Integration of a Tape Roll for Decay Spectroscopy to Control the Build-Up of Background Radioactivity

This internship aims to minimize background radioactivity by devising a new design for the decay chamber of a decay spectroscopy station (DSS). The DSS is coupled to the collinear resonance ionization spectroscopy (CRIS) experiment at the end of its beamline at the Isotope Separator On Line DEvice (ISOLDE) facility at CERN in Switzerland. The CRIS experiment is dedicated to understanding the hyperfine structure of exotic nuclei, identifying exotic isotopes via their characteristic decays, and studying purified samples, including separated isomers. The existing design of the DSS chamber, i.e., carbon foil-based ladder system, was replaced with Mylar® tape-based system by designing a new frame for the integration of Mylar® Tape for the DSS chamber. The new geometry was simulated with GEANT4 code to simulate beta decay of $^{120}$Ag isotope and the detection of beta into the silicon detectors. The efficiency of two silicon detectors was found to be 81.93% which is an excellent result obtained for simulating a $^{120}$Ag beam implant on Mylar® tape as the distance from PIPS to Mylar® tape and APIPS to Mylar® tape is reduced in the new design. In parallel, characterization studies for the existing and new tape station for IDS experiments were done at KU Leuven, and findings were used as a new reference point for the DSS for the CRIS experiment. The idea is to adopt the same design of the tape station being used for IDS and to make changes in the existing design of the DSS chamber where the beam will be implanted, including the experimental requirements of CRIS (e.g., ultra-high vacuum). As the CRIS experimental studies require ultra-high vacuum conditions, i.e., $10^{-10}$ mbar compared with IDS that requires only $10^{-6}$ mbar, vacuum conditions for the IDS’ tape roll were tested twice: first with an empty chamber and then with tape plate integrated with tape roll, one stepper motor and two servo motors. As a result, the vacuum pump was operated for more than twenty-four hours, and the required vacuum pressure, i.e., $10^{-6}$ mbar, was achieved. However, this highlighted how a different solution must be investigated to reach the requirements for operation at CRIS. Initial pre-experimental tests with the IDS tape station and the new tape frame design have been presented and discussed with the CRIS team at CERN during the CRIS Collaboration Meeting in the first week of May 2021. Recommendations from the CRIS collaboration were implemented in this study.