8 research outputs found
Measuring cosmogenic Li9 background in a reactor neutrino experiment
Cosmogenic isotopes 9Li and 8He produced in the detector are the most
problematic background in the reactor neutrino experiments designed to
determine precisely the neutrino mixing angle theta13. The average time
interval of cosmic-ray muons in the detector is often on the order of the
lifetimes of the 9Li and 8He isotopes. We have developed a method for
determining this kind of background from the distribution of time since last
muon for muon rate up to about 20 Hz when the background-to-signal ratio is
small, on the order of a few percents.Comment: 9 pages, 3 figures. To appear in NIM
Hindrance of the excitation of the Hoyle state and the ghost of the state in C
While the Hoyle state (the isoscalar excitation at 7.65 MeV in
C) has been observed in almost all the electron and inelastic
scattering experiments, the second excited state of C at MeV, believed to be an excitation of the Hoyle state, has not
been clearly observed in these measurements excepting the high-precision \aap
experiments at and 386 MeV. Given the (spin and isospin zero)
-particle as a good probe for the nuclear isoscalar excitations, it
remains a puzzle why the peak of the state could not be clearly
identified in the measured \aap spectra. To investigate this effect, we have
performed a microscopic folding model analysis of the \ac scattering data at
240 and 386 MeV in both the Distorted Wave Born Approximation (DWBA) and
coupled-channel (CC) formalism, using the nuclear transition densities given by
the antisymmetrized molecular dynamics (AMD) approach and a complex CDM3Y6
density dependent interaction. Although AMD predicts a very weak transition
strength for the direct excitation, our detailed analysis
has shown evidence that a weak \emph{ghost} of the state could be
identified in the 240 MeV \aap data for the state at 10.3 MeV, when the
CC effects by the indirect excitation of the state are taken into
account. Based on the same AMD structure input and preliminary \aap data at 386
MeV, we have estimated relative contributions from the and
states to the excitation of C at MeV as well as
possible contamination by state.Comment: Accepted for publication in Phys. Lett.
Missing monopole strength of the Hoyle state in the inelastic +C scattering
Analyses of the inelastic +C scattering at medium energies
have indicated that the strength of the Hoyle state (the isoscalar 0
excitation at 7.65 MeV in C) seems to exhaust only 7 to 9% of the
monopole energy weighted sum rule (EWSR), compared to about 15% of the EWSR
extracted from inelastic electron scattering data. The full monopole transition
strength predicted by realistic microscopic -cluster models of the
Hoyle state can be shown to exhaust up to 22% of the EWSR. To explore the
missing monopole strength in the inelastic +C scattering, we
have performed a fully microscopic folding model analysis of the inelastic
+C scattering at to 240 MeV using the
3- resonating group wave function of the Hoyle state obtained by
Kamimura, and a complex density-dependent M3Y interaction newly parametrized
based on the Brueckner Hartree Fock results for nuclear matter. Our folding
model analysis has shown consistently that the missing monopole strength of the
Hoyle state is not associated with the uncertainties in the analysis of the
+C scattering, but is most likely due to the short lifetime and
weakly bound structure of this state which significantly enhances absorption in
the exit +C channel.Comment: Accepted for publication in Physics Letters