The ionization quenching factor (IQF) is defined as the fraction of energy released by a recoil in a medium through ionization compared with its total kinetic energy. At low energies, in the range of a few keV, the ionization produced in a medium falls rapidly and systematic measurements are needed. We report measurements carried out at such low energies as a function of the pressure in He4 at 350, 700, 1000 and 1300 mbar. In order to produce a nucleus moving with a controlled energy in the detection volume, we have developed an Electron Cyclotron Resonance Ion Source (ECRIS) coupled to an ionization chamber by a differential pumping. The quenching factor of He4 has been measured for the first time down to 1 keV recoil energies. An important deviation with respect to the phenomenological calculations has been found allowing an estimation of the scintillation produced in He4 as a function of pressure. The variation of the IQF as a function of the percentage of isobutane, used as quencher, is also presented.
@article{arxiv.0810.1137,
title = {Ionization Quenching Factor Measurement of Helium 4},
author = {D. Santos and F. Mayet and O. Guillaudin and Th. Lamy and S. Ranchon and A. Trichet and P. Colas and I. Giomataris},
journal= {arXiv preprint arXiv:0810.1137},
year = {2008}
}