9836054
Resonance parameters of the first 1/2+ state in 9Be and astrophysical implications
Spectra of the Be-9(e, e') reaction have been measured at the Superconducting Darmstadt Electron Linear Accelerator at an electron energy of E-0 = 73 MeV and scattering angles of 93 degrees and 141 degrees with high-energy resolution up to excitation energies of E-x = 8 MeV. The astrophysically relevant resonance parameters of the first excited 1/2(+) state of Be-9 have been extracted in a one-level approximation of R-matrix theory, resulting in resonance energy E-R = 1.748(6) MeV and width Gamma(R) = 274(8) keV, which are in good agreement with the latest Be-9(gamma, n) experiment but with considerably improved uncertainties. However, the reduced B(E1) transition strength deduced from an extrapolation of the (e, e') data to the photon point is smaller by a factor of two. Implications of the new results for possible production of C-12 in neutron-rich astrophysical scenarios are discussed.
41679008
Proton capture to excited states of O 16 : M 1 , E 1 , and Gamow-Teller transitions and shell model calculations
We have measured excitation functions of the ..gamma..-rays resulting from the bombardment of /sup 15/N by polarized and unpolarized protons in the energy range E/sub p/ = 2.5 to 9.5 MeV with emphasis on identifying dipole decays to the first (0/sup +/) and second (3/sup -/) excited states in /sup 16/O. Resonances in ..gamma../sub 12/ are observed at E/sub x/ = 16.21, 16.45, 16.82, 17.12, 18.03, 18.98, 19.90 and 20.41 MeV. The 16.21 and 17.12 MeV resonances in ..gamma../sub 12/ are identified as M1-decays of the 1/sup +/ T = 1 states to the 6.05 MeV 0/sup +/ state in /sup 16/O. The measured ratio of reduced strengths B(m1,..gamma../sub 1/)/(B(M1,..gamma../sub 0/) is 0.48 +- 0.03 for decays from the 16.21 MeV state and 0.55 +- 0.04 for decays from the 17.12 MeV state. The 18.03 MeV resonance is due to a 3/sup -/ T = 1 state in /sup 16/O with a strength Gamma/sup p/Gamma/sub gamma 2//Gamma = (1.96 +- 0.27) eV and the 18.98 MeV resonance is due to the 4/sup -/ T = 1 stretched particle-hole state with a strength of (0.85 +- 0.10) eV. We determine absolute particle and ..gamma.. widths for these states. The M1 ..gamma../submore » 2/-width of the 18.98 MeV state, (7.1 +- 3.1) eV, is in agreement with a shell-model calculation. Resonances in ..gamma../sub 3/ are observed at 16.82 and 17.27 MeV and in ..gamma../sub 4/ at 17.88 MeV. The excitation energies and widths of these levels as well as the strengths of the ..gamma.. transitions suggest T = 1 character for all of the resonances for which capture ..gamma..-rays are observed. Correspondences of our resonances to levels in /sup 16/N are given. We compare ..gamma.. widths, including ground-state M1 decays, and allowed ..beta.. transition rate in A = 16 nuclei with shell model calculations and obtain rough agreement. Additional shell model calculations for M1 and GT (Gamow-Teller) decays in the A-14, 15, 17 and 18 nuclei are presented, which indicate that GT matrix elements are quenched by approx. 20% relative to shell model predictions and also relative to the spin part of the M1 matrix elements.« less
120853289
The 52,54Cr(p, n)52,54Mn and 57,58Fe(p, n)57,58Co reactions at Ep = 120 MeV
Abstract Differential cross sections for the (p, n) reaction on 52, 54 Cr and 57, 58 Fe have been measured for angles up to θ lab = 10.5° and 14.6°, respectively, using 120 MeV protons. The observed angular distributions are used to evaluate the location and strength of Gamow-Teller resonances. A shell-model calculation of this strength distribution is presented and compared with the experimental results. The M1 strength for 52 Cr is also calculated and compared with available results from (e, e') and (p, p') experiments. A comparison is made with other If 7 2 nuclei.
34139540
Shape of the beta spectra in the A=14 system.
35436961
Predicted features of the beta decay of neutron-rich sd-shell nuclei
The Gamow-Teller beta-decay transitions of sd-shell nuclei with five or more excess neutrons are calculated from complete (0d/sub 5/2/, 1s/sub 1/2/, 0d/sub 3/2/)-space shell-model wave functions. These wave functions are obtained from diagonalizations of a model Hamiltonian formulation which reproduces observed energy-level structures throughout the sd shell. The calculations are carried out with both the ''free-nucleon'' normalization for the Gamow-Teller single-nucleon matrix elements and one based on the empirical values obtained for these quantities from a comparison of corresponding theoretical and experimental Gamow-Teller magnitudes near the line of stability. The phase-space factors f which connect the reduced Gamow-Teller strengths to the total half-lives and the individual decay probabilities are calculated both from the energies obtained in the shell-model calculations and, alternatively, from hybrid energy spectra in which available experimental energies are substituted for the corresponding calculated values wherever possible. Comparisons of the beta-decay predictions to existing experimental results are presented and discussed.
56232513
Search for physics beyond the standard model via a polarization-asymmetry correlation experiment on In-107
We report on a new precision measurement of the longitudinal polarization of positrons emitted by polarized 107In nuclei. Preliminary results yield a lower limit of 303 GeV/c2 for the mass of a possible, predominantly right-handed, W gauge boson, if interpreted in the framework of the manifest, left-right symmetric model. In more general left-right symmetric models our result is complementary to those from muon decay experiments and to results from searches for a similar particle in collider experiments. Our data also provide new results on possible tensor contributions to the weak interaction.
11457012
X-Ray Emission from Early-Type Galaxies: A Complete Sample Observed by ROSAT
To test the cooling flow model of early-type galaxies, we obtained a complete magnitude-limited sample of 34 early-type galaxies, observed with the PSPC and the HRI on ROSAT. The X-ray-to-optical distribution of galaxies implies a lower envelope, which is consistent with the stellar emission inferred from Cen A. When this stellar component is removed, the gaseous emission is related to the optical luminosity by LX ∝ LBm, where m = 3.0-3.5, which is significantly steeper than the standard theory (m = 1.7). The dispersion about the correlation is large, with a full range of 30-100 in LX for fixed LB. The X-ray temperature is related to the velocity dispersion temperature as TX ∝ Tσn, where n=1.43±0.21, although for several galaxies, TX is about twice Tσ. The excessively hot galaxies are generally the most luminous and are associated with the richest environments. We suggest a model whereby the environment influences the X-ray behavior of these galaxies: early-type galaxies attempt to drive partial or total galactic winds, which can be stifled by the pressure of their environment. Stifled winds should lead to hotter and higher luminosity systems, which would occur most commonly in the richest environments, as observed.
17355301
The Effect of Environment on the X-Ray Emission from Early-Type Galaxies
In order to further our understanding of the phenomena of X-ray emission from early-type galaxies, we obtained an optically flux-limited sample of 34 elliptical and S0 galaxies, observed with high and low angular resolution detectors on ROSAT. Our previous analysis of this sample suggested that the most X-ray-luminous galaxies were in rich environments. Here we investigate environmental influences quantitatively and find a positive correlation between LX/LB and the local galaxy density. Since the local galaxy density is usually related to the density of hot intergalactic gas, we suggest that this correlation occurs because the X-ray luminosity is enhanced, either through accretion of the intergalactic gas or because the ambient medium stifles galactic winds. When the ambient medium is unimportant, partial or global galactic winds can occur, reducing LX/LB. These effects lead to the large observed dispersion in LX at fixed LB. We discuss details of the data processing not previously presented, and examine the dependence of LX on the choice of outer source radius and background location. We also compare the temperature deduced for these galaxies from different analyses of ROSAT and ASCA data. The ASCA and ROSAT temperatures are found to be similar, provided that the same metallicities and Galactic absorption columns are used.