Coulomb breakup of 8B and the flux of 8B neutrinos from the Sun

A kinematically complete measurement was made of the Coulomb dissociation of ⁸B nuclei on a Pb target at 83 MeV/nucleon. The cross-section was measured at low relative energies in order to infer the astrophysical S-factor for the ⁷Be(p,γ)⁸B reaction. A first-order perturbation theory analysis of the reaction dynamics including E1, E2, and M1 transitions was employed to extract the E1 strength relevant to neutrino-producing reactions in the solar interior. By fitting the measured cross-section from E _rel = 130 keV to 400 keV, we find S ₁₇(0) = 17.8^+1.4 _-1.2 eV b. Semiclassical 1st-order perturbation theory and fully quantum-mechanical continuum-discretized coupled-channels analyses yield nearly identical results for the E1 strength relevant to solar-neutrino flux calculations, suggesting that theoretical reaction mechanism uncertainties need not limit the precision of Coulomb-breakup determinations of the ⁷Be(p,γ)⁸B S-factor. A recommended value of S ₁₇(0) based on a weighted average of this and other measurements is presented. This recommendation implies a revised value for the theoretical flux of ⁸B solar neutrinos, which is also given.-1 Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"Present address: Kernfysisch Versneller Instituut, Zernikelaan 25, 9747 AA Groningen, The Netherlands; e-mail: davids@kvi.nl     

Merrifield-Simmons Index and Its Entropy of the 4-8-8 Lattice

The Merrifield-Simmons index is a topological index used in structural chemistry for quantifying relevant properties of molecular structure. This index, in different names, has been studied on the square, triangular and hexagonal lattices by using the method of transfer matrix. To compute the Merrifield-Simmons index of more complicated lattices such as the 4-8-8 and triangular Kagomé lattices, the use of multi-step transfer matrices is needed. In this paper we introduce the concept of transfer multiplicity and use multi-step transfer matrices to derive a rigorous upper and lower bound for the entropy of Merrified-Simmons index of the 4-8-8 lattice. We show that this method can be used to deal with other complex 2-dimensional lattices.     

First principle study on the bonding mechanism of nanoring structure Ga8As8

The stable ring structure of Ga₈As₈ has been found by the first principle calculations previously. Here we use the full-potential linearized augmented plane wave (FP-LAPW) method within the framework of the density functional approach to investigate the electronic structure and bonding mechanism of the ring structure. The stable and equilibrium ring structure is confirmed again and the relationship between the nanoring structure and the bulk materials is obtained by the comparison of the density of states (DOS) and bonding charge density of the ring structure with that of the bulk GaAs materials. The valence charge density and the bonding charge density of the ring structure are obtained, and then the bonding characteristics are analyzed. The calculations reveal that the bonding of the ring structure of Ga₈As₈ is with covalent bonding characteristic and in the same time the homo-bond Ga-Ga in the side face of the ring structure is found.     

Determination of the 8B neutrino spectrum

We have measured the total energy of the alpha particles following the beta decay of 8B by implanting 8B into a planar silicon surface barrier detector. Calibration was performed using alpha particles following the beta decay of 20Na, similarly implanted. The alpha spectrum is used to infer the 8B neutrino spectrum which is an important input in the interpretation of experiments that detect energetic neutrinos from the Sun. The alpha spectrum reported here is in disagreement with the previous best measurement which used two detectors in coincidence.     

Theoretical study of the phosphorescence of 8-azasteroids

We have used quantum chemical methods for a theoretical study of the luminescent characteristics (including estimating the rate constants for intramolecular T₁ → S₀ electronic transitions) of the molecules of four immunoactive compounds of the 8-azasteroid class. We have established that the T₁ state is localized on the enaminodicarbonyl moiety that is common to all the molecules. We have shown that for the studied compounds, the phosphorescence spectra and the physical mechanisms for deactivation of the lower triplet state T₁ are similar. For all the compounds, the results of the theoretical study are consistent with the corresponding conclusions of experimental studies of 8-azasteroids. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 751–755, November–December, 2006.     

Calculating low-altitude trapped particle fluxes with the NASA models AP-8 and AE-8

Accessing the NASA trapped radiation models AP-8 and AE-8 with (B,L) values obtained with modern geomagnetic field models causes an unrealistic secular increase of the predicted flux over low altitude orbits. We show the secular variation of the orbit-averaged particle flux along the LDEF orbit and the mission dose, obtained using the AP-8 trapped radiation models with an epoch-dependent magnetic field. The artificially increased epoch-dependent fluxes and doses are compared to the flux and dose obtained with a consistent and more correct procedure for predicting fluxes with the NASA models. This procedure has been implemented in the radiation analysis software package UNIRAD developed and distributed by BIRA-IASB.     

The trigonometric $$E_8$$ E 8 R-matrix

Letters in Mathematical Physics - An expression for the R-matrix associated with $${\mathcal {U}}_q({\widehat{\mathfrak e_8}})$$ in its 249-dimensional representation is given using the...     

Superconductivity of the graphite intercalation compounds KHgC8 and RbHgC8

Superconductivity was observed in the graphite intercalation compounds, KHgC₈ and RbHgC₈, using an AC induction technique. The transition temperatures were 1.90K and 1.44K for KHgC₈ and RbHgC₈ respectively. A full Meissner effect was observed for KHgC₈ with a temperature dependant anisotropy in critical field with a value of 25 ± 5 at T_c.     

Optical properties of the semiconductor 7, 7′, 8, 8′, tetracyanoquinodimethane (TCNQ)

Summary The reflectivity and absorption spectra of 7, 7′, 8, 8′ tetracyanoquinodimethane thin films, in the visible and near-ultraviolet range, have been measured. Samples have been grown and characterized by means of elemental microanalysis and differential scanning calorimetry (DSC) in order to obtain the purity degree. The experimental optical spectra are interpreted on the basis of a calculation of the electronic molecular energy levels by the complete neglect of differential-overlap method in a new parametrization scheme. Work partially supported by the Ministero della Pubblica Istruzione through the G.N.S.M.     

Multiband superconductivity in the Chevrel phases SnMo6S8 and PbMo6S8

Sub-Kelvin scanning tunneling spectroscopy in the Chevrel phases SnMo6S8 and PbMo6S8 reveals two distinct superconducting gaps with Δ1=3 meV, Δ2～1.0 meV and Δ1=3.1 meV, Δ2～1.4 meV, respectively. The gap distribution is strongly anisotropic, with Δ2 predominantly seen when scanning across unit-cell steps on the (001) sample surface. The spectra are well fitted by an anisotropic two-band BCS s-wave gap function. Our spectroscopic data are confirmed by electronic heat capacity measurements, which also provide evidence for a twin-gap scenario.     

Theg-factor of the 8+ isomer of142Eu

Theg-factor of the 8⁺ isomer of¹⁴²Eu with mean lifeτ=9 ns, has been measured by the time-differential perturbedγ ray angular distribution (TDPAD) method. The 8⁺ isomer was populated with the reaction¹¹⁴Cd(³²S,p3n)¹⁴²Eu at 155 MeV. The obtained valueg(8⁺)=0.51(3) agrees with shell model calculations using effective single-particle moments taken from neighbouring nuclei. A main configurationπh_11/2?(vh _11/2)^?1 has been confirmed for the 8⁺ isomer.     

Doppler-free spectroscopy of the 8s state of Cs

Doppler-free two-photon spectroscopy and ion detection in a thermionic diode were used to measure the hyperfine splitting and absolute term energy of the 8S state of Cs. The results, a=219.3(2) MHz for the magnetic dipole coupling constant, and E(8S)=24317.1499(4) cm^-1 for the term value of the c.g. of the 8S state relative to the c.g. of the ground state, agree well with earlier, less precise measurements. The hyperfine coupling also agrees well with a recent relativistic Hartree-Fock calculation.     

Microscopic calculations for the 8Li system

A microscopic multi-channel cluster model calculation for the ⁸Li scattering system has been performed. Diagonal phase shifts, channel coupling strengths, and eigenphases are presented. For comparison, the ⁸Li bound and quasibound states have been investigated by a refined resonating group calculation. The results of both types of calculations are in excellent agreement. In the energy region up to the ⁵He-t threshold the calculated S-matrix elements, the energy eigenvalues, and the overlaps of the normalized functions with the eigenvectors explain the origin of the experimentally detected levels and moreover give predictions for the existence of additional levels.     

Powder EPR of Gd3+ in the superconductors SnMo6S8 and PbMo6S8

EPR spectra at 35 and 60 GHz of Gd³⁺ diluted (～1%) in powdered SnMo₆S₈ and PbMo₆S₈ are presented and interpreted. The crystal field is found to be axial, with D = b₂⁰=-760 gauss and -740 Gauss for the tin and lead compounds respectively. Values are obtained for <J(q)> and J(q = 0). Below T_c the impurity to conduction electron relaxation rate is no longer proportional to temperature but decreases more rapidly. From this temperature dependence we extract a value for $\text{2Δ}\text{kT}{}_{\mathrm{c}}$ of roughly 5 for both compounds.     

A study of the second excited state of8Be by the10B(d,α2)8Be-reaction

The second excited state of⁸Be has been studied by analysis of the coincidence spectra of the reaction¹⁰B(d, α)2α forE _d =1.0-2.0 MeV. The excitation energy was found to be 12.0±0.4 MeV, and the reduced width 0.85±0.12 MeV. Differential crosssections of the (d, α ₂)-reaction were deduced.