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This PhD dissertation arises with the idea of providing pulsed neutron sources with different energies and angular distributions at Centro Nacional de Aceleradores (CNA) in Seville (Spain), which could be generated by 7Li(p,n) and D(d,n) reactions. In order to provide pulsed beams, a chopping/bunching system has been installed and commissioned, as well as new equipment has been added to better monitor and control the beam in a new dedicated neutron line of the Tandem Accelerator at CNA. The goal of this project was the first measurement of the 7Li(p,n)7Be (Ep = 1912 keV) angular-energy neutron field at the implemented HiSPANoS time-of-fight facility at CNA from 2:5 to 130 keV. The measurement has been performed in the summer of 2018. In order to carry out the measurement, a lithium-metallic target, acquisition system, and data analysis became essential to develop. Afterwards, given the experience acquired, a novel neutron feld, 7Li(p,n)7Be at Ep = 1950 keV, was measured at HiSPANoS time-of-fight facility. This measurement is of interest in Boron Neutron Capture Therapy (BNCT) as neutron source.

The 3 MV Tandem Pelletron accelerator at the Spanish Accelerator Laboratory (CNA) has been recently upgraded to produce pulsed ion beams for neutron Time-Of-Flight (TOF) measurements. The upgrade has consisted of two actions: a pulsing system installed at the low energy part of the Tandem accelerator and a new line fully equipped. The pulsing system provides approximately one nanosecond pulse width of protons with variable repetition rates from kHz down to MHz. The new line is equipped with conventional devices and a pick-up for timing measurements with high resolution. The properties of the whole system have been tested Under various working conditions and they are described in some detail., This work was supported by the Spanish projects FPA2013-47327-C2-1-R, FPA2014-53290-C2-2-P, FPA2016-77689-C2-1-R, J. de Andalucía P11-FQM-8229, FIS2015-69941-C2-1-P (MINECO-FEDER, EU), AECC-PS16163811PORR and the funding agencies of the participating institutes.

This PhD dissertation arises with the idea of providing pulsed neutron sources with different energies and angular distributions at Centro Nacional de Aceleradores (CNA) in Seville (Spain), which could be generated by 7Li(p,n) and D(d,n) reactions. In order to provide pulsed beams, a chopping/bunching system has been installed and commissioned, as well as new equipment has been added to better monitor and control the beam in a new dedicated neutron line of the Tandem Accelerator at CNA. The goal of this project was the first measurement of the 7Li(p,n)7Be (Ep = 1912 keV) angular-energy neutron field at the implemented HiSPANoS time-of-fight facility at CNA from 2:5 to 130 keV. The measurement has been performed in the summer of 2018. In order to carry out the measurement, a lithium-metallic target, acquisition system, and data analysis became essential to develop. Afterwards, given the experience acquired, a novel neutron feld, 7Li(p,n)7Be at Ep = 1950 keV, was measured at HiSPANoS time-of-fight facility. This measurement is of interest in Boron Neutron Capture Therapy (BNCT) as neutron source.

Background: The 7 Li(p, n) 7 Be reaction is one of the most used nuclear reaction for accelerator-based neutron sources. There are few experimental cross section data in the double-value energy region and they are discrepant, as are the reaction yields. Purpose: We derive the 7 Li(p, n) 7 Be reaction cross section, and measure with small uncertainty the 197Au(n, γ ) 198Au spectrum-averaged cross section at neutron energy around 30 keV. Method: By irradiating Li metal targets over the proton energy range of 1879 to 1960 keV, thick target yields were measured using the generated 7 Be activity. Based on the theoretical description of the reaction yield, accelerator parameters and reaction cross sections are derived. Gold foils were activated with the neutron field generated by the (p, n) reaction on a Li target at a proton energy of about a half keV above the reaction threshold. Results: The thick target yield is well reproduced when the Breit-Wigner single-resonance formula for s-wave particles is used to describe the reaction cross section. The ratio between neutron and proton widths was found to be equal to n/p = 5.4 1 − Tth/Tp. The detailed balance principle is used to obtain the cosmologically important time-reversed 7 Be(n, p) 7 Li reaction cross section. The measured 197Au(n, γ ) 198Au spectrum-averaged cross section agrees with the value calculated from the ENDF/B-VIII.0 library. Conclusions: We demonstrated the feasibility of deriving the 7 Li(p, n) 7 Be reaction cross section from the thick target yield. Using the ratio between neutron and proton widths obtained in this work reduces the uncertainty in calculating the reaction cross section to a factor of 2.3. International Atomic Energy Agency Contract No. 17883. G.M.-H

Trabajo presentado en la European Nuclear Physics Conference (EUNPC), celebrado en San Domenico Center, (Bolonia, Italia), del 2 al 7 de septiembre de 2018 -- Trabajo presentado en las X Jornadas CPAN (Centro Nacional de Física de Partículas, Astropartículas y Nuclear), celebradas en Salamanca (España), del 29 al 31 de octubre de 2018, The neutron research activities with the Tandem Pelletron Accelerator at CNA in Seville (Spain) is based on the development of neutron sources with different energy and angular distributions, which could be generated by 7Li(p,n) and D(D,n) reactions. The neutron beam characterization is done using the Time of Flight technique (TOF). The TOF technique allows measuring neutron induced cross section as a function of the neutron energy, which can be obtained from the flight time that a neutron spends to travel over known path. To implement TOF technique one needs pulsed ion beams. In order to provide pulsed beams, CNA team and NEC staff are currently working on a chopping/bunching system installation and commissioning, as well as the addition of new equipment to better monitor and control the beam in a new neutron line. The beam chopper consists of a pair of electrically deflecting plates, mounted in parallel to the initial ion beam. One plate is normally polarized with dc voltage deflecting the beam on an absorbing beam catcher. The second one is supplied with an electronic switch. Both work together producing an oscillation of the beam in the transverse direction, thus creating a beam pulse. The bunching unit, being made up involving a pair of tubular electrodes, is mounted coaxially to the ion beam, after the pulsing unit. The electrodes are supplied with radiofrequency voltage phase locked to the different frequencies of the chopping system. The entrance and the exit gaps of the tubular bunching electrodes are used for the time compression of the beam pulse. The other new devices are: a beam profile monitor (BPM), two magnetic steerers, two manual slits, a Faraday cup, and a Pick-Up. The chopping/bunching system has been designed to deal with a primary beam of protons or deuterium. The first tests with protons show a pulsed beam with a FWHM of the order of ns and expected frequency. These promising results will lead the way to various research lines in Seville, among them are nuclear energy production, radiation protection, cancer therapy by neutron irradiation, radio- biological and nuclear structure research.