Three-Frequency Composite Multipulse Nuclear Quadrupole Resonance Technique for Explosive Detection

New method of multifrequency nuclear quadrupole resonance (NQR) for the explosive detection has been proposed. This technique consists of application of the series of composite excitation circles, each consisting of two or three successive pulses of different frequencies. In this work, we study in detail the multipulse sequence consisting of n excitation sets, each set consists of three pulses. The first pulse is applied with frequency ?? _?, the second pulse with frequency ?? ₀, and the third pulse with frequency ?? _?C, but with a shifted phase. The NQR signal is detected at the frequency ?? ₊. The maximal amplitude of the detected signal is obtained by tuning the pulse parameters at frequencies ?? _? and ?? ₀. We have shown that the phase of the NQR signal at the frequency ?? ₊ second part of the composite pulse with the frequency ?? ₀ the signals with different phases to suppress the spurious signals. The method could be used for increasing the NQR signal, avoiding the spurious signals and improving the reliability of NQR detection. Possible applications of the method for the explosive detection are also discussed.     

Inelastic proton scattering on Neutron-Rich sulphur isotopes

The proton scattering on unstable³⁸S nuclei has been measured in inverse kinematics by using a³⁸S secondary beam at 39 MeV/nucleon. The first 2⁺ state is seen at 1.2 MeV excitation energy and its angular distribution is extracted. Optical and folding model calculations are compared with the elastic and the 2 ₁ ⁺ angular distributions and the β₂ value is determined to be 0.35±0.04. This value is compared with the corresponding result from a Coulomb excitation measurement and theM _n/M_p value is extracted.     

Effect of M+2 ions on the luminescence of Pb+2 in NaCl

The effect of additional doping with M⁺² ions on the luminescence of NaCl:Pb⁺² has been systematically investigated. The data show that the same two emissions at 310 and 380 nm are observed for mixed Pb⁺²-M⁺² clusters as for Pb⁺² aggregates. Moreover, the presence of a M⁺² ion associated to a Pb⁺² ion in a mixed cluster shifts the 310 nm emission (predominantly observed for free Pb⁺²-vacancy dipoles) to 380 nm. The results are consistent with the Fukuda's model, involving an emission at 310 nm from tetragonal (T) minima in the adiabatic potential energy surface (APES) and another one from less symmetry (X) minima at 380 nm. The data for NaCl:Pb⁺²:Mn⁺², show that an excitation transfer is taking place from the X minima of the ³T_1u state of Pb⁺² to Mn⁺².     

Diffraction dissociation in the reaction p+p→Λ°+K++p at the CERN ISR

The exclusive reaction pp→Λ°K⁺p has been studied at 0.1<?t_pp<0.6 GeV² and energies √s=45 GeV and 53 GeV at the CERN ISR. Diffractive excitation p→Λ°K⁺ occurs predominantly in the mass range M(Λ°K⁺)≈2.1 GeV and peaks at 1.7 GeV. The cross section for pp→Λ°K⁺p is 10±3μb for M(Λ°K⁺)<2.5 GeV, and the t_pp dependence is exp (bt) with b=7.0±0.5 GeV^?2.     

Solvent Suppression in High-Resolution 1H NMR Spectroscopy Using Conventional and Phase Alternated Continuous Wave Free Precession

Solvent suppression is frequently mandatory in ¹H high-resolution nuclear magnetic resonance (NMR), especially for those experiments designed for non-deuterated solvent, normally used in protein and in vivo analysis, and also in liquid chromatography-NMR. Here, simple pulse sequences, which are based on continuous wave free precession (CWFP), consisting of a train of pulses separated by a time interval $ T_{\text{p}} \ll T_{2}^{*} $ , is applied to suppress one or more solvent signals in ¹H high-resolution NMR experiments, because of its dependency on the offset frequency. The conventional CWFP pulse sequence, that uses pulses with the same phase and duration, introduces some phase anomaly in the Fourier-transformed spectrum. This problem is minimized when the pulses are applied with phase alternation by π/2 in relation to the preceding pulse. Some problems with signal intensity can also be minimized using a shorter pulse width. Both CWFP and phase alternated CWFP can be easily used to suppress two solvent signals simultaneously, just using the correct T _p value, that must be equal to the inverse of frequency difference (?ν) between both signals to be suppressed. After modifications, we could introduce the CWFP train into 2D routine pulse sequences.     

Phase transition in ammonium sulphate at -50°C: A study of librational mode softening by paramagnetic NH3+ probes

Paramagnetic NH₃⁺ probes in irradiated (NH₄)₂SO₄ crystals were used to study the phase transition at -50°C. The ¹⁴N hyperfine tensor was found to be nearly uniaxial and assumed to represent NH₄⁺ orientations in the lattice, thereby allowing their change with temperature in the range between -40 and -150°C to be investigated. Although soft modes in this material have not been found in far infrared measurements, it is evident from the present EPR studies that optically coupled B_1M lattice modes involving NH₄⁺ librational motion soften at the transition point, as predicted theoretically by Sawada, Takagi and Ishibashi. It was also found in this experiment that occurrence of an antiparallel orientational coupling between the two dissimilar NH₄⁺ sublattices is responsible for the excitation of the coupled B_1M modes.     

Luminescence of orthovanadates M 3 + M3+(VO4)2 and M 2 + M4+ (VO4)2

The absorption, excitation, and luminescence spectra of vanadates of type M ₃ ⁺ M³⁺(VO₄)₂ and M ₂ ⁺ M⁴⁺(VO₄)₂ are studied, where M⁺ is Na, K, Rb, Cs; M³⁺ is Al, Sc; M⁴⁺ is Zr, Sn, Ti. The luminescence spectra maxima are located at 490–510 nm, while those of the excitation spectra are at 360–375 nm. Temperature characteristics of luminescence and thermostimulated luminescence are studied. The question of activation of complex vanadates by rare-earth ions is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 24–28, March, 1976.     

Resolution of a Coulomb reorientation ambiguity in 18O

Elastic scattering data and inelastic excitation of the lowest 2⁺ state in ¹⁸O from 120 MeV ¹⁸O incident on ²⁰⁸Pb are analyzed in coupled channels including couplings to the second 2⁺ state of ¹⁸O. This analysis favors the positive sign for the product of the four E2 matrix elements, p₄ = M₀₁₂₁,M₀₁₂₂M₂₁₂₂M₂₁₂₁ where M_ij = ?〈i∥M(E2)∥j〉. This is in agreement with shell-model calculations.     

Neutrino production of M+ and E+ heavy leptons (II)

A theoretical analysis is made of possible experimental searches for the production of M⁺ heavy leptons in inclusive neutrino reactions by detection of their decay into μ⁺. Distributions of observable energy E_obs (sum of hadron and muon energies) and of the apparent y variable y_obs(y_obs=E_had/E_obs) are presented. These distributions are used to discuss the problem of distinguishing M⁺ production from effects of antineutrino admixtures in a neutrino beam.     

Electroexcitation of magnetic dipole and other modes in46Ti and48Ti

With high-resolution inelastic electron scattering measurements on⁴⁶Ti and⁴⁸Ti the excitation mechanism of the transition into low lying J^π=1⁺ states is investigated. The experimental evidence of considerable contribution of the orbital part of theM1 operator to the total transition strength is given by a model dependent analysis of form factors. The possibility of physical relationship to low lying J^π=1⁺ states in the rare earth nuclei is discussed in various models. MoreoverE2 form factors and good candidates forM3 form factors are presented.     

Associated average charged particle multiplicities in K+p interactions at 32 GeV/c

The average charged particle multiplicities, 〈n_R(M_X²)〉, in the reactions K⁺p → π^?X and K⁺p → K⁰X at 32 GeV/c are studied as functions of the mass squared M_X² of the “associated” system X. A comparison with the corresponding results obtained at lower incident momenta is presented.     

Self-induced three-level echo

A new type of three-level photon echo has been predicted and analytically described. In contrast to the conventional three-level echo, whose formation involves three resonant ultrashort excitation pulses spaced in time, two of which are resonant to different optically allowed and adjacent transitions with different frequencies, the echo predicted arises under the conditions of formation of the conventional two-pulse echo and requires only two pump pulses of the same frequency. A theory is developed for the conditions of experiments on generation of a superradiance pulse at the ³ P ₀-³ H ₆ transition in impurity praseodymium ions in the LaF₃ matrix upon ultrashort coherent excitation of the adjacent optically allowed ³ H ₄-³ P ₀ transition in praseodymium. It is shown that the superradiance pulse after its deexcitation does not polarize the medium at the ³ P ₀-³ H ₆ generation transition and completely eliminates polarization at the ³ H ₄-³ P ₀ excitation transition. However, simultaneously, the superradiance pulse transfers the optical coherence from the excitation transition to the optically forbidden ³ H ₆-³ H ₄ transition. Thus, the phase memory about the effect of the excitation superradiance pulse is retained in the medium within a time interval that is shorter than the irreversible relaxation time of the optically forbidden transition.     

Shape coexistence and other aspects of nuclear structure in40Ar

Theγ-decay of⁴⁰Ar has been studied by particle-γ-ray coincidence measurements in the³⁷Cl(α, pγ) reaction at 12 and 13 MeV bombarding energy. Particle-γ-ray angular correlations and linear polarizations ofγ-rays were measured at 12 MeV. A lifetime measurement using the Doppler-shift attenuation method was performed at 11 MeV. The coexistence of spherical and deformed states in⁴⁰Ar could be concluded from the observation of aK ^π=0⁺ rotational band which has itsI ^π=0⁺ through 6⁺ members at 2,121, 2,524, 3,515 and 4,959 KeV excitation energy. The intrinsic quadrupole moment derived fromB(E2) values is ∥Q ₀∥=1,320 _?120 ⁺⁶⁰ mb. Negative-parity states with high spin were observed at 4,858(5^?), 4,494(5^?), 4,226(4^?) and 4,991 KeV(4^?) excitation energy. A complete account of all levels below 5 MeV excitation energy is obtained by a model in which twod _3/2 proton holes couple weakly to the⁴²Ca levels below 4.75 MeV excitation energy.     

The F-spin symmetric limits of the neutron-proton interacting boson model

The F-spin symmetric limits U(5), SU(3), and O(6) of the neutron-proton interacting boson model are studied. The conditions for and consequences of F-spin symmetry are investigated. In each of the three limits closed expressions for the following properties are given: the excitation energies; the M1, E2, and M3 excitation strengths from the ground state to all 1⁺, 2⁺, and 3⁺ states; the M1 and E2 decay of the nonsymmetric 1⁺ and 2⁺ states; and the dipole and quadrupole moments of maximal F-spin states and of the nonsymmetric 1⁺ and 2⁺ states. The predictions for these properties are compared with the experimental data.     

Quantum beats in two-photon resonance fluorescence

The two-photon resonance fluorescence spectrum of a three-level atom is shown to consist of the low frequency modes in addition to the high frequency ones in the limit of high photon densities. The spectral function for the low frequency modes consists of two lorentzian lines describing: the peak occuring at the renormalized beat frequency Δ₊ and that of the zero-photon excitation at the frequency Δ_-, where Δ_±=Δ-3Ω²/2ω_a±Ω²u/2ω_a, u²=1+(2Δω_a/Ω ²)². Here, 2Δ is the energy splitting between the two excited states, ω_a is the photon energy of the pump field and Ω is the Rabi frequency. The peak at the renormalized beat frequency Δ₊ occurs provided that the condition (2Δω_a/Ω²)² > 1 is satisfied. The two-photon laser spectroscopy is expected to be a useful tool for the observation of the low frequency modes in question.     

Spectroscopic properties, energy transfer and structural analysis of Sr2CeO4:M+ and Sr2CeO4:Eu3+, M+ (M+ = Li+, Na+, K+)

The room-temperature luminescent emission characteristics of Sr₂CeO₄:M⁺ and Sr₂CeO₄:Eu³⁺,M⁺ (M⁺ = Li⁺, Na⁺, K⁺) have been investigated under UV excitation. By introducing appropriate alkali metal cations dopants (Li⁺, Na⁺, K⁺) into the crystalline lattice, not only emission color of the blue-white-emitting Sr₂CeO₄ doped with low Eu³⁺ content can be tuned to green, but also the red emission intensity of Sr₂CeO₄ doped with high Eu³⁺ concentration is strengthened significantly. The relevant mechanisms have been elucidated in detail.     

EHD size distribution in pure Ge at pulse optical excitation

The cyclotron resonance (CR) kinetics of free carriers surrounding electron-hole drops (EHD) was investigated in pure Ge (N_D = N_A = 10¹¹cm^?3). We observed the fast decay of the CR amplitude at the long delay time after the excitation pulse [1], that may be connected with intense evaporation of the drops, when the EHD radius has achieved the critical value. The method for investigation of EHD size distribution was proposed for case of pulse excitation. The Gaussian EHD size distribution has been found.     

Excitation of bands of the first negative system of the N 2 + ion in collisions of N+ and O+ ions with N2 molecules

Absolute values of the excitation cross sections of the (0,0) bands [for O⁺(⁴ S), O⁺(² P)-N₂ pairs] and the (0,0), (0,1), (1,2), and (2,3) bands [for N⁺(³ P)-N₂ pairs] of the first negative system of the N ₂ ⁺ ion have been measured in collisions with nitrogen molecules of nitrogen and oxygen ions in the ground state and in a metastable state in the interval of ion energies 1–10 keV. The process of excitation of the (0,0) band of the first negative system of the N ₂ ⁺ ion by oxygen ions in the metastable ² P state is of a quasi-resonant character. The presence in the beam of ions in metastable states was monitored by measuring the excitation efficiency of the (0,0) band λ3914 Å of the N ₂ ⁺ ion in different operating regimes of the highfrequency ion source. For N⁺ ions in the ³ P ground state, as the collision frequency is decreased the relative vibrational population of the v′=1 and v′=2 levels of the B ²Σ _u ⁺ state of the N ₂ ⁺ ion is observed to deviate strongly from the value calculated in the Franck-Condon model.