Nucl.Instrum.Meth.A503:649-657,2003 The background induced by radioactive impurities of $^{208}\rm Tl$ and
$^{214}\rm Bi$ in the source of the double beta experiment NEMO-3 has been
investigated. New ...methods of data analysis which decrease the background from
the above mentioned contamination are identified. The techniques can also be
applied to other double beta decay experiments capable of measuring
independently the energies of the two electrons.
The double beta decay of 100Mo to the 0^+_1 and 2^+_1 excited states of 100Ru is studied using the NEMO 3 data. After the analysis of 8024 h of data the half-life for the two-neutrino double beta ...decay of 100Mo to the excited 0^+_1 state is measured to be T^(2nu)_1/2 = 5.7^{+1.3}_{-0.9}(stat)+/-0.8(syst)x 10^20 y. The signal-to-background ratio is equal to 3. Information about energy and angular distributions of emitted electrons is also obtained. No evidence for neutrinoless double beta decay to the excited 0^+_1 state has been found. The corresponding half-life limit is T^(0nu)_1/2(0^+ --> 0^+_1) > 8.9 x 10^22 y (at 90% C.L.). The search for the double beta decay to the 2^+_1 excited state has allowed the determination of limits on the half-life for the two neutrino mode T^(2nu)_1/2(0^+ --> 2^+_1) > 1.1 x 10^21 y (at 90% C.L.) and for the neutrinoless mode T^(0nu)_1/2(0^+ --> 2^+_1) > 1.6 x 10^23 y (at 90% C.L.).
The background induced by radioactive impurities of \(^{208}\rm Tl\) and \(^{214}\rm Bi\) in the source of the double beta experiment NEMO-3 has been investigated. New methods of data analysis which ...decrease the background from the above mentioned contamination are identified. The techniques can also be applied to other double beta decay experiments capable of measuring independently the energies of the two electrons.
The present study is based on a sample of 407 775 single muons and 12 559 muon bundles with zenith angles smaller than 60{degree}, observed in the 12.3 m{times}6 m{times}6 m Frejus proton-decay ...detector, at a depth of 4850 hg/cm{sup 2}. The variation of the vertical muon intensity with depth is given. Using a maximum-likelihood method, the muon lateral distribution of underground bundles is investigated as a function of muon multiplicity and zenith angle. The same method yields the true multiplicity distribution at the site depth, corrected for all detection effects.
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