Decay Rates Of Nuclei Research Articles

Single crystal HPGe (80%) versus BGO shielded CLOVER detector for high precision decay rate measurements: a comparative study

In this study, various detector configurations have been investigated in order to explore the optimal condition for decay rate measurements of radioactive samples using gamma spectroscopy technique. A limitation of detecting low energy gamma rays from decaying radioactive nuclei, is the Compton background which can be significantly reduced by rejecting Compton scattered events through active Bismuth germanate (BGO) shielding. On the other hand, for a CLOVER detector without BGO shielding, one can place the radioactive samples very close to the detector for enhancing geometrical efficiency. A single crystal High Purity Germanium (HPGe) detector can also be used for decay rate measurements. In order to measure the decay rate of nuclei decaying via gamma emission with reasonable intensity, optimal close geometry options have been investigated for various HPGe detector configurations.

Double- β decay matrix elements from lattice quantum chromodynamics

A lattice quantum chromodynamics (LQCD) calculation of the nuclear matrix element relevant to the $nn\to ppee\overline{\nu}_e\overline{\nu}_e$ transition is described in detail, expanding on the results presented in Ref. [1]. This matrix element, which involves two insertions of the weak axial current, is an important input for phenomenological determinations of double-$\beta$ decay rates of nuclei. From this exploratory study, performed using unphysical values of the quark masses, the long-distance deuteron-pole contribution to the matrix element is separated from shorter-distance hadronic contributions. This polarizability, which is only accessible in double-weak processes, cannot be constrained from single-$\beta$ decay of nuclei, and is found to be smaller than the long-distance contributions in this calculation, but non-negligible. In this work, technical aspects of the LQCD calculations, and of the relevant formalism in the pionless effective field theory, are described. Further calculations of the isotensor axial polarizability, in particular near and at the physical values of the light-quark masses, are required for precise determinations of both two-neutrino and neutrinoless double-$\beta$ decay rates in heavy nuclei.

Exotic structure and decay of medium mass nuclei near the drip lines

Nuclei at or near the N=Z line are of particular interest as micro-laboratory for fundamental effects. The simulation of many astrophysical objects requires the knowledge of properties and decay rates of nuclei near the drip lines. The structure and dynamics of proton-rich A70 nuclei and neutron-rich A100 nuclei are influenced by shape coexistence and mixing. A realistic description of shape coexistence phenomena requires beyond-mean-field approaches. Results concerning the self-consistent description of exotic phenomena including anomalies in mirror energy differences of proton-rich nuclei, triple shape coexistence in neutron-rich N=58 Sr and Zr isotopes as well as Gamow-Teller β-decay strength distributions, half-lives, and β- delayed neutron emission probabilities of neutron-rich nuclei in the A100 mass region obtained in the frame of the complex Excited Vampir model using realistic effective interactions in large model spaces are presented.