New half life limits for theβ β 2v+0v decay of76Ge to the excited states of76Se from the Heidelberg-Moscow ββ experiment

Half life limits for theββ _2v+0v decay of⁷⁶Ge to excited states of⁷⁶Se are deduced from the background spectrum of a passive shielding of zone refined germanium (139.5 kg). A special low-activity HPGe-detector (102 ccm) was mounted inside this shielding to search for the transition photons emitted in the decay of the excited states. The resulting limits for the (0⁺→2 ₁ ⁺ and the (0⁺→0 ₁ ⁺ ) transition are 6.3·10²⁰ y (68%cl).     

Measurement of the ββ decay half-life of 130Te with the NEMO-3 detector

We report results from the NEMO-3 experiment based on an exposure of 1275 days with 661 g of (130)Te in the form of enriched and natural tellurium foils. The ββ decay rate of (130)Te is found to be greater than zero with a significance of 7.7 standard deviations and the half-life is measured to be T(?)(2ν) = [7.0 ± 0.9(stat) ± 1.1(syst)] × 10(20) yr. This represents the most precise measurement of this half-life yet published and the first real-time observation of this decay.     

A highly efficient HPGE gamma-ray spectrometer for investigating ββ decay to excited states

A new low-background spectrometer based on a HPGe detector with a sensitive volume of 600 cm³ is developed to investigate rare nuclear processes such as resonance neutrinoless double electron capture and two-neutrino double beta decay to excited states of daughter nuclei. The spectrometer is installed at the Modane underground laboratory (France) at a depth of 4800 m w.e. The spectrometer background is measured and the spectrometer sensitivity is determined for measuring sources of double beta decay.     

Search forββ decay of76Ge to the excited states in76Se

Lower limits on the half-life of theββ(2v+0v) decay of⁷⁶Ge to the excited states in⁷⁶Se have been obtained using the results of low-background measurements with a HPGe detector surrounded by passive germanium shielding: T_1/2(0⁺ → 2 ₁ ⁺ ) >1.1 · 10²¹ y, T_1/2(0⁺ → 0 ₁ ⁺ ) > 1.7 · 10²¹ y, T_1/2(0⁺ → 2^2/+) > 1.4 ·10²¹ y.     

New bound to the probability of 76Ge ββ decay to the 0 1 + 76Se level

Measurements were carried out at the underground low-background laboratory of the Baksan Neutrino Observatory using a detection system involving four ultrapure germanium detectors made from enriched ⁷⁶Ge. The sensitivity of the experiment to the detection of a ⁷⁶Ge double beta decay to the excited levels of the ⁷⁶Se nucleus was determined. As a result of 228-day measurements, the new bound to the time of ⁷⁶Ge half-decay to the ⁷⁶Se 0 ₁ ⁺ excited level is found to be T _1/2(2ν2β)≥6.2×10²¹ years (90% confidence level).     

Suppression of the neutrinoless ββ decay?

The neutrinoless ββ decay rates of ⁷⁶Ge, ⁸²Se, ^{128, 130}Te are calculated in the quasi-particle random appproximation using a realistic effective NN interaction. The reduction of the 0νββ decay nuclear matrix elements due to ground-state correlations is much weaker than that of the 2νββ decay matrix elements, and we can deduce stringent limits on the Majorana neutrino mass and the right-handed leptonic currents from experimental data on νββ decay.     

The effects of doubly excited states on ionization balance

The effects of highly doubly excited states on ionization balance are investigated. In the calculation, A Collisional-Radiative model in Detailed-Configuration-Accounting (DCA) is applied to population calculations for NLTE plasmas. Configuration-averaged rate coefficients that needed in the rate equations are obtained based on the first order perturbation theory. The Hatree-Fock-Slater self-consistent-field method is used to calculate the electron wave functions. The mean ionization stage of high-Z plasma Lu is presented. The comparison shows that the mean ionization stage increases more than 3 stages when doubly excited states 5l6l' and 5l5l' are not included in the population calculations.     

The effects of doubly excited states on ionization balance

The effects of highly doubly excited states on ionization balance are investigated. In the calculation, A Collisional-Radiative model in Detailed-Conflguration-Accounting （DCA） is applied to population calculations for NLTE pl＆smas. Configuration-averaged rate coefficients that needed in the rate equations are obtained based onthe first order perturbation theory. The Hatree-Fock-Slater self-consistent-field method is used to calculate theelectron wave functions. The mean ionization stage of high-Z plasma Lu is presented. The comparison shows thatthe mean ionization stage increases more than 3 stages when doubly excited states 5l6l＇ and 5l5l＇ are not included in the population calculations.     

Radiative decay from doubly to singly excited states of He via generalization of Laguerre-type orbitals： A non-orthogonal formalism

By taking full account of the non-orthogonality of the orbitals between the low-lying doubly excited states ¹P^o and the singly excited states ¹S^e and ¹²D^e of He, the corresponding radiative decay rates have been investigated theoretically via analytic generalized Laguerre-type atomic orbitals at a nearly numerical multi-configuration self-consistent field accuracy in a general non-orthogonal configuration interaction scheme. From these rates, we calculate the VUV photon emission and metastable atom spectra, and both are found to be in good qualitative agreement with recent excellent measurements. We obtain, successfully, the enhancement of the VUV photon spectrum, experimentally observed at the energy of (2s4p-4s2p)/(2p,3d) ¹P^o as compared with other nearby lying states. The mechanism proposed by Odling-Smee et al is verified, implying that taking appropriate account of the overlap existing between orbitals of the low-lying doubly excited and singly excited states (especially important for the compact orbitals) can reveal basic physical dominant mechanism and is crucial in understanding these spectra.     

New limits on generation mixing for massive neutrinos from π→ev decay

Improved upper limits of generation-mixing amplitudes U_ie are presented for the electron-flavour in the heavy neutrino mass range of 20–70 MeV/c². In conjunction with astrophysical considerations the new limits tend to exclude altogether the existence of heavy neutrinos in the investigated mass range.     

New measurement of the π → μνγ decay

We have measured the branching ratio of the radiative decay π → μνγ. The energies of the gamma-ray and of the muon were both measured and the Dalitz-plot distribution of the decay was obtained. The data agree well with the theoretical prediction (QED internal bremsstrahlung) down to a γ-ray energy of 1 MeV. The discrepancy reported in a previous experiment is not confirmed.     

A study on excited states dipole moments of 9,9′-bianthryl

The influence of an external electric field on the fluorescence intensity of 9,9′-bianthryl in non-polar and medium polar solvents and solvent mixtures is studied experimentally. The results show that the single fluorescence band observed in these solvents is not due to a homogeneous transition between two states.     

Shell Model description of the ββ decay of Xe

We study in this Letter the double beta decay of ¹³⁶Xe with emission of two neutrinos which has been recently measured by the EXO-200 Collaboration. We use the same shell model framework, valence space, and effective interaction that we have already employed in our calculation of the nuclear matrix element (NME) of its neutrinoless double beta decay. Using the quenching factor of the Gamow–Teller operator which is needed to reproduce the very recent high resolution ¹³⁶Xe (³He, t) ¹³⁶Cs data, we obtain a nuclear matrix element M^2ν=0.025 MeV⁻¹${\mathrm{M}}^{2\nu }=0.025{\text{MeV}}^{-1}$ compared with the experimental value M^2ν=0.019(2) MeV⁻¹${\mathrm{M}}^{2\nu }=0.019(2){\text{MeV}}^{-1}$.     

Identification of the 109Xe and 105Te α-decay chain

The α-decay chain ¹⁰⁹Xe → ¹⁰⁵Te → ¹⁰¹Sn was identified at the Holifield Radioactive Ion Beam Facility. Advances in digital electronics have made possible the identification of both alpha emitters in the same experiment despite the disparate half-lives of 13 ±2 ms and 620 ±70 ns for ¹⁰⁹Xe and ¹⁰⁵Te, respectively. Two α-decay transitions were observed from ¹⁰⁹Xe with Q_α values of 4067 ±10 and 4217 ±8 keV. One transition between the ground states of ¹⁰⁵Te and ¹⁰¹Sn was observed with a Q_α value of 4889 ±6 keV. Using the measured half-lives, branching ratios, and Q_α values the reduced α-decay widths, δ², were determined. Comparison of the δ² value for ¹⁰⁵Te with ²¹³Po indicates a “superallowed" character in the α emission of ¹⁰⁵Te.     

Phase and population decay of image-potential states – the influence of defects

Quantum-phase and population decay of image-potential states have been investigated by two-photon photoemission with femtosecond time resolution. The influence of steps and defects on quasielastic and inelastic scattering processes is illustrated for a vicinal Cu(119) surface and diluted adsorbate layers of CO and Cu on Cu(001). Received: 19 April 2000 / Accepted: 2 September 2000 / Published online: 12 October 2000     

Partial α-decay half-lives of ground to ground and ground to excited states of Thorium family

Partial half-lives and Q-values of allowed α-decay for Thorium family are evaluated by using the WKB approximation. In order to calculate the partial half-lives, transition probabilities from ground to ground and ground to excited states of daughter nuclei are obtained. The α-decay potential barrier includes deformed volume, surface, and Coulomb parts in the deformed liquid drop model (DLDM), deformed Woods-Saxon nuclear potential and centrifugal term. The quadrupole and the hexadecapole deformations are considered in the calculations. Calculated half-lives are compared to the results of other theoretical models as well as experimental data. Comparison of the present study and other theoretical methods with experimental data indicated that the predicted half-lives using current approach are well agreed with the experimental data than results of UMADAC and CPPMDN theoretical models. Moreover, the evaluated half-lives correspond well with the Geiger-Nuttall empirical formula.     

Study of the reaction130Te(n, γ)131Te

Energies and intensities of the gamma-ray transitions following the thermal neutron capture in¹³⁰Te are determined. The neutron separation energy for¹³¹Te is evaluated to be 5929.4 ±±0.3 keV. A statistically significant correlation between the reduced transition intensities and the spectroscopic factors from the (d, p) reactions is found. Evidence for the presence of potential capture mechanism is given.On leave fromAl-Faateh University, Physics Department, P.O. Box 13371, Tripoli, Libya.     

New Measurement of the π0 radiative decay width

High precision measurements of the differential cross sections for π0 photoproduction at forward angles for two nuclei, 12C and 208Pb, have been performed for incident photon energies of 4.9-5.5 GeV to extract the π0→γγ decay width. The experiment was done at Jefferson Lab using the Hall B photon tagger and a high-resolution multichannel calorimeter. The π0→γγ decay width was extracted by fitting the measured cross sections using recently updated theoretical models for the process. The resulting value for the decay width is Γ(π0→γγ)=7.82±0.14(stat)±0.17(syst) eV. With the 2.8% total uncertainty, this result is a factor of 2.5 more precise than the current Particle Data Group average of this fundamental quantity, and it is consistent with current theoretical predictions.     

New bounds on the number of bound states for Schrödinger operators

We consider the Schrödinger operatorH = – +V(|x|) onR ³. Letn denote the number of bound states with angular momentum (not counting the 2 + 1 degeneracy). We prove the following bounds onn . LetV 0 and d/dr r ^1-2p (-V)^{1 –p} 0 for somep [1/2, 1) then

ββ(2ν) decay of 100Mo to the first excited 0+ state of 100Ru

The rate of the double-beta ββ(2ν) decay of ¹⁰⁰Mo to the first 0⁺ excited state in ¹⁰⁰Ru is measured by a γγ-coincidence technique in which two HPGe detectors are used to detect the two γ rays (E _γ1=590.76 keV and E _γ2=539.53 keV) from the daughter nucleus ¹⁰⁰Ru as it deexcites to the ground state via the transition sequence 0⁺ → 2⁺ → 0⁺. In contrast to all previous ββ-decay experiments, this technique provides data that are essentially background-free. By using a 1.05-kg isotopically enriched (98.4%) disk of ¹⁰⁰Mo, 22 coincidence events (with the background estimated at 2.5 events) are detected in 440 d of measuring time, which translates into a half-life time of [5.9 _?1.1 ^+1.7 (stat.)±0.6(syst.)]×10²⁰ yr.