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Ionization Quenching Factor Measurement of Helium 4
D. Santos1, F. Mayet1, O. Guillaudin1, T. Lamy1, S. Ranchon1, A. Trichet1, P. Colas2, I. Giomataris2

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.
1 :  LPSC - Laboratoire de Physique Subatomique et de Cosmologie
2 :  IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers (ex DAPNIA)
Physique/Astrophysique/Cosmologie et astrophysique extra-galactique

Planète et Univers/Astrophysique
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