Order alpha(2) corrections to the decay rate of orthopositronium

Order alpha(2) corrections to the decay rate of orthopositronium are calculated in the framework of nonrelativistic QED. The resulting contribution is found to be in significant disagreement with one set of experimental measurements, though another experiment is in agreement with theory.     

New limits on the single-γ decay of orthopositronium

We have searched for the exotic annihilation of orthopositronium, o-Ps → a⁰ + γ, where a⁰ denotes a neutral particle of mass m_a < 2m_e. For the ratio of this decay mode to the 3γ decay mode, upper limits have been derived in the range 5 × 10^?6?1 × 10^?6 (for m_a varying from 100 to 900 keV). This result excludes the hypothesis that this exotic decay is responsible for the discrepancy between the theoretical and experimental values of the orthopositronium lifetime.     

Some {\rm O}(\alpha^2) annihilation type contributions to the orthopositronium width

We consider some radiative corrections to the lowest order annihilation diagram for the orthopositronium decay rate. The insertion of the renormalized vertex correction in the annihilation graph gives . We compute also the contribution of the square of the lowest order annihilation amplitude, which turns out to be . Finally, we obtain a term arising from the correction to the light–light scattering block due to the exchange of one coulombic photon, in agreement with earlier computations. Received: 10 December 1997 / Published online: 24 March 1998     

Perturbation of the decay rate of90m Nb by implantation in metals

The perturbation of the decay constant of^90m Nb implanted in various transition metals (Zr, Nb, Hf, Ta, Ag and Au) has been determined by direct half-life measurements. Particular care was taken to evaluate and minimize possible systematic errors. The maximum relative change found is ν_Au?ν_Nb/ν_Nb=(4.5±0.8)%     

Unified approach to alpha decay calculations

With the discovery of a large number of superheavy nuclei undergoing decay through α emissions, there has been a revival of interest in α decay in recent years. In the theoretical study of α decay the α-nucleus potential, which is the basic input in the study of α-nucleus systems, is also being studied using advanced theoretical methods. In the light of these, the Wentzel–Kramers–Brillouin (WKB) approximation method often used for the study of α decay is critically examined and its limitations are pointed out. At a given energy, the WKB expression uses barrier penetration formula for the determination of the transmission coefficient. This approach utilizes the α-nucleus potential only at the barrier region and ignores it elsewhere. In the present era, when one has more precise experimental information on decay parameters and better understanding of α-nucleus potential, it is desirable to use a more precise method for the calculation of decay parameters. We describe the analytic S-matrix (SM) method which gives a procedure for the calculation of decay energy and mean life in an integrated way by evaluating the resonance pole of the S-matrix in the complex momentum or energy plane. We make an illustrative comparative study of WKB and S-matrix methods for the determination of decay parameters in a number of superheavy nuclei.     

Mass corrections to the tau decay rate

In this note radiative corrections to the total hadronic decay rate of the τ-lepton are studied employing perturbative QCD and the operator product expansion. We calculate quadratic quark mass corrections to the decay rate rationR _τ to the order0(α _s ² m²) and find that they contribute appreciably to the Cabbibo supressed decay modes of the τ-lepton. We also discuss corrections of mass dimensionD=4, where we emphasize the need of a suitable choice of the renormalization scale of the quark and gluon condensates.     

A discussion of contributions to the 0 vββ decay from the pion-charge-exchange mechanisms

In this paper we discuss the contributions to the amplitude of the 0νββ decay, mediated by the heavy neutrino, from the two kinds of pion-charge-exchange mechanisms. The pion-double-charge-exchange mechanism is much more important for the 0νββ decay in nuclei, compared to the pion-single-charge-exchange mechanism.     

Radiative corrections to the light muonic atoms decay rate

Radiative corrections to the decay rate in low-Z hydrogen-like muonic atoms are considered. The correction is due to the Uehling potential and it has the relative order of α. The numerical results are reported for the 2p → 1s transition for atoms with nuclear charge up to Z = 10.     

Studies of the alpha decay of U

The decay of ²³³U through the first and second excited states of ²²⁹Th has been studied using a uranium oxide source. The half-life of the first excited state of ²²⁹Th was found to be less than 1.9 nsec; it decays by an almost pure M1 transition. The half-life of the second excited state of ²²⁹Th was found to be 0.5±0.2nsec; this level de-excites by E2 cross-over radiation in 96% of events. Contrary to expectations, an anisotropic alpha-gamma angular correlation was not found, and the probable reason for this is discussed.     

Theoretical approaches to alpha decay half-lives of super-heavy nuclei

We consider the systematics of α-decay half-lives of super-heavy nuclei versus the decay energy and the total α-kinetic energy. We calculate the half-lives using the experimental Q_α values. The computed half-lives are compared with the experimental data and with existing empirical estimates and are found to be in good agreement.Also, we obtain α-preformation factors from the ratio between theoretical and experimental results for some superheavy nuclei and evaluate the standard deviation. The results indicate the acceptability of the approach.