Dissertação para obtenção do Grau de Doutor em
FísicaThis work of this thesis was dedicated to the application of the Micro-AMS(Accelerator Mass spectrometry with micro-beam) to the study of nuclear reactions relevant to Astrophysics, namely reactions involving the radioisotope 36Cl.
Before this could be done, the system had to be installed, tested and optimized. During the installation and testing phase, several isotopes were measured, principally lead and platinum isotopes, which served to show the potential of this technique for applications to Material science and archeology. After this initial stage, the work with 36Cl began.
36Cl is one of several short to medium lived isotopes (as compared to the earth age) whose
abundances in the earlier solar system may help to clarify its formation process. There are two generally accepted possible models for the production of this radionuclide: it originated from the ejecta of a nearby supernova (where 36Cl was most probably produced via the s-process by neutron
irradiation of 35Cl) and/or it was produced by in-situ irradiation of nebular dust by energetic particles(mostly, p, a, 3He -X-wind irradiation model).
The objective of the present work was to measure the cross section of the 35Cl(n,γ)36Cl nuclear reaction which opened the possibility to the future study of the 37Cl(p,d)36Cl and 35Cl(d,p)36Cl nuclear
reactions, by measuring the 36Cl content of AgCl samples with Micro-AMS, taking advantage of the very low detection limits of this technique for chlorine measurements.
For that, the micro-AMS system of the CTN-IST laboratory had to be optimized for chlorine measurements, as to our knowledge this type of measurements had never been performed in such a system (AMS with micro-beam).
This thesis presents the results of these developments, namely the tests in terms of precision and reproducibility that were done by comparing AgCl blanks irradiated at the Portuguese National Reactor with standards produced by the dilution of the NIST SRM 4943 standard material. With these results the cross section of the 37Cl(n,γ)36Cl was calculated
