On the exponential decay of correlation functions

We use the properties of subharmonic functions to prove the following results, First, for any lattice system with finite-range forces there is a gap in the spectrum of the transfer matrix, which persists in the thermodynamic limit, if the fugacityz lies in a regionE of the complex plane that contains the origin and is free of zeros of the grand partition function (with periodic boundary conditions) as the thermodynamic limit is approached. Secondly, if the transfer matrix is symmetric (for example, with nearest and next-nearest neighbor interactions in two dimensions), and if infinite-volume Ursell functions exist that are independent of the order in which the various sides of the periodicity box tend to infinity, then these Ursell functions decay exponentially with distance for all positivez inE. (For the Ising ferromagnet with two-body interactions, exponential decay holds forz inE even if the range of interaction is not restricted to one lattice spacing). Thirdly, if the interaction potential decays moreslowly than any decaying exponential, then so do all the infinite-volume Ursell functions, for almost all sufficiently small fugacities in the case of general lattice systems, and for all real magnetic fields in the case of Ising ferromagnets.     

Beta-alpha correlation in the decay of 20Na

We have measured the β-α angular correlation in the allowed positron decay of ²⁰Na to the 7.42 MeV state of ²⁰Ne. The correlation is of the form $\text{1 +}\text{a}\text{cos}\text{θ +}\text{p}\text{cos}{}^2\text{θ}$. We find $\text{p}\text{= ?0.003 ± 0.005}$ in reasonable agreement with expectations based on the conserved vector current theory.     

Influence of turbulence strength on temporal correlation of scintillation

Through extensive laboratory experimentation we demonstrate that the temporal frequency content of turbulence-induced scintillation strongly depends on the temperature gradient exerted at the propagation path of a collimated laser beam. We find a power law relating the turbulence strength induced by convection with the vertical temperature gradient and we show that the cutoff frequency of scintillation shows an approximately linear growth with turbulence strength, measured by angle-of-arrival fluctuations. The impact of these findings are discussed in the context of free-space optical communications.     

Gamma-ray emission in competition with neutron emission in the beta decay of Br

Evidence is presented for the existence of a γ-ray at 5594.7±0.6 keV following beta decay of ⁸⁷Br. This observation indicates population of neutron unbound levels in ⁸⁷Kr from which photon emission competes successfully with neutron emission.     

Millimeter wavelength radiation emission during dielectric aging

The current-voltage characteristic for a metal — thick insulator — metal structure has been investigated by applying high voltage impulses on a variety of industrial insulators. It appears that, in the high field regime (1MV/cm) S-type Negative Differential Conductance may occur, leading to self sustained conductivity oscillations possibly originating in field dependent carrier mobility. The phenomenon is associated with radiation emission during thermalization of hot electrons. Measurements have established the presence of millimeter wavelength radiation during prebreakdown and breakdown stages. The radiation emission intervals within a high-voltage pulse application and response have also been investigated.     

Beta-delayed triton emission in the decay of 8He

A β-delayed triton branch with an intensity of (0.9 ± 0.1)% has been observed in the decay of ⁸He. The triton energy spectrum was measured with a specially designed ΔE − E telescope. These data as well as an earlier measured β-delayed neutron spectrum cannot be explained from the known levels in ⁸Li, but it turns out that the main features of both the delayed triton and the delayed neutron spectra from ⁸He could be understood if one assumes a new state in ⁸Li at about 8.8 MeV excitation energy.     

Application of pulse decay discrimination liquid scintillation counting for indoor radon measurement

The pulse decay discrimination (PDD) liquid scintillation technique has been applied to optimise radon counting by the Pico-Rad method. A dermination limit (with 10% relative error) of 4.8 Bqm^?3 for indoor radon measurement has been achieved for optimal PDD setting with a radon elution cocktail containing 20% (v/v) of Ultima Gold AB in Instafluor. From a practical point of view this procedure allows a shortening of the counting time to 1 hour after 48 hours exposure to detectors. This method has been applied to indoor radon determinations in 626 places (municipal offices and private dwellings) in the Lódz region. These measureents resulted in an average concentration of 21.4 Bqm^?3 and a median value of 15.1 Bqm^?3. Analysis of the data indicates that most indoor radon comes from the underlying soil, which contains relatively little²²⁶Ra (10–20 Bqkg^?1).     

Beta-delayed proton and alpha emission in the decay of 17Ne

The beta-delayed proton and alpha spectra from ¹⁷Ne have been studied with Si-detectors. The Gamow-Teller strength in the decay of ¹⁷Ne has been extracted and compared with a two-particle-one-hole shell-model calculation. The experimental strength is quenched by a factor of 0.82 with respect to the calculated one. Furthermore, the decay scheme has been improved and is discussed in some detail. The proton emitting levels in ¹⁷F are very broad and the line shapes are strongly influenced by phase-space effects. Interference between peaks corresponding to the same intermediate spin is a prominent feature emerging clearly with the good resolution and statistics of the present work.     

Directional correlation studies in the decay of177gLu

Directional gamma-gamma correlations of the strong 208.4–112.9 keV and of the weak 71.6–249.7 keV cascade transitions in the decay of^177gLu have been measured. The correlation coefficientsA ₂₂=?0.208±0.012 of the strong andA ₂₂=?0.105±0.005 of the weak cascade have been determined. The mixing ratioE2/M1 of ?3.7±0.3 for the 112.9 keV transition and theM2/E1 of ?0.0173±0.0065 for the 71.6 keV transition have been obtained. The deducedM2 admixture in the 71.6 keV transition is in good agreement with the theoretical estimates of Weisskopf and of Nilsson.

     

Study of the decay

Using data from the FOCUS (E831) experiment at Fermilab, we present a new measurement for the Cabibbo-suppressed decay mode D⁰→K⁺K⁻π⁺π⁻. We measure: Γ(D⁰→K⁺K⁻π⁺π⁻)/Γ(D⁰→K⁻π⁻π⁺π⁺)=0.0295±0.0011±0.0008. An amplitude analysis has been performed in order to determine the resonant substructure of this decay mode. The dominant components are the decays D⁰→K₁(1270)⁺K⁻, D⁰→K₁(1400)⁺K⁻ and D⁰→ρ(770)⁰(1020).     

New-generation large-area muon scintillation counters with wavelength shifter fiber readout for CDF II

New scintillation counters have been designed and constructed for upgrading the CDF detector at Fermilab Tevatron. A novel light collection technique using wavelength shifting fibers, together with a high-quality polystyrene-based scintillator UPS 923A, has resulted in compact counters with good and stable light collection efficiency over their lengths extending up to 320 cm. The design, construction, and performance of the counters are presented. Properties of the fibers and the scintillator, such as light output, light attenuation, decay time, and long-term stability, are investigated. It is found that the polystyrene-based scintillator, unlike the polyvinyltoluene-based one, has properties more adequate for long-term experiments. The text was submitted by the authors in English. On leave from NPL, Samarkand State University, Uzbekistan. On leave from HEPI, Tbilisi State University, Georgia.     

Dynamical decay of nuclei at high temperature: Competition between particle emission and fission decay

A generalized diffusion equation is propounded to follow the time evolution of an excited nucleus towards fission including along the particle decay. This theoretical model is built in order to try to analyse the anomalous behaviour of particle emission observed in many experimental data for heavy-ion induced reactions. Some calculations for the systems¹⁹⁴Hg,¹⁷⁰Yb and²⁴⁸Cf are presented. A possible extension of this generalized formalism is suggested to deal more consistently with the experimental data.     

Evidence for the radioactive decay of Ra by C emission

Using a magnetic spectrometer and an intense ²²⁶Ra source, first evidence for the radioactive decay of ²²⁶Ra by ¹⁴C emission was obtained leading to a measured branching ratio relative to -particles of (3.2±1.6)×10⁻¹¹. In addition, the decay of ²²²Ra by ¹⁴C emission, previously reported, was clearly observed and an upper limit was set for the emission of ³⁴Si from ²⁴¹Am.