26401416
Weak pion-nucleon coupling strength: New constraint from parity mixing in 18F.
The circular polarization of the 1.081 MeV γ rays from 18F has been measured to be (1.7±5.8)×10-4. 18F was produced by a 4.05 MeV 3He+ beam impinging on a recirculating water target with a thin entrance window. The circular polarization was measured with four magnetic transmission polarimeters, each backed by a 150 cm3 n-type Ge detector. A fast data acquisition system limited overall peak losses to 30% at a count rate of 60 kHz per detector. Supplementary experiments were carried out to investigate the sensitivity of the circular polarization measurement to systematic variations of beam position and intensity. These effects were found to be negligible relative to the statistical uncertainty. The experimental result is interpreted in terms of an isovector parity-nonconserving matrix element between the ‖0+,T=1,1.042 MeV〉 and ‖0-,T=0,1.081 MeV〉 states in 18F that is dominated by the weak pion exchange contribution. The present result for the weak pion-nucleon coupling strength is ‖fπ1‖=(0.4-0.4+1.4)×10-7, which is significantly smaller than recent theoretical predictions based on the Weinberg-Salam model.
122471417
Radiative decay of the second excited state of C-12
The branching ratio GAMMA/sub rad//GAMMA for the electromagnetic decay of the 7.655 MeV second excited state of $sup 12$C has been measured by detecting the $sup 12$C (0.0 MeV) recoils in coincidence with $alpha$ particles from the $sup 13$C($sup 3$He,$alpha$$sub 2$)$sup 12$C (7.65 MeV) reaction at E3)=4.00 MeV. Coincidence events were identified by means of time-of-flight, energy, and kinematic constraints. Thus, of all the $sup 12$C nuclei formed in the second excited state, only those decaying to the $sup 12$C ground state by either $gamma$-ray or positron-electron pair emission were selected. Hence the experiment provides a direct measurement of GAMMA/sub rad//GAMMA, where GAMMA/sub rad/=GAMMA/sub $gamma$ + e+-/, and gives GAMMA/sub rad//GAMMA= (4.15 +- 0.34) x 10$sup -4$, which is in good agreement with other recent measurements, and suggests that the previously accepted value of GAMMA/sub rad//GAMMA= (2.9 +- 0.3) times 10$sup -4$ may be too low. The significance of this result is discussed with respect to helium burning rates in stars.
117853216
Core-Excited High-Spin Isomers in 212Rn
We have observed isomeric states in /sup 212/Rn with very high angular momenta (up to J/sup ..pi../ = 30/sup +/). The four isomers of highest spin contain core-excited neutron configurations, the spins of which are strongly aligned with those of the valence protons. The isomerism appears to result from a lowering of the excitation energies by 1 to 2 MeV compared to a sum of the unperturbed values for the constituent configurations.
121991652
Measurement of the relativistic Doppler effect using 8.6-MeV capture $gamma$ rays
122285344
A Heavy Water Detector to Resolve the Solar Neutrino Problem
Abstract The observation of the following three reactions: ν e d→ppe; ν x e→ ν x e ; and ν x d→ ν x pn (where ν x is any left- handed neutrino) in a heavy water Cerenkov detector which is being designed, allows the solar 8 B v e flux, spectrum and direction to be measured. In addition, the total solar 8 Bν c neutrino flux, direction and integral spectrum, independent of neutrino flavor, may be determined to provide several independent methods to resolve the solar neutrino problem.
119657975
Solar neutrinos, SNO and SNOLAB
The Sudbury Neutrino Observatory is a 1000 tonne heavy water Cherenkov detector situated 2 km underground in INCO's Creighton mine near Sudbury, Ontario, Canada. In the first two phases of the project reported to date, the charged current reaction on deuterium has been used to measure the flux and energy spectrum of solar electron neutrinos and the neutral current reaction has been used to measure the total flux of active neutrinos. Clear evidence of neutrino flavour change has been observed and the total active flux is found to be in agreement with solar model calculations. The experimental third phase with an array of neutron detectors is in progress. The expansion of the underground laboratory to create an international facility known as SNOLAB will be completed in 2007. A number of international experiments for the future detection of lower energy solar neutrinos, geo-neutrinos, dark matter and double beta decay are described.
602043
Cosmological limits on deviations from phi2 potentials in oscillating scalar cold dark matter models.
We consider the consequences for oscillating scalar cold dark matter models of a scalar field phi which oscillates in a potential which deviates slightly from a phi2 potential. We consider a correction to the phi2 potential of the form Kphi2ln(phi2) + lambda(phi)phi4. Upper bounds on \K\ and \lambda)phi)\ are obtained as a function of the phi mass by requiring that the effects of the pressure introduced by the correction to the potential do not disrupt the conventional cold dark matter scenario for structure formation. The results are applied to some cosmological models of recent interest. In particular, it is shown that a scalar identified with the pseudo Goldstone boson of a U(1) symmetry explicitly broken by neutrino masses (suggested iri connection with late-time phase transitions) is inconsistent with the MSW solution of the solar neutrino problem if it is to account for dark matter. In addition it is shown that a cold dark matter model in which the Compton wavelength of a very light scalar particle accounts for the large-scale structure of the Universe is also ruled out by the effects of pressure on structure formation.