Speaker
Mr
Federico Pinna
(INFN)
Description
Since the discovery of the neutrino oscillations, which imply non-zero neutrino mass, neutrino physics and the study of the neutrino-less double beta decay (0νββ) have received ever growing interest. Several experiments are currently trying to detect the 0νββ event and to measure the half-life, which is inversely proportional to the squared neutrino effective mass. The NUMEN project aims to get more information on the transition matrix of a 0νββ event by measuring the cross section of the Double Charge Exchange (DCE) process. Albeit different, the two processes share the initial and final states of the two nuclei involved; acquiring information on the far more probable DCE could significantly help the 0νββ research. A DCE event is nonetheless rare, so that a high beam current of about 50 µA is needed to obtain sufficient statistics. On the other hand, to keep a good resolution in the energy measurement, the target cannot exceed few hundreds of nm in thickness. The copious heat generated by the beam in the thin target must be dissipated by a proper cooling apparatus. The first target to be designed was a disk clamped at the boundaries by a cold frame; analytical calculi proved it to be unable to tolerate the heat. Since that was due mainly to the low thermal conductivity of the target materials (Tin, Selenium, Germanium, Tellurium and Cadmium), a substrate of Highly Oriented Pyrolytic Graphite was added. The heat can pass from the target to the substrate through a large area and can be quickly dissipated to the cold frame thanks to the highly conductive graphite. To estimate the performance of the target/substrate system, a MatLab code was written. Numerical calculations are encouraging, showing that every target could be used under an intense ion beam.
A great effort was put also in the fabrication of the prototypes for the Sn/graphite target. Tin has been deposited on graphite substrates by thermal evaporation and with different thermal processes. Post deposition annealing proved to be of little effect, while heating up the substrate during the deposition of the material led to very good results, in terms of homogeneity and smoothness of the film.
Finally, a preliminary test for the heat dissipation in a Sn/Graphite target was performed. The target was heated with an IR laser (λ=808nm) set at several output powers, then the results were compared with numerical calculations; results were promising for future tests.
Primary author
Mr
Federico Pinna
(INFN)
