Study of the133Cs(γ,n)132Cs reaction

The photoneutron spectrum from the¹³³Cs(γ, n)¹³²Cs reaction induced by 9.720 MeV neutron capture gamma-rays has been studied with a³He-spectrometer. The energies and relative intensities of the emitted neutrons were determined. AQ-value of 8,986 +/?2 keV is suggested. The data reveal the existence of seventeen excited states in¹³²Cs in the region up to 551 keV.     

(MgO)(-)(n) (n = 1-5) clusters: multipole-bound anions and photodetachment spectroscopy

Photoelectron spectra of (MgO)(-)(n) (n = 1-5) reveal a surprising trend: The electron binding energy decreases from n = 1 to 4, and then increases from 4 to 5. Ab initio calculations suggest this pattern is related to the electrostatic interaction between the extra electron and the charge distribution of the neutral cluster. This interaction is significant in MgO (-) and (MgO)-5, for which the lowest nonvanishing multipole moment (LNM) is a dipole; it is smaller for (MgO)-2 and (MgO)-3, for which a quadrupole is the LNM; and it is the smallest for (MgO)-4, for which an octopole is the LNM. The cubic (MgO)-4 is the first octopole-bound anion yet observed experimentally and characterized theoretically.     

Multi-photon processes in the Zeeman structure of atomic Cs trapped in solid helium

We report magnetic resonance experiments with optical detection performed on cesium atoms trapped in a crystalline ^Hematrix. Multi-photon transitions, i.e., processes in which several radio-frequency photons are absorbed simultaneously in a given hyperfine Zeeman multiplet of the ground state, were the central topic of these studies. The long relaxation times of spin coherences of Cs in solid He allow such transitions to be spectrally resolved in fields as low as 1 mT. We observed all allowed multi-photon transitions up to the M=8 transition in the F=4 state. We compare the experimental spectra with theoretical spectra obtained from numerical solutions of the Liouville equation that include optical pumping and the interaction with the static and oscillating fields. Multi-photon transitions may find applications in magnetometry, suppress systematic effects in EDM experiments, and allow the study of relaxation phenomena in doped He crystals. The demonstration of these features is still hindered by inhomogeneous line broadening. PACS 76.70.Hb; 32.80.Wr; 32.30.Dx; 32.60.+i     

Pressure-tuned collapse of the Mott-like state in Ca(n+1)Ru(n)O(3n+1) (n=1,2): Raman spectroscopic studies

We report a Raman scattering study of the pressure-induced collapse of the Mott-like phases of Ca3Ru2O7 (T(N)=56 K) and Ca2RuO4 (T(N)=110 K). The pressure dependence of the phonon and two-magnon excitations in these materials indicate (i) a T approximately 0 pressure-induced collapse of the antiferromagnetic (AF) insulating phase above P(*) approximately 55 kbar in Ca3Ru2O7 and P(*) approximately 5-10 kbar in Ca2RuO4, (ii) a remarkable insensitivity of the exchange interaction to pressure in both systems, and (iii) evidence for persistent AF correlations above the critical pressure of Ca2RuO4, suggestive of phase separation involving AF insulator and ferromagnetic metal phases.     

Optical properties of CsI(Na) and heat-treated pure CsI

On the basis of the similarity of luminescence properties of CsI(Na) crystals and heat-treated crystals of pure CsI excited in the long wavelength tail of the fundamental absorption, the effect of sodium in CsI(Na) is tentatively explained.     

Stability of (3)He(2)(4)He(n) and (3)He(3)(4)He(n) L=0 clusters

We have studied the stability of mixed (3)He/(4)He clusters in L=0 states by the diffusion Monte Carlo method, employing the Tang-Toennies-Yiu He-He potential. The clusters (3)He(4)He(N) and (3)He(2)(4)He(N) are stable for N>1. The lighter atoms tend to move to the surface of the cluster. The minimum number of 4He atoms able to bind three 3He atoms in a L=0 state is nine. Two of three fermionic helium atoms stay on the surface, while the third one penetrates into the cluster.     

Measurement of intrinsic radioactive backgrounds from the ~(137)Cs and U/Th chains in CsI(Tl) crystals

The inorganic Cs I(Tl) crystal scintillator is a candidate anti-compton detector for the China Dark matter Experiment. Studying the intrinsic radiopurity of the Cs I(Tl) crystal is an issue of major importance. The timing,energy and spatial correlations, as well as the capability of pulse shape discrimination provide powerful methods for the measurement of intrinsic radiopurities. The experimental design, detector performance and event-selection algorithms are described. A total of 359×3 kg-days data from three prototypes of Cs I(Tl) crystals were taken at China Jinping Underground Laboratory(CJPL), which offers a good shielding environment. The contamination levels of internal isotopes from137 Cs,232Th and238 U series, as well as the upper bounds of235 U series are reported.Identification of the whole α peaks from U/Th decay chains and derivation of those corresponding quenching factors are achieved.     

PuC^n＋（n=1,2,3）分子离子的势能函数与稳定性

用密度泛函B3LYP方法对PuC^n (n=1,2,3)分子离子进行理论研究,结果表明：PuC^ 、PuC^2 分子离子能稳定存在,基态电子状态是X^8∑^-(PuC^ )和X^9∑^-(PuC^2 ),并导出了相应的几何性质、力学性质和光谱数据。PuC^3 (^6∑、^8∑）分子离子不能稳定存在。     

Interface control of emergent ferroic order in Ruddlesden-Popper Sr(n+1)Ti(n)O(3n+1)

We discovered from first principles an unusual polar state in the low n Sr(n+1)Ti(n)O(3n+1) Ruddlesden-Popper (RP) layered perovskites in which ferroelectricity is nearly degenerate with antiferroelectricity, a relatively rare form of ferroic order. We show that epitaxial strain plays a key role in tuning the "perpendicular coherence length" of the ferroelectric mode, and does not induce ferroelectricity in these low-dimensional RP materials as is well known to occur in SrTiO(3). These systems present an opportunity to manipulate the coherence length of a ferroic distortion in a controlled way, without disorder or a free surface.     

Relaxation mechanisms of multi-quantum coherences in the Zeeman structure of atomic Cs trapped in solid He

This paper extends our previous work on near-degenerate magnetic resonance transitions in alkali ground states involving the simultaneous absorption of multiple radio-frequency quanta. New experimental results with an improved spectral resolution were obtained with cesium atoms trapped in the cubic phase of a helium crystal. The main objective of the paper is a theoretical study of the influence of stochastic perturbations of given multipole orders on the various multi-photon coherences. Algebraic and numerical results for perturbations of both dipolar and quadrupolar symmetry are presented. The present experimental resolution does not yet allow us to distinguish between these two most likely relaxation mechanisms. Nonetheless, the experimental spectra are very well described when allowing in the calculations for a magnetic field inhomogeneity of 2×10^-5. PACS 76.70.Hb; 32.80.Wr; 32.30.Dx; 32.60.+i     

First-principles study on the optical properties for CsI crystal with a pair of V_(Cs)~(1-)-V_I~(1+)

The electronic structures and optical properties of both the perfect CsI crystal and the crystal containing a pair of V_(Cs)~1-V_1~(1+) are calculated using CASTEP code with the lattice structure optimized.The calculated results indicate that the optical symmetry of the CsI crystal coincides with the lattice structure geometry of the CsI crystal.The absorption spectrum of the CsI crystal containing a pair of V_(Cs)~(1-)-V_1~(1+) also does not occur in the visible and near-ultraviolet range.It reveals tha...     

Size-induced effect on cathode luminescence spectra of CsI(Na) and CsI(Tl) crystals

We investigated the cathode luminescence characteristics of CsI(Na)and CsI(Tl)crystals by the spectrum and structure properties at room temperature.We fabricated three different sizes of CsI(Na)and CsI(Tl)crystals and measured their luminescence spectra under cathode rays.We found that CsI(Na)cathode luminescence peaks appear at 420 and 305 nm,and CsI(Tl)cathode luminescence peaks are 540 and 410 nm,the grain size affects CsI(Na)luminescence significantly,and the Na-related420 nm luminescence intensified relatively when the average grain size reaches~20μm,which becomes weak when the grain size is down to nano-scale.But the cathode luminescence spectra of CsI(Tl)crystals with different size have no obvious changes.Our explanations for these phenomena are that the different impurities in the same host material CsI lead to different luminescence mechanisms.These cathode luminescence characteristics indicate the suitability of CsI(Na)and CsI(Tl)crystals to match photomultiplier tube for large area crystal detector development.     

Luminescence and decay times of CsI:In+

Luminescence spectra of single crystals of CsI:In⁺ excited in the A(304 nm), B(288 nm), C(268 nm) and D(257 nm) absorption bands have been studied in the temperature range 4.2–300 K. Excitation in the A band at 4.2 K gives rise to the principal emission at 2.22 eV accompanied by a partly-overlapping weak band at 2.49 eV. An additional emission band at about 2.96 eV is observed on excitation in the B, C or D bands. Yet another emission band located at 2.67 eV is excited only in the D band. The relative intensities of the bands are very sensitive to excitation wavelength as well as to temperature. The origin of all these bands is assigned in terms of a model for the relaxed excited states (RES). All the luminescence spectra were resolved into an appropriate number of skew-Gaussian components. Moments analysis leads to a value of (1.35 ± 0.02) × 10¹³ rad s^-1 for the effective frequency (ω_eff) of lattice vibrations coupled to the RES. At the lowest temperature, the radiative decay times of each of the intracenter emission bands (2.22, 2.49 and 2.96 eV) show a slow decay ( ～ 10–100 μs) and a fast decay ( ～ 10–100 ns). The 2.96 eV band, which is assigned to an emission process which is the inverse of the D-band absorption, exhibits a single decay mode ( ～ 10 μs). The intrinsic radiative decay rates (k₁, k₂), the one-phonon transition rate (K) and the second-order spin-orbit splitting (D) for the RES responsible for the principal emission are: k₁ = (6.0±-0.3)×10³ s^-1, k₂ = (1.33±-0.06)×10⁵ s^-1, K = (2.4±-0.4)×10⁷ s^-1 and D = (13.8±-0.5) cm^-1.     

C(n)(2) profile measurement from Shack-Hartmann data

C(n)(2) profile monitoring usually relies on the exploitation of wavefront slope correlations or of scintillation pattern correlations. Scintillation is rather sensitive to high turbulence layers whereas wavefront slope correlations are mainly due to layers close to the receiving plane. Wavefront slope and scintillation correlations are therefore complementary. A Shack-Hartmann wavefront sensor (SHWFS) is currently used to measure wavefront slopes only. But it could also be sensitive to scintillation as the average intensity in a given subaperture can be obtained by adding pixel intensities in the subaperture focal plane up. With slopes and scintillation being recorded simultaneously, their correlation is also theoretically available. We propose to exploit wavefront slope and scintillation correlations recorded with a SHWFS to retrieve the C(n)(2) profile. Two measurement methods are exposed. In CO-SLIDAR (Coupled SLODAR SCIDAR), correlations of SHWFS data recorded on two separated stars are exploited. SCO-SLIDAR (Single CO-SLIDAR) relies on the same principle as CO-SLIDAR, but SHWFS data are recorded on a single star. Results of C(n)(2) estimation from simulated SHWFS data are presented.     

The local structure of Cs(I) and Cs(II) in a Cs2ZnCl4 single crystal studied by nuclear magnetic resonance

The rotation patterns of the ¹³³Cs (I=7/2) nuclear magnetic resonance (NMR) in a Cs₂ZnCl₄ single crystal grown by using the slow evaporation method were measured in two mutually perpendicular crystal planes. Two different groups of Cs resonances were recorded; this result points to the existence of two types of crystallographically inequivalent Cs(I) and Cs(II). The angular dependences of the NMR spectra led to different values for the quadrupole coupling constants and asymmetry parameters: e²qQ/h=148 kHz and η=0.11 for the Cs(I) ion, and e²qQ/h=274 kHz and η=0.66 for the Cs(II) ion. The EFG tensors of Cs(I) and Cs(II) are asymmetric, and the orientations of the principal axes of the EFG tensors do not coincide. Only, the principal Y-axes of the EFG tensors coincide for the Cs(I) and Cs(II) sites. The Cs(I) ion is surrounded by 11 chlorine ions, making it rather free and high in symmetry. The Cs(II) ion has only nine neighbors and seems to be more tight than the Cs(I) ion.     

Fast light of CsI（Na） crystals

The responses of different common alkali halide crystals to alpha-rays and gamma-rays are tested in this research. It is found that only CsI(Na) crystals have significantly different waveforms between alpha and gamma scintillations, while others do not exhibit this phenomena. The rise time of the fast light is about 5 ns and the decay time is 17±12 ns. It is suggested that the fast light of CsI(Na) crystals arises from the recombination of free electrons with self-trapped holes of the host crystal CsI. Self-absorption limits the emission of fast light of CsI(Tl) and NaI(Tl) crystals.     

Photo- and radiation-chemical transformations of carbonate ions in CsI and CsI(Tl) crystals

It is shown that irradiation of CsI and CsI(Tl) crystals containing carbonate and hydroxyl ions induces radiation defects there in the form of color centers, HCO ₃ ^- ions, and H₂O molecules. HCO ₃ ^- ions are formed in the bulk of crystals, whereas water molecules are formed only in the surface layer. IR spectra offered no evidence of decomposition of CO ₃ ^2- ions into CO and CO ₂ ^- and of formation of CO ₃ ^- ions in the course of growth nor in the course of irradiation of CsI(CO₃) and CsI(Tl, CO₃) crystals. Electron activator color centers in CsI(Tl, CO₃) crystals are likely to be stabilized by hole near-activator centers and by HCO ₃ ^- ions produced in radiation-induced chemical reactions.     

61Cu(61Ni) and 133Ba(133Cs) Mössbauer emission spectroscopy of Tl2Ba2Ca n−1CunO2n+4

The parameters of the electric-field gradient tensor at copper and barium sites in the Tl₂Ba₂Ca _n?1Cu_nO_2n+4 (n=1,2,3) lattice have been determined by ⁶¹Cu(⁶¹Ni) and ¹³³Ba(¹³³Cs) Mössbauer emission spectroscopy, and calculated in the point-charge approximation. The calculated parameters can be reconciled with experiment if one assumes that the holes produced as the valence state of a part of thallium atoms is lowered are localized predominantly on the oxygen sublattice lying in the same plane with copper atoms [in the Cu(2) plane in the Tl₂Ba₂Ca₂Cu₃O₁₀ lattice]. ¹³³Ba(¹³³Cs) Mössbauer emission spectroscopy data agree qualitatively with the proposed models of charge distribution in the Tl₂Ba₂Ca _n?1Cu_nO_2n+4 lattices.     

Generalization of the N(p)N(n)N(p)N(n) scheme and the structure of the valence space

The N(p)N(n) scheme, which has been extensively applied to even-even nuclei, is found to be a very good benchmark for odd-even, even-odd, and doubly-odd nuclei as well. There are no apparent shifts in the correlations for these four classes of nuclei. The compact correlations highlight the deviant behavior of the Z = 78 nuclei and are used to deduce effective valence proton numbers near Z = 64 as well as to study the evolution of the Z = 64 subshell gap.