Semi-empirical method of calculation of quenching factors for scintillators is described. It is based on classical Birks formula with the total stopping powers for electrons and ions which are calculated with the ESTAR and SRIM codes, respectively. Method has only one fitting parameter (the Birks factor kB) which can have different values for the same material in different conditions of measurements and data treatment. A hypothesis is used that, once the kB value is obtained by fitting data for particles of one kind and in some energy region (e.g. for a few MeV α particles from internal contamination of a detector), it can be applied to calculate quenching factors for particles of another kind and for another energies (e.g. for low energy nuclear recoils) if all data are measured in the same experimental conditions and are treated in the same way. Applicability of the method is demonstrated on many examples including materials with different mechanisms of scintillation: organic scintillators (solid C 8 H 8 , and liquid C 16 H 18 , C 9 H 12 ); crystal scintillators (pure CdWO 4 , PbWO 4 , ZnWO 4 , CaWO 4 , CeF 3 , and doped CaF 2 (Eu), CsI(Tl), CsI(Na), NaI(Tl)); liquid noble gases (LXe). Estimations of quenching factors for nuclear recoils are also given for some scintillators where experimental data are absent (CdWO 4 , PbWO 4 , CeF 3 , Bi 4 Ge 3 O 12 , LiF, ZnSe).

This paper reports on the development of a technology involving 100 Mo-enriched scintillating bolometers, compatible with the goals of CUPID, a proposed nextgeneration bolometric experiment to search for neutrinoless double-beta decay. Large mass (∼ 1 kg), high optical quality, radiopure 100 Mo-containing zinc and lithium molybdate crystals have been produced and used to develop high performance single detector modules based on 0.2-0.4 kg scintillating bolometers. In particular, the energy resolution of the lithium molybdate detectors near the Q-value of the doublebeta transition of 100 Mo (3034 keV) is 4-6 keV FWHM. The rejection of the α-induced dominant background above 2.6 MeV is better than 8σ . Less than 10 µBq/kg activity of 232 Th ( 228 Th) and 226 Ra in the crystals is ensured by boule recrystallization. The potential of 100 Mo-enriched scintillating bolometers to perform high sensitivity double-beta decay searches has been demonstrated with only 10 kg×d exposure: the two neutrino double-beta decay half-life of 100 Mo has been measured with the up-to-date highest accuracy as T 1/2 = [6.90 ± 0.15(stat.) ± 0.37(syst.)] × 10 18 years. Both crystallization and detector technologies favor lithium molybdate, which has been selected for the ongoing construction of the CUPID-0/Mo demonstrator, containing several kg of 100 Mo.

The computer code DECAY4 is developed to generate initial energy, time and angular distributions of particles emitted in radioactive decays of nuclides and nuclear (atomic) deexcitations. Data for description of nuclear and atomic decay schemes are taken from the ENSDF and EADL database libraries. The examples of use of the DECAY4 code in several underground experiments are described.