Project Overview

This internship at the Laboratory of Subatomic Physics and Cosmology (LPSC) focused on characterizing a neutron detector for the RICOCHET experiment. The project's goal was to observe the Coherent Elastic Neutrino-Nucleus Scattering (CeνNS), a rare phenomenon that could provide valuable insights into neutrino properties.

Research Context

The RICOCHET experiment faces significant challenges in detecting CeνNS events due to:

• Extremely rare occurrence of events
• Minimal energy deposition (only 1 μK heating)
• Complex detection system using a germanium crystal cooled by a cryostat
• Installation near a nuclear reactor at the Institut Laue-Langevin (ILL)

Experimental Work

The project involved characterizing a spherical hydrogen gas (H₂) neutron detector with a 5 cm diameter. We worked with two distinct neutron sources:

• Americium-Beryllium source: Producing a continuous neutron spectrum (0-10 MeV)
• GENEPI2 accelerator: Generating mono-energetic 14 MeV neutrons

Simulation Approaches

Two complementary simulation methods were developed and validated:

• MATLAB Simulation: A simplified model focusing on elastic scattering between neutrons and gas protons
• GEANT4 Simulation: A comprehensive approach accounting for all possible interactions, including those with the steel detector housing

Key Findings

• Successfully validated both simulation models against AmBe source data
• Discovered that ~2/3 of high-energy neutron events originated from steel housing interactions
• Identified significant impact of neutron scattering from concrete walls
• Developed an optimized mixed-energy simulation model (30% at 14 MeV, 70% distributed between 0-14 MeV)

Physical Principles

The detection principle relies on the energy deposition of particles in matter. Below is the energy loss per unit length (dE/dx) as a function of particle energy, a fundamental concept in our detector characterization:

Skills Applied

• Particle physics data analysis
• Monte Carlo simulation techniques (GEANT4)
• Scientific programming (MATLAB)
• Chi-square minimization for calibration
• Energy spectrum analysis and interpretation