共查询到20条相似文献,搜索用时 0 毫秒
1.
M. Idrish Miah 《Optik》2011,122(20):1811-1813
Spin polarization in semiconductors was investigated by pump-probe measurements, where the transmissions of the samples were monitored with probe pulses with same and opposite circular polarizations. The spin polarization as a function of the pump-probe delay was estimated, and the polarization was found to decay in a sub-ns timescale. It was also found that the polarization depends strongly on photon energy of the pump beam. The pumping energy dependence of the spin polarization was discussed based on the inter-band transition probabilities. 相似文献
2.
M. Yaguchi M. Mihara M. Fukuda D. Nishimura H. Uenishi K. Iwamoto M. Wakabayashi J. Ohno Y. Kamisho Y. Morita T. Minamisono K. Matsuta 《Hyperfine Interactions》2013,220(1-3):79-82
Spin polarization of short-lived β-emitting nucleus 29P (I π = 1/2?+?, T 1/2 = 4.14 s) produced through the 28P(d, n) 29P reaction was studied as functions of the incident deuteron energy E d and the recoil angle θ of 29P. New optimum condition was found at E d = 3.3 MeV and θ = 30° where polarization of 29P is ?(4.1 ± 0.7) %. 相似文献
3.
Groh DE Mantica PF Stuchbery AE Stolz A Mertzimekis TJ Rogers WF Davies AD Liddick SN Tomlin BE 《Physical review letters》2003,90(20):202502
Spin polarization of 37K nuclei produced via single proton pickup from a 9Be target by a beam of 150 MeV/nucleon 36Ar has been observed. Positive spin polarization with magnitude (8.5+/-0.6)% was deduced near the peak of the 37K momentum distribution. The variation of the spin polarization as a function of outgoing 37K momentum is explained by a classical conservation model, as previously applied to describe the induced spin polarization observed for fragments produced in intermediate-energy heavy-ion reactions, with the condition that the picked-up proton has an average momentum equal to the Fermi momentum and is aligned along the incident beam direction. 相似文献
4.
V. Horsfjord 《Nuclear Physics A》1975,253(1):216-230
We have considered the polarization effects for monopole and quadrupole electron excitations of nuclei in the oxygen region. A phenomenological method has been used in order to extrapolate empirical values for the polarization charges, from the real photon limit, to higher momentum transfers. We find in most cases polarization charges that are nearly constant, for momentum transfers up to 2 or 3 fm?1. Hence we have provided a justification in the oxygen region for the assumption most frequently made when experiment and theory are compared. 相似文献
5.
M. P. L'pez-Sancho F. Guinea J. A. Vergés E. Louis 《Zeitschrift für Physik B Condensed Matter》1996,101(2):283-288
The low energy spin and charge excitations in the 2D Hubbard model near half filling are analyzed. The RPA spectra derived from inhomoheneous mean field textures are analyzed. Spin excitations show a commensurate peak at half filling, incommensurate peaks near half filling, and a broad background typical of a dilute Fermi liquid away from half filling. Charge excitations, near half filling, are localized near (0,0), and they occupy a small portion of the Brillouin Zone, in a way consistent with the existence of a small density of carriers, and a small Fermi surface. At higher hole densities, they fill the entire BZ, and can be understood in terms of a conventional Fermi liquid picture. The results are consistent with the observed features of the high-Tc superconductors. 相似文献
6.
Jing-Jing Li Dan-Yang Pang Yan-Lin Ye Jian-Ling Lou Xiao-Fei Yang Yang Liu Biao Yang 《中国物理C(英文版)》2019,43(12):124102-124102-7
In order to describe charge exchange reactions at intermediate energies,we implemented as a first step the formulation of the normal eikonal approach.The calculated differential cross-sections based on this approach deviated significantly from the conventional DWBA calculations for CE reactions at 140 MeV/nucleon.Thereafter,improvements were made in the application of the eikonal approximation so as to keep a strict three-dimensional form factor.The results obtained with the improved eikonal approach are in good agreement with the DWBA calculations and with the experimental data.Since the improved eikonal approach can be formulated in a microscopic way,it is easy to apply to CE reactions at higher energies,where the phenomenological DWBA is a priori difficult to use due to the lack,in most cases,of the required phenomenological potentials. 相似文献
7.
A. V. Blinov I. A. Vanyushin V. E. Grechko S. M. Zombkovsky L. A. Kondratyuk Yu. V. Korolev Ya. M. Selector V. V. Soloview V. F. Turov I. V. Chuvilo V. N. Shulyachenko 《Nuclear Physics A》1990,510(4):803-816
The basic characteristics of the quasi-elastic charge exchange reaction p3He→ nFppp are investigated using the 80 cm ITEP liquid-hydrogen bubble chamber, which is exposed to beams of 3He nuclei with momenta of 2.5 and 5 GeV/c (the kinetic energy of primary protons in the rest system of the nucleus are, respectively, Tp = 0.318 and 0.978 GeV). The experimental data are compared with the predictions of the Glauber-Sitenko multiple scattering theory and of the pole model, taking into account the interaction between spectator nucleons in the final state. In the mass spectrum of the 3p system at 3.05 GeV a clearly denned structure has been revealed, which is not described within the pole model. A possible resonance origin of the given structure is discussed. 相似文献
8.
Stokmaier M Goll G Weissenberger D Sürgers C Löhneysen HV 《Physical review letters》2008,101(14):147005
The spin polarization P of the transport current through the interface between superconducting Al and ferromagnetic Fe is determined by means of Andreev reflection at nanostructured point contacts. We observe a systematic decrease of P with decreasing contact resistance. Our data provide evidence for the reduction of P by spin-orbit scattering and thus establish a link between density of states and transport spin polarizations. 相似文献
9.
A selfconsistent perturbation calculation for the impurity spin polarization and susceptibility as function of temperature and applied magnetic fields is carried out within the Tomonaga model for spin Kondo systems. 相似文献
10.
A. Werthmüller A. Adamczak R. Jacot‐Guillarmod F. Mulhauser L.A. Schaller L. Schellenberg H. Schneuwly Y.‐A. Thalmann S. Tresch 《Hyperfine Interactions》1998,116(1-4):1-16
The charge exchange reaction of negative muons from the
atom to oxygen has been measured in gaseous mixtures of H2 + O2. The measurements were performed at three different relative oxygen concentrations ranging from 0.2% to 0.8% and total pressures 3.5–15 bar. A mean transfer rate of
, describing the transfer from the ground state of thermalized
atoms to oxygen, was determined. In order to investigate the energy dependence of the transfer rate, Monte Carlo simulations of the
thermalization and the muon transfer were carried out. The comparison of measured and simulated time spectra yielded an epithermal transfer rate
=3.9
1011 s-1 in the energy interval 0.12–0.22 eV. The analysis with the model of Two components shows that all measured time spectra can be reproduced with the same set of parameters. 相似文献
11.
Gan Z 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,143(1):136-143
Polarization inversion spin exchange at the magic angle (PISEMA) [J. Magn. Reson. A 109, 270 (1994)] is an important experiment in NMR structural characterization of membrane proteins in oriented lipid bilayers. This paper presents a theoretical and experimental study of the spin dynamics in PISEMA to investigate the line-narrowing mechanism. The study focuses on the effect of neighboring protons on the spin exchange of a strongly coupled spin pair. The spin exchange is solved analytically for simple spin systems and is numerically simulated for many-spin systems. The results show that the dipolar couplings from the neighboring protons of a strongly coupled spin pair perturb the spin exchange only in the second order, therefore it has little contribution to the linewidth of PISEMA spectra in comparison to the separated-local-field spectra. The effects from proton resonance offset and the mismatch of the Hartmann-Hahn condition are also discussed along with experimental results using model single-crystal samples. 相似文献
12.
The charge exchange reaction
at 1 GeV projectile proton energy is studied in the multiple-scattering expansion technique. This reaction is considered in a special kinematics, when the momentum transfer from the beam proton to the fast neutron is close to zero. The differential cross-section and a set of polarization observables are calculated. It was shown that the contribution of the final-state interaction between two protons is very significant.Received: 29 April 2004, Published online: 5 October 2004PACS:
21.45. + v Few-body systems - 13.75.-n Hadron-induced low- and intermediate-energy reactions and scattering (energy
10 GeV) - 25.45.Kk Charge-exchange reactions 相似文献
13.
Microscopic analysis of baryonic exchange mechanisms in the dd → nHe reaction at intermediate energy
J. M. Laget 《Nuclear Physics A》1981,370(3):479-495
The dd → n3He reaction is analysed, at the microscopic level, in terms of the exchange of one nucleon or the exchange of one nucleon and one pion. Each mechanism dominates the cross section in well-separated kinematical regions. The sensitivity of the model to its different ingredients (and especially to the two- or three-nucleon wave functions) is studied. 相似文献
14.
Fu R Tian C Kim H Smith SA Cross TA 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,159(2):167-174
The effect of the Hartmann-Hahn mismatch delta = omega(eff)-omega(1S) during polarization inversion spin exchange at the magic angle (PISEMA) has been investigated, where omega(eff) and omega(1S) represent the amplitudes of the 1H effective spin-locking field at the magic angle and the 15N RF spin-locking field, respectively. During the PISEMA evolution period, the exact Hartmann-Hahn match condition (i.e., delta = 0) yields a maximum dipolar scaling factor of 0.816 for PISEMA experiments, while any mismatch results in two different effective fields for the first and second half of each frequency switched Lee-Goldburg (FSLG) cycle. The mismatch effect on the scaling factor depends strongly on the transition angle from one effective field to the other within each FSLG cycle as well as on the cycle time. At low RF spin-lock amplitudes in which the FSLG cycle time is relatively long, the scaling factor rapidly becomes smaller as omega(1S) becomes greater than omega(eff). On the other hand, when omega(1S) < omega(eff), there is relatively little effect on the scaling factor with variation in delta. As a result, the presence of RF inhomogeneities may significantly broaden the line-width in the dipolar dimension because of the mismatch effect. Higher RF spin-lock amplitudes result in a relatively small variation for the scaling factor. Furthermore, ramped amplitude of the 15N RF spin-lock field in synchronization with the flip-flop of the FSLG sequence minimizes the transition angle between the two effective fields within the FSLG cycle. It is shown experimentally that such a ramped amplitude not only gives rise to the same scaling factor but also results in a narrower dipolar line-width in comparison with the rectangular amplitude. 相似文献
15.
We will describe a possible dynamical origin of the energy dependence of charge exchange cross sections. Our main assumption is local compensation of charge in a certain class of many particle final states. 相似文献
16.
YU. E. KANDRASHKIN W. VOLLMANN D. STEHLIK K. SALIKHOV A. VAN DER EST 《Molecular physics》2013,111(9):1431-1443
The magnetic field/microwave frequency dependence of the spin polarized EPR spectra of the sequential spin correlated radical pairs P+A? 1 and P+F? x in type I photosynthetic reaction centres is investigated. Experimental data are presented for photosystem (PS) I and reaction centres of heliobacteria at × band (9.7 GHz) and K band (24 GHz). In photosystem I at ambient temperatures the lifetime of A ? 1 is ~290 ns and both states are observable by transient EPR. In heliobacteria, electron transfer to Fx occurs within ~600 ps and only the state P+F? x is observed. The experimental data show a net polarization of P+ in the state P+F? x, which displays a clear dependence on the strength of the external field. The net polarization generated in sequential radical pairs is expected to pass through a maximum as a function of the Zeeman energy when the characteristic time of singlet-triplet mixing is comparable with the lifetime of the precursor. In PS I, the precursor lifetime (290ns) is much longer than the characteristic time of singlet-triplet mixing at × band (9 GHz, 3 kG) and K band (24 GHz, 8 kG). As a result, the observable net polarization decreases with the field strength in this region. In contrast, in heliobacteria, the precursor lifetime (600 ps) is much shorter than the characteristic time of singlet-triplet mixing, and the net polarization increases in the same range of Zeeman energies. The polarization patterns in these two systems can be described using the specific limiting cases of a short lived and long lived precursor radical pair and written as a sum of several contributions. The spectra are simulated on this basis using parameters derived entirely from independent experimental data, and good agreement between the experimental polarization patterns is obtained. The calculated polarization patterns are sensitive to spin dynamics on a timescale much shorter than the spectrometer response time, and the expected influence of a 10 ns component in the electron transfer, as observed optically in some PS I, preparations is discussed. No significant influence from such a component is found in the spin polarization patterns of PS I from the cyanobacterium Synechocystis 6803. 相似文献
17.
B. Esposito F. Felicetti A. Marini I. Peruzzi M. Piccolo F. Ronga A. Nigro F. Vanoli D. Bisello M. Nigro L. Pescara P. Sartori R. Bernabei P. Monacelli G. Piano Mortari L. Paoluzi F. Sebastiani 《Physics letters. [Part B]》1977,67(2):239-242
We present results for the total cross section of e+e? annihilation into two hadrons at 1.6 GeV: σππ = σKK = (1.8 ± 1.1) × 10-33 cm2.From these values we obtain the time-like electromagnetic form factors these mesons: |Fπ|2 = 0.24 ± 0.14 and |FK|2 = 0.46 ± 0.26. 相似文献
18.
We have suggested a new parameterization scheme for determining the reaction cross section at intermediate beam energies which reproduces the experimental data very well over a wide range of targets and projectiles both normal as well as exotic. In the present scheme the asymmetry aspect of large neutron/proton number has also been properly incorporated. 相似文献
19.
The applicability of the average exchange model as a tool for describing electron spin polarization in micelles is investigated by comparison with analytical and numerical results. The analytical results are used for the interpretation of the various types of dependence, while the numerical results are used for quantitative tests. It is demonstrated that the dephasing effect of the exchange interaction has a significant influence both on the time dependence and on the stationary value of the polarization. Dephasing arising from the exchange interaction is not included in the average exchange model, and therefore the spin dynamics are not described correctly. The average exchange model can only be used to estimate the frequency and the stationary value of the polarization, and only in the case of very slow singlet-triplet mixing, weak exchange interaction, and low reactivity of the radicals. 相似文献
20.
G. Bizard F. Bonthonneau J.L. Laville F. Lefebvres J.C. Malherbe R. Regimbart J. Duflo F. Plouin 《Nuclear Physics B》1975,85(1):14-30
21 differential cross section measurements of the np → pn charge-exchange reaction have been carried out at the synchrotron Saturne (Saclay), for incident neutron momenta between 1 and 2 GeV/c and in the squared four-momentum transfer range 0 ? ?t ? 0.4 (GeV/c)2. The π exchange peak is seen at all the incident momenta. The s dependence of the very forward slope of this peak shows weak structures near the threshold of inelastic channels. 相似文献