Double-beta decay: Present status

The present status of double-beta-decay experiments (including the search for 2β ⁺, ECβ ⁺, and ECEC processes) are reviewed. The results of the most sensitive experiments are discussed. Average and recommended half-life values for two-neutrino double-beta decay are presented. Conservative upper limits on effective Majorana neutrino mass and the coupling constant of the Majoron to the neutrino are established as 〈m _ν 〉 < 0.75 eV and 〈g _ee 〉 < 1.9 × 10⁻⁴, respectively. Proposals for future double-betadecay experiments with a sensitivity for the 〈m _ν 〉 at the level of 0.01–0.1 eV are considered.     

Double-beta decay in gauge theories

Neutrinoless double-beta decay is a very important process both from the particle and nuclear physics point of view. From the elementary particle point of view, it pops up in almost every model, giving rise among others to the following mechanisms: (a) the traditional contributions like the light neutrino mass mechanism as well as the j _L –j _R leptonic interference (λ and η terms), (b) the exotic R-parity-violating supersymmetric (SUSY) contributions. Thus, its observation will severely constrain the existing models and will signal that the neutrinos are massive Majorana particles. From the nuclear physics point of view, it is challenging, because (1) the nuclei, which can undergo double-beta decay, have complicated nuclear structure; (2) the energetically allowed transitions are suppressed (exhaust a small part of all the strength); (3) since in some mechanisms the intermediate particles are very heavy one must cope with the short distance behavior of the transition operators (thus novel effects, like the double-beta decay of pions in flight between nucleons, have to be considered; in SUSY models, this mechanism is more important than the standard two-nucleon mechanism; and (4) the intermediate momenta involved are quite high (about 100 MeV/c). Thus one has to take into account possible momentum-dependent terms of the nucleon current, like modification of the axial current due to PCAC, weak magnetism terms, etc. We find that, for the mass mechanism, such modifications of the nucleon current for light neutrinos reduce the nuclear matrix elements by about 25%, almost regardless of the nuclear model. In the case of heavy neutrino, the effect is much larger and model-dependent. Taking the above effects into account, the needed nuclear matrix elements have been obtained for all the experimentally interesting nuclei A=76, 82, 96, 100, 116, 128, 130, 136, and 150. Then, using the best presently available experimental limits on the half-life of the 0νββ decay, we have extracted new limits on the various lepton-violating parameters. In particular, we find 〈m _ν〉 < 0.3 eV/c ², and, for reasonable choices of the parameters of SUSY models in the allowed SUSY parameter space, we get a stringent limit on the R-parity-violating parameter λ′₁₁₁<4.0×10^?4.     

Double-beta decay and neutrino mass

Recent achievements in the study of double-beta (ββ) decay are presented. We discuss the potential of this process to search, beyond Standard Model physics, for the QRPA-based methods used for the calculation of the relevant nuclear matrix elements and the derivation of the neutrino mass from both ββ-decay calculations and neutrino oscillation and cosmological data. The key position of the ββ-decay experiments in resolving the neutrino absolute mass is highlighted.     

Nearly mass-degenerate Majorana neutrinos: Double-beta decay and neutrino oscillations

Assuming equal tree-level Majorana masses for the standard-model neutrinos, either from the canonical seesaw mechanism or from a heavy scalar triplet, I discuss how their radiative splitting may be relevant to neutrinoless double-beta decay and neutrino oscillations.     

Double-beta decay of 48Ca in the TGV experiment

The low-background, high-sensitivity Ge multidetector spectrometer TGV is used to study the double-beta decay of ⁴⁸Ca. Additional suppression of the recorded background is achieved with neutron shielding and a method for distinguishing β particles from γ rays by detector-pulse rise time. The estimates T _1/2 ^γγ2ν = (4.2 ± 2.4) × 10¹⁹ yr and T _1/2 ^γγ0ν > 1.5 × 10²¹ yr (at a 90% C.L.) for the double-beta decay of ⁴⁸Ca are obtained.     

Double-beta decay to the excited states (Experiment)

The brief review on the decay to excited states of daughter nuclei is performed. New positive result of experiments with ¹⁰⁰Mo for transition to 0⁺ excited state in ¹⁰⁰Ru are presented.     

Double-beta decay with the NEMO experiment: Status of the NEMO 3 detector

The NEMO 3 detector, devoted to search for the neutrinoless double-beta decay, will be able to reach the sensitivity to 〈m _ν〉 of the order of 0.1 eV. The expected performance of the detector for signal detection and both internal and external background rejection is presented. A specific study of the neutron-induced background is given. The NEMO Collaboration is now mounting the detector in the Fréjus underground laboratory.     

Double-beta decay Q values of Cd and Te

The Q values of the ¹¹⁶Cd and ¹³⁰Te double-beta decaying nuclei were determined by using a Penning trap mass spectrometer. The new atomic mass difference between ¹¹⁶Cd and ¹¹⁶Sn of 2813.50(13) keV differs by 4.5 keV and is 30 times more precise than the previous value of 2809(4) keV. The new value for ¹³⁰Te, 2526.97(23) keV is close to the Canadian Penning trap value of 2527.01 ± 0.32 keV (Scielzo et al., 2009) [1], but differs from the Florida State University trap value of 2527.518 ± 0.013 keV (Redshaw et al., 2009) [2] by 0.55 keV (2σ). These values are sufficiently precise for ongoing neutrinoless double-beta decay searches in ¹¹⁶Cd and ¹³⁰Te. Hence, our Q values were used to compute accurate phase-space integrals for these double-beta decay nuclei. In addition, experimental two-neutrino double-beta decay nuclear matrix elements were determined and compared with the theoretical values. The neutrinoless double-beta decay half-lives for these nuclei were estimated using our precise phase-space integrals and considering the range of the best available matrix elements values.     

Recent advances in studies of magnetically soft amorphous microwires

In this paper, we present the giant magneto-impedance (GMI) effect (real part of longitudinal impedance, Z, and of the off-diagonal impedance) and hysteretic magnetic properties of amorphous glass-coated microwires with different compositions possessing nearly zero, positive and negative magnetostriction constant and metallic nucleus diameter ranging between 6 and 16 μm. Enhanced soft magnetic properties (low coercivity of about 4 A/m) and high-GMI effect have been observed in Co-rich microwires with vanishing magnetostriction constant. The magnetic anisotropy field of these microwires depends on the ratio between metallic diameter, d and total microwires diameter, D. Stress-sensitive magnetic properties have been obtained in Fe-rich microwires after stress annealing: hysteresis loop stress-annealed (SA) microwires drastically changes under applied stress. A variety of hysteresis loops with different hysteresis loops can be obtained in Fe-rich microwires changing the conditions (time and/or temperature) of the stress annealing. The obtained results allow us to tailor the microwire magnetic properties for magnetic sensors applications through selection of their composition and/or geometry and by thermal treatment.     

我国超声波疗法实验研究和临床应用的近期进展

本文通过对第四届全国超声治疗学术会议（１９９７年１０月１７－２１日于南京）论文的综合介绍,显示我国超声波疗法在实验研究与临床应用方面所取得的成就。     

Recent advances in optodynamics

The term optodynamics has been introduced to describe a wide range of optically induced dynamic phenomena, which play an important role in laser–material processes as well as in laser-assisted medical applications. In view of laser material processing, a laser beam is not only considered as a tool, but also as a generator of information about the material’s transformation. The information is retained and conveyed by different kinds of optically induced mechanical motions, such as shock, acoustic and ultrasound waves, and cavitation bubbles. Special emphasis is given to the recent investigations of linear momentum transformation during the laser–material interaction and to the on-line monitoring of laser material processing.     

Recent experimental studies on 252Cf ternary fission

The rare ternary fission (TF) process was hitherto studied mainly by inclusive measurements of the energies and fractional yields of the light charged particles (LCPs) from fission, or by experiments on the angular and energy correlation between LCPs and fission fragments (FF). The present article briefly describes a series of recent correlation measurements on ²⁵²Cf(sf) TF that include either the registration of neutrons and γ rays with LCPs and FFs, or the coincident registration of two LCPs. The population of excited states in LCPs has been identified, as well as the formation of neutron-unstable nuclei as short-lived intermediated LCPs, the sequential decay of particle-unstable LCP species into charged particle pairs, and “quaternary” fission with the emission of two charged particles right at scission.     

Proton conducting ceramics: Recent advances

A general introduction into the field of high temperature ceramic proton conductors (HTPCs) is given. Results of two typical studies involving these HTPCs are discussed. In the first part a study of the processes occurring during water vapor exposure of bulk ceramic proton conductors, BaCe_0.9Y_0.1O_2.95 (BCY10) and BaCe_0.8Y_0.2O_2.9 (BCY20), is presented. A disc of a HTPC was connected to a mass spectrometer in a vacuum system permitting the identification of the species crossing the ceramic-vacuum interface. Exposing the other side of the sample to D₂O led to a strong signal of D₂O⁺ after a certain lag time. From these lag times the tracer diffusivity of hydrogen could be determined as a function of temperature. The permeation of steam consisted of two components: a fast component, given by the diffusivities of deuterons (protons), and a slow component, assigned to chemical diffusion of deuterons (protons) coupled to oxygen vacancies. The data also suggested the possibility of participation of even more complex defects in this chemical diffusion. Dilatometry measurements of different specimens of BCY10 and BCY20 also revealed quite clearly this two-phase pattern during protonation. Diffusion measurements on protonic ceramic membranes using H ₂ ¹⁸ O permitted the determination of the tracer diffusivity of oxygen. All of the above measurements were interpreted in the light of the chemical diffusion model developed by Kreuer et al. The second part deals with composites of proton conductors and inorganic compounds such as carbonates, hydroxides, chlorides, and fluorides following the work of B. Zhu. Conductivities of such composites are presented. Nernst potentials of various electrochemical cells with these composites are discussed. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.