CALCULATIONS OF THE EIGENVALUES OF PURE QUADRUPOLE INTERACTION IN MOSSBAUER-EFFECT STUDIES

Two approximate formulae to calculate the eigenvalues of pure quadrupole interaction in Mossbauer effect studies have been proposed and the eigenvalue coefficients in the formulae have been given for various excited states and ground states of the nucleus with different spin. All the eigenvalues of pure quadrupole interaction between both excited state and ground state of nucleus with spin I = 3/2 divided-by 9/2 and the electric-field gradient with different asymmetry parameter (eta = 0 divided-by 1.0) have been calculated by these formulae. The results show that the accuracies in all the calculations are more satisfactory or same in comparison with those obtained by the formula of Shenoy and Dunlap, especially when the asymmetry parameter of electric-field gradient is larger than 0.8 for the nucleus with spin I = 5/2.

Photodissociation of o-dichlorobenzene at 266 nm

The photodissociation o-dichlorobenzene at 266 nm has been investigated using the universal crossed molecular beam technique. Photofragment translational energy distribution P(E-t) and angular distribution of photofragments have been obtained and it is estimated that 23% of the available energy is assigned to translational energy. The anisotropy parameter is determined to be 0.4. From P(E-t) and beta we deduce that o-C6H4Cl2 photodissociation is a slow process. Ab initio calculation has been performed and it shows that the parent molecule has a larger geometry deformation in its excited states comparing with that of the ground state. The possible dissociation mechanism has also been proposed. (C) 1999 Elsevier Science B.V. All rights reserved.

Low-lying non-normal parity states in B-8 measured by proton elastic scattering on Be-7

A new measurement of proton resonance scattering on Be-7 was performed tip to the center-of-mass energy of 6.7 MeV using the low-energy RI beam facility CRIB (CNS Radioactive Ion Beam separator) at the Center for Nuclear Study of the University of Tokyo. The excitation function of Be-7 + p elastic scattering above 3.5 MeV was measured Successfully for the first time, providing important information about the resonance structure of the B-8 nucleus. The resonances are related to the reaction rate of Be-7(p.gamma)B-8. which is the key reaction in solar B-8 neutrino production. Evidence for the presence of two negative parity states is presented. One of them is a 2(-) state observed as a broad s-wave resonance, the existence of which had been questionable. Its possible effects on the determination of the astrophysical S-factor of Be-7(p.gamma)B-8 at solar energy are discussed. The other state had not been observed in previous measurements, and its spin and parity were determined as 1(-). (C) 2009 Elsevier B.V. All rights reserved.

Low-lying states of heavy nuclei within the nucleon pair approximation

In this article we perform systematic calculations on low-lying states of 33 nuclei with A=202-212, using the nucleon pair approximation of the shell model. We use a phenomenological shell-model Hamiltonian that includes single-particle energies, monopole and quadrupole pairing interactions, and quadrupole-quadrupole interactions. The building blocks of our model space include one J=4 valence neutron pair, and one J=4,6,8 valence proton pair, in addition to the usual S and D pairs. We calculate binding energies, excitation energies, electric quadrupole and magnetic dipole moments of low-lying states, and E2 transition rates between low-lying states. Our calculated results are reasonably consistent with available experimental data. The calculated quadrupole moments and magnetic moments, many of which have not yet been measured for these nuclei, are useful for future experimental measurements.

New high-lying odd-parity excited levels of atomic uranium

We report the measurement of 112 new high-lying odd-parity excited levels of U I in the energy region 35 678-36 696 cm(-1). These levels were obtained with a setup composed of a Nd:YAG-laser-pumped pulsed dye laser system, an atomic beam device, a time-of-flight mass spectrometer, and a boxcar integrator. (C) 2000 Optical Society of America [S0740-3224(99)02309-7] OCIS code: 300.0300.

Three-photon-excited upconversion luminescence of Ce3+: YAP crystal by femtosecond laser irradiation

Infrared to ultraviolet and visible upconversion luminescence was demonstrated in trivalent cerium doped YAlO3 crystal (Ce3+: YAP) under focused infrared femtosecond laser irradiation. The fluorescence spectra show that the upconverted luminescence comes from the 5d-4f transitions of trivalent cerium ions. The dependence of luminescence intensity of trivalent cerium on infrared pumping power reveals that the conversion of infrared radiation is dominated by three-photon excitation process. It is suggested that the simultaneous absorption of three infrared photons pumps the Ce3+ ion into upper 5d level, which quickly nonradiatively relax to lowest 5d level. Thereafter, the ions radiatively return to the ground states, leading to the characteristic emission of Ce3+. (c) 2005 Optical Society of America.

Selectively excited photoluminescence of GaAs1-xNx single quantum wells

GaAsN bulk and GaAsN/GaAs single quantum wells grown by molecular beam epitaxy are studied by selectively excited photoluminescence (PL) measurements. A significant difference is observed in the PL spectra when the excitation energy is set below or above the band gap of GaAs for the GaAsN/GaAs quantum well samples, while the spectral features of GaAsN bulk are not sensitive to the excitation energy. The observed difference in PL of the GaAsN/GaAs quantum well samples is attributed to the exciton localization effect at the GaAsN/GaAs interfaces, which is directly correlated with the transfer and trap processes of the photogenerated carriers from GaAs into GaAsN through the heterointerfaces. This interface-related exciton localization effect can be greatly reduced by a rapid thermal annealing process, making the PL be dominated by the intrinsic delocalized transition in GaAsN/GaAs. (C) 2003 American Institute of Physics.

Doubly excited 2s2p P-1,3(1) resonances in photoionization of helium

The multi-configuration Dirac Fock (MCDF) method is implemented to study doubly excited 2s2p P-1,3(1) resonances of the helium atom and the interference between photoionization and photo excitation autoionization processes. In order to reproduce the total photoionization sprectra, the excited energies from the ground 1s(2) S-1(0) state to the doubly excited 2s2p P-1,3(1) states and the relevant Auger decay rates and widths are calculated in detail. Further more, the interference profile determined by the so-called Fano parameters q and rho(2) is also reproduced. Good agreement is found between the present results and other available theoretical and experimental results. This indeed shows a promising way to investigate the Fano resonances in photoionization of atoms within the MCDF scheme, although there are some discrepancies in the present calculations of the 2s2p P-3(1) state.

gamma-vibrational states in superheavy nuclei

Recent experimental advances have made it possible to study excited structure in superheavy nuclei. The observed states have often been interpreted as quasiparticle excitations. We show that in superheavy nuclei collective vibrations systematically appear as low-energy excitation modes. By using the microscopic Triaxial Projected Shell Model, we make a detailed prediction on gamma-vibrational states and their E2 transition probabilities to the ground state band in fermium and nobelium isotopes where active structure research is going on, and in (270)Ds, the heaviest isotope where decay data have been obtained for the ground-state and for an isomeric state.

Discovery of Highly Excited Long-Lived Isomers in Neutron-Rich Hafnium and Tantalum Isotopes through Direct Mass Measurements

A study of cooled Au-197 projectile-fragmentation products has been performed with a storage ring. This has enabled metastable nuclear excitations with energies up to 3 MeV, and half-lives extending to minutes or longer, to be identified in the neutron-rich nuclides Hf-183,Hf-184,Hf-186 and Ta-186,Ta-187. The results support the prediction of a strongly favored isomer region near neutron number 116.

Extracting single-particle information for the superheavy mass region by studying excited structure in transfermium nuclei

Recent experimental advances have made it possible to study spectroscopy in very heavy nuclei. We show that from the excited high-spin structure of transfermium isotopes, one may gain useful information on single-particle states for the superheavy mass region, which is the key to locating the anticipated 'island of stability'. In this work, we employ the Projected Shell Model for Cf, Fm, and No isotopes to study rotation alignment of the particles that occupy particular high-j intruder orbitals.

Two-quasiparticle K-isomeric states in strongly deformed neutron-rich Nd and Sm isotopes: a projected shell-model analysis

Motivated by recent spectroscopy data from fission experiments, we apply the projected shell model to study systematically the structure of strongly deformed, neutron-rich, even-even Nd and Sm isotopes with neutron number from 94 to 100. We perform calculations for rotational bands up to spin I = 20 and analyze the band structure of low-lying states with quasiparticle excitations, with emphasis given to rotational bands based on various negative-parity two-quasiparticle (2-qp) isomers. Experimentally known isomers in these isotopes are described well. The calculations further predict proton 2-qp bands based on a 5(-) and a 7(-) isomer and neutron 2-qp bands based on a 4(-) and an 8(-) isomer. The properties for the yrast line are discussed, and quantities to test the predictions are suggested for future experiment.

VIV-UV excited luminescent properties of LnCa4O(BO3)3 : RE3+(Ln = Y, La, Gd; Re=Eu, Tb, Dy, Ce)

Calcium lanthanide oxyborate doped with rare-earth ions LnCa(4)O(BO3)(3):RE3+ (LnCOB:RE, Ln = Y, La, Gd, RE = Eu, Tb, Dy, Cc) was synthesized by the method of solid-state reaction at high temperature. Their fluorescent spectra were measured from vacuum ultraviolet (VUV) to visible region at room temperature. Their excitation spectra all have a broadband center at about 188 nm, which is ascribed to host absorption. Using Dorenbos' and J phi rgensen's work [P. Dorenbos, J. Lumin. 91 (2000) 91, R. Resfeld, C.K. J phi rgensen. Lasers and Excite States of Rare Earth [M], Springer, Berlin, 1977, p. 45], the position of the lowest 5d levels E(Ln,A) and charge transfer band E-ct were calculated and compared with their excitation spectra.Eu3+ and Tb3+ ions doped into LnCOB show efficient luminescence under VUV and UV irradiation. In this system, Ce3+ ions do not show efficient luminescence and quench the luminescence of Tb3+ ions when Tb3+ and Ce3+ ions are co-doped into LnCOB. GdCOB doped with Dy3+ shows yellowish white light under irradiation of 254 nm light for the reason that Gd ions transfer the energy from itself to Dy.

NATURAL RADIATIVE LIFETIMES OF THE EXCITED-LEVELS OF THULIUM

The radiative lifetimes of eight excited levels of thulium have been measured with the method of stepwise excitation from the 4f13(F-degrees-7/2)6s2(1S0)\7/2\ ground state to the states studied using two pulsed dye lasers. Optical transients were recorded through observing fluorescences and evaluated with regard to the decay time. The accuracy of the measured lifetime values is about 10%.