[en] Absolute measurements of neutron fluence are an essential prerequisite of neutron-induced cross section measurements, dosimetric investigations and neutron beam lines characterisation. Independent and precise neutron flux measurements can be performed with respect to the H(n,p) elastic cross section. However, the use of silicon proton recoil detectors is not straightforward below incident neutron energy of 1 MeV, due to a high background in the detected proton spectrum. A new gaseous proton-recoil detector based on a double ionisation chamber, has been designed to answer the challenge. The detector is constituted by a H-rich deposit (polypropylene, mylar foil or tristearin deposit), and a segmented ΔE-E ionization chamber (4*4*12 cm³), read by a 64 pads Micromegas-based detection plane. The chamber is filled with gas (CF₄ or N₂-CO₂) at an adjustable pressure, from few tens of mbar to few tens of 100 mbar, to reduce as much as possible the detector sensitivity to Compton electrons. Tests have confirmed the low electron sensitivity of the detector, making it well suited for neutron energies down to 200 keV in a gammas and electrons dense environment. The ΔE-E coincidences, coupled to a 3D proton track analysis, enables the disentanglement between direct and scattered neutrons

[en] DESIR is the low-energy part of the SPIRAL2 ISOL facility under construction at GANIL. DESIR includes a high-resolution mass separator (HRS) with a designed resolving power m/Δm of 31,000 for a 1 π-mm-mrad beam emittance, obtained using a high-intensity beam cooling device. The proposed design consists of two 90-degree magnetic dipoles, complemented by electrostatic quadrupoles, sextupoles, and a multipole, arranged in a symmetric configuration to minimize aberrations. A detailed description of the design and results of extensive simulations are given