31 research outputs found
Astrophysical S_{17}(0) factor from a measurement of d(7Be,8B)n reaction at E_{c.m.} = 4.5 MeV
Angular distribution measurements of H(Be,Be)H and
H(Be,B) reactions at ~4.5 MeV were performed to
extract the astrophysical factor using the asymptotic normalization
coefficient (ANC) method. For this purpose a pure, low emittance Be beam
was separated from the primary Li beam by a recoil mass spectrometer
operated in a novel mode. A beam stopper at 0 allowed the use of a
higher Be beam intensity. Measurement of the elastic scattering in the
entrance channel using kinematic coincidence, facilitated the determination of
the optical model parameters needed for the analysis of the transfer data. The
present measurement significantly reduces errors in the extracted
Be(p,) cross section using the ANC method. We get
~(0)~=~20.7~~2.4 eV~b.Comment: 15 pages including 3 eps figures, one figure removed and discussions
updated. Version to appear in Physical Review
Uncomputably noisy ergodic limits
V'yugin has shown that there are a computable shift-invariant measure on
Cantor space and a simple function f such that there is no computable bound on
the rate of convergence of the ergodic averages A_n f. Here it is shown that in
fact one can construct an example with the property that there is no computable
bound on the complexity of the limit; that is, there is no computable bound on
how complex a simple function needs to be to approximate the limit to within a
given epsilon
Isotopic dependence of the giant monopole resonance in the even-A ^{112-124}Sn isotopes and the asymmetry term in nuclear incompressibility
The strength distributions of the giant monopole resonance (GMR) have been
measured in the even-A Sn isotopes (A=112--124) with inelastic scattering of
400-MeV particles in the angular range
--. We find that the experimentally-observed GMR energies
of the Sn isotopes are lower than the values predicted by theoretical
calculations that reproduce the GMR energies in Pb and Zr very
well. From the GMR data, a value of MeV is obtained
for the asymmetry-term in the nuclear incompressibility.Comment: Submitted to Physical Review Letters. 10 pages; 4 figure
A Model Electron-Density Profile for Noontime Equatorial Lower Ionosphere
80-85D- and E- region electron-density profiles over Colombo (lat., 06° 54'N) have been deduced by using AI-absorption data at frequencies 2.0, 2.2 and 2.6 MHz spread over half a solar cycle during 1964-68. The noontime absorption data, normalized with respect to zenith angle and solar activity variations are subjected to harmonic analysis. The mean value obtained in the harmonic analysis is taken as the absorption value at the frequency freed from all seasonal, zenith angle and solar activity effects. In deriving the electron-density distribution, an arbitrary electron-density profile computed from well-known production and loss processes in the lower ionosphere is first considered and then this profile is adjusted by trial and error until the computed values of absorption and virtual height, using the generalized Sen-WyIler theory, are in good agreement with the noontime mean values mentioned at all the frequencies. Further, in regard to the seasonal variation of absorption at Colombo, it is found that the semi-annual component is the dominant one and its phase agrees remarkably with the phase of the semi-annual osciIlation of the air density in the lower thermosphere