AbstractThe NEMO-3 results for the double-$$\beta $$ β decay of $$^{150}$$ 150 Nd to the 0$$^+_1$$ 1 + and 2$$^+_1$$ 1 + excited states of $$^{150}$$ 150 Sm are reported. The data recorded during 5.25 year with 36.6 g of the isotope $$^{150}$$ 150 Nd are used in the analysis. The signal of the $$2\nu \beta \beta $$ 2 ν β β transition to the 0$$^+_1$$ 1 + excited state is detected with a statistical significance exceeding 5$$\sigma $$ σ . The half-life is measured to be $$T_{1/2}^{2\nu \beta \beta }(0^+_1) = \left[ 1.11 ^{+0.19}_{-0.14} \,\left( \hbox {stat}\right) ^{+0.17}_{-0.15}\,\left( \hbox {syst}\right) \right] \times 10^{20}$$ T 1 / 2 2 ν β β ( 0 1 + ) = 1 . 11 - 0.14 + 0.19 stat - 0.15 + 0.17 syst × 10 20 year, which is the most precise value that has been measured to date. 90% confidence-level limits are set for the other decay modes. For the $$2\nu \beta \beta $$ 2 ν β β decay to the 2$$^+_1$$ 1 + level the limit is $$T^{2\nu \beta \beta }_{1/2}(2^+_1) > 2.42 \times 10^{20}~\hbox {year}$$ T 1 / 2 2 ν β β ( 2 1 + ) > 2.42 × 10 20 year . The limits on the $$0\nu \beta \beta $$ 0 ν β β decay to the 0$$^+_1$$ 1 + and 2$$^+_1$$ 1 + levels of $$^{150}$$ 150 Sm are significantly improved to $$T_{1/2}^{0\nu \beta \beta }(0^+_1) > 1.36 \times 10^{22}~\hbox {year}$$ T 1 / 2 0 ν β β ( 0 1 + ) > 1.36 × 10 22 year and $$T_{1/2}^{0\nu \beta \beta }(2^+_1) > 1.26 \times 10^{22}~\hbox {year}$$ T 1 / 2 0 ν β β ( 2 1 + ) > 1.26 × 10 22 year .

The positron annihilation lifetimes were measured using a 48V positron source in noncentrosymmetric cubic single crystals of CoSi, FeSi and MnSi. The following lifetimes were determined from the positron annihilation time spectra: 168(1) ps for CoSi, 114(1) ps for FeSi and 111(1) ps for MnSi. For single-crystal CoSi, the positron annihilation lifetime was also determined with a 22Na positron source. For CoSi, the lifetimes obtained from different positron sources are consistent. The differences in the positron annihilation lifetimes in MnSi and FeSi, on the one hand, and in the Weyl semimetal CoSi, on the other hand, are possibly caused by the formation of a positron + electron bound state (positronium).

The new metastable high-pressure high-temperature synthesized hexagonal Laves phase compound YbZn2 was investigated. The unit cell parameters, low-temperature Sommerfeld coefficient and Debye temperature were determined. X-ray absorption studies and calculations based on dynamical mean-field theory (DMFT) showed the intermediate valence behavior of YbZn2 with mean Yb valence about 2.55. The values of hyperfine electric parameters in Zn (6h) sites were determined by means of 111Cd-time differential perturbed angular correlations and theoretical density functional calculations. DMFT calculations showed that the main contribution to the electron density of states at the Fermi level is due to Yb 4f electrons, while Zn spd electrons lie much lower in energy.

Hyperfine interactions in the Bi1−xLaxFeO3 ferrites (where x = 0.0225, 0.075, 0.9) have been studied by means of 57Fe Mössbauer spectroscopy and 140Ce time differential perturbed angular γ–γ correlation methods. The information about the line shift δ, the lattice εlat and the magnetic εmag contributions to the quadrupole shift ε, isotropic His and anisotropic Han contributions to the hyperfine magnetic field Hhf on 57Fe nuclei, anharmonicity parameter m, distribution of the hyperfine magnetic field p(Hhf), and supertransferred hyperfine magnetic fields on 140Ce probe nuclei were obtained. In all studied compounds, the Fe ions are in a high-spin trivalent state. In the compounds with x = 0.0225 and 0.075 spatially modulated cycloidal magnetic structures exist. It was found that the sign of the effective constant of magnetic anisotropy Keff changes with the variation of x from 0.0225 to 0.075. The substitution of Bi by La increases the value of the hyperfine magnetic field on 57Fe nuclei from 494 kOe in Bi0.9775La0.0225FeO3 to 520 kOe in Bi0.1La0.9FeO3, i.e. by 26 kOe, while the corresponding supertransferred hyperfine magnetic field on 140Ce probe nuclei decreases.

The III phase of experiment TGV-2 to search for β+β+, β+EC, EC/EC decay of 106Cd was performed at the Modane underground laboratory (LSM, France, 4800 m w.e.). 16 foils (∼23.2 g) of enriched 106Cd were measured using the 32-detector low background HPGe spectrometer TGV-2 during 42500 h. New limit on 2νEC/EC decay of 106Cd to the ground 0+ state of 106Pd - T1/2 > 7.2 × 1020 y at 90% C.L was obtained. The limits on 2νβ+β+, 2νβ+EC decay of 106Cd, and 2νECEC decay of 106Cd to excited states of 106Pd were significantly improved in comparison with previous phase II of the TGV-2 experiment.

A novel metastable phase of DyGe2.85 synthesised in the AuCu3-structure under high pressure, has been studied by means of the magnetic susceptibility and electrical resistivity measurements (under the pressure P≤3.1 GPa), neutron powder diffraction and time-differential γ-γ perturbed angular correlations (TDPAC) using 111Cd nuclear probes. Two distinct phase transitions have been found in this compound as the temperature is lowered. We assign the first transition occurring at the temperature TCDW=80 K with charge density wave formation and the second transition at TN≈18 K with an antiferromagnetic spiral ordering of Dy magnetic moments, and discuss a close relationship between them.

The principal aspects of 44Ti application in time-differential γγ perturbed-angular-correlation method (TDPAC) for studying condensed matter are discussed. In the presented spectrometer modification, the efficiency of 44Ti application can be considerably increased by using thin NaI scintillator crystals. Promising techniques for 44Ti production and a method for synthesizing samples are described. Examples of TDPAC studies of titanium (rutile TiO2) and scandium (Sc2O3) oxide samples are shown.

We have studied the C14 hexagonal Laves phase of YbAg$_2$ at normal conditions and under external pressure up to 19 GPa by the time-differential perturbed angular $\gamma-\gamma$ correlation spectroscopy (TDPAC) using $^{111}$Cd probe nuclei. Under pressure the valence of Yb undergoes a two stage transition from 2.8 to 3. The two stage scenario is characterized by two distinct quadrupole frequencies of $^{111}$Cd probes in silver sublattice, monotonically increasing with pressure and saturating at 8 and 16 GPa. Our experimental data are compared with the density functional studies of the electron band structure of YbAg$_2$, whose results are used for discussion and interpretation of these experiments. We have found that there are two different electric field gradients at inequivalent silver sites and that $4d$-states of silver participate in metal bonding, allowing for the formation of the hexagonal Laves phase.

Temperature dependencies of the electrical resistivity, magnetic susceptibility, and heat capacity have been obtained in the cubic phase of TbGe2.85 (the AuCu3 structure), synthesized at high pressure. The macroscopic measurements indicate that a charge density wave is formed below 145 K and an antiferromagnetic ordering is realized below 19 K. Hyperfine interaction data obtained with the time differential perturbed angular correlation method with Cd-111 probes inserted in the TbGe2.85 lattice suggest that the charge density wave is incommensurate in the temperature region 19-145 K, but becomes commensurate below 19 K. The neutron diffraction reveals a complex antiferromagnetic spiral structure in the magnetically ordered phase. We discuss relations between the charge density wave and helical ordering in TbGe2.85 and TbPd3.

A new experimental run of searching for EC/EC decay of Cd-106 was performed at the Modane underground laboratory (4800 m w.e.) using the TGV-2 spectrometer and similar to 23.2 g Cd-106 with enrichment of 99.57%. The limit on 2 nu EC/EC decay of Cd-106 -T-1/2(2 nu EC/EC) > 3.1x10(20) y, at 90% C. L was obtained from the preliminary calculation of experimental data accumulated for 7018 h of measurement. The limits on the resonance neutrino-less double electron capture decay of Cd-106 were obtained from the measurement of similar to 23.2 g of Cd-106 with the low-background HPGe spectrometer OBELIX lasted 395 h -T-1/2(KL, 2741 keV) > 0.9x10(20) y and T-1/2(KK, 2718 keV) > 1.4x10(20) y at 90% C.L.

A new experiment devoted to searches for double electron capture in 106Cd decay is being performed at the Modane underground laboratory (4800 mwe) with the 32-detector TGV-2 spectrometer. The limit T 1/2(2νEC/EC) > 2.0×1020 yr at a 90%confidence level (C.L.) was obtained from a preliminary analysis of data obtained over 2250 h of measurements with about 23.2 g sample enriched in the isotope 106Cd to 99.57%. The limits T 1/2(KL, 2741 keV) > 0.9 × 1020 yr and T 1/2(KK, 2718 keV) ≫ 1.4 × 1020 yr at a 90% C.L. on the neutrinoless decay of 106Cd were obtained from measurements performed with the Obelix low-background spectrometer from high-purity germanium (HPGe spectrometer) for a sample of mass about 23.2 g enriched in the isotope 106Cd.

Time differential perturbed gamma gamma angular correlation spectroscopy on Cd-111 nuclei probes inserted in ZrZn1.9 is used to measure the magnetic hyperfine fields at Zr and Zn sites and the electric-field gradient V-zz at Zn sites as a function of temperature at various pressures and as a function of pressure at the temperature 4 K. Our data indicate that the local magnetic moment of Zr in the magnetically ordered state is substantially larger than its value obtained from the macroscopic measurements. The transformation between paramagnetic and magnetically ordered states is considered as a fluctuation-induced first-order transition. We conclude that ZrZn2 is not a simple ferromagnet and discuss a possible type of its magnetic ordering.

A new technology for diamond detection in kimberlite based on the tagged neutron method is proposed. The results of experimental researches on irradiation of kimberlite samples with 14.1-MeV tagged neutrons are discussed. The source of the tagged neutron flux is a portable neutron generator with a built-in 64-pixel silicon alpha-detector with double-sided stripped readout. Characteristic gamma rays resulting from inelastic neutron scattering on nuclei of elements included in the composition of kimberlite are registered by six gamma-detectors based on BGO crystals. The criterion for diamond presence in kimberlite is an increased carbon concentration within a certain volume of the kimberlite sample.

The results of using a stationary setup for detecting and identifying explosives using the tagged neutron method (or associated particle imaging (API) method) have been presented. The source of 14.1-MeV tagged neutron beams is an ING-27 portable neutron generator made by VNIIA (Moscow). It contains an embedded 64-pixel silicon α detector with double-sided strip readout developed by the Joint Institute for Nuclear Research (JINR). The setup was tested for the identification of more than 30 explosives.

A new multi-detector spectrometer based on Timepix silicon pixel detectors is developed to investigate the 2ν EC / EC decay of 106 Cd. The detectors have high efficiency for recording two low-energy KX radiation quanta emitted during 2ν EC / EC decay. The ability of pixel detector to identify α, β, and γ particles and precisely localize them allows us to suppress background radiation efficiently. Test measurements for an assembly of two pixel detectors in an underground laboratory were performed. They showed the possibility of using them in the search for the 2ν EC / EC decay of 106 Cd.

Gamma detectors based on BGO crystals were designed and developed at the Joint Institute for Nuclear Research. These detectors are used in explosives and narcotics detection systems. Key specifications and design features of the detectors are presented. A software temperature-compensation method that makes it possible to stabilize the gamma detector response and operate the detector in a temperature range from −20 to 50°C is described.

The tagged neutron technique (TNT) is analyzed in terms of its application for detecting dangerous substances hidden in underwater objects. The use of the technique for solving these problems is justified theoretically. The main characteristics of a prototype detector aimed at detecting explosives in a water environment are determined.