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The HERON project is an effort to develop a detector for low-energy solar neutrinos in real time by observing their elastic scattering from electrons using superfluid helium as the target material. By applying appropriate electric fields, the recoil electron can be separated from the positive ion, drifted upward to the liquid–vacuum interface, transmitted through the surface with the aid of a vortex ring, and detected using a calorimeter. By studying the correlation of the 16 eV photon signal produced by scintillation and the single-electron signal, we can locate a neutrino event in a large detector and distinguish it from the background events involving multiple Compton scattering. [Copyright &y& Elsevier]

The dependence on an applied electric field of the ionization current produced by an energetic electron stopped in liquid helium can be used to determine the spatial distribution of secondary electrons with respect to their geminate partners. An analytic expression relating the current and distribution is derived. The distribution is found to be non-Gaussian with a long tail at larger distances. [ABSTRACT FROM AUTHOR]

Abstract: Results are presented for a simulation carried out to test the precision with which a detector design (HERON) based on a superfluid helium target material should be able to measure the solar pp and 7Be fluxes. It is found that precisions of ±1.68% and ±2.97% for pp and 7Be fluxes, respectively, should be achievable in a 5-year data sample. The physics motivation to aim for these precisions is outlined as are the detector design, the methods used in the simulation and sensitivity to solar orbit eccentricity. [Copyright &y& Elsevier]

The response of a magnetic calorimeter with a sapphire crystal serving as an X-ray absorber has been studied as a function of temperature. Several different Au films were used to connect thermally the magnetic sensor to the absorber. The amplitude and time dependence of the signal resulting from the absorption of an X-ray were fit using an idealized model for the calorimeter. The values of the various parameters resulting from a fit of the data are internally consistent and provide a physical understanding of the processes determining the performance of the calorimeter. The fraction of the energy of the X-ray that is captured by the film without having first been down-converted to thermal phonons in the sapphire is found to depend on both the area and the thickness of the film. The rate at which the energy is transferred between thermal phonons in the sapphire and the electrons in the film is determined by the electron/phonon interaction in the gold. Also, an additional heat capacity was observed to be present in the sapphire, which, for want of a better means of characterization, is ascribed to the tunneling systems. The magnitude of this additional heat capacity and its thermal coupling to the lattice has been studied. [Copyright &y& Elsevier]

Abstract: Prototype metallic magnetic calorimeters (MMC), in which the magnetization of Au:Er sensors has been measured using a DC SQUID, have shown excellent energy resolution for soft X-rays. However, the results to date have been obtained with devices assembled by hand, placing a small ( diameter), thin disk of the Au:Er alloy within the loop of the SQUID. This is an unacceptable method for fabricating large focal-plane arrays of detectors required for the next generation of X-ray telescopes. We are therefore investigating the properties of vapor-deposited films produced by DC magnetron sputtering using an Au:Er alloy target. The magnetic properties of thick Au:Er films have been investigated from room temperature down to 40mK. The measured magnetization matches theoretical values down to 200mK. The films have the same Er concentration as in the target material. At lower temperatures there is indication of enhanced magnetic interactions among the Er ions. We are studying the dependence of this interaction on the parameters used in the deposition process. [Copyright &y& Elsevier]