Measurement of double beta decay of 100Mo to excited states in the NEMO 3 experiment

The double beta decay of 100Mo to the 0^+_1 and 2^+_1 excited states of 100Ru is studied using the NEMO 3 data. After the analysis of 8024 h of data the half-life for the two-neutrino double beta decay of 100Mo to the excited 0^+_1 state is measured to be T^(2nu)_1/2 = [5.7^{+1.3}_{-0.9}(stat)+/-0.8(syst)]x 10^20 y. The signal-to-background ratio is equal to 3. Information about energy and angular distributions of emitted electrons is also obtained. No evidence for neutrinoless double beta decay to the excited 0^+_1 state has been found. The corresponding half-life limit is T^(0nu)_1/2(0^+ --> 0^+_1) > 8.9 x 10^22 y (at 90% C.L.). The search for the double beta decay to the 2^+_1 excited state has allowed the determination of limits on the half-life for the two neutrino mode T^(2nu)_1/2(0^+ --> 2^+_1) > 1.1 x 10^21 y (at 90% C.L.) and for the neutrinoless mode T^(0nu)_1/2(0^+ --> 2^+_1) > 1.6 x 10^23 y (at 90% C.L.).Comment: 23 pages, 7 figures, 4 tables, submitted to Nucl. Phy

Pulse Shape Analysis and Identification of Multipoint Events in a Large-Volume Proportional Counter in an Experimental Search for 2K Capture Kr-78

A pulse shape analysis algorithm and a method for suppressing the noise component of signals from a large copper proportional counter in the experiment aimed at searching for 2K capture of Kr-78 are described. These signals correspond to a compound event with different numbers of charge clusters due to from primary ionization is formed by these signals. A technique for separating single- and multipoint events and determining the charge in individual clusters is presented. Using the Daubechies wavelets in multiresolutional signal analysis, it is possible to increase the sensitivity and the resolution in extraction of multipoint events in the detector by a factor of 3-4.Comment: 10 pages, 8 figures. submitted to Instruments and Experimental Techniques; ISSN 0020/441

Tunneling from a correlated 2D electron system transverse to a magnetic field

We show that, in a magnetic field parallel to the 2D electron layer, strong electron correlations change the rate of tunneling from the layer exponentially. It results in a specific density dependence of the escape rate. The mechanism is a dynamical Mossbauer-type recoil, in which the Hall momentum of the tunneling electron is partly transferred to the whole electron system, depending on the interrelation between the rate of interelectron momentum exchange and the tunneling duration. We also show that, in a certain temperature range, magnetic field can enhance rather than suppress the tunneling rate. The effect is due to the magnetic field induced energy exchange between the in-plane and out-of-plane motion. Magnetic field can also induce switching between intra-well states from which the system tunnels, and a transition from tunneling to thermal activation. Explicit results are obtained for a Wigner crystal. They are in qualitative and quantitative agreement with the relevant experimental data, with no adjustable parameters.Comment: 16 pages, 9 figure

Limits on different Majoron decay modes of 100^{100}Mo and 82^{82}Se for neutrinoless double beta decays in the NEMO-3 experiment

The NEMO-3 tracking detector is located in the Fr\'ejus Underground Laboratory. It was designed to study double beta decay in a number of different isotopes. Presented here are the experimental half-life limits on the double beta decay process for the isotopes $^{100}$Mo and $^{82}$Se for different Majoron emission modes and limits on the effective neutrino-Majoron coupling constants. In particular, new limits on "ordinary" Majoron (spectral index 1) decay of $^{100}$Mo ($T_{1/2} > 2.7\cdot10^{22}$ y) and $^{82}$Se ($T_{1/2} > 1.5\cdot10^{22}$ y) have been obtained. Corresponding bounds on the Majoron-neutrino coupling constant are $< (0.4-1.9) \cdot 10^{-4}$ and $< (0.66-1.7) \cdot 10^{-4}$.Comment: 23 pages includind 4 figures, to be published in Nuclear Physics

Percolation model for structural phase transitions in Li1−x_{1-x}Hx_xIO3_3 mixed crystals

A percolation model is proposed to explain the structural phase transitions found in Li$_{1-x}$H$_x$IO$_3$ mixed crystals as a function of the concentration parameter $x$. The percolation thresholds are obtained from Monte Carlo simulations on the specific lattices occupied by lithium atoms and hydrogen bonds. The theoretical results strongly suggest that percolating lithium vacancies and hydrogen bonds are indeed responsible for the solid solution observed in the experimental range $0.22 < x < 0.36$.Comment: 4 pages, 2 figure

Technical design and performance of the NEMO3 detector

The development of the NEMO3 detector, which is now running in the Frejus Underground Laboratory (L.S.M. Laboratoire Souterrain de Modane), was begun more than ten years ago. The NEMO3 detector uses a tracking-calorimeter technique in order to investigate double beta decay processes for several isotopes. The technical description of the detector is followed by the presentation of its performance.Comment: Preprint submitted to Nucl. Instrum. Methods A Corresponding author: Corinne Augier ([email protected]

Investigation of hydrogen bond dynamics in NH₄IO₃·2HIO₃ crystal by NQR

The pressure dependence of the quadrupole coupling constant e²Qqzz and electric field gradient tensor asymmetry parameter η have been obtained from the analysis of ¹²⁷l nuclear quadrupole resonance spectra at 77 K. It was shown that the phase transition mechanism in the crystal cannot be described as ordinary ordering of protons in bifurcated hydrogen bonds. The two-stage mechanism of the phase transition is discussed.Барическая зависимость константы квадрупольного взаимодействия и параметра асимметрии η тензора градиента электрического поля были получены из анализа спектров ядерного квадрупольного резонанса на ядрах ¹²⁷l при 77 К. Показано, что механизм фазового перехода в кристалле не может быть описан как обычное упорядочение протонов бифурцированных водородных связей. Обсуждается двухступенчатый механизм фазового перехода.Барична залежність константи квадрупольної взаємодії e²Qqzz та параметра асиметрії і тензора градієнта електричного поля було одержано з аналізу спектрів ядерного квадрупольного резонансу на ядрах ¹²⁷l при 77 К. Показано, що механізм фазового переходу в кристалі не може бути описаний як звичайне упорядкування протонів біфуркованих водневих зв’язків. Обговорюється двоступінчастий механізм фазового переходу

NQR investigation of crystal structure peculiarities of layered Pbₓ₋₁Cdₓl₂ semiconductors

The ¹²⁷l NQR spectra of semiconductor mixed crystals Pbₓ₋₁Cdₓl₂ at 77 K have been investigated. It is shown that at low values of Cdl₂ concentration, the intra-layer symmetry of the basic crystal becomes distorted considerably. This occurs due to formation of the intra-layer mechanical strains which are defined by the size difference between the main and impurity atoms (Pb and Cd, respectively). At x>0.10, intra-layer heterophasic two-dimensional Cdl₂ islets have been shown to be formed. The results are discussed that evidence the formation of amorphous glassy phase of the mixed Pbₓ₋₁Cdₓl₂ crystal at x>0.10.Досліджено спектри ¹²⁷l ЯКР нових напівпровідникових змішаних кристалів Pbₓ₋₁Cdₓl₂ при 77 К. Показано, що при низьких значеннях концентрації Cdl₂ відбувається значне викривлення внутрішньошарової симетрії базового кристала Pb₂ . Це є наслідком формування внутрішньошарових механічних напруг, котрі визначаються різницею розмірів основних та домішкових атомів (відповідно РЬ та Cd). Показано, що при х>0,1 утворюються внутрішньошарові гетерофазні (острівкові) структури Cdl₂. Обговорюються питання відносно утворення склоподібної фази змішаного кристала Pbₓ₋₁Cdₓl₂ при х>0,1.Исследованы спектры ¹²⁷l ЯКР новых полупроводниковых смешанных кристаллов Pbₓ₋₁Cdₓl₂ при 77 К. Показано, что при низких значениях концентрации Cdl₂ происходит существенное искажение внутрислоевой симметрии базового кристалла Pb₂. Это происходит благодаря формированию внутрислоевых механических напряжений, которые определяются различием размеров основных и примесных атомов (соответственно РЬ и Cd). Показано, что при х>0,10 образуются внутрислоевые гетерофазные (островковые) структуры Cdl₂. Обсуждаются результаты, указывающие на образование стеклоподобной аморфной фазы смешанного кристалла Pbₓ₋₁Cdₓl₂ при х>0,10