High power lasers, such as APOLLON facility at Saclay, are a new type of neutron sources, with neutrons that can reach a few tens of MeV and a very high intensity (1E8 neutrons per laser pulse). They allow to reproduce in laboratory the rapid process of nucleosynthesis. However, it is imperative to properly characterize the neutron yield produced by the ion spallation reactions generated by the laser-target interaction. The proposed thesis aims to study and measure the neutron emission from the APOLLON laser facility with two main parts: • the design of a complete simulation chain, ranging from the interaction between high intensity laser and matter to nuclear interactions producing the neutron field. The simulations will be carried out using different codes, whether for laser-target interaction or the production and transport of neutrons; • further development of an activation spectrometer (SPAC). The activation technique is perfectly suitable for measuring intense neutron fields with a strong gamma component. The characterization of the spectrometer will be carried out at the IRSN reference facilities and in intense neutron fields, in particular that of the PTB (Germany). Finally, the SPAC spectrometer will be used to characterize the neutron field at APOLLON laser facility. This thesis will take place jointly between LULI (CNRS, polytechnic school) and LMDN (IRSN). All of this work will be the subject of several publications in peer-reviewed international journals. The planned progress of the thesis is as follows: First part (within LULI, Saclay): 1. Bibliography on high power lasers producing neutrons; 2. Getting started with simulation codes; 3. Establishment of a complete simulation chain; 4. Writing of a scientific publication on the results of the simulations. Second part (within LMDN, Cadarache): 1. Further development of the SPAC activated spectrometer; 2. Getting started with the gamma spectrometry tools associated with the SPAC; 3. Training in data analysis; 4. Characterization of SPAC at IRSN facilities and intense neutron fields; 5. Writing of a scientific publication on PSPC and its characterization. Third part (LULI and / or LMDN): 1. Setting up and carrying out spectrometry campaigns at the APOLLON neutron field with the SPAC; 2. Analysis of the results and comparisons with the simulations; 3. Writing of a scientific publication on the results of measurements with APOLLON; 4. Writing of the thesis manuscript and preparation for the defense. ​