Calibração de um detector de nêutrons no âmbito do experimento SBND

Abstract

This work refers to the description and calibration of a scintillation detector whose purpose is to characterize the background neutrons, induced by a neutrino beam, in the experiment Short-Baseline Near Detector (SBND). The SBND is an integral part of the Short-Baseline Neutrino (SBN) program, located in Fermilab (USA), with the main objectives to serve as a basis for comparison for the other two SBN detectors and, independently, to study the neutrino-argon cross-section with unprecedented accuracy. The accuracy in identification of neutrinos depends fundamentally on the identification of spurious interactions, the background. The neutrino beam itself induces a noise when they interact with the rock and concrete immediately before the detector, inserting neutrons that can be mistakenly identified as if they were the result of an interaction with the target (liquid argon). To assist in the characterization of this neutron background, a mobile detector was built and took measures inside the moat where the SBND is being installed. The calibration of this detector is fundamental for the characterization of these neutrons, especially their energy spectrum. The Calibration should be based on measurements previously established with three gammas emitting sources, 22-Na, 137-Cs and 252-Cf, the latter also emitting neutrons. These sources have known spectral lines, which allow the calibration. For the purposes of this dissertation, the calibration technique is presented via compton threshold identification (Compton edge), starting from the raw data from the electronic acquisition, culminating in the average charge of the 137-Cs and 22-Na ranges. In relation to the 252-Cf, a pulse shape discrimination was applied in order to separate neutrons from the gammas. Finally, all data from the sources were evaluated to verify whether they can be used in calibration, if yes, calibration can be used in the future to characterize neutrons' background from neutrino beam interactions.