Measurement of gamow-teller strength for 176Yb --> 176Lu and the efficiency of a solar neutrino detector

We report a 0 degrees 176Yb(p,n)176Lu measurement at IUCF where we used 120 and 160 MeV protons and the energy dependence method to determine Gamow-Teller (GT) matrix elements relative to the model independent Fermi matrix element. The data show that there is an isolated concentration of GT strength in the low-lying 1(+) states making the proposed Low Energy Neutrino Spectroscopy detector (based on neutrino captures on 176Yb) sensitive to pp and 7Be neutrinos and a promising detector to resolve the solar neutrino problem.     

Shape evolution and test of the critical-point symmetry X(5) in 176Os

The lifetimes of excited states in the yrast band of 176Os have been measured up to I = 20h level using the Doppler shift attenuation method. The high-spin states of 176Os were populated via fusion evaporation reaction 152Sm(28Si,4n)176Os at a beam energy of 140 MeV. The results support an X(5) structure for 176Os at low spin. This structure disappears at high spin and shows a symmetry rotor character. The shape change of 176Os is similar to that of 178Os.     

The quadrupole moment of176Lu

The intrinsic quadrupole moment of¹⁷⁶Lu has been determined by Coulomb excitation with α-particles to be 6.98±0.10 b. Evidence for a new level at approximately 578 keV with presumably collective structure is presented.     

Excitation of giant spin-isospin multipole vibrations in Fe and Ni

Data on (p,n) reactions at 120 and 160MeV have been used to study the excitation of spin-isospin multipole vibrations in ^{54, 56}Fe and ^{58, 60}Ni. In particular, transitions characterized by L = 0 transfer are identified as spin-isospin transitions (excitation of Gamow-Teller states) or as isospin transitions (excitation of isobaric analog states). An effort is made to estimate Gamow-Teller strength, B(GT), at excitation energies between 20–40 MeV. A comparison between GT and M1 strengths is presented for ^{58, 60}Ni. Shell-model calculations for total strengths, Σ B(GT), are compared with the observed results.     

Study of the104Ru(d,p)-reaction at 14 MeV

The reaction¹⁰⁴Ru(d, p) was investigated with high resolution (5 keV) at the Munich MP tandem using the Q3D spectrograph in conjunction with the precision time-of-flight system. The ground stateQ-value was determined as Q=3,684.5±1 keV. Proton spectra were measured at 7 angles in the range of 6.1°–65°. 19 levels could be identified in the excitation energy range 0–730 keV. Transferredl-values and spectroscopic factors of these levels were derived with the aid of DWBA calculations.     

High-spin states of 174, 176Yb studied in Coulomb excitation with Kr AND Xe beams

Rotational states up to spin 20⁺ (18⁺) in ¹⁷⁴Yb (¹⁷⁶Yb) have been Coulomb excited using beams of ¹³⁶Xe. Lifetimes up to and including the 14⁺ state have been measured using Doppler-broadened lineshape techniques with ¹³⁶Xe and ⁸⁶Kr beams. An annular gas-scintillation counter has been developed in order to perform particle-γ coincidence studies. Moments of inertia in ^{174, 176}Yb behave very regularly, showing no signs of backbending effects. The measured lifetimes are in agreement with the rotational model predictions, and the measured cross sections for Coulomb excitation of the high-spin states are in agreement with the semiclassical Winther-de Boer calculation.     

Spectroscopy of double-beta and inverse-beta decays from 100Mo for neutrinos

Spectroscopic studies of two beta rays from 100Mo are shown to be of potential interest for investigating both the Majorana nu mass by neutrinoless double beta decay (0nubetabeta) and low energy solar nu's by inverse beta decay. With a multiton 100Mo detector, coincidence studies of correlated betabeta from 0nubetabeta, together with the large Q value ( Q(betabeta)), permit identification of the nu-mass term with a sensitivity of approximately 0.03 eV. Correlation studies of the inverse beta decay and the successive beta decay of 100Tc, together with the large capture rates for low energy solar nu's, make it possible to detect, in real time, individual low energy solar nu in the same detector.     

Proton capture by 176Yb in the giant dipole resonance region

The proton capture cross section for the reaction ¹⁷⁶Yb(p, γ)¹⁷⁷Lu has been measured for incident proton energies between 6 and 24 MeV. The excitation function for this deformed nucleus agrees remarkably well with the results of previous studies on spherical nuclei, e.g. ¹⁴²Ce(p, γ)¹⁴³Pr. The results indicate that the giant dipole resonance (GDR) is strongly excited as predicted by the direct-semidirect (DSD) model. It is found that the model describes reasonably well the excitation function. In the low-energy proton range, where the excitation function increases rapidly with proton energy, the observed cross section is significantly higher than the DSD predictions. The difference can only partly be explained by compound nucleus contributions. In the high-energy end, the predicted cross section tends to be too high primarily due to an increasing contribution of direct capture to orbitals with large angular momenta.     

Quantum-Hall activation gaps in graphene

We have measured the quantum-Hall activation gaps in graphene at filling factors nu=2 and nu=6 for magnetic fields up to 32 T and temperatures from 4 to 300 K. The nu=6 gap can be described by thermal excitation to broadened Landau levels with a width of 400 K. In contrast, the gap measured at nu=2 is strongly temperature and field dependent and approaches the expected value for sharp Landau levels for fields B>20 T and temperatures T>100 K. We explain this surprising behavior by a narrowing of the lowest Landau level.     

Microwave resonance of the bubble phases in 1/4 and 3/4 filled high Landau levels

We have measured the diagonal conductivity, sigma(xx), in the microwave regime of an ultrahigh mobility two dimensional electron system. We find a sharp resonance in Re[sigma(xx)] versus frequency when nu>4 and the partial filling of the highest Landau level, nu(*), is approximately 1/4 or 3/4 and temperatures <0.1 K. The resonance appears for a range of nu(*) from 0.20 to 0.38 and again from 0.64 to 0.80. The peak frequency f(pk) changes from approximately 500 to approximately 150 MHz as nu(*)=1/2 is approached. This range of f(pk) shows no dependence on nu where the resonance is observed. The quality factor, Q, of the resonance is maximum at about nu(*)=0.25 and 0.74. We interpret the resonance as due to a pinning mode of the bubble phase crystal.     

Determination of the short-wavelength propagation threshold in the collective excitations of liquid ammonia

The dynamics structure factor S(Q,E) of liquid ammonia l-NH3 at T = 200 K and at its vapor pressure has been measured by inelastic x-ray scattering (IXS) in the 1-15 nm(-1) momentum transfer ( Q) range. Contrary to previous IXS studies on other associated liquids and glasses, in l-NH3 a large inelastic signal is observed up to Q = 15 nm(-1). This, enabling S(Q,E) measurements as a function of Q at constant E transfer, allows us to demonstrate experimentally the transition from a propagating dynamics regime, where the acoustic excitation energy linearly disperses with Q, to a high-Q regime, where it is no longer possible to observe a dominant excitation in the S(Q,E).     

Observation of multiple magnetorotons in the fractional quantum Hall effect

Magnetorotons in the dispersions of collective gap excitation modes of fractional quantum Hall liquids are measured in resonant inelastic light scattering experiments. Two deep magnetoroton minima are observed at nu = 2/5, while a single deep minimum is resolved at nu = 1/3. The observations are the first evidence of multiple roton minima in gap excitations of the quantum liquids. The results support Chern-Simons and composite fermion calculations that predict multiple roton minima for states with nu>1/3.     

On the conversion of triple- to single-quantum coherences in MQMAS NMR

A systematic experimental and numerical evaluation of several basic approaches to multiple-quantum magic angle spinning (MQMAS) NMR is presented for spin-32 nuclei. The approaches use identical MQ excitation, via a single RF pulse of high power, and three types of methods for conversion to observable coherence: (a) nutation by strong continuous wave pulse; (b) rotation-induced adiabatic coherence transfer (RIACT), and (c) fast amplitude modulation (FAM-1). The optimization strategies and maximum achievable MQMAS efficiencies of (87)Rb in RbNO(3) and LiRbSO(4) are investigated using several coherence transfer schemes under a wide range of experimental parameters. These parameters include the strength of the RF magnetic field nu(RF), the sample rotation speed nu(R), the length of the conversion period, and the modulation frequency in FAM-1. The data provide new insights into the spin dynamics involved in these techniques and the experimental guidelines for achieving the best sensitivity. The RF requirements for maximum efficiency of conversion depend on the method to be used. In general, FAM-1 performs better than the nutation and RIACT methods in terms of efficiency and off-resonance behavior, especially when nu(RF) is small compared to the quadrupole frequency nu(Q). The experiments performed using nutation, RIACT, and FAM-1 methods yield similar resolution in the isotropic dimension, regardless of nu(RF).     

空间光混频器分光比调整与90°相位差补偿方法

对空间光混频器的90°相位差补偿的几种方法进行了比较分析,并在此基础之上提出了两种新方法.第一种方法采取旋转本振光支路的1/4波片来补偿相位差,旋转信号光支路的第一个1/2波片来调整I路与Q路分光比;第二种方法通过旋转本振光支路的1/2波片和1/4波片到计算出来的角度来实现预定的相位差和分光比.对两种方法进行仿真分析和系统实验.采用第一种方法时,1/4波片快轴与x轴的夹角在-10°~10°变化时,相位差补偿范围为-14°~29°,分光比在0.7~1.4范围内变化;当1/2波片的快轴与y轴的夹角在35°~55°变化时,分光比在0.47~2.1范围内变化.采用第二种方法求解出I/Q路相位差分别为80°、85°、90°、95°、100°,I/Q路分光比分别为0.5、0.75、1、1.5、2时,1/2波片的快轴和1/4波片的快轴的位置.采用这两种方法均可以简单而精确地实现设定的相位差和分光比,有利于光锁相环的相位锁定以及解调出的信号强度的提高.     

Time differential perturbed angular correlations of Gd160 implanted into ferromagnetic Gd and of Yb176 into Fe and Ni

Time differential perturbed angular correlation measurements of Gd¹⁶⁰ in ferromagnetic Gd at various temperatures and of Yb¹⁷⁶ in Fe and Ni have been performed following Coulomb excitation with a pulsed beam and recoil implantation. Using the theory of combined static magnetic and electric hyperfine interaction the measured time spectra are reasonably well reproduced, the magnetic fields and electric field gradients being in agreement with other works. A phase shift of the Larmor precession, however, points to anomalous hyperfine fields acting on the nuclei in a very short time interval after the beam pulse.     

H(2)-Broadening Coefficients in the nu(4) Band of NH(3)

H(2)-broadening coefficients have been measured for 66 rovibrational lines of NH(3) at room temperature in the (P)P and (R)P branches of the nu(4) band in the range 1470-1600 cm(-1), using a high-resolution Fourier transform spectrometer. The collisional widths are obtained by fitting Voigt profiles to the measured shapes of the lines. The broadening coefficients are found to decrease on the whole as J increases and they increase with K for a given J value. The results are compared with those calculated from a semiclassical model in which the inversion vibration of NH(3) and collision-induced transitions with DeltaK = 0 and DeltaK = +/- 3 are taken into account. The intermolecular potential used includes electrostatic, induction, and dispersion energy contributions. The calculations performed by considering only DeltaK = 0 transitions provide significantly lower broadenings but with a satisfactory J and K dependence. The same trends are obtained for the broadening coefficients in inversion-rotation transitions and in the Q branch of the nu(1) parallel band of NH(3). Copyright 2001 Academic Press.     

First High-Resolution Infrared Observation of the Symmetry-Forbidden nu(5) Band of (10)B(2)H(6)

Spectra of (10)B monoisotopic diborane, B(2)H(6), have been recorded at high resolution (2-3 x 10(-3) cm(-1)) by means of Fourier transform spectroscopy in the region 700-1300 cm(-1). A thorough analysis of the nu(18) a-type, nu(14) c-type, and nu(5) symmetry-forbidden band has been performed. Of particular interest are the results concerning the nu(5) symmetry-forbidden band, which is observed only because it borrows intensity through an a-type Coriolis interaction with the very strong nu(18) infrared band located approximately 350 cm(-1) higher in wavenumber. The nu(5) band has been observed around 833 cm(-1) and consists of a well-resolved Q branch accompanied by weaker P- and R-branch lines. Very anomalous line intensities are seen, with the low K(a) transitions being vanishingly weak, and Raman-like selection rules observed. The determination of the upper state Hamiltonian constants proved to be difficult since the corresponding energy levels of each of the bands are strongly perturbed by nearby dark states. To account for these strong localized resonances, it was necessary to introduce the relevant interacting terms in the Hamiltonian. As a result the upper state energy levels were calculated satisfactorily, and precise vibrational energies and rotational and coupling constants were determined. In particular the following band centers were derived: nu(0) (nu(5)) = 832.8496(70) cm(-1), nu(0) (nu(14)) = 977.57843(70) cm(-1), and nu(0) (nu(18)) = 1178.6346(40) cm(-1). (Type A standard uncertainties (1varsigma) are given in parentheses.) Copyright 2000 Academic Press.     

CdTe:Li晶体中ALi°受主与电子及激子的相互作用

用两种不同方法实现了在CdTe晶体中Li杂质的低温扩散。其中后一种无Te预扩散的方法是首次报导的。为研究在CdTe:Li中ALi°受主与电子和激子的相互作用,分析了各种发光机制中的动力学过程,观测了(e,ALi°)及(ALi°,X)发光的激发光强度效应。(ALi°、X)束缚激子可以热离解成一个自由电子和一个自由空穴而留下一个中性受主ALi°,其束缚能为Eb=4meV。在不同强度的光激发下,研究了(e,ALi°)辐射复合中电子—声子耦合。当杂质中心不变时,平均声子数N～0.1基本上保持不变,它是杂质中心波函数半径的一个量度。若假定杂质中心上电荷分布为Gaussian形,计算出表征电荷在杂质中心局域程度的常数α～160Å。     

The time dependence and efficiency of excitation of three-quantum coherence in proton spectroscopy of proteins

The time dependence and efficiency of excitation of three-quantum (3Q) coherence is examined for the peaks that are commonly observed in 'H NMR 3Q spectra of proteins. The algebraic expressions for the various contributions to each 3Q coherence are tabulated. Plots of the excitation efficiency versus the length of the excitation period are shown. These results provide guidelines for optimizing the length of the 3Q excitation period to obtain either a wide range of 3Q signals in the spectrum or the excitation of specific 3Q signals with maximum efficiency.     

Topologically protected qubits from a possible non-Abelian fractional quantum Hall state

The Pfaffian state is an attractive candidate for the observed quantized Hall plateau at a Landau-level filling fraction nu=5/2. This is particularly intriguing because this state has unusual topological properties, including quasiparticle excitations with non-Abelian braiding statistics. In order to determine the nature of the nu=5/2 state, one must measure the quasiparticle braiding statistics. Here, we propose an experiment which can simultaneously determine the braiding statistics of quasiparticle excitations and, if they prove to be non-Abelian, produce a topologically protected qubit on which a logical Not operation is performed by quasiparticle braiding. Using the measured excitation gap at nu=5/2, we estimate the error rate to be 10(-30) or lower.