Preliminary measurements in 2008 and purification
At the first stage of the experiment, sample of metallic Mo powder (99.5% of 100Mo) was measured. Mass of the sample was 1009 g. Data collected during 1927 h gave indication on the existence of the peak at 540 keV (with area corresponding to T1/2 ~ 3×1020 yr), while at the energy of 591 keV where the second peak should be located, there was no significant statistical evidence of its existence. Only limit on half life has been derived as T1/2 > 6×1020 yr at 90% C.L..
In a process of chemical purification, 100Mo metal was transformed to molybdenum oxide (100MoO3) with mass of 1199 g. Purification procedure effectively removed pollution by 40K (counting rate in the peak of 1461 keV with the 100MoO3 sample was 14 times lower than that with the 100Mo sample), 137Cs (6 times lower rate in 662 keV peak), and lead also to reduction in U/Th contamination.
The obtained sample of 100MoO3 was measured for 18120 h. The data acquisition system allowed to accumulate the energy spectra of the individual detectors and to take into account the coincidence between the detectors during the data analysis as well. The statistics was accumulated in 136 independent runs. The energy calibration was performed before and after the measurements with the 100MoO3 sample.