A CVD Diamond Detector for (n,a) Cross-Section Measurements

A novel detector based on the chemical vapor deposition (CVD) diamond technology has been developed in the framework of this PhD, for the experimental determination of (n,a) cross-sections at the neutron time-of-flight facility n_TOF at CERN. The 59Ni(n,a)56Fe cross-section, which is relevant for astrophysical questions as well as for risk-assessment studies in nuclear technology, has been measured in order to validate the applicability of the detector for such experiments. The thesis is divided in four parts. In the introductory part the motivation for measuring (n,a) cross-sections, the experimental challenges for such measurements and the reasons for choosing the CVD diamond technology for the detector are given. This is followed by the presentation of the n_TOF facility, an introduction to neutron-induced nuclear reactions and a brief summary of the interaction of particles with matter. The CVD diamond technology and the relevant matters related to electronics are given as well in this first part of the thesis. The second part is dedicated to the design and production of the Diamond Mosaic-Detector (DM-D) and its characterization. The 59Ni(n,a)56Fe cross-section measurement at n_TOF and the data analysis are discussed in detail in the third part of the thesis, before the summary of the thesis and an outlook to possible future developments and applications conclude the thesis in the forth part. In this work, the Diamond Mosaic-Detector, which consist of eight single-crystal (sCVD) diamond sensors and one ’Diamond on Iridium’ (DOI) sensor has proven to be well suited for (n,a) cross-section measurements for 1 MeV < E < 22 MeV. The upper limit is given by the thickness of the sensors, d = 150 um, while the lower limit is dictated by background induced by neutron capture reactions in in-beam materials. The cross-section measurement was focussed on the resonance integral of 59Ni(n,a)56Fe at En = 203 eV, with the aim of clarifying the discrepancies between the measurements by Harvey 1976 [2] and Koehler 1999 [3]. The results from the measurement of this reaction with the DM-D at n_TOF in 2012 confirm rather the measurement of Harvey, given a resonance integral 6.7% below these data and 12.4% above the results of Koehler. The determined cross-section confirms that the current evaluated nuclear data files overestimate the cross-section at the resonance.