24 research outputs found
Evidence for a three-nucleon-force effect in proton-deuteron elastic scattering
Developments in spin-polarized internal targets for storage rings have
permitted measurements of 197 MeV polarized protons scattering from vector
polarized deuterons. This work presents measurements of the polarization
observables A_y, iT_11, and C_y,y in proton-deuteron elastic scattering. When
compared to calculations with and without three-nucleon forces, the
measurements indicate that three-nucleon forces make a significant contribution
to the observables. This work indicates that three-body forces derived from
static nuclear properties appear to be crucial to the description of dynamical
properties.Comment: 8 pages 2 figures Latex, submitted to Phys. Rev. Letter
Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five r-process Rich, Metal-Poor Stars, and Rare Earth Lab Data
Recent radiative lifetime measurements accurate to +/- 5% using laser-induced
fluorescence (LIF) on 43 even-parity and 15 odd-parity levels of Ce II have
been combined with new branching fractions measured using a Fourier transform
spectrometer (FTS) to determine transition probabilities for 921 lines of Ce
II. This improved laboratory data set has been used to determine a new solar
photospheric Ce abundance, log epsilon = 1.61 +/- 0.01 (sigma = 0.06 from 45
lines), a value in excellent agreement with the recommended meteoritic
abundance, log epsilon = 1.61 +/- 0.02. Revised Ce abundances have also been
derived for the r-process-rich metal-poor giant stars BD+17 3248, CS 22892-052,
CS 31082-001, HD 115444 and HD 221170. Between 26 and 40 lines were used for
determining the Ce abundance in these five stars, yielding a small statistical
uncertainty of 0.01 dex similar to the Solar result. The relative abundances in
the metal-poor stars of Ce and Eu, a nearly pure r-process element in the Sun,
matches r-process only model predictions for Solar System material. This
consistent match with small scatter over a wide range of stellar metallicities
lends support to these predictions of elemental fractions. A companion paper
includes an interpretation of these new precision abundance results for Ce as
well as new abundance results and interpretations for Pr, Dy and Tm.Comment: 84 pages, 8 Figures, 14 Tables; To appear in the Astrophysical
Journal Supplemen
New Rare Earth Element Abundance Distributions for the Sun and Five r-Process-Rich Very Metal-Poor Stars
We have derived new abundances of the rare-earth elements Pr, Dy, Tm, Yb, and
Lu for the solar photosphere and for five very metal-poor, neutron-capture
r-process-rich giant stars. The photospheric values for all five elements are
in good agreement with meteoritic abundances. For the low metallicity sample,
these abundances have been combined with new Ce abundances from a companion
paper, and reconsideration of a few other elements in individual stars, to
produce internally-consistent Ba, rare-earth, and Hf (56<= Z <= 72) element
distributions. These have been used in a critical comparison between stellar
and solar r-process abundance mixes.Comment: 48 pages, 11 figures, 12 tables: To appear in the Astrophysical
Journal Supplemen
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The Argonne laser-driven D target: Recent developments and progress
The first direct measurements of nuclear tensor polarization p{sub zz} in a laser-driven polarized D target have been performed at Argonne. We present p{sub zz} and electron polarization P{sub e} data taken at a magnetic field of 600 G in the optical pumping cell. These results are highly indicative that spin-temperature equilibrium is achieved in the system. To prevent spin relaxation of D and K atoms as well as the molecular recombination of D atoms, the walls of the laser-driven D target are coated with organosilane compounds. We discuss a new coating technique, the {open_quotes}afterwash{close_quotes}, developed at Argonne which has yielded stable atomic fraction results when the coating is exposed to K. We also present new coating techniques for glass and Cu substrates