Neutron-based calibration of a Recoil Proton Telescope for fast neutrons spectroscopy

A Recoil Proton Telescope (RPT), allowing real-time fast neutron spectrometry, has been developed at the IPHC laboratory (Strasbourg, France). The set-up includes a neutron converter, a three-planes tracking part made of pixelated CMOS sensors and a final Si(Li) diode to measure recoil proton energy. The diode calibration is a key component for a precise neutron spectrum reconstruction. The relationship between the charge measured in the diode and the corresponding energy is a function of the temperature and radiation damage, so it must be verified periodically. However, the difficulties to access facilities providing protons with calibrated energies limit the possibility to reassess this calibration on a regular basis. In this paper, we present a straightforward method for RPT neutron-based calibration of the Si(Li) diode which is interesting for high precision measurements at reference neutron sources.