PhD Thesis Defense | Pablo Herrero Gómez

Published: June 19, 2023

Development of sensors for individual barium ion identification in the context of the NEXT experiment

June 23, 11:00

CFM Auditorium

Candidate: Pablo Herrero Gómez

Supervisors:  Celia Rogero Blanco and Francesc Monrabal Capilla


This thesis encompasses the first steps in the development of a chemo-sensor for individual Barium dication detection to be implemented in the NEXT experiment. The sensor works by converting chemical properties of the ion into a detectable optical signal. Using fluorescent chemo-sensors may be a unique tool in the field of neutrino physics. The NEXT experiment searches for the neutrinoless double beta decay of Xe-136. In this reaction two electrons and the Ba++ dication are produced. Detecting the Ba ion in delayed coincidence with the two electrons would make the NEXT experiment background free. This required adapting fluorescence chemo-sensors to the ultra-dry environment of NEXT. The sensor is built by immobilising fluorescent molecules on an appropriate surface which preserves its photochemical properties. To this end, atomically-precise molecular deposition and characterization techniques were used. Additionally, a fluorescence microscope has been developed to meet these conditions and requirements.

Scheme of the Barium-tagging sensor: molecules immobilised on a surface capture a single Ba ion produced in the 0νββ decay and shift their fluorescence color. An optical system detects this fluorescence signal and tags the presence of Ba++.


Fluorescent molecules: (right) complexated with Ba++ ion (orange) and emitting in blue. (Left) free molecules emitting in green