p3H complex phase shifts from several possible solutions.  相似文献   

14.
The angular correlation between momenta of 5He and its decay products has been calculated for the peripheral fragmentation of 6He using a two-step model in a sudden approximation: (1) One neutron knock-out leading to the unbound nucleus 5He. (2) Subsequent decay of 5He undisturbed by the target in an α-particle and a neutron. Angular correlations measured in a recent experiment dealing with the peripheral fragmentation of 240 MeV/u 6He on a carbon target can be well described by a dominant 5He 3/2? ground state configuration plus a small admixture of ≈ 7% of the first excited 1/2? state. The influence of an s-state admixture as well as a contribution of the momentum transfer to the correlation function are investigated. The results obtained for 6He are then used as a touch stone for a discussion of the methods to investigate peripheral fragmentation of other Borromean halo nuclei like 11Li and 14Be. It is shown that the evidence on the possible existence of low-lying s-states in 10Li and 13Be can be derived from the corresponding angular correlations.  相似文献   

15.
Gartner  B.  Ackerbauer  P.  Breunlich  W. H.  Cargnelli  M.  Fischer  A.  Kammel  P.  King  R.  Kminek  G.  Lauss  B.  Marton  J.  Prymas  W.  Steininger  E.  Zmeskal  J.  Petitjean  C.  Chatellard  D.  Egger  J. -P.  Jeannet  E.  Hartmann  F. J.  Kosak  A.  Mühlbauer  M.  von Egidy  T.  Piller  C.  Schaller  L. A.  Schellenberg  L.  Schneuwly  H.  Thalmann  Y. -A.  Tresch  S.  Werthmüller  A. 《Hyperfine Interactions》1996,101(1):249-255
Muon transfer from the ground state of muonic deuterium to a helium atom proceeds mainly via the formation of a muonic molecule in an excited state. A large number of decay X rays ( 6.8 keV) from these (dµHe)* molecules were observed for the4He as well as for the3He case. The time distributions of these X rays allow the determination of the ground state transfer rate. The simultaneous employment of Ge/Si-detectors and CCDs for the same target conditions allows the determination of the branching ratio of radiative to nonradiative decay for the first time.  相似文献   

16.
The lifetime of the positive muon (τμ +) can be directly associated with the Fermi Coupling Constant (G F ), which is one of the most basic parameters of the Standard Model. However, the current experimental accuracy of the τμ + is ∼30 ppm and it has not been improved for more than 15 years. We propose a new experiment for a pulsed muon facility such as RIKEN-RAL to measure the muon lifetime with multi-decay per one time window method. The advantage of our setup, no time window limitation, enables us to test the exponential decay law (EDL) in the long decay time region at the same time. The preliminary analysis set a new upperlimit for the EDL deviation in the muon decay. We accumulated ∼1010 muon decays and analysis is in progress. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

17.
The energy and time distributions of the decay X-rays of excited, metastable, molecular (dμHe)*-resonances were measured. The comparison of the observed energy spectra with calculated ones suggests that decay from the rotational state J = 1 dominates at the investigated conditions. The muon transfer rates from ground state deuterium to the helium isotopes 3He and 4He at low temperatures were determined from the time distributions of these spectra. Additionally, the temperature dependence of the muon transfer rate was clearly established in deuterium / 4He mixtures. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

18.
We present a simple model to describe the line-profile of velocity modulated ions. This model is based on Langevin's theory of the mobility and on the independence of the electric field strength on the discharge current in the ideal positive column. A comparison of time constants responsible for the drift of the ions, the concentration, and the ignition and extinction of the discharge itself is essential for a rough understanding of the velocity modulation. The behaviour of H3O+ ions in an ac glow discharge was examined. Under our experimental conditions the line-profile can be explained by a temporal dependence of the velocity which is close to a square-wave. Due to this particular temporal dependence the amplitude of the signal only depends on the concentration modulation, while the line-shape is a simple difference line-profile.  相似文献   

19.
Chemical etching of the (100) face of p-type Si by aqueous K2Cr2O7 was investigated with a contactless transient photoconductivity method, i.e. the time-resolved microwave conductivity (TRMC) method, after ns laser pulse excitation and with XPS, UPS, and LEED. TRMC transients after etching show a much slower decay that is explained by a decrease of surface recombination velocity. XPS indicates the formation of a mixed oxide of SiIII and Crv. During heating to 600°C this layer first transforms to a SiIV-CrIII oxide. After heating to 1200°C the oxide and Cr at the surface have disappeared, as indicated by UPS (He I and He II) and LEED (sharp 2×1 LEED pattern). However, XPS still shows the presence of Cro which evidently is diffused into the bulk. This can also be deduced from the transient photoconductivity measurements as TRMC transients at this stage show a fast decay rate that must be due to an increased bulk decay rate of excess charge carriers.  相似文献   

20.
On applying voltage to a thin film Al-Al2O3-M system, one observes a decrease of the leakage current with time. After a long period (103–104 s) the current settles at a new value, lower by several orders of magnitude. After shortcircuiting the sample, there appears a discharge current of reversed polarity, with decay time again of the order of 103 s. This effect has been reproducibly observed in the temperature range 80–500 K. The present paper is devoted to the experimental study of this relaxation phenomenon in dependence on the parameters of the system (thickness of the dielectric layer, temperature, and material of the upper electrode).The paper is based on RNDr Thesis of the first author.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号