Developing the Recoil Distance Doppler-Shift technique towards a versatile tool for lifetime measurements of excited nuclear states

Abstract

In this article, the Recoil Distance Doppler-Shift (RDDS) method which is extensively used in nuclear structure physics to determine level lifetimes and absolute transition probabilities is reviewed. Especially, it is aimed to present new developments and variants of the technique which have evolved mainly in the past 25 years. After a short and comprehensive description of the basic elements of the plunger technique, the new variants are presented. This comprises the RDDS technique using γγ-coincidences, RDDS measurements in combination with particle detectors for selecting specific reaction channels, RDDS after Coulomb excitation, RDDS after fission and RDDS using a gas target. In addition, the concept of a differential plunger is discussed with respect to its specific features and typical experimental setups. Examples of differential plunger measurements with recoil tagging, recoil decay tagging and after deep inelastic reactions, Coulomb excitation in inverse reaction kinematics as well as after reactions with fast radioactive beams at energies of 50–100 MeV/u are given. The second focus of the review is dedicated to today’s plunger devices and related hardware. The concepts of specific plunger devices which accommodate the specific demands of the aforementioned RDDS applications including specific feedback systems for controlling target–stopper/degrader separations in-beam are presented. Also discussed are target and stopper/degrader foil related issues like foil preparation, mounting and stretching as well as specific features of the foil behavior in-beam (temperature, blistering, wrinkling and carbon build-up). The third focus is devoted to the data analysis. The concept of the Differential Decay Curve Method (DDCM) is presented as an alternative approach for the analysis of RDDS data measured as singles or as γγ-coincidences. For the latter, different gating possibilities are discussed, e.g. gating from above and gating from below the level of interest and gating on fractional components. Finally, the simulation of line-shapes and its application is presented.