| Grant number: | 15/14530-7 |
| Support Opportunities: | Regular Research Grants |
| Start date: | November 01, 2015 |
| End date: | October 31, 2017 |
| Field of knowledge: | Physical Sciences and Mathematics - Physics - Atomic and Molecular Physics |
| Principal Investigator: | Vito Roberto Vanin |
| Grantee: | Vito Roberto Vanin |
| Host Institution: | Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil |
| Associated researchers: | Alessio Mangiarotti ; Francisco Tadeu Degasperi ; José María Fernández Varea ; Marcos Nogueira Martins ; Marina Fallone Koskinas ; Mauro da Silva Dias ; Nora Lia Maidana |
Abstract
We propose to measure atomic inner shell ionization cross sections by electron impact of elements scattered over the periodic table, because of the theoretical and practical importance of the phenomenon. This study is part of the working plan of the center for research on the interactions of photons and electrons with matter, NAP-FEM, USP. One of the three experimental lines of the Sao Paulo Microtron will provide the electron beam, with energy between 10 keV and 5 MeV. The cross-section is deduced from the characteristic X-ray production rate measured with solid-state detectors. Thin targets and their characterization will be obtained in collaboration with other laboratories of USP's Institute of Physics. The calibration standards of X-ray intensity will be developed in collaboration with the Nuclear Metrology Laboratory of IPEN-CNEN / SP. The ionization cross sections are key parameters in the measurement of electron and X-rays interaction phenomena with matter and are required in the simulations of photons and electrons transport. The previous cross section results obtained by our group have accuracy comparable to the best available data, with relative uncertainty between 10% and 15%. With the funds requested in this project, we will set up an experimental arrangement and develop methods of analysis that will allow obtaining results with relative precision of about 5%. We will also measure the angular distribution of the L X-rays in elements of high atomic number, and verify whether the L3 shell vacancies generated by electron impact are aligned with the incident particle momentum. The observation of this possible alignment is an open question, with controversial and conflicting experimental evidence. Both the degree of atomic alignment by electron impact, which depends on the differences between the cross sections for the production of vacancy with different angular momentum projection quantum number, and the accurate experimental values of total cross section will provide strict tests of the theoretical calculations. From the literature review and the analysis of our previous experiments, we concluded that the probable causes of the inconsistencies observed between the results from different experiments are: the non-uniformity of the target; incorrect measurement of the photon detection efficiency between 3 and 50 keV; inaccurate determination of the X-ray spectrum live time. In the experiment on the angular distribution, preliminary measurements indicate that we can achieve a definitive result using an arrangement to measure the production of X-rays simultaneously at various angles, solving the difficulties related to target non-uniformity. Regarding the problems of efficiency and live time, we will continue the work related to the measurement and calibration of solid-state detectors efficiency and determine the emission intensity of X-rays in the decay of radioisotopes that can be adopted as efficiency calibration standards between 3 and 10 keV. Success in these studies will contribute to establish the Microtron of São Paulo as a reference in the study of the phenomena of interaction of photons and electrons with energies between 10 keV and 5 MeV. (AU)
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