Mathematics – Probability
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........26p&link_type=abstract
Thesis (PH.D.)--BROWN UNIVERSITY, 1994.Source: Dissertation Abstracts International, Volume: 55-07, Section: B, page: 2825.
Mathematics
Probability
2
Scientific paper
The sun is one of the most intensely studied astronomical objects. However, the solar neutrino problem remains one of the major unsolved problems in low energy particle physics. All four currently operating solar neutrino experiments measure a neutrino flux of only between 28% and 63% of that predicted by the Standard Solar Model. New experiments are needed in order to resolve the apparent deficit of solar neutrinos. In this thesis, results are presented for a prototype solar neutrino detector which uses superfluid helium as a target. The prototype consists of a 3 liter helium target maintained at 40 mK by a dilution refrigerator, and a low mass calorimeter suspended above the liquid surface. An 241Am film immersed in the helium provides 5.5 MeV alpha particles which are detected in the experiment. In the detection process, the alpha particle deposits a fraction of its energy in rotons and phonons which travel ballistically in the liquid at low temperatures. The excitations which reach the free surface have a finite probability of evaporating helium atoms from the surface and the evaporation signal is detected by the calorimeter mounted above the liquid. The experimental results show that the alpha particle deposits a substantial fraction of its energy in the liquid producing predominately rotons with momentum near the roton minimum of the dispersion curve (1.91 A^{-1}). In addition, the evaporation signal produced by the rotons has been observed and is shown to be peaked directly above the alpha source in the detector. The results also indicate that the magnitude of the evaporation signal depends on both the energy and the initial direction of the alpha particle stopped in the helium target. Finally, these results are compared to Monte Carlo simulations and the implications for a full scale detector are discussed.
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