ON POSSIBILITY TO SET A LIMIT ON NEUTRINO MASS WITH PRECISE
MEASUREMENTS OF THE 115In-115Sn MASS DIFFERENCE

	In recent experiment [1], beta decay of 115In to the first
excited level of 115Sn was observed at the first time. Probability 
of the decay is extremely low: 1.2e-6 in comparison with decay to 
the ground state of 115Sn, and corresponding half-life is 
T1/2=3.7e20 years.
	The low probability of decay is related with very small 
energy release, Q. With the most recent value of 115In-115Sn atomic 
mass difference of 499+-4 keV [2] and energy of the 115Sn first 
excited level of 497.4 keV, the Q value is 1.6+-4 keV, probably the 
lowest known Q value for observed beta decays. Calculations based on
systematics of log ft values give lower value of Q=460 eV [1].
	However, theoretical predictions at these energies are quite 
uncertain, and both estimations give only indication that the Q 
value could be very small. Because mass of neutrino, emitted in beta
decay, cannot be greater than Q, such a situation has a potentiality
to bring out a limit on neutrino mass, which could lay in the range 
of eV. The best way to clarify the situation would be a direct
experimental measurement of the 115In-115Sn mass difference with
precision of ~100 eV at the first step, and better in case of need 
[3].

References:
1. C.M. Cattadori et al., Nucl. Phys. A 748 (2005) 333. 
2. G. Audi et al., Nucl. Phys. A 729 (2003) 337.
3. C.M. Cattadori et al., nucl-ex/0509020 (Phys. At. Nucl. in press).