143 research outputs found
Particle Detection by Evaporation from Superfluid Helium
We report the first experiments in which 5-MeV alpha particles are detected via evaporation from a bath of superfluid helium. The α excites phonons and rotons in the liquid helium, and these excitations are sufficiently energetic to evaporate helium atoms when they reach the free surface of the liquid. The approximate overall efficiency of this process has been determined, and we compare this with expectations. We have also been able to detect evaporation induced by a flux of Îłâs from a 137Cs source
Removal of superfluid helium films from surfaces below 0.1 K
We have constructed an apparatus that is able to maintain a heliumâfree surface at low temperature (Tâ€0.1 K) in a cell containing superfluid helium. We discuss the considerations involved in the design of this device, and describe tests that we have made to confirm that a filmâfree surface has been produced
Progress report of a research program in experimental high energy physics, 1 September 1974--31 August 1975
Phonon amplification using evaporation and adsorption of helium
We report the results of experiments designed to investigate the feasibility of amplifying a phonon signal using the evaporation of helium from a superfluid film and its subsequent readsorption onto a helium-free surface. We envision a multistage amplifier in which helium is evaporated from a wafer with a helium film only on one side and then adsorbed onto the film-free surface of a similar wafer. The phonons created by the adsorption reach the film on the opposite side of the wafer and potentially desorb more helium than was evaporated by the first wafer. The amplification would come from the high ratio of the binding energy of a helium atom to a film-free surface relative to the binding energy to the liquid. A number of experiments are reported that investigate the efficiencies of the individual steps of the process. The gain per stage is found to be about 3 for high-energy densities in which multiphonon processes are possible. At low-energy densities, the energy deposited into a film-free wafer is found to be less than the original input energy, with the ratio of output to input energy 0.2. Since in applications requiring amplification the phonon density produced by the adsorption of helium on a wafer will be low, the configuration we have studiedâphonons produced in silicon coated with a saturated He4 filmâwill not result in amplification. However, other configurations might improve the efficiency enough to make an amplifier possible
Angular Distribution of Rotons Generated by Alpha Particles in Superfluid Helium: A Possible Tool for Low Energy Particle Detection
We report measurements of the distribution of rotons generated by α particles interacting in a bath of superfluid helium. The roton flux is found to be anisotropic; it is about 4 times larger transverse to the track direction than along it. This asymmetry may provide a powerful tool in particle and astrophysics experiments where sensitivity to low energy recoil track direction is important
10,000 Standard Solar Models: a Monte Carlo Simulation
We have evolved 10,000 solar models using 21 input parameters that are
randomly drawn for each model from separate probability distributions for every
parameter. We use the results of these models to determine the theoretical
uncertainties in the predicted surface helium abundance, the profile of the
sound speed versus radius, the profile of the density versus radius, the depth
of the solar convective zone, the eight principal solar neutrino fluxes, and
the fractions of nuclear reactions that occur in the CNO cycle or in the three
branches of the p-p chains. We also determine the correlation coefficients of
the neutrino fluxes for use in analysis of solar neutrino oscillations. Our
calculations include the most accurate available input parameters, including
radiative opacity, equation of state, and nuclear cross sections. We
incorporate both the recently determined heavy element abundances recommended
by Asplund, Grevesse & Sauval (2005) and the older (higher) heavy element
abundances recommended by Grevesse & Sauval (1998). We present best-estimates
of many characteristics of the standard solar model for both sets of
recommended heavy element compositions.Comment: ** John N. Bahcall passed away on August 17, 2005. Manuscript has 60
pages including 10 figure
Solar Neutrinos: Radiative Corrections in Neutrino-Electron Scattering Experiments
Radiative corrections to the electron recoil-energy spectra and to total
cross sections are computed for neutrino-electron scattering by solar
neutrinos. Radiative corrections change monotonically the electron recoil
spectrum for incident \b8 neutrinos, with the relative probability of observing
recoil electrons being reduced by about 4 \% at the highest electron energies.
For and \be7 neutrinos, the recoil spectra are not affected
significantly. Total cross sections for solar neutrino-electron scattering are
reduced by about 2 \% compared to previously computed values. We also calculate
the recoil spectra from N and O neutrinos including radiative
corrections.Comment: 40 pages, uuencoded, Z-compress file
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