Proc. Neutrino Astrophysics - MPP Theory Group
Proc. Neutrino Astrophysics - MPP Theory Group
Proc. Neutrino Astrophysics - MPP Theory Group
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162<br />
Figure 1: Calorimetric β − spectrum of 187 Re plus a multi-lines X-ray fluorescence spectrum<br />
due to an external calibration source (see text).<br />
The isotope 163 Ho decays by electron capture (EC) with the subsequent emission of an<br />
electron neutrino. The EC decay is followed by the emission of Auger electrons and X-rays<br />
due to the electronic cloud excitation of the daughter atom. For each occupied energy level<br />
from which the electron capture is energetically allowed, there is a line in the calorimetric<br />
energy spectrum. The effect of a finite neutrino mass should manifest itself as a variation of<br />
the ratios of the relative EC probabilities. Measuring N lines of the calorimetric spectrum,<br />
it is possible to set N − 1 simultaneous constraints on the neutrino mass and the end-point<br />
value Q from the relative ratios of the integral value of each spectral line.<br />
Enclosing the 163 Ho source in a suitable absorber of a micro-calorimeter it has been<br />
possible to measure [2, 3] four lines of the calorimetric spectrum (see Fig. 2.a), but the<br />
statistics of this measurement is not high enough to set a significant limit on the neutrino<br />
mass. Considering a zero value of the neutrino mass, the end-point energy has been calculated<br />
by a fit procedure and it is turned out to be Eend−point = (2800 ±50)eV. Taking into account<br />
this end-point value it should be possible to set a kinematical limit to the neutrino mass by<br />
means of this calorimetric method lower than 170 eV/c 2 in 50 days of data taking. Running<br />
more than one detector at the same time it will be possible to further improve the achievable<br />
mass limit. Although the limit on neutrino mass could not be competitive with the achievable<br />
limit on electron anti-neutrino mass, we believe it is meaningful to set independent limits on<br />
the masses of the electron neutrino and anti-neutrino.<br />
Another important application of this kind of detector is the measurement of the solar<br />
neutrino flux in radiochemical solar neutrino experiments. In these experiments the integrated<br />
value of the solar neutrino flux is measured counting the extracted isotope which is