Neutrino-less Double Electron Capture - a tool to research for Majorana neutrinos

The possibility to observe the neutrino-less double $\beta$ decay and thus to prove the Majorana nature of neutrino as well as provide a sensitive measure of its mass is a major challenge of to-day's neutrino physics. As an attractive alternative we propose to study the inverse process, the radiative neutrino-less double electron capture $0 \nu 2EC$. The associated monoenergetic photon provides a convenient experimental signature. Other advantages include the favourable ratio of the $0 \nu 2EC$ to the competing $2\nu 2EC$ capture rates and, very importantly, the existence of coincidence trigger to suppress the random background. These advantages partly offset the expected longer lifetimes. Rates for the $0\gamma 2EC$ process are calculated. High Z atoms are strongly favoured. A resonance enhancement of the capture rates is predicted at energy release comparable to the $2P-1S$ atomic level difference. The resonance conditions are likely to be met for decays to excited states in final nuclei. Candidates for such studies are considered. The experimental feasibility is estimated and found highly encouraging.Comment: New figure added, table updated, physical background discusse

Compound and precompound γ-ray entry lines from measured multiplicities and energies in α-induced reactions

Multiplicities of quasi-continuum γ-rays have been measured for the 160Gd(α, xnγ) reactions as a function of bombarding energy and for the 4n exit channel also as a function of γ-ray energy. Increase of beam energy causes initially an increase of the energy and angular momentum of the entry line in the residual nucleus until the neutron “drip line” is reached. This can be understood in terms of competing compound and precompound processes

K X-ray multiplicities for rare earth atoms produced in (H.I., xn) nuclear reactions

K X-ray multiplicities are determined for a number of nuclear reaction products in the rare earth region. It is shown that if certain conditions are fulfilled the values of these multiplicities can be considered as characteristic for the reaction residues independently of the reaction used. They can thus be used for the quantitative determination of cross sections

Intensity and multipolarity of low-energy components in the quasicontinuum γ-ray spectrum following α- And C12-induced reactions

Measurements of K-shell ionization yields for (α,xn) and (C12,xn) evaporation residues exclude the existence of a large M1 component in the quasicontinuum spectrum of well-deformed Dy nuclei below 500 keV. Upper intensity limits are deduced for M1, E1, and E2 components

LES NOYAUX DE TRANSITION 189Ir ET 187Ir SONT-ILS TRIAXIAUX ?

Les niveaux excités des noyaux 189Ir et 187Ir ont été étudiés par réaction (α, 2nγ) sur le faisceau du cyclotron de Grenoble. Les schémas détaillés qui ont été établis mettent en évidence : 1) des états de parité positive qui s'interprètent comme appartenant aux deux bandes 3/2+ | 402 | (fondamental) et 1/2+ | 400 | mélangées par interaction de Coriolis (noyaux a symétrie axiale de déformation positive) ; 2) une bande découplée construite sur un état 9/2- (h 9/2) décrite de manière équivalente par un modèle à symétrie axiale et déformation positive ou par un modèle a particule-plus-rotor asymétrique ; 3) une structure complexe pour les niveaux de parité négative associés à l'isomère 11/2- (h 11/2). Ce système est correctement prédit par le modèle à rotor asymétrique

Selection of heavy ion reaction channels via particle K X-ray coincidences

To identify the residual nuclei in very asymmetric heavy-ion reactions heavy-ion K X-ray coincidences have been measured. The usefulness and limitations of this method are discussed, and its feasibility is demonstrated in a study of the 14N+197Au reaction at 140 MeV

Angular momentum dependence of incomplete fusion reactions

γ-ray multiplicities associated with various reaction channels have been measured for the 14N + 197Au system at Elab = 115 and 168 MeV. Channel selection accomplished via charged ejectile-KX-ray coincidence measurements permitted distinction between reactions with two or more charged fragments in the final state. For the former type of reactions the angular momentum dependence expected for (binary) incomplete fusion reactions is obserbed. For the latter, the same angular momentum dependence is found if sequential decay of the primary light fragment is assumed

Negative parity bands in 100Ru and 150Sm and the interacting boson approximation

Ground-state band members up to Jπ = 10+ in 100Ru and up to 14+ in 150Sm and odd-spin negative parity states up to 15− in both nuclei have been identified from (α, 4n) in-beam γ-ray and conversion electron spectra. The data are interpreted in terms of interacting quadrupole and octupole bosons

Multipolarity of quasicontinuum γ-rays from collective high-spin states in 152Dy

Measured internal conversion coefficients for quasicontinuum transitions in 152Dy in the spin range of 30–50 establish their predominantly stretched E2 character. Those transitions are attributed to triaxial bands near the yrast line as calculated in terms of the cranking approximation using the Woods-Saxon potential