The Czech Republic and JINR. Long-Term Fruitful

The new emblem (left) and main setup unit (right) of SuperNEMO collaboration
Experiment TGV (Telescope Germanium Vertical) was performed in wide
cooperation with scientists of the Czech Republic — I.Štekl, P.Čermák, F.Mamedov, P.Beneš
(IEAP CTU Prague), A.Kovalík (DLNR JINR Dubna, NPI CAS Řež) [16-21]. Two of them
(I.Štekl, P.Čermák) prepared their PhD theses on the basis of the TGV experimental results.
The low background experiment TGV was performed at the Modane Underground
Laboratory LSM using 13.6 g of 106 Cd (enrichment 75%) and the low background
spectrometer TGV-2, composed of 32 HPGe detectors.
LN2
N2
LN Dewar
TGV‐2
Borated Polyethylene
Cold finger
Pb
Cu
1 m
Signal wires
30
PA
SM
The TGV setup
The purpose of the experiment TGV was the investigation of one of the double beta
decay processes – double electron capture (EC/EC) of 106 Cd. In contrast to the β - β - -decay,
where the two-neutrino mode of the process has been experimentally measured for several
isotopes, other double beta decay processes have never been observed in direct experiments,
neither for two-neutrino nor for neutrinoless modes. The 106 Cd isotope is one of the most
favorable candidates for studying EC/EC decay. The 2νEC/EC decay of 106 Cd is characterized
by emission of only two palladium (Pd) X-rays (~21 keV). The 0νEC/EC resonant decay of
106 106
Cd is expected to 2741.0 keV excited state of Pd and accompanied by emission of γ2741
keV or by γ2229 -γ512 keV cascade.
New limits (at 90% C.L.) on double beta decays of 106 Cd (T1/2(0νEC/EC) > 1.7×10 20 yr
and T1/2(2νEC/EC) > 4.2×10 20 yr) were obtained in the experiment TGV. The latter value is
more than 2 orders of magnitude higher than those obtained in experiments of other groups
and reaches theoretical predictions ranging from 1.0×10 20 yr to 5.5×10 21 yr. The TGV result
for 2νEC/EC of 106 Cd allows one to expect the detection of this rare process in the future.