Experimental Maxwellian neutron spectrum determination with thermal temperature about 30 keV for MACS calculations.

Musacchio González E., Mastinu P., Praena J., Macias M

Comunicazione
I - Fisica nucleare e subnucleare
Aula Palazzo dell'Emiciclo - Sala B. Croce - Venerdì 27 h 09:00 - 12:00
One of the most interesting topics in nuclear astrophysics is related to nucleosynthesis of the elements beyond iron, which are mainly produced via neutron-capture reactions. The neutron capture cross section data are the fundamental ingredient for the calculation of the stellar reaction rates and thus the possibility of reproducing the observed abundance of the elements in the Universe. The Maxwellian-Averaged Cross Section (MACS) is the quantity needed for the calculation of the stellar reaction rate. A direct measurement of the MACS, under certain conditions, can be performed by neutron activation analysis (NAA) providing a neutron beam with the stellar spectrum, i.e. a Maxwell-Boltzmann Neutron Spectrum (MBNS). Previous to perform any MACS measurement, neutron spectrum determination is mandatory, and this is the purpose of this work. A method based on the idea of shaping the proton beam energy to shape the neutron beam spectrum was used in order to produce a MBNS. For that, a proton energy of 3285 MeV and, as proton energy shaper, an aluminum foil of 55 $\mu$m thickness were employed. To determine the neutron spectrum, neutron spectrometry by time of flight (TOF) was implemented, having a 500 kHz proton pulsed beam from Tandem accelerator at Centro Nacional de Aceleradores (CNA), in Seville. The time width was kept around 2 ns allowing to measure the neutron energy down to 1 keV in a flight path of 60 cm. Preliminary results of the MBNS will be reported in the contribution.