Abstract
LOREX (LORandite EXperiment) addresses the determination of the solar (pp) neutrino flux during the last four million years by exploiting the reaction 205Tl+νe→ 205Pb+e-with an incomparably low-energy threshold of 50 keV for the capture of solar neutrinos. The ratio of205Pb/205Tl atoms in the Tl-bearing mineral lorandite provides, if corrected for the cosmic-ray induced background, the product of the flux of solar neutrinos and their capture probability by205Tl, averaged over the age of lorandite. To get the mean solar neutrino flux itself, four problems have to be addressed: (1) the geological age of lorandite, (2) the amount of background cosmic-ray-induced205Pb atoms which strongly depends on the erosion rate of the lorandite-bearing rocks, (3) the capture probability of solar neutrinos by205Tl and (4) the extraction of lorandite and the appropriate technique to “count” the small number of205Pb atoms in relation to the number of205Tl atoms. This paper summarizes the status of items 1 (age) and 3 (neutrino capture probability) and presents in detail the progress achieved most recently concerning the items 2 (background/erosion) and 4 (“counting” of205Pb atoms in lorandite).
Highlights
To get the mean solar neutrino flux itself, four problems have to be addressed: 1 the geological age of lorandite, 2 the amount of background cosmicray-induced 205Pb atoms which strongly depends on the erosion rate of the lorandite-bearing rocks, 3 the capture probability of solar neutrinos by 205Tl and 4 the extraction of lorandite and the appropriate technique to “count” the small number of 205Pb atoms in relation to the number of 205Tl atoms
This paper summarizes the status of items 1 age and 3 neutrino capture probability and presents in detail the progress achieved most recently concerning the items 2 background/erosion and 4 “counting” of 205Pb atoms in lorandite
The determination of the long-time average of the solar neutrino flux Φν with the thalliumbearing mineral lorandite, TlAsS2, from the mine of Allchar, Macedonia, is based on the neutrino capture reaction proposed by Freedman et al, 1976 1 : 205Tl νe −→ 205Pb e−
Summary
The determination of the long-time average of the solar neutrino flux Φν with the thalliumbearing mineral lorandite, TlAsS2, from the mine of Allchar, Macedonia, is based on the neutrino capture reaction proposed by Freedman et al, 1976 1 : 205Tl νe −→ 205Pb e−. The average flux Φν over the exposure time a age of lorandite since its mineralization follows from the common activation equation: Φν N−1 T − B σε −1 λ 1 − exp −λa −1, 1.2 where N is the total number of 205Tl atoms, T the total number of 205Pb atoms, B the number of 205Pb atoms induced by background reactions mainly 205Tl μ p, n 205Pb , σ the solar neutrino capture cross-section of 205Tl, ε the overall detection efficiency, λ the decay constant of 205Pb and a the geological age of lorandite i.e., the age of mineralization. 2 the background of 205Pb atoms produced by cosmic radiation mainly μ p, n reactions and by natural radioactivity must be determined quantitatively. In this context the knowledge of the erosion rate of the overburden rocks during the existence of lorandite is of utmost importance: background and erosion,. 4 how can the expected ultra-low abundance of 205Pb be reliably measured: detection of 205Pb
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