Search

A long-term measurement was conducted to search for α, double-α and double-β decays with γ quanta emission in naturally occurring osmium isotopes. This study took advantage of two ultra-low background HPGe detectors and one ultra-low background BEGe detector at the Gran Sasso National Laboratory (LNGS) of the INFN. Over almost 5 years of data were taken using high-purity osmium samples of approximately 173 g. The half-life limits set for α decays of 184Os to the first 2+ 103.6 keV excited level of 180W (T1/2 ≥ 9.3 × 1015 yr) and of 186Os to the first 2+ 100.1 keV of 182W (T1/2 ≥ 4.8 × 1017 yr) exceed substantially the present theoretical predictions that are at level of T1/2 ~ (0.6–3) × 1015 yr for 184Os and T1/2 ~ (0.3–2) × 1017 yr for 186Os. New half-life limits on the 2EC and ECβ+ decay of 184Os to the ground and excited levels of 184W were set at level of T1/2 > 1016–1017 yr; a lower limit on the 2β– decay of 192Os to the 2+ 316.5 keV excited level of 192Pt was estimated as T1/2 ≥ 6.1 × 1020 yr. The half-life limits for 2α decay of 189Os and 192Os were set for the first time at level of T1/2 > 1020 yr. [ABSTRACT FROM AUTHOR]

From 7 naturally occurring Nd isotopes, 5 are unstable in relation to α decay. If an excited level of the daughter nucleus is populated, or the daughter nucleus is unstable, γ quanta can be emitted. We used an ultra-low background spectrometry system with 4 high purity germanium (HPGe) detectors (about 225 cm3 volume each) to search for such decays using a highly purified Nd-containing sample with mass of 2.381 kg. Measurements were performed at the INFN Gran Sasso underground laboratory (with an overburden of about 3600 m w.e.) during 51,237 h. Half-life limits for α decays of 143Nd and 145Nd were determined to be T1/2(143Nd) > 1.1 × 1020 year and T1/2(145Nd) > 2.7 × 1019 year at 90% C.L. This is an increase of three and two orders of magnitude, respectively, compared with the most restrictive values currently given in literature. A limit for α decay of 144Nd to the excited level of 140Ce with Eexc = 1596.2 keV was determined for the first time as T1/2(144Nd → 140Ce*) > 9.3 × 1020 year. Restriction for the α decay of 146Nd to the excited level of 142Ce with Eexc = 641.3 keV was increased by 3 orders of magnitude to T1/2(146Nd → 142Ce*) > 1.4 × 1021 year. For α and 2α decays of 148Nd, first T1/2 limits were set as 4.2 × 1018 year and 2.1 × 1020 year, respectively. [ABSTRACT FROM AUTHOR]

Low background anisotropic detectors can offer a unique way to study those dark matter (DM) candidate particles able to induce nuclear recoils through the directionality technique. This approach is based on studying the correlation between the nuclear recoils' direction and the Earth motion in the galactic rest frame. Thanks to the anisotropic features of such detectors, a signal, induced by the DM candidates, is expected to change with a particular behaviour as a function of the sidereal time. The ZnWO has unique features and it is an excellent candidate for the purposes. Both the light output and the scintillation pulse shape depend on the impinging direction of heavy particles (p, , nuclear recoils, etc.) with respect to the crystal axes and can supply two independent modes to study the directionality and to discriminate the radiation (that does not give rise to any anisotropic effects). In this work, the measurements to study the anisotropic response of a ZnWO scintillation detector to particles and to nuclear recoils, induced by neutron scattering, are briefly summarised. [ABSTRACT FROM AUTHOR]

A search for double-beta decay of 190 Pt and 198 Pt with emission of γ -ray quanta was realized at the HADES underground laboratory with a 148 g platinum sample measured by two ultralow-background HPGe detectors over 8946 h. The isotopic composition of the platinum sample has been measured with high precision using inductively coupled plasma mass spectrometry. New lower limits for the half-lives of 190 Pt relative to different channels and modes of the decays were set on the level of lim T 1 / 2 ∼ 10 14 – 10 16 year. A possible exact resonant 0 ν K N transition to the 1,2 1326.9 keV level of 190 Os is limited for the first time as T 1 / 2 ≥ 2.5 × 10 16 year. A new lower limit on the double-beta decay of 198 Pt to the first excited level of 198 Hg was set as T 1 / 2 ≥ 3.2 × 10 19 year, one order of magnitude higher than the limit obtained in the previous experiment. [ABSTRACT FROM AUTHOR]

Abstract—The effect of charge-carrier drift on the plasmon excitation modes (plasmons) in a Dirac electron liquid in graphene with a displaced Fermi level is considered. The dispersion relations for plasmons are obtained using the electromagnetic approach and hydrodynamic description of the electron liquid. Damped and amplified plasmon eigenmodes are studied numerically depending on the relationship of the magnitudes and directions of the direct electrical current and the plasmon phase velocity. [ABSTRACT FROM AUTHOR]

The half-life of 212 Po was measured with the highest up-to-date accuracy as T 1 / 2 = 295.1 (4) ns by using thorium-loaded liquid scintillator. [ABSTRACT FROM AUTHOR]

Cadmium-116 is one of the favorable candidates for neutrinoless double-beta decay ( 0 ν β β ) searches from both theoretical and experimental points of view, in particular thanks to the high energy of the decay (2813.49 keV), the possibility of the industrial enrichment in 116 Cd and its use in the well-established production of cadmium tungstate crystal scintillators. In this work, we present low-temperature tests of two 0.6 kg 116 CdWO 4 crystals enriched in 116 Cd to 82 % as scintillating bolometers. These detectors were operated underground, with one at the Laboratoire Souterrain de Modane (LSM) in France and the second at the Laboratorio Subterraneo de Canfranc (LSC) in Spain. The two crystals are coupled to bolometric Ge light detectors in order to register the scintillation light. The double readout of heat and scintillation enables reduction in the background in the region of interest by discriminating between different populations of particles. The main goal of these tests is the study of the crystals' radiopurity and the detectors' performance. The achieved results are extremely promising, in particular, the detectors demonstrate a high energy resolution (11–16 keV FWHM at 2615 keV) and a high-efficiency discrimination of the alpha background ( ∼ 20 σ ). These results, achieved for the first time with large mass enriched 116 CdWO 4 crystals, demonstrate prospects of the bolometric technology for high-sensitivity searches of 116 Cd 0 ν β β decay. [ABSTRACT FROM AUTHOR]

Anisotropic scintillators can offer a unique possibility to exploit the so-called directionality approach in order to investigate the presence of those Dark Matter (DM) candidates inducing nuclear recoils. In fact, their use can overcome the difficulty of detecting extremely short nuclear recoil traces. In this paper we present recent measurements performed on the anisotropic response of a ZnWO 4 crystal scintillator to nuclear recoils, in the framework of the ADAMO project. The anisotropic features of the ZnWO 4 crystal scintillators were initially measured with α particles; those results have been also confirmed by the additional measurements presented here. The experimental nuclear recoil data were obtained by using a neutron generator at ENEA-CASACCIA and neutron detectors to tag the scattered neutrons; in particular, the quenching factor values for nuclear recoils along different crystallographic axes have been determined for three different neutron scattering angles (i.e. nuclear recoils energies). From these measurements, the anisotropy of the light response for nuclear recoils in the ZnWO 4 crystal scintillator has been determined at 5.4 standard deviations. [ABSTRACT FROM AUTHOR]

The first ever search for α decays to the first excited state in Yb was performed for six isotopes of hafnium (174, 176, 177, 178, 179, 180) using a high purity Hf sample of natural isotopic abundance with a mass of 179.8 g. For 179 Hf, also α decay to the ground state of 175 Yb was searched for thanks to the β -instability of the daughter nuclide 175 Yb. The measurements were conducted using an ultra-low-background HPGe-detector system located 225 m underground. After 75 days of data taking no decays were detected but lower bounds for the half-lives of the decays were derived on the level of lim T 1 / 2 ∼ 10 15 - 10 18 a. The decay with the shortest half-life based on theoretical calculation is the decay of 174 Hf to the first 2 + 84.3 keV excited level of 170 Yb. The experimental lower bound was found to be T 1 / 2 ≥ 3.3 × 10 15 a. [ABSTRACT FROM AUTHOR]

The first direct search for the double electron capture ( 2 ε ) and the electron capture with positron emission ( ε β + ) in 144Sm to the ground state and to the excited levels of 144Nd was realized by measuring --over 1899h-- a 342g sample of highly purified samarium oxide (Sm2O3) with the ultra-low background HP-Ge γ spectrometer GeCris (465cm3) at the STELLA facility of the Gran Sasso National Laboratory (LNGS). No effect was observed and half-life limits were estimated at the level of T 1 / 2 ∼ (0. 1 - 1. 3) × 10 20 yr (90% C.L.). Moreover, for the first time half-life limits of the double beta ( 2 β - ) decay of 154Sm to several excited levels of 154Gd have been set; they are at the level of T 1 / 2 ∼ (0. 06 - 8) × 10 20 yr (90% C.L.). [ABSTRACT FROM AUTHOR]

The spectrum of amplification of terahertz radiation in a structured active graphene bilayer consisting of two identical periodic graphene microribbon arrays separated by a thin dielectric barrier layer is theoretically investigated. The system supports optical and acoustic plasmon modes. The resonant frequencies of the optical and acoustic modes change oppositely with the dielectric-layer thickness, which allows plasmon-mode anticrossing. It is shown that the investigated graphene structure is characterized by a strong plasmon response and giant terahertz-radiation amplification at plasma resonance frequencies in the vicinity of the anticrossing between the optical and acoustic plasmon modes at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: The dependence of the plasmon terahertz resonant frequency in the generation mode on the quasi-Fermi energy in the active (ungated) region of graphene with an inverse charge carrier population and on the Fermi energy in the gated p- and n-type regions in a periodic p-i-n structure based on graphene with injection pumping is theoretically investigated. It is shown that electrically frequency-tunable nanoscale plasmon graphene amplifiers and generators operating in a broad terahertz frequency range at room temperature can be designed. [ABSTRACT FROM AUTHOR]

The absorption/amplification spectrum of terahertz radiation in inhomogeneous graphene ( n-i-p-i structure) with a periodic dual metal grating is theoretically investigated. It is shown that the amplification of terahertz radiation sharply increases at the plasmon-resonance frequency, when losses due to electron scattering and emission are balanced by the plasmon gain (related to the stimulated radiative interband recombination of electron-hole pairs in the inverted region of graphene). [ABSTRACT FROM AUTHOR]

A search for double electron capture ( $2\varepsilon$ ), electron capture with positron emission ( $\varepsilon\beta^{+}$ ), and double positron emission ( $2\beta^{+}$ ) in Ce and Ce was realized with a 465 cm ultra-low background HP Ge $ \gamma$ spectrometer over 2299 h at the Gran Sasso underground laboratory. A 627 g sample of cerium oxide deeply purified by liquid-liquid extraction method was used as a source of $\gamma$ quanta expected in double $\beta$ decay of the cerium isotopes. New improved half-life limits were set on different modes and channels of double $\beta$ decay of Ce and Ce at the level of $T_{1/2} > 10^{17} - 10^{18}$ yr. [ABSTRACT FROM AUTHOR]

The terahertz absorption spectrum in a periodic array of graphene nanoribbons located on the surface of a dielectric substrate with a high refractive index (terahertz prism) is studied theoretically. The total absorption of terahertz radiation is shown to occur in the regime of total internal reflection of the terahertz wave from the periodic array of graphene nanoribbons, at the frequencies of plasma oscillations in graphene, in a wide range of incidence angles of the external terahertz wave even at room temperature. [ABSTRACT FROM AUTHOR]

It is shown theoretically that stimulated generation of terahertz radiation by plasmons in graphene with a planar distributed Bragg resonator is possible at two different frequencies for each plasmon mode. This behavior may be attributed to the superradiance of the collective plasmon mode, which is associated with superlinear increase in the radiative damping of the plasmons with increase in pumping power. As a result, the curves of the radiative damping and the plasmon gain as a function of the pumping power intersect at two points corresponding to different generation conditions. [ABSTRACT FROM AUTHOR]

An Erratum to this paper has been published: https://doi.org/10.3103/S0027134922050137 [ABSTRACT FROM AUTHOR]

A new type of ultra-broadband near-field antenna for terahertz frequencies is proposed. This antenna is a short-period planar metal array. It is theoretically shown that irradiation of the short-period array antenna by a plane homogeneous terahertz waves excite a highly inhomogeneous near electric field near the metal array. In this case, the amplitude of the excited inhomogeneous near electric field is almost independent of frequency in the entire terahertz frequency range. The excitation of plasma oscillations in a two-dimensional electron system using the antenna under study is numerically simulated in the resonant and non-resonant plasmonic response modes. This type of antenna can be used for developing ultra-broadband plasmonic detectors of terahertz radiation. [ABSTRACT FROM AUTHOR]

The radioactive contamination of a BaF scintillation crystal with mass of 1.714 kg was measured over 101 hours in the low-background DAMA/R&D set-up deep underground (3600 m w.e.) at the Gran Sasso National Laboratories of INFN (LNGS, Italy). The half-life of Po (present in the crystal scintillator due to contamination by radium) was measured as $ T_{1/2}({}^{212}Po)$ = 298.8±0.8( stat.)±1.4( syst.) ns by the analysis of the events' pulse profiles. The Rn nuclide is known as 100% decaying via the emission of the $ \alpha$ particle with T = 3.82 d; however, its $ \beta$ decay is also energetically allowed with $ Q_{\beta}=24\pm 21$ keV. Search for decay chains of events with specific pulse shapes characteristic for $ \alpha$ or for $ \beta/\gamma$ signals and with known energies and time differences allowed us to set, for the first time, the limit on the branching ratio of Rn relatively to $ \beta$ decay as $ B_{\beta} < 0.13$ % at 90% C.L. (equivalent to limit on partial half-life $ T_{1/2}^{\beta}> 8.0$ y). The half-life limits of Pb, Rn and Ra relatively to 2 $ \beta$ decays are also improved in comparison with the earlier results. [ABSTRACT FROM AUTHOR]

The theory of the plasmon resonance excitation in the plasmonic-crystal structure on a dielectric substrate is presented. The effect of the plasmon resonance intensity oscillation as a function of the substrate thickness is predicted. It is shown that the enhancement of the plasmon resonance intensity occurs in a broad terahertz frequency range in the structure on a membrane substrate. [ABSTRACT FROM AUTHOR]

It is shown that strong plasmon resonances can be excited in the totally gated two-dimensional electron gas with lateral contacts by incoming electromagnetic wave. In such a structure, the plasmon resonance linewidth shrinks down to the minimal theoretical value determined by the electron scattering in two-dimensional electron system. [ABSTRACT FROM AUTHOR]

A search for double- $ \beta$ processes in 96Ru and 104Ru was realized in the underground Gran Sasso National Laboratories of the INFN (Italy) with the help of ultra-low background HPGe $ \gamma$ spectrometry. After 158h of data taking with 473g ruthenium sample, new improved limits on double-beta processes in 96Ru have been established on the level of 1018-1019yr. For the first time the double-beta decay of 104Ru to the 2+ 1 excited level of 104Pd has been restricted as T1/2 > 3.5×1019 yr. [ABSTRACT FROM AUTHOR]