Particle detection by evaporation from superfluid helium

Abstract

We report the first experiments in which 5-MeV alpha particles are detected via evaporation from a bath of superfluid helium. The a 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 r's from a 137 Cs source.

The Solar Neutrino Problem

“…The reader is referred to the recent review by Lanou (1995). There are significant challenges motivating these efforts, e.g., neutrino detection by coherent scattering off nuclei and real-time detectors for pp neutrinos, such as the superfluid 4 He detector HERON (Bandler et al 1992) and the high-pressure helium time projection chamber HELLAZ (Laurenti et al 1994). …”

Progress on HERON: A real-time detector for P-P solar neutrinos

“…Fortunately, although its cross-section is low (∼ 10 −45 cm 2 ) the expected flux is high (∼ 6 × 10 10 cm −2 · s −1 for p-p neutrinos in the standard solar model) so that ∼10 tons of target would yield about 20 p-p events and 7 7 Be events per day with recoil energies above 50 keV. HERON would use superfluid helium as the target material.…”

“…The combination of these experiments is expected to give the first "smoking gun" evidence for or against oscillation of solar neutrinos. The maximum recoiling electron energy from elastic scattering of the principal 7 Be line is 665 keV; while that from the p-p continuum is only 261 keV. The upcoming BOREXINO detector, based on the use of a highly purified liquid scintillator, will give the first direct window on the 7 Be flux in real-time using the elastic scattering reaction but is not expected to access the p-p flux because of internal backgrounds at the lowest energies.…”

“…Detection reactions with accurately known cross sections for the p-p and 7 Be neutrinos are available -for the ground state transitions in Ga and for elastic electron scattering. The continuing gallium-based detectors ( GNO and SAGE), with increased statistics and improved systematic errors, will provide more precise measures of the ν e flux for energies > 0.23 MeV.…”

“…A real-time experiment utilizing spectral measurements for the flavor-mixed and precisely known elastic cross-section is needed to provide the essential, but presently missing, sensitivity to the components ν µ,τ of the low energy flux. An experiment with this capability would also be sensitive to the 7 Be neutrinos and, if done by a technique with very different systematics from BOREXINO, could provide an important corroboration of that important measurement.…”