Compact neutron sources for Nuclear Physics: from accelerator-based to laser-driven neutron beams

Pulsed neutron beams are a valuable tool in nuclear physics with applications in a wide variety of fields, including fission and fusion, astrophysics, homeland security, medicine, cultural heritage, avionics, and other industrial or research applications. Despite the potential use of neutron beams, the transfer of knowledge outside large research centers is limited by the huge size and complexity of conventional high-intensity neutron sources and the progressive shutdown of research reactors. Recently, the neutron beams user community is focusing its attention on developing small-scale and compact neutron sources as a complement to major facilities to fully exploit all the possibilities of these techniques. In this context, laser-driven ion sources are garnering the interest of the nuclear physics community due to the fast development of ultra-short (~fs) and ultra-high power (> 1019 W/cm2) lasers and their applications as compact particle accelerators. Laser-driven neutron sources (LDNS) are particularly attractive for nuclear physics applications based on the time-of-flight technique thanks to their short pulse length and high instantaneous flux. There are several recent works about neutron production by laser reaching fluxes per pulse competitive to those of conventional neutron sources, but there is a lack of studies in terms of their application to nuclear physics experiments. Laser-driven neutron applications will have to rely on detection systems that are commonly used in nuclear physics experiments with conventional neutron sources, and whose behavior needs first to be characterized in the environment resulting from the laser-plasma interaction and the particularities of a laser-driven source. In this context, there has been a lot of effort aimed at mitigating the impact of the harsh prompt radiation and the electromagnetic background in sensitive neutron diagnostics, mostly based on single-shot PW-class and TW-class lasers at high repetition rates. However, the typical current-mode operation of neutron detectors in LDNS experiments is not suitable to carry out neutron-induced nuclear reaction experiments, since those require the detection of single signals corresponding to the observables from the individual reactions and processes involved. In this thesis, a study on the feasibility of time-of-flight nuclear reaction measurements in the complex environment of an LDNS has been carried out at the DRACO laser facility of the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in Dresden, Germany, producing neutron shots at 0,02 Hz in a high-power system in stable conditions. In addition to conventional scintillators and bubble detectors operated in current/integrated mode, multi-shot neutron production made it possible to use a neutron and charged particle detector with low efficiency, i.e. diamond detector, to measure individual signals from fast neutron interactions. This itself is a milestone in the path towards nuclear physics time-of-flight experiments at LDNS and, to achieve it, a dedicated signal analysis routine had to be developed for the diamond detector. The characterization of the neutron source resulting from two different nuclear reactions, Cu(p,n) and LiF(p,n), by means of the individual signals and the time-of-flight technique, has been positively validated against Monte Carlo simulations, confirming the feasibility of measuring single fast neutron interactions at an LDNS. The results obtained at DRACO, the characteristics of the LDNS, and the performance of the detectors are compared and contextualized with the results obtained in the commissioning of a conventional accelerator-based compact neutron source: the HiSPANoS neutron source at Centro Nacional de Aceleradores (CNA) in Sevilla, Spain. In this facility, different fast neutron beams have been obtained by means of Be(d,n) and Li(d,n) reactions in thick targets, which provide white neutron beams up to 10 and 20 MeV respectively, as well as of D(d,n) reactions, covering an energy range between 2 and 6 MeV with quasi-monoenergetic neutron beams. The characterization was carried out with conventional fast organic scintillators and applying the time-of-flight technique again. Based on the results and the comparative analysis of both experiments, the neutron production per pulse at DRACO has been established to be superior. Also of high interest, the main drawbacks and issues faced at DRACO are identified, and possible solutions are proposed as a first step towards experiments on fast neutron-induced reactions at laser-driven neutron sources.

Author dc:creator

• Millán Callado, María de los Ángeles

Advisors dc:contributor.advisor

• Fernández Martínez, Begoña
• Guetrrero Sánchez, Carlos

Statement dc:rights

• Attribution-NonCommercial-NoDerivatives 4.0 Internacional

Licence dc:rights.uri

• http://creativecommons.org/licenses/by-nc-nd/4.0/

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/11441/155735

OAI identifier oai:identifier

oai:idus.us.es:11441/155735