Systematics of the odd-even effect in the resonance ionization of Os and Ti

Measurements of the odd-even effect in the mass spectrometric analysis of Ti and Os isotopes by resonance ionization mass spectrometry have been performed for ΔJ = + 1, 0 and -1 transitions. Under saturating conditions of the ionization and for ΔJ = + 1 transitions odd-even effects are reduced below the 0.5% level. Depending on the polarization state of the laser large odd isotope enrichments are observed for ΔJ = 0 and -1 transitions which can be reduced below the 0.5% level by depolarization of the laser field

Systematics of isotope ratio measurements with resonant laser photoionization sources

Sources of laser-induced even-even and odd-even isotopic selectivity in the resonance ionization mass spectroscopy of Os and Ti have been investigated experimentally for various types of transitions. A set of conditions with regard to laser bandwidth and frequency tuning, polarization state and intensity was obtained for which isotopic selectivity is either absent or reduced below the 2 % level

Correlated Isotope Fractionation and Formation of Purple FUN Inclusions

Allende coarse-grained inclusions characterized by a distinct purple color and high spinel contents (≤ 50 vol.%) exhibit a higher frequency of FUN isotopic anomalies (≈20%) than the general CAI population (≤6%). We used the ion microprobe to measure Mg, Si, Cr and Fe isotopic compositions of three Purple Spinel-rich Inclusions (PSI = ψ) which are petrographically similar to Type B CAl to investigate: 1) variations in isotopic fractionation within inclusions, including secondary phases; 2) correlated isotopic fractionation; and 3) excess ^(26)Mg

Laser-induced isotopic effects in titanium resonance ionization

Titanium isotope ratios have been measured by resonance ionization mass spectrometry (RIMS) with special emphasis on the nature of laser-induced isotopic selectivity. A pronounced wavelength dependence of even mass isotope ratios is caused by large nuclear volume effects near the magic neutron number 28 in ^(50)Ti . Optical isotope shifts, ranging from 0.07 to 0.21 cm^(-l), between ^(50)Ti and ^(46)Ti were measured for several transitions. The ^(50)Ti/^(46)Ti and ^(48)Ti/^(46)Ti ratios, nevertheless, exhibited only mass-dependent fractionation, in which the lighter Ti isotopes were enriched by ~2.5%/amu, when the laser operating parameters were properly controlled. Odd-even mass isotopic selectivity in the resonant ionization process was also examined for several transitions as a function of the laser polarization state and intensity. Under saturating conditions for a ΔJ= +1 transition and a high degree of laser depolarization for a ΔJ = 0 transition, the odd-even isotopic enhancement was reduced below the 2% level. The Ti isotope data agree with our previous results for Os and indicate that, by a careful choice of resonance transitions and laser operating parameters, isotope ratios can be measured accurately and reliably with RIMS

Absolute Determination of the 22Na(p,g) Reaction Rate in Novae

Gamma-ray telescopes in orbit around the Earth are searching for evidence of the elusive radionuclide 22Na produced in novae. Previously published uncertainties in the dominant destructive reaction, 22Na(p,g)23Mg, indicated new measurements in the proton energy range of 150 to 300 keV were needed to constrain predictions. We have measured the resonance strengths, energies, and branches directly and absolutely by using protons from the University of Washington accelerator with a specially designed beamline, which included beam rastering and cold vacuum protection of the 22Na implanted targets. The targets, fabricated at TRIUMF-ISAC, displayed minimal degradation over a ~ 20 C bombardment as a result of protective layers. We avoided the need to know the stopping power, and hence the target composition, by extracting resonance strengths from excitation functions integrated over proton energy. Our measurements revealed that resonance strengths for E_p = 213, 288, 454, and 610 keV are stronger by factors of 2.4 to 3.2 than previously reported. Upper limits have been placed on proposed resonances at 198-, 209-, and 232-keV. We have re-evaluated the 22Na(p,g) reaction rate, and our measurements indicate the resonance at 213 keV makes the most significant contribution to 22Na destruction in novae. Hydrodynamic simulations including our rate indicate that the expected abundance of 22Na ejecta from a classical nova is reduced by factors between 1.5 and 2, depending on the mass of the white-dwarf star hosting the nova explosion.Comment: 20 pages, 18 figures; shortened paper, accepted in Phys. Rev.

Probing Correlated Ground States with Microscopic Optical Model for Nucleon Scattering off Doubly-Closed-Shell Nuclei

The RPA long range correlations are known to play a significant role in understanding the depletion of single particle-hole states observed in (e, e') and (e, e'p) measurements. Here the Random Phase Approximation (RPA) theory, implemented using the D1S force is considered for the specific purpose of building correlated ground states and related one-body density matrix elements. These may be implemented and tested in a fully microscopic optical model for NA scattering off doubly-closed-shell nuclei. A method is presented to correct for the correlations overcounting inherent to the RPA formalism. One-body density matrix elements in the uncorrelated (i.e. Hartree-Fock) and correlated (i.e. RPA) ground states are then challenged in proton scattering studies based on the Melbourne microscopic optical model to highlight the role played by the RPA correlations. Effects of such correlations which deplete the nuclear matter at small radial distance (r $<$ 2 fm) and enhance its surface region, are getting more and more sizeable as the incident energy increases. Illustrations are given for proton scattering observables measured up to 201 MeV for the $^{16}$O, $^{40}$Ca, $^{48}$Ca and $^{208}$Pb target nuclei. Handling the RPA correlations systematically improves the agreement between scattering predictions and data for energies higher than 150 MeV.Comment: 20 pages, 7 figure

Unitarity constraint for threshold coherent pion photoproduction on the deuteron and chiral perturbation theory

The contribution of the two-step process gamma + d -> p + n -> pi0 + d to the imaginary part of the amplitude for coherent pion production on the deuteron is calculated exploiting unitarity constraints. The result shows that this absorptive process is not negligible and has to be considered in an extraction of the elementary neutron production amplitude from the gamma + d -> pi0 + d cross section at threshold. In addition, it is argued that a consistent calculation of gamma + d -> pi0 + d in baryon chiral perturbation theory beyond next-to-leading order requires the inclusion of this absorptive process.Comment: 11 pages revtex including 2 postscript figure

Comparison of optical model results from a microscopic Schr\"odinger approach to nucleon-nucleus elastic scattering with those from a global Dirac phenomenology

Comparisons are made between results of calculations for intermediate energy nucleon-nucleus scattering for 12C, 16O, 40Ca, 90Zr, and 208Pb, using optical potentials obtained from global Dirac phenomenology and from a microscopic Schr\"odinger model. Differential cross sections and spin observables for scattering from the set of five nuclei at 65 MeV and 200 MeV have been studied to assess the relative merits of each approach. Total reaction cross sections from proton-nucleus and total cross sections from neutron-nucleus scattering have been evaluated and compared with data for those five targets in the energy range 20 MeV to 800 MeV. The methods of analyses give results that compare well with experimental data in those energy regimes for which the procedures are suited.Comment: 22 pages, 12 figure